Embed Size (px)
Citation preview
1
GUIDED BY :Dr. ELLORA MADAN(M.D.S.)
PRESENTED BY :SWATI AGARWALP.G. 1 YEAR
2
1. INTRODUCTION2. PROKARYOTES AND EUKARYOTES3. UNIVERSAL PRINCIPLE OF LIVING CELLS4. CELL MEMBRANE AND DYNAMICS5. NUCLEUS AND NUCLEOLUS - CYTOPLASM - ORGANELLES AND INCLUSIONS8.CYTOSKELETON9.SUMMARY10.CONCLUSION
3
The cell is the structural and functional unit of all living cells, sometimes called the "building blocks of life.
• Unicellular organism• Multicellular organism
Cell …Latin cella, a small room. Coined by Robert Hooke…
4
Schleiden (botanist) and Schwann (zoologist) (1839)
make individual observations about cells and form the cell theory.
Its postulates state that:1.All living things are composed of cells. 2.The cell is the simplest structural unit of all
living things.
50 years later RUDOLF VIRCHOW said “All cells come from pre-existing cells”
5
Over billions years ago, living organism divided into 3 main divisions.
1.Archae PROKARYOTES2.Bacteria3.Eucarya EUKARYOTES
(protist, algae, plants, fungi, animal
cells)
6
1. Nuclear body •Bounded by a nuclear membrane.
•Contains one or more paired, linear chromosomes .
•Nucleolus present.
2. Cell division •By mitosis. •Usually by binary fission.
PROKARYOTESEUKARYOTES
•Not bounded by a nuclear membrane.
•Usually contains one circular chromosome.
•No nucleolus.
7
PROKARYOTESEUKARYOTES
3. Cytoplasmic membrane
• Fluid phospholipid bilayer.
• Capable of endocytosis (phagocytosis and pinocytosis) and exocytosis.
•Fluid phospholipid bilayer usually lacking sterols.
•Incapable of endocytosis and exocytosis.
4. Cytoplasmic structures
•Chloroplasts serve for photosynthesis.•Mitotic spindle- cell division.•microtubules, actin micofilaments, and intermediate filaments are present.
•No chloroplasts and mitotic spindles.
• Internal membrane-bound organelles are absent.
8
PROKARYOTESEUKARYOTES
5. Respiratory enzymes and electron transport chains
•Located in the mitochondria.
•Located in the cytoplasmic membrane.
6. Cell wall
• Usually composed of cellulose but never containing peptidoglycan.
• Animal cells and protozoans lack cell walls
• Have cell walls composed of peptidoglycan.
9
PROKARYOTESEUKARYOTES
7. Locomotor organelles
•May have flagella or cilia.
•Some have flagella
•No cilia.
10
1. Genetic information stored in one-dimensional chemical sequences in DNA (occasionally RNA) is duplicated and passed on to daughter cells.
2. Genetic information contained in base sequence of DNA determines the amino acid sequence of a protein and its three-dimensional structure.
11
3. Macromolecular structures assemble from sub-units, by self assembly of their constituent molecules.
The protein, nucleic acid and lipid molecules themselves contain the information that is required to assemble complex structures.
12
4. Membranes grow by expansion of pre-existing membranes.
Organelles such as mitochondria and ER, form only by growth and division of preexisting organelles and are inherited maternally.
ER plays the central role in membrane biogenesis as the site of phospholipid synthesis. 13
5. Signal receptor interactions target cellular constituents to their correct locations.
Specific recognition signals incorporated into the structures of protein and nucleic acids route these molecules to their proper cellular compartments. Receptors recognize these signals and guide each molecule to its compartment.
6. Cellular constituents move by diffusion, pumps and motors. 14
7. Receptors and signalling mechanisms allow cell to adapt to environmental conditions.
Minute to minute decisions generally involve the reception of chemical or physical stimuli from outside the cell and processing of these stimuli to change the behavior of the cell.
15
The fluid living content of the cell that consists of two major divisions, the cytoplasm and the nucleoplasm (cell nucleus) is called the “PROTOPLASM”
It is composed mainly of nucleic acids, proteins, lipids, carbohydrates, and inorganic salts.
Smallest unit of protoplasm capable of independent existence is the “CELL”.
CELL
NUCLEUS CYTOPLASM 16
Components within these compartments are:
1. ORGANELLES(metabolically active internal organs)
2. INCLUSIONS(metabolically inactive accumulations)
Electron microscope reveals fibrillar elements in cytoplasm which are neither organelles nor inclusions, grouped under third category,
3. CYTOSKELETON17
Protoplasm is the living contents of a cell that is surrounded by the plasma membrane.
Protoplasm of the nucleus is karyoplasm or nucleoplasm, and that external to it is the cytoplasm.
Is a gel like, viscous fluid, transparent and organized in a colloidal suspension.
The principle elements of protoplasm are carbon, oxygen, hydrogen, nitrogen and in lesser amounts calcium, magnesium, phosphate, sulfur, iodine, sodium, potassium and traces of many other elements.
Water constitute 75% of cell by weight.
18
It is an amorphous matrix commonly referred to as the HYALOPLASM or CELL SAP.
The peripheral cytoplasm immediately underlying the limiting membrane of the cell contains few, if any organelles and is known as ECTOPLASM, and that comprising the bulk of the cell is known as ENDOPLASM.
19
20
Cells particularly fibroblasts, muscle fibers, pericytes, Schwann cells and some epithelial cells, bear a fuzzy coating also known as glycocalyx.
It is especially thick over the microvilli of gut epithelium and can be resolved with light microscope.
Histochemical studies reveal chemical composition to be mostly glycoproteins and to the lesser extent glycolipids.
21
FUNCTIONS Protection: cushions the plasma membrane and protects it from chemical injury.
Immunity to infection: enables the immune system to recognize and selectively attack foreign organisms.
Cell adhesion: binds cell together so that the tissues do not fall apart.
Inflammation regulation: coating on endothelial walls in blood vessels prevents leukocytes from rolling/binding in healthy sites.
22
Micrograph of the brush border of the intestinal epithelial cell
23
Composed of lipids and proteins.
Form the barrier between each cell and its environment.
