The Cellular Level of Organization - University Of Illinois · The Cellular Level of Organization ... the overall function of cellular transport ... is distinct from molarity because

© 2012 Pearson Education, Inc.

PowerPoint® Lecture Presentations prepared by Jason LaPres Lone Star College—North Harris

3 The Cellular Level of Organization

NOTE: Presentations extensively modi6ied for use in MCB 244 & 246 at the University of Illinois by Drs. Kwast & Brown (2013-‐2014)


An Introduction to Cells: Learning Outcomes

•  Understand the basic anatomy & physiology (function) of the cell, including structure/function of the plasma membrane and cellular organelles (For a review of basic cell biology, please read pp. 63 – 85, sec1 – 4).

•  Understand the difference between osmolarity and tonicity.

•  Understand and be able to describe the different types of membrane transport (passive vs. active; uniport vs. symport vs. antiport; endocytosis vs. exocytosis).

•  Describe the overall function of cellular transport systems.

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An Introduction to Cells •  Cell Theory

•  Developed from Robert Hooke’s research

•  Cells are the building blocks of all plants and animals

•  All cells come from the division of preexisting cells

•  Cells are the smallest units that perform all vital physiological functions

•  Each cell maintains homeostasis at the cellular level

•  Two General Classes of Cells: 1. Germ (sex) cells

a. Sperm b. Oocyte

2. Somatic cells (soma = body) All body cells except sex cells

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Defining the Cell’s Boundary Plasma membrane (cell membrane) separates cytoplasm from the

extracellular fluid (interstitial fluid)

•  Cytoplasm = all materials within the cell except for the nucleus •  Cytosol = liquid •  Intracellular structures collectively known as organelles

•  Functions of the Plasma Membrane

•  Physical isolation •  Barrier

•  Regulates exchange with environment •  Ions and nutrients enter •  Wastes eliminated and cellular products released

•  Monitors the environment •  Extracellular fluid composition •  Chemical signals

•  Structural support •  Anchors cells and tissues 4


The Cytosol & Organelles

•  Cytosol (fluid) •  Dissolved materials: nutrients, ions, proteins, and wastes

•  High potassium/low sodium (Na+/K+-ATPase pump)

•  High protein

•  High carbohydrate/low amino acid and fat (the latter found primarily in adipose tissue)

•  Organelles •  Membranous

•  endoplasmic reticulum (ER), the Golgi apparatus, lysosomes, peroxisomes, and mitochondria

•  Non-membranous •  Includes the cytoskeleton, microvilli, centrioles, cilia, ribosomes,

and proteasomes

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The Anatomy of a Model Cell (Fig 3-1)

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Figure 3-1 Anatomy of a Model Cell

Proteins organized in fine filaments or slender tubes Functions Strength and support; movement of cellular structures and materials

Plasma Membrane

Functions Isolation; protection; sensitivity; support; controls entry and exit of materials

Free ribosomes

= Plasma membrane

= Nonmembranous organelles

= Membranous organelles Microfilament

Microtubule

Lipid bilayer containing phospholipids, steroids, proteins, and carbohydrates

Cytosol (distributes materials

by diffusion)

Cytoskeleton

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= Plasma membrane


= Membranous organelles

Microvilli Membrane extensions containing microfilaments

Function Increase surface area to facilitate absorption of extra-cellular materials

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= Plasma membrane = Nonmembranous organelles


Proteasomes Hollow cylinders of proteolytic enzymes with regulatory proteins at their ends

Functions Breakdown and recycling of damaged or abnormal intracellular proteins

Cilia Cilia are long extensions containing microtubule doublets in a 9 + 2 array (not shown in the model cell)

Function Movement of material over cell surface

Ribosomes RNA + proteins; fixed ribosomes bound to rough endoplasmic reticulum, free ribosomes scattered in cytoplasm