It also divides the cytoplasm of eukaryotes into compartments, including the nucleus and membrane bound organelles.
24
UNDER ELECTRON MICROSCOPE
•Thin dense lines (2.5-3nm)• Separated by an electron lucent Intermediate zone (3.5-4nm)
25
A fluid mosaic modelA bilayer of lipids with mobile globular proteins
26
A lipid bilayer is a sheet of lipids, arranged so that the hydrophilic phosphate heads point “out” to the water on either side of the bilayer and the hydrophobic tails point “in” to the core of the bilayer.
This arrangement results in two “leaflets” which are each a single molecular layer.
27
Lipids self-assemble into this structure because of the hydrophobic effect, which creates an energetically unfavorable interaction between the hydrophobic lipid tails and the surrounding water.
Thus, a lipid bilayer is typically held together by entirely non-covalent forces that do not involve formation of chemical bonds between individual molecules.
28
LIPIDS form the framework of biological membranes.
Anchor soluble proteins. Store energy.
Carry information as intracellular hormones and as intracellular secondary messenger.
29
MAJOR LIPIDS FOUND IN BIOLOGICAL MEMBRANES:
Phosphoglycerides
Sphingolipids
Sterols
Glycolipids
Triglycerides30
Phosphoglycerides = glycerol + alcohol + 2 fatty acids.
More than half of the fatty acids in the membrane have one or more double bonds, which create bend in the aliphatic chain.
These bends contribute to the fluidity of the bilayer fatty acids.
Phosphoglycerides are amphiphilic.
31
The aliphatic chain of fatty acids are HYDROPHOBIC.
The carboxyl groups of fatty acids and the head group of phosphoglycerides are HYDROPHILIC.
32
The several head groups confer distinctive properties to the various phosphoglycerides.
Enzymes can interconvert all phosphoglyceride head groups and remodel fatty acid chains.
These enzymes are located on the cytoplasmic surface of smooth endoplasmic reticulum.
33
Of the phospholipids, the most common head group is phosphatidylcholine (PC), accounting for about half the phospholipids in most mammalian cells.
Other head groups are also present to varying degrees and can include phosphatidylserine (PS) phosphatidylethanolamine (PE) and phosphatidylglycerol (PG).
34
These alternate head groups often confer specific biological functionality.
PS presence on the extracellular membrane face of erythrocytes is a marker of cell apoptosis,
whereas PS in growth plate vesicles is necessary for the nucleation of hydroxyapatite crystals and subsequent bone mineralization.
35
Most sugar containing lipids are Sphingolipids.
Derive its name from sphingosine, which is a nitrogenous compound containing base that is the structural counterpart of glycerol and one fatty acid of phosphoglyceride.
Glycosphingolipids - consist of 1 or more sugar. - sugar head group of some glycosphingolipids serve as receptors for viruses. 36
They are simply glycerol with fatty acids esterified to all 3 carbons.
They form large oily droplets in the cytoplasm that are convenient way to store fatty acids as reserves of metabolic energy.
In adipose cells, specialized for lipid storage, the triglyceride droplet occupies most of the cytoplasm.
37
MEMBRANE PROTEINS• A membrane protein is a protein molecule that is attached to, or associated with the membrane of a cell or an organelle.
Membrane proteins can be divided into several categories:
•Integral membrane proteins which are permanently bound to the lipid bilayer.
•Peripheral membrane proteins that are temporarily associated with lipid bilayer or with integral membrane proteins.
38
Lipid-anchored proteins bound to lipid bilayer through lipidated amino acid residues.
In addition, pore-forming toxins and many antibacterial peptides are water-soluble molecules, but undergo a conformational transition upon association with lipid bilayer and become reversibly or irreversibly membrane-associated.
39
Membrane proteins have various functions:
Some are cell adhesion molecules that anchor
cells to their neighbors or to basal laminas.
Some function as pumps, actively transporting ions
across the membrane.
Some function as carriers, transporting substances
down electrochemical gradients by facilitated
diffusion. 40
Some are ion channels, which when activated permit the passage of ions into or out of the cell.
Some function as receptors that binds neurotransmitters and hormones, initiating physiologic changes inside the cell.
They also function as enzymes, catalyzing reactions at the surface of the membrane.
41
CARRIER PROTEINS
•Move specific molecules through the membrane one at a time.
Channel proteins
• Channel proteins extend through the bilipid layer.• They form a pore through the membrane that can move molecules in several ways.
42
43
Accomplished primarily by :
1.Exocytosis2.Endocytosis3.Movement through ion channels4.Primary and secondary active transport.
44
Vesicles containing material for export are ticketed to the cell membrane, where they bind via:
1.v- SNARE/t- SNARE arrangement.The area of fusion then breaks down, leaving
the contents of the vesicle outside and the cell membrane intact.
Secretion from the cell occurs via two pathways:
Non constitutive Constitutive45
46
Non constitutive Pathway
Proteins from the golgi apparatus initially enter secretory granules, where processing of prohormones to mature hormones occurs before exocytosis.
Constitutive Pathway
Involves the prompt transport of proteins to the cell membrane in vesicles, with little or no processing or storage.
47
48
Of various types:1.Phagocytosis (Cell eating) is the process by
which bacteria, dead tissue, or other bits of microscopic material are engulfed by cells such as PMNL’s, of the blood.
Material makes contact with the cell membrane, which then invaginates.
The invagination is pinched off, leaving the engulfed material in the membrane enclosed vacuole and the cell membrane intact.
49
2. Pinocytosis (cell drinking) is essentially the same process, the difference being that the substances ingested are in solution and not visible under the microscope.
Endocytosis
Constitutive Clathrin mediated
50
Constitutive endocytosis is not a specialized process.
Clathrin mediated occurs at membrane indentations where the protein clathrin accumulates.
Clathrin molecule have the shape of triskelions, with three legs radiating from a central hub.
As a result these molecules form a geometric array that surrounds the endocytic vesicle.
At the neck of this vesicle, a GTP protein called dynamin is involved in pinching off the vesicle, therefore the protein is called as “pinchase”.
51
Once the complete vesicle is formed, the clathrin falls off and the three legged proteins recycle to form another vesicle.
The vesicle fuses with and dump its contents into an early endosome.
From it , a new vesicle can bud off and return to the cell membrane which alternately can become a late endosome.
This fuse with a lysosome in which the contents are digested by the lysosomal proteases. 52
53
Areas of cell membrane especially rich in cholesterol and sphingolipids are known as rafts.
These rafts are probably the precursors of flask shaped membrane depressions called caveolae when their walls become infiltrated with a protein called caveolin that resembles clathrin.
54
Some non polar molecules including O2 and N2 and small uncharged polar molecules such as CO2 diffuse across the lipid membranes of cells.
Membrane is permeable to very limited substances, so the substances cross the membrane by endocytosis, exocytosis, and transport proteins, that forms channels for ions or transport substances such as urea, glucose, and amino acids.
55
Even water is transported through simple diffusion being supplemented throughout the body with various water channels (aquaporins).
Transport proteins have been studied through patch clamping Cell attached patch clamp.
Inside out patch
Whole cell recording
56
Some transport proteins are simple aqueous ion channels, that make them effective for a given substance such as Ca2+
Others are gated i.e. they have gates that open .
Gated Voltage gated
Ligand gated External eg:- acetylcholine,
GABA Internal eg:- intracellular Ca2+, cAMP, or G proteins.
57
Other transport proteins are carriers that bind ions and other molecules and then change their configuration, moving the bound molecule from one side of the cell membrane to the other.
Molecules move from areas of high concentration to areas of low concentration(down their chemical gradient).
Cations move to negatively charged areas whereas anions move to positively charged areas(down their electrical gradient).
As no energy input is required for the same the process is called facilitated diffusion.
58
Other carriers transport substances against their electrical and chemical gradients and requires energy and is called active transport.
• Moves substances from low to high concentration.
• Requires the use of carrier proteins.
59
Carrier proteins used in active transport include:
-Uniporters – move one molecule at a time.-Symporters – move two molecules in the same
direction. -Antiporters – move two molecules in opposite
directions Eg:- Na+- K+ ATPase which moves three Na+ out of the cell in exchange for each two K+ that moves into the cell.
60
The glucose uniporter transports glucose across membranes
The ligand bindingsite is exposed onthe upper membranesurface
The ligand bindingsite is now exposed onthe lower membranesurface
The carrier isnow ready totransport anothermolecule
61
Coupled transport-glucose-Na+ symporter captures the energy
from Na+ diffusion to move glucose against a concentration gradient
62
Sodium-potassium (Na+-K+) pump (Antiporter)
• ATP energy is used to change the conformation of the carrier protein.
63
Many receptors for chemical messengers have been identified.
These proteins are not static components of the cell, but their numbers increase and decrease in response to various stimuli, and their properties change with changes in physiologic conditions.
When a hormone or neurotransmitter is present in excess, the number of active receptors generally decreases (down regulation) and vice versa.
64
In the case of receptors in the membrane, receptor mediated endocytosis is responsible for down regulation sometimes.
Ligand receptor complexes move laterally in the membrane coated pits, where they are taken into the cell by endocytosis (internalization).
This decreases the number of receptors in the membrane while some receptors are replaced by de novo synthesis in the cell.
65
Mechanism of action of chemical messengers :
Ligands such as acetylcholine bind directly to ion channels in the cell membrane.
Thyroid and steroid hormones,etc. enter the cells and act on one or another family of structurally related cytoplasmic or nuclear receptors.
66
The activated receptor binds to DNA and increases transcription of selected mRNAs.
Many other ligands in the ECF bind to receptors on the surface of cells, and many of them trigger the release of intracellular mediators such as cAMP, IP3,
and DAG that initiate changes in the cell function.
Consequently, the extracellular ligands are called “first messengers” and the intracellular mediators are called “second messengers”
67
68
Second messengers bring about many short-term changes in cell function by altering enzyme function, triggering exocytosis, and also transcripting various genes.
This is done in part by activating transcription factors already present in the cell, and these factors induce the transcription of immediate early genes.
The product of these genes activate other genes which produce long term effects.
69
When activated, many of the membrane receptors initiate release of second messengers via GTP (G proteins) binding proteins.
The second messengers generally activate protein kinases, enzymes that catalyze the phosphorylation of tyrosine and serine residues in proteins.
In insulin receptor, the intracellular portions of the receptors themselves are protein kinases, and in some instances, they phosphorylate themselves (autophosphorylation).
70
Other receptors, such as, cytokine receptors, are not protein kinases themselves but readily initiate phosphorylation of many intracellular proteins.
Stimulation of TranscriptionWhen hormones bind to their receptor inside the
cells, the conformation of the receptor protein is changed.
The receptor hormone complex moves to DNA, where it binds to enhancer elements.
71
The triiodothyronine (T3) receptors bind hormones in the nucleus.
The glucocorticoid receptor is located mainly in the cytoplasm but migrates promptly to the nucleus as soon as it binds to the ligand.
Binding of the receptor hormone complex to DNA increases the transcription of mRNAs encoded by the gene to which it binds.
72
A common way to translate a signal to a biologic effect inside cells is by way of nucleotide regulatory proteins (G proteins) that bind GTP.
GTP is guanosine analog of ATP.
When the signal reaches a G protein, the protein exchanges GDP for GTP.
The GTP protein complex brings the effect and the inherent GTPase activity of the protein converts GTP to GDP.
73
The GTPase activity is accelerated by a family of RGS (regulators of G protein signaling) proteins that accelerate the formation of GDP.
Small G proteins are involved in many cellular functions.
Members of the Rab family Rho/Rac family, mediates
of these proteins regulate interactions between the
the rate of vesicle traffic cytoskeleton and between the ER, membrane. the Golgi apparatus, lysosome, endosome, and the cell membrane. 74
A third family is the Ras family, regulates growth by transmitting signals from the cell membrane to the nucleus.
These G proteins are made up of three subunits: α,β,γ.
75
α subunit is bound to GDP
GDP is exchanged for GTP
α subunit separates from the combined β and γ subunits
β and γ subunits do not separate and β γ also activates a variety of effectors.
Ligand binds to coupled receptor
76
Intrinsic GTPase activity of the α subunit converts GTP to GDP
Reassociation of the α with the β γ subunit.