Function Protein synthesis 9



= Plasma membrane


= Membranous organelles Secretory vesicles

CYTOSOL

Centrosome and Centrioles

Centrosome

Centrioles

Cytoplasm contains two centrioles at right angles; each centriole is composed of 9 microtubule triplets in a 9 + 0 array Functions Essential for movement of chromosomes during cell division; organization of microtubules in cytoskeleton

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Golgi apparatus Stacks of flattened membranes (cisternae) containing chambers

Functions Storage, alteration, and packaging of secretory products and lysosomal enzymes

Mitochondria

Double membrane, with inner membrane folds (cristae) enclosing important metabolic enzymes

Functions Produce 95% of the ATP required by the cell

Endoplasmic reticulum (ER) Network of membranous channels extending throughout the cytoplasm

Functions Synthesis of secretory products; intracellular storage and transport

Rough ER modifies and packages newly synthesized proteins

Smooth ER synthesizes lipids and carbohydrates

Peroxisomes Vesicles containing degradative enzymes

Functions Catabolism of fats and other organic compounds, neutralization of toxic compounds generated in the process

NUCLEUS

= Plasma membrane




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Peroxisomes Vesicles containing degradative enzymes

Functions Catabolism of fats and other organic compounds, neutralization of toxic compounds generated in the process

Lysosomes

Free ribosomes

Vesicles containing digestive enzymes

Functions Intracellular removal of damaged organelles or pathogens

= Plasma membrane = Nonmembranous organelles



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Chromatin

Nuclear envelope

Nucleolus (site of rRNA

synthesis and assembly of

ribosomal subunits)

Nuclear pore

NUCLEOPLASM

NUCLEUS Nucleoplasm containing nucleotides, enzymes, nucleoproteins, and chromatin; surrounded by a double membrane, the nuclear envelope

Functions: Control of metabolism; storage and processing of genetic information; control of protein synthesis


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3-1 Plasma Membrane •  Membrane Lipids (phospholipids, glycolipids & cholesterol: ~42% by wt.)

•  Double layer of phospholipid molecules

•  Hydrophilic heads—toward watery environment, both sides

•  Hydrophobic fatty-acid tails—inside mem.

•  Barrier to ions and water—soluble cmpds

•  Membrane Proteins (~55% by weight) •  Integral proteins

•  Within the membrane

•  Peripheral proteins

•  Bound to inner or outer surface of the membrane

•  Membrane Carbohydrates (proteoglycans, glycoproteins & -lipids : ~3% by wt.) •  Extend outside cell membrane; form “sticky” glycocalyx coat (lubricates, anchors,

act as receptors, and in recognition by the immune system) 14


3-1 Plasma Membrane •  Membrane Proteins

•  Anchoring proteins (stabilizers) •  Attach to inside or outside structures

•  Recognition proteins (identifiers) •  Label cells as normal or abnormal

•  Enzymes •  Catalyze reactions

•  Receptor proteins •  Bind and respond to ligands (ions, hormones)

•  Carrier proteins •  Transport specific solutes through membrane

•  Channels •  Regulate water flow and solutes through membrane

•  Membrane Carbohydrates •  Functions of the glycocalyx:

•  Lubrication and protection

•  Anchoring and locomotion

•  Specificity in binding (receptors)

•  Recognition (immune response) 15


Figure 3-7 Protein Synthesis

DNA

mRNA

Ribosome

Nucleus

Cytoplasm

Rough ER

Protein released into cytoplasm

Smooth ER

Transport vesicle

Nuclear pore

Central Dogma in Biology 1.  DNA transcribed to mRNA

2.  Ribosomes translate mRNA to make proteins

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Cisternae

Lysosome

Secreting vesicle

Exocytosis at cell surface

Trans face of Golgi complex

Membrane renewal vesicle

Membrane renewal

Cis face of Golgi

complex

Figure 3-7 Protein Synthesis, Modification and Export

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3-5 Diffusion and Osmosis

•  Membrane Transport

•  The plasma (cell) membrane is a barrier, but:

•  Nutrients must get in

•  Products and wastes must get out

•  Permeability determines what moves in and out of a cell, and a membrane that:

•  Impermeable: lets nothing in or out

•  Freely Permeable: lets anything pass

•  Selectively Permeable: restricts movement of certain (selective) substances

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•  Plasma membrane is selectively permeable

•  Allows some materials to move freely

•  Restricts other materials

•  Selective permeability restricts materials based on: •  Size

•  Electrical charge

•  Molecular shape

•  Lipid/water solubility 19




•  Transport through a plasma membrane can be:

•  Active (requiring energy [ATP])

•  Passive (no energy required)

•  Diffusion (passive)

•  Carrier-mediated transport (passive or active)

•  Vesicular transport (active)

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•  Diffusion •  All molecules are constantly in motion

•  Molecules in solution move randomly

•  Random motion causes mixing

•  Concentration is the amount of solute in a solvent

•  Concentration gradient •  More solute in one part of a solvent than another

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•  Factors Influencing Diffusion •  Distance the particle has to move

•  Molecule Size •  Smaller is faster

•  Temperature •  More heat, faster motion

•  Concentration Gradient •  The difference between high and low concentrations

•  Electrical Forces

•  Opposites attract, like charges repel

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Diffusion across Plasma Membranes

•  Can be simple (through lipid bilayer) OR channel mediated

•  Materials that diffuse by simple diffusion •  Lipid-soluble compounds

(alcohols, fatty acids, and steroids)

•  Dissolved gases (oxygen

and carbon dioxide)

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3-5 Diffusion across the Plasma membrane •  Channel-mediated diffusion

•  Works for small, water-soluble compounds and ions

•  Factors influencing channel-mediated diffusion: •  Size, Charge, Interaction with the channel (leak)

Figure 3-15 Diffusion across the Plasma Membrane

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•  Osmosis: A Special Case of Diffusion •  Osmosis is the diffusion of water—in this case—

across the cell membrane

•  More solute molecules, lower concentration of water molecules

•  Membrane must be freely permeable to water, selectively permeable to solutes

•  Water molecules diffuse across membrane toward solution with more solutes (less water)

•  Volume increases on the side with more solutes

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Figure 3-16 Osmosis

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3-5 Osmolarity and Tonicity •  Osmolarity is a measure of solute concentration (number of osmoles (Osm)

of solute per liter) •  Osmolarity is distinct from molarity because it measures moles of solute particles

rather than moles of solute--distinction arises because some compounds can dissociate in solution whereas others cannot.

•  Tonicity describes the osmotic effect of a solution on a cell (shrinks, swells, or no change) •  two fluids may have equal osmolarity but different tonicity (e.g., because the

cell is selectively permeable to some but not all solutes)

•  Isotonic (iso- = same, tonos = tension) •  A solution that does not cause osmotic flow of water in or out of a cell

•  Hypotonic (hypo- = below) •  A solution that causes the cell to swell (for erythrocyte [RBC], if it burst = hemolysis)

•  Hypertonic (hyper- = above)

•  A solution that causes the cell to shrink (called crenation for erythrocyte) 27


Figure 3-17 Osmotic Flow across a Plasma Membrane

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3-6 Carriers & Vesicles: Carrier-Mediated Transport •  Carrier-Mediated Transport •  Of ions and organic substrates

•  Characteristics •  Specificity

•  One transport protein, one set of substrates

•  Saturation Limits •  Rate depends on transport proteins, not substrate

•  Regulation •  Cofactors such as hormones

•  Cotransport (symport) •  Two substances move in the same direction at the same time

•  Countertransport (antiport) •  One substance moves in while another moves out 29


3 Classes of Carrier Proteins •  Uniport (Uniporter)

•  Transport of a single molecule. •  e.g., GLUT1 - glucose carrier

•  Symport (Symporter) •  Cotransport of two dissimilar solutes together (obligatorily coupled)

•  A gradient of one substrate--usually an ion--may drive uphill transport of a co-substrate (i.e., against a conc. gradient). •  e.g: glucose-Na+ symport, in plasma membranes of some epithelial cells

(next slide)

•  Antiport (Antiporter) •  “Exchange diffusion” where one solute is exchanged for another (also

called countertransport by your book).