Termination of effector activation.
Many G proteins are modified by having specific lipids attached to them, i. e. they are lipidated.
Trimeric G proteins may be myristolated, palmitoylated, or prenylated.
77
78
All the heterotrimeric G protein coupled receptors are proteins that span the cell membrane seven times (Serpentine Receptors).
May be palmitoylated.
Small ligands bind to the amino acid residues in the membrane and large polypeptide and protein ligands bind to the extracellular domains, which are bigger and better developed in the receptors for polypeptides and proteins.
79
80
The link between membrane binding of a ligand that causes prompt increase in the cytoplasmic Ca 2+ concentration is often Inositol Triphosphate (inositol, 1,4,5 triphosphate; IP3).
When one of these ligands bind to its receptor, activation of receptor produces activation of phospholipase C on the inner surface of membrane via Gq.
81
The isoforms PLCβ1 and PLC β2 of phospholipase C are activated by G proteins ,
They catalyze the hydrolysis of phosphatidylinositol 4,5 diphosphate (PIP2) to form IP3 and diacylglycerol (DAG).
Tyrosine kinase linked receptors can also produce IP3 and DAG by activating PLCγ1.
The IP3 diffuses to the ER, where it triggers the release of Ca2+ into the cytoplasm.
82
DAG is a second messenger, stays in cell membrane, where it activates one of the seven subspecies of protein kinase C.
Precursor of PIP2is phosphatidylinositol- present in cell membrane phosphatidyl 4 phosphate (PIP)
DAG IP3 PIP2
Phosphatidic acid cytosine diphosphate diacylglycerol Phosphatidylinositol
hydrolysis
Inositol
83
84
Another important second messenger.
Formed from ATP by the action of the enzyme adenyl cyclase and converted to physiologically inactive AMP by the action of enzyme phosphodiesterase.
Activates protein kinase A
Catalyzes the phosphorylation of proteins changing
their conformation and altering their activity. 85
86
87
INSIDE THE CELL
88
1. Nucleolus
2. Nucleus
3. Ribosome
4. Vesicle
5. Rough Endoplasmic Reticulum
6. Golgi apparatus (or "Golgi body")
7. Cytoskeleton
8. Smooth endoplasmic reticulum
9. Mitochondrion
10.Vacuole
11.Cytosol
12.Lysosome
13.Centriole89
• The largest organelle of the cell.
• Except for the mature erythrocyte, it is present in all cells of the body.
• It may be disk-shape, round, oval, kidney shaped, lobulated or irregular.
• Nucleus is flexible and adapt to changes in cell shape (like muscle contraction, pressure of blood on lining cells of blood vessel).
90
• The irreversible condensation of chromatin in the nucleus of a cell undergoing necrosis, is termed as pyknosis.
• Severe injury leading to death may be accompanied by rupture of nuclear membrane and the escape of granular contents into the cytoplasm. This process is known as karyorrhexis.
• Dissolution of nuclear granules is known as karyolysis.
91
• Is a double lipid bilayer that encloses the genetic material.
• Serves as the physical barrier, separating the contents of the nucleus (DNA in particular) from the cytoplasm.
• Many nuclear pores are inserted in the nuclear envelope, which facilitate and regulate the exchange of materials (proteins such as transcription factors, and RNA) between the nucleus and the cytoplasm.
• The outer membrane is continuous with the RER.92
• The inner nuclear membrane is the primary residence of several inner nuclear membrane proteins.
• The outer and inner nuclear membrane are fused at the site of nuclear pore complexes. The structure of the membrane also consists of ribosomes.
• The inner nuclear membrane is connected to the nuclear lamina, a network of intermediate filaments composed of various lamins (A, B1, B2, & C).
• The lamina acts as a site of attachment for chromosomes and provides structural stability to the nucleus.
93
• The space between the two membranes that make up the nuclear membrane itself is called the perinuclear space (also called the perinuclear cisterna, NE Lumen), and is usually about 20 - 40 nm wide.
• The nuclear membrane has been postulated to play a role in the organization and transcriptional activity of chromatin.
94
95
• It is like rounded refractile body usually eccentrically placed in the nucleus.
• Is a non-membrane bound structure composed of proteins and nucleic acids found within the nucleus.
• In electron microscope, the nucleolus appear as a three dimensional network of anastomosing dense strands. This network called the nucleolema or pars granulosa, which is made up of 15nm ribonucleoprotein particles in a matrix of fine filaments.
96
• These so called fibrillar centers contain the nucleolar organizer regions of those chromosomes possessing nucleolar genes.
• Nucleolar genes code for ribosomal RNA and their
transcription occur in this area.
97
• Immediately surrounding each of these paler areas is a rim of electron dense filaments referred to as pars fibrosa or dense fibrillar component of the nucleolus.
• Early steps in the processing of RNA precursor molecules and RNA protein assembly occurs here.
• The ribosomal proteins are synthesized in the cytoplasm and targeted to the intranuclear site of assembly by nucleolar localization-signal sequences on the molecules.
98
• The resulting ribonucleoprotein particles accumulates in pars granulosa, where later steps of maturation of the ribosomal subunits are carried out.
• The nucleolus disappears during cell division and is reformed in the daughter cells during reconstruction of their nuclei.
• It develop from the several nucleolar-organizing regions in the set of chromosomes, but their subsequent coalescence usually reduces the number of nucleoli in the interphase nucleus to one or two.
99
• The protein synthetic activities of the cytoplasm are dependent on the functional integrity of the nucleolus.
• Its destruction by the laser beam results in cessation of incorporation of RNA precursors into the ribosomes on which protein synthesis depends.
100
• The cellular material outside the nucleus but within the plasma membrane; consists of the following:
Cytosol - cellular fluid (mainly water) with dissolved proteins, salts, sugars, and other solutes.
Organelles – specialized internal structures with specialized function.
• Membranous organelles - have bilipid
membraneNucleus, mitochondria, peroxisomes, lysosomes,
endoplasmic reticulum, Golgi apparatus.