•  Often exhibit "ping pong" kinetics –1st is transported and released causing a conformational change in the protein that facilitates the transport of the 2nd. •  e.g., mitochondrial ADP/ATP exchanger (inner membrane), Na+K+-ATPase

3-6 Carriers & Vesicles: Carrier Protein Classes

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3-6 Carriers & Vesicles: Carrier-Mediated Transport •  Facilitated Diffusion (Passive)

•  Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids)

•  Molecule binds to receptor site on carrier protein

•  Protein changes shape, molecules pass through

Fig. 3-18

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3-6 Carriers & Vesicles: Carrier-Mediated Transport •  Active transport (primary or

secondary): •  molecules move against a concentration

gradient •  requires energy, such as ATP

•  ion pumps move ions (e.g., Na+, K+, Ca2+, Mg2+)

•  exchange pump counter-transports two ions at the same time

Primary Active Transport •  For Na+/K+-ATPase, moves 3 Na+ out

and 2 K+ into the cell per ATP.

•  electrogenic as it results in an unequal charge across the membrane

•  antiport carrier protein (countertransport)

• 

Figure 3–19 The Sodium–Potassium Exchange Pump (Na+/K+-ATPase)

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3-6 Carriers & Vesicles: Carrier-Mediated Transport •  Secondary Active Transport

•  Transport mechanism itself does not directly require energy •  Example: Glucose uptake via glucose-Na+ symport

•  Na+ concentration gradient drives glucose transport •  Na+/K+-ATPase pumps Na+ back out

Figure 3–20 Secondary Active Transport

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3-6 Carriers and Vesicles: Vesicular Transport

•  Vesicular Transport (Bulk Transport)

•  Materials move into or out of cell in vesicles

•  Endocytosis – the cell takes in macromolecules by forming new

vesicles from the plasma membrane (3 types)

1. Phagocytosis – “cell eating” – for solid substances

2. Pinocytosis - “cell drinking” – for dissolved substances

3. Receptor-Mediated (receptors = glycoproteins)

•  Exocytosis - transport vesicles migrate to plasma membrane,

fuse with it and release their contents

•  Granules or droplets are released from the cell 34


Figure 3-21 Receptor-Mediated Endocytosis EXTRACELLULAR FLUID

Exocytosis

Ligand receptors

Coated vesicle

Ligands binding to receptors

Endocytosis

Ligands

Ligands removed Secondary

lysosome

Primary lysosome

F u s i o c h m e n t

CYTOPLASM

Receptor-Mediated Endocytosis

Target molecules (ligands) bind to receptors in plasma membrane.

Areas coated with ligands form deep pockets in plasma membrane surface.

Pockets pinch off, forming endosomes known as coated vesicles.

Coated vesicles fuse with primary lysosomes to form secondary lysosomes.

Ligands are removed and absorbed into the cytoplasm.

The lysosomal and endosomal membranes separate.

The endosome fuses with the plasma membrane, and the receptors are again available for ligand binding.

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Figure 3-22 Pinocytosis and Phagocytosis

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Table 3-2 Mechanisms Involved in Movement across Plasma Membranes

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Chapter 3 Summary Questions and Goals

•  Be able to describe the overall function of the cell’s major organelles.

•  Be able to describe the various mechanisms for transporting substances across the plasma membrane.

•  Know the 3 types or classes of carrier proteins, the difference between passive and active transport (both primary and secondary).

•  Know the difference between tonicity and osmolarity.

•  Be able to describe the 3 types of mechanisms by which bulk substances enter the cell.

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The Cellular Level of Organization - University Of Illinois · The Cellular Level of Organization ... the overall function of cellular transport ... is distinct from molarity because