• Non membranous - no membrane presentRibosomes, centrosome, centrioles, basal bodies
101
Cytoskeleton - protein filaments and tubules that provide support, movement within the cell; cellular skeleton
Cytoplasmic Inclusions - chemicals such as glycogen, fat, and pigments
102
• In cytoplasm of nearly all cells there is an extensive system of membrane bound canaliculi called the ER.
• In electron micrographs it is represented by branching tubular profiles of varying length.
• The tubules may be locally expended into broad flat saccules called CISTERNAE (often spaced in parallel row).
• Two morphologically and functionally distinct types are identified :
- ROUGH ENDOPLASMIC RETICULUM - SMOOTH ENDOPLASMIC
RETICULUM 103
104
• In 1800s cytologists describe coarse clumps of material in the basal cytoplasm of secretory epithelial cells that stain intensely with basic dyes.
• They called it ERGASTOPLASM.
• Later on this basophilic material of such cells was identified as RIBONUCLEOPROTEIN.
• Most abundant in glandular cells that secrete proteins.
• 20 – 25nm particles associated with rough ER are called ribosomes.
105
• Complex structures consisting of ribonucleic acid and 20 or more proteins.
• At high magnifications, a larger and a smaller subunit can be resolved in each ribosomes, and it is the larger subunit that is bound to the membrane of the reticulum.
• Cluster of ribosomes are also found free in the cytoplasmic matrix.
• Both bind and free are sites where amino acids are assembled in the synthesis of proteins.
106
• Ribosomes usually occur in clusters of 10 or more linked together by their common attachment to the long molecule of mRNA. Such units of several ribosomes bound to the same strand of mRNA are called polyribosomes or polysomes.
• As amino acids are added to their ends, the former polypeptide chains elongate from the larger subunit of each ribosome, into the underlying membrane of the RER, into its lumen.
• Small vesicles containing newly synthesized proteins pinch off from the ER and are transported to the second organelle, THE GOLGI COMPLEX. 107
• Less extensive than the RER.
• The smooth reticulum is involved in the synthesis of fatty acids and other lipids.
• Greatest abundance in cells of steroid secreting endocrine glands.
• The smooth endoplasmic reticulum serves to metabolize the steroids and produced the final steroid hormone.
108
• In liver, play an important role in the synthesis of lipid component of VLDL that are carriers of cholesterol in the blood.
• Its principal function is the sequestration of the calcium ions that controls muscle contraction.
• Proteins synthesized in the endoplasmic reticulum, are transported to the golgi complex for further processing, concentration and packaging in secretory granules for discharge from the cell.
109
• The convex surface, to which secretory protein is transported from the endoplasmic reticulum, is called the cis-face of the organelle and opposite side is the trans-face.
• The transport of the material from the cis- to the trans-face of the organelle is believed to depend on the vesicles budding off from one cisternae and fusing with the next in the stack.
• The terminal cisternae on the trans side of the organelle often has distended segments forming condensing vacuoles that are precursors of secretory granules.
• Other portion of terminal cisternae form the specialized region of the organelle, called the trans-golgi network.
110
111
Golgi complex have 3 functionally distinct compartments through which proteins pass in sequence.
•The highly fenestrated initial cisterna has the unique property of being heavily stained by prolong exposure to osmium, this is the cis-compartment.
•The next few cisternae that react positively with NADPase and N-acetyl glucosamine (AGT), form the intermediate compartment.
•Number of succeeding cisternae that stain for thiamine pyrophosphatase (TTPase), sialyl transferase (ST), galactosyl transferase (GT) constitute the trans-compartment.
112
• The sorting takes place at the trans face of the golgi complex.
• There, certain proteins are condensed into secretory granules, others are packaged in smooth surface small vesicles, and still others are enclosed in vesicles having a bristle like coating.
• The majority of vesicles appear to arise from the trans-golgi network.
• The secretory granules move to the cell for exocytosis.
• Coated vesicles transport newly synthesized enzymes to late endosomes and then to lysosomes.
• The smooth vesicles may be involved in membrane recycling.
113
• Previously network of tubules associated with the terminal cisternae was identified as a potential site of biogenesis of lysosomes and was termed as GERL to indicate its close relation to the golgi (G), its continuity with the ER, and its role in the lysosome formation (L).
• This network of anastomosing tubules is now considered to be an integral part of the golgi complex and now the term GERL has been replaced by the term TRANS-GOLGI NETWORK.
114
• After newly synthesized lysosomal enzymes have been transferred from the endoplasmic reticulum to the golgi, specific oligosaccharide chains rich in mannose are phosphorylated in the 6-carbon position.
• This modification serve as a label, enabling these enzyme to bind to mannose-6-phosphate receptors (these receptors and their ligands are found to be concentrated in the trans-golgi network)
• Where they are packed in small vesicles that fuse specifically with the membrane of developing lysosomes. 115
116
• In general they are round, ovoid, or highly irregular, electron dense bodies 0.25-0.8µm in diameter.
• Their interior may appear homogenous or may consist of dense granules of varying size in a less dense matrix.
• They may contain crystals or concentric system of lamellae, interpreted as myelin form of phospholipid.
• They cannot be confidently identified by morphological criteria alone. Histochemical demonstration of acid phosphatase or other hydrolases in their interior is required for verification.
117
• Lysosomes are abundant in polymorphonuclear leukocytes of the blood and in tissue macrophages which are cell types specialized for phagocytosis.
• When bacteria are engulfed by these cells they are taken into the cytoplasm in the membrane bounded phagocytosis vacuole or phagosome.
• Lysosomes then gather around this vacuole and their membrane fuse with its membrane, releasing into its interior hydrolytic enzymes that destroy the ingested bacterium.
118
• However, indigestible residues, in small amounts may persist in membrane bounded residual bodies. These may coalesce into larger masses that are variously designated as wear and tear pigments or lipofushsin pigment.
119
• Lysosomes are the cell's waste disposal system .They digest almost everything. One exception is asbestos. They are used for the digestion of macromolecules by :
•Phagocytosis (ingestion of other dying cells or larger extracellular material, like foreign invading microbes),•Endocytosis (where receptor proteins are recycled from the cell surface), and •Autophagy (where in old or unneeded organelles or proteins, or microbes that have invaded the cytoplasm are delivered to the lysosome). •Autophagy may also lead to autophagic cell death, a form of programmed self-destruction, or autolysis, of the cell, which means that the cell is digesting itself. 120
• Although lysosomes usually carry out their digestive function, there are few situations in which lysosomal enzymes are released from the cells.
• Osteoclasts, cells specialized for the remodeling of the bone, secrete enzymes into a sealed cavity between the cell and underlying bone to digest the bone matrix.
• Also, at site of inflammation, where leukocytes are actively phagocytizing bacteria, lysosomes may fuse with a forming phagosomes before its complete closure and enzymes may escape, destroying collagen and elastin in the surrounding connective tissue.
121
• The morphology of mitochondria varies somewhat from cell to cell, each mitochondrion is in essence a sausage-shaped structure.
• Are the power-generating units of the cell and are most plentiful and best developed in parts of cells where energy-requiring processes take place.
122
• The mitochondrial membranes are bound compartments and these compartments or regions include :
•outer membrane,
•intermembrane space,
•inner membrane,
•cristae
•matrix
123
• The outer mitochondrial membrane, which encloses the entire organelle, has a protein-to-phospholipid ratio similar to that of the eukaryotic plasma membrane (about 1:1 by weight).
• It contains large numbers of integral proteins called porins. These porins form channels that allow molecules to freely diffuse from one side of the membrane to the other.
• Larger proteins can enter the mitochondrion if a signalling sequence at their N-terminus binds to a large multisubunit protein called translocase of the outer membrane, which then actively moves them across the membrane. 124
• The intermembrane space is the space between the outer membrane and the inner membrane.
• Because the outer membrane is freely permeable to small molecules, the concentrations of small molecules such as ions and sugars in the intermembrane space is the same as the cytosol.
• One protein that is localized to the intermembrane space is cytochrome c.
125
• The inner mitochondrial membrane contains proteins with several functions:
•Those that perform the redox reactions of oxidative phosphorylation.
•ATP synthase, which generates ATP in the matrix. •Specific transport proteins that regulate metabolite passage into and out of the matrix. •Protein import machinery.
126
• The inner membrane is rich in an unusual phospholipid, cardiolipin
• Unlike the outer membrane, the inner membrane doesn't contain porins and is highly impermeable to all molecules.
• All ions and molecules require special membrane transporters to enter or exit the matrix.
• In addition, there is a membrane potential across the inner membrane formed by the action of the enzymes of the electron transport chain. 127
• The inner mitochondrial membrane is compartmentalized into numerous cristae, which expand the surface area of the inner mitochondrial membrane, enhancing its ability to produce ATP.
• These folds are studded with small round bodies known as F1 particles or oxysomes. These are not simple random folds but rather invaginations of the inner membrane, which can affect overall chemiosmotic function.
128
• The matrix is the space enclosed by the inner membrane. It contains about 2/3 of the total protein in a mitochondrion.
• The matrix is important in the production of ATP with the aid of the ATP synthase contained in the inner membrane.
• The matrix contains a highly-concentrated mixture of hundreds of enzymes, special mitochondrial ribosomes, tRNA, and several copies of the mitochondrial DNA genome.
• Of the enzymes, the major functions include oxidation of pyruvate and fatty acids, and the citric acid cycle.
129
• Mitochondria have their own genome, and there is much less DNA in the mitochondrial genome than in the nuclear genome, and 99% of the proteins in the mitochondria are the products of nuclear genes
• At the time of fertilization, the egg nucleus and sperm nucleus each contribute equally to the genetic makeup of the zygote nucleus.
•In contrast, the mitochondria, and therefore the mitochondrial DNA, usually comes from the egg only. The sperm's mitochondria enter the egg but do not contribute genetic information to the embryo.
130
• Instead, paternal mitochondria are marked with ubiquitin to select them for later destruction inside the embryo.
•Mitochondria are, therefore, in most cases inherited down the female line, known as maternal inheritance
• Diseases caused by mutation in the mtDNA include Kearns-Sayre syndrome, MELAS syndrome and Leber's hereditary optic neuropathy.
•In the vast majority of cases, these diseases are transmitted by a female to her children, as the zygote derives its mitochondria and hence its mtDNA from the ovum. 131
Mitochondria play a central role in many other metabolic tasks, such as:• Regulation of the membrane potential • Apoptosis-programmed cell death
• Calcium signaling (including calcium-evoked apoptosis)
• Cellular proliferation regulation
• Regulation of cellular metabolism
• Steroid synthesis132
• Some mitochondrial functions are performed only in specific types of cells. For example, mitochondria in liver cells contain enzymes that allow them to detoxify ammonia, a waste product of protein metabolism.
• A mutation in the genes regulating any of these functions can result in mitochondrial diseases.
133
• They are not present as regular cytoplasmic component of all cells.
• They are most often present in developing gametes, certain epithelia and in some cells of fetal tissues i.e. pyramidal cells and neuroblasts of the cerebral cortex.
• They are the double membrane organelles intimately associated with the nucleus.
134
Recent studies have suggested that lamellar body is a specialization of the ER concerned with accelerated or stage-specific neuronal protein synthesis during cell maturation.
Data also suggested that they may participate in modification, storage and transportation of metabolites.
135
• Peroxisomes (also called microbodies) are organelles found in virtually all eukaryotic cells. • They are involved in the :•catabolism of very long chain fatty acids, branched chain fatty acids, polyamines.•biosynthesis of plasmalogens, etherphospholipids critical for the normal function of mammalian brains and lungs.
• They also contain approximately 10% of the total activity of enzymes in the pentose phosphate pathway, which is important for energy metabolism.
136
Metabolic Functions
• A major function of the peroxisome is the breakdown of very long chain fatty acids through beta-oxidation.
• In animal cells, the very long fatty acids are converted to medium chain fatty acids, which are subsequently shuttled to mitochondria where they are eventually broken down to carbon dioxide and water.
• The first reactions in the formation of plasmalogen in animal cells also occur in peroxisomes. Plasmalogen is the most abundant phospholipid in myelin.
• Deficiency of plasmalogens causes profound abnormalities in the myelination of nerve cells, which is one reason why many peroxisomal disorders affect the nervous system. 137
138
• Peroxisomes also play a role in the production of bile acids important for the absorption of fats and fat-soluble vitamins, such as vitamins A and K. Skin disorders are features of genetic disorders affecting peroxisome function as a result.
• Peroxisomes contain oxidative enzymes, such as catalase, D-amino acid oxidase, and uric acid oxidase. However the last enzyme is absent in humans, explaining the disease known as gout, caused by the accumulation of uric acid.
• In cell biology, the centrosome is an organelle that serves as the main microtubule organizing center (MTOC) of the animal cell as well as a regulator of cell-cycle progression.
• It was discovered by Edouard Van Beneden in 1883 and was described and named in 1888 by Theodor Boveri.
• In suitably stained cells, appear as a small, more or less spherical area with a texture differing slightly from that of the surrounding cytoplasm.
139
• In its center are two short rods, the centrioles.
• In may also contain variable number of small dense bodies called centriolar satellites.
• Centrioles are cylindrical structures about 0.2µm in diameter and 0.5-0.7µm in length, with an electron dense wall surrounding an electron lucent central cavity.
• Embedded in the wall are 9 evenly spaced triplet microtubules (set at an angle of 400 to its respective tangent).
140
In nine triplet sets (star-shaped), they form the centrioles
141
Contd…
142
• This oblique orientation of the triplets result in a pattern resembling the vanes of a turbine.
• Long axis of each triplet are usually perpendicular to one another.
• The centriolar satellites seem to serve as microtubule organizing centers, becoming sites of nucleation of the microtubules that will form the mitotic spindle.
• The centrosome is rich in tubulin, but it is not clear which of its component is responsible for initiating microtubule formation.
• The association of centrioles with the poles of the spindle, in animal cells, may have involved as a device for ensuring that both daughter cells receive a pair.
143
• Centrosomes are composed of two orthogonally arranged centrioles surrounded by an amorphous mass of protein termed the pericentriolar material (PCM).
• The PCM contains proteins responsible for microtubule nucleation and anchoring, including γ-tubulin, pericentrin and ninein.
• In general, each centriole of the centrosome is based on a nine triplet microtubule assembled in a cartwheel structure, and contains centrin, cenexin and tektin.
144
The eukaryotic cytoskeleton. Actin filaments are shown in red, microtubules in green, and the nuclei are in blue.
145
• The cytoskeleton (also CSK) is a cellular "scaffolding" or "skeleton" contained within the cytoplasm and is made of protein.
• Is present in all cells; it was once thought to be unique to eukaryotes, but recent research has identified the prokaryotic cytoskeleton.
• It has structures such as flagella, cilia and lamellipodia that plays important roles in both intracellular transport (for example the movement of vesicles and organelles) and cellular division.
146
• Eukaryotic cells contain three main kinds of cytoskeletal filaments,
• microfilaments,• intermediate filaments• microtubules.
• The cytoskeleton provides the cell with structure and shape.
147
FUNCTIONS:
• Positioning of proteins and organelles• Cell shape and structure• Shape changes• Ameboid locomotion• Muscle contraction• Support to microvilli• Viscoelastic and contractile property of cytoplasm
148
• They are most abundant in the ectoplasm (cortex) of the cell, a gel-like peripheral zone of cytoplasm immediately beneath the cell membrane.
• During change in cell shape they depolymerize, returning subunits to that pool, and then repolarize into filaments with different orientation.
• These are the thinnest filaments of the cytoskeleton.
149
• They are composed of linear polymers of actin subunits, and generate force by elongation at one end of the filament coupled with shrinkage at the other, causing net movement of the intervening strand.
• They also act as tracks for the movement of myosin molecules that attach to the microfilament and "walk" along them.
150
Actin exists in cells as bundles and networks: actin-binding proteins crosslink the filaments
151
Contd…• Locomotion of cell depends on interaction of actin filaments with the actin binding protein myosin. • The myosin form highly ordered arrays of relatively thick filaments that interdigitate with actin filaments.
• The deployment of actin filaments in the cytoplasm is influenced by a number of actin binding proteins.
Profilin – binds to G-actin monomer, preventing polymerization and thus helps to maintain a supply of monomer that can be drawn on as needed to form new actin filament.
Capping protein – binds to the end of an actin filament, limiting further increase in its length.
152
Fimbrin – rigidly binds adjacent actin filaments, in parallel, to form bundles.
Filamin – forms flexible links between intersecting microfilaments, stabilizing 3-D network.
Gelsolin – insert itself between subunits of a filament, breaking it into shorter fragments.
Vinculin and α-actinin – mediate the binding of actin filaments to the cell membrane at intercellular junctions and at the cell base.
SPECTRIN another type of microfilament especially prominent in erythrocytes connects a component of plasma membrane (ankyrin) to adjacent actin filaments.
153
154
• These filaments, around 10 nanometers in diameter, are more stable (strongly bound) than actin filaments, and heterogeneous constituents of the cytoskeleton.
• Like actin filaments, they function in the maintenance of cell-shape by bearing tension (microtubules, by contrast, resist compression).
• Intermediate filaments organize the internal tridimensional structure of the cell, anchoring organelles and serving as structural components of the nuclear lamina and sarcomeres.
• They also participate in some cell-cell and cell-matrix junctions.
• Formed by a large, heterogeneous group of proteins
At least 5 major filament types
•Keratin - epithelial cells•Neurofilaments – neurons•Vimentin-containing filaments – fibroblasts and other mesenchymal derivatives•Desmin – smooth, striated and cardiac muscle•Glial filaments – non-neural cells of CNS: astrocytes, oligodendrocytes and microglial cells.
155
KERATIN FILAMENTS
• They are most abundant in the stratified squamous epithelium.
• The so called tonofilaments are bundles of keratin filaments.
• In other epithelial cells, they often form a network around the nucleus with bundles radiating to the periphery where they terminate in local specializations of the membrane for cell to cell attachments.
• Unlike microtubules and microfilaments, they do not undergo rapid assembly and disassembly.
Their function is mainly mechanical, stabilizing the shape of the cell and strengthening its attachment to other cells and to the basal lamina.
156
Contd…DESMINThey form the loose network around and between the contractile elements.It transmit the pull of the contractile proteins and ensures a uniform distribution of tensile force throughout the smooth muscle cell.
NEUROFILAMENTS• They are oriented parallel to the long axis of the nerve axon.• They provide internal support and help to maintain the gelated state of the axoplasm.
157
158
There are number of polypeptides associated with the intermediate filaments.
Filaggrin – found in epidermal cells, binds to keratin filaments, causing them to aggregate in bundles.Plectin – located at sites of vimentin intermediate filaments and is responsible for their linkage into a cytoskeletal network.Synamin – found in muscle having similar role.
• Microtubules are hollow cylinders about 23 nm in diameter (lumen = approximately 15 nm in diameter), most commonly comprising 13 protofilaments which, in turn, are polymers of alpha and beta tubulin.
• They are commonly organized by the centrosome (microtubule organizing center of the cell).
159
• The polymers project from the centrosome, where the γ tubulin is present that is necessary for the “nucleation” of the polymers.
• There is a + end projecting into the cytoplasm and a – end that often remains anchored in the centrosome.
160
In nine triplet sets (star-shaped), they form the centrioles
161
Contd…
• In nine doublets oriented about two additional microtubules (wheel-shaped) they form cilia and flagella.
• The formation is commonly referred to as a "9+2" arrangement, wherein each doublet is connected to another by the protein dynein.
• As both flagella and cilia are structural components of the cell, and are maintained by microtubules, they can be considered part of the cytoskeleton.
162
163
They play key roles in:
•Intracellular transport (associated with dyneins and kinesins, they transport organelles like vesicles).
•The mitotic spindle.
•Synthesis of the cell wall in plants.
164
MICROTUBULES ASSOCIATED PROTEINS (MAPS)
Kinesin – it is responsible for movement of vesicle along microtubules.• One end is bound to the vesicle while the other end undergo cyclic interaction with the microtubule which moves the vesicle towards plus end.
Cytoplasmic Dynein – to achieve two-way traffic, it moves vesicle towards the minus end.
Dynamin – it forms regularly spaced cross-bridges between neighboring microtubules.• Serve as a motor for sliding some microtubules of the bundle with respect to other, causing elongation.
Axoplasmic dynein – it is a motor for ciliary motion. 165
• Originally they were considered to be non-living cytoplasmic bodies such as secretion granules, mineral deposits, and particulate matter taken into the cell.
• Inclusion is now a generic term applied to a variety of cytoplasmic constituents including crystals, pigments, and stored foods including proteins, carbohydrates and fats.
166
CRYSTALS
• Crystals have been observed as free particles in the cytoplasm and are associated with the major type of organelles like lysosomes, and mitochondria.
• They are found in eosinophils.
• Iron containing crystals, recovered from RBC’s are the most commonly encountered.
167
PIGMENTS• Pigments found in some cells may impart color to the tissue.• Certain pigments are the product of tissue components and are classified as endogenous pigments.• Those which are introduce into the body are exogenous pigments.
Exogenous pigments:•The most common exogenous pigment is variety of carotenes found in vegetables such as carrots and tomatoes. It is fat soluble, therefore term lipochrome is used sometimes.• It imparts yellow hue to the tissue and excessive intake may cause carotenemia, in which skin appear yellow or red. 168
• Salts of silver and gold used in treatment of various cardiovascular disorders and arthritis, when administered in massive doses, results in grey subcutaneous deposits.
• Lead poisoning is blue streak on the gums known as the gingival lead line.
Endogenous pigments( lipofuscin, melanin and haemoglobin)
• Lipofuscin in fresh tissue preparations ranges in color from yellow to bronze and because of its lipid component may be visualized in histologic sections with fat stain.
• It occurs as granular aggregations in cardiac muscle and in hepatic, nerve, and certain cells of brain. (indigestible residues
of lysosomal activity)
169
Contd…
170
• Melanin, a nitrogenous pigment with a color range from tan to dark brown, produced in the presence of strong light rays by melanocytes which originate in the neural crest.
• Hemoglobin (oxygen carrying pigment of RBC), at the end of their limited life span, these cells are phagocytized by macrophages in spleen and liver and broken down in lysosomes to hemosiderin(iron containing, ferritin) and bilirubin.
• Hemosiderin accumulates in phagocytic cells resulting in a
distinct brown color of certain areas of the spleen.
171
PROTEINSCoupling of amino acids to form proteins occur on the ribosomes. Those not used immediately are reserved by the cell for later use in metabolism, organelle production, mitosis according to the cell or tissue demands.
CARBOHYDRATES•Starches and sugars are reduced to glucose during digestion and are stored in cells as glycogen.• Routine histologic preparations employing H & E staining remove glycogen from the cell so that the cytoplasm appears vacuolated.
• Electron microscope reveal glycogen inclusions as minute particles 15 to 30 nm in diameter.
• They may be scattered throughout the cytoplasm as beta particles or in clusters or rosettes as alpha particles.
• Glycogen is normally confined to the cytoplasm, but in diabetes and rare glycogen storage disease, it may accumulate in the nucleus.
172
Contd…
• There are two basic cellular designs-prokaryotic and eukaryotic.
• Eukaryotic cells are usually much larger and more functionally complex than are prokaryotic cells.
• Prokaryotic cells consist of a single membrane-bound compartment in which nearly all cellular functions occur.
• Eukaryotic cells contain numerous membrane-bound compartments called organelles; different organelles carry out different functions.
• The defining organelle of eukaryotic cells is the nucleus, which contains the cell's chromosomes and serves as its control center.
173
• For a cell to function properly, the movement of molecules into and out of the nucleus must be carefully controlled.
• Traffic across the nuclear envelope occurs through nuclear pores, which contain a multiprotein nuclear pore complex that serves as gatekeeper.
• Both passive and active transport of materials occurs through these nuclear pore complexes.
• Active import and export of proteins and RNAs involves built-in signals that target cargo to the correct compartment
174
Contd…
• The cytoskeleton is an extensive system of fibers that serves as a structural support for eukaryotic cells.
• Elements of the cytoskeleton also provide the machinery for moving vesicles inside cells and for moving the cell as a whole through the flagella or cilia.
• Cell motility and the movement of vesicles inside cells both depend on motor proteins, which can convert chemical energy into movement.
175
176
THANK YOU
