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The Tour of the Cell. Chapter 6. The Fundamental Units of Life. All living things composed of cells Cell structure correlated to cell function All cells descend from existing cells. Microscopy. Light microscope = visible light through specimen magnified by lenses Up to 1000X. - PowerPoint PPT Presentation
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The Tour of the Cell
Chapter 6
The Fundamental Units of Life
• All living things composed of cells• Cell structure correlated to cell function• All cells descend from existing cells
Microscopy
• Light microscope = visible light through specimen magnified by lenses– Up to 1000X
• Electron microscopes (EMs)
• Scanning EM (SEM) focus beam of electrons onto surface 3-D image
• Transmission EM (TEM) • focus beam of electrons through specimen • internal structures
• Gills of fish yeast
• HIV
Cell Fractionation
centrifugeseparates cell
components
Homogenization
Homogenate
Differential centrifugation
Tissuecells
TECHNIQUE
Supernatant poured into next tube
TECHNIQUE (cont.)
Homogenate
Pellet
Supernatant
1000 g 10 min
20,000g 20 min
80,000g 60 min
150,000g 3 hr
Nuclei, debris mitochondria membranes ribosomes
• Prokaryotic cells= Archaea and Bacteria• No nucleus, no membrane-bounded organelles• DNA in nucleoid region
0.5 µm
Eukaryotic cells = Plants, Animals, Fungi, Protista•DNA in nucleus•Organelles•Membrane bounded
•Cytoplasm = fluid + organelles•Cytosol = fluid
Featured scientist: Robert Hooke 1635-1703
Best CLM of its time!Micrographia was a best seller
The famous slide:
. . . I could exceedingly plainly perceive it to be all perforated and porous, much like a Honey-comb, but that the pores of it were not regular. . . . these pores, or cells, . . . were indeed the first microscopical pores I ever saw, and perhaps, that were ever seen, for I had not met with any Writer or Person, that had made any mention of them before this. . .
1. The plasma membrane = selective barrier allows passage of oxygen, nutrients, waste etc
• Composed of phospholipid bilayer
Features of cells
2. Surface to Volume ratio high
•Small cells have greater surface area relative to volume
•Larger organisms do not have larger cells than smaller organisms
Human Rat
The Eukaryotic Cell
1. The Nucleus
Hela cells
A. Nuclear envelope (NE)
–Double membrane; each a bilayer–Pores regulate entry and exit of molecules
from nucleus
Nuclear lamina fibrous proteins maintain shape of nucleus
Lamin A and lamin B can bind histones – may have role in chromosome organization
B. Chromatin = DNA + proteins
•Chromosomes = strands of chromatin
C. Nucleolus –Assembles ribosomes
• D. Nucleoplasm– Viscous fluid of nucleus
2. Ribosomes: Protein Factories
• Assemble amino acids into polypeptides– cytosol (free ribosomes)– RER/NE (bound ribosomes)
3. The Endomembrane System
• Components– Nuclear envelope– Endoplasmic reticulum (ER)– Golgi apparatus– Lysosomes– Vacuoles– *Plasma membrane
A. The Endoplasmic Reticulum
• >half of total membrane• continuous with nuclear envelope– Smooth ER – lacks ribosomes
1.Synthesizes lipids2.Metabolizes carbohydrates3.Detoxifies poison4.Stores calcium
• Rough ER (RER)
– Ribosomes assemble proteins thread through ER lumen transport vesicles
– Membrane factory
B. The Golgi Apparatus
• flattened membranous sacs called cisternae• cis and trans face
trans face(“shipping” side of Golgi apparatus)
• Functions of the Golgi apparatus:– Modifies proteins from ER– Sorts and packages protein into transport vesicles
Golgi makes polysaccharides in plants
Smooth ER
Nucleus
Rough ER
Plasma membrane
cis Golgi
trans Golgi
Where do the vesicles go?
• Virtual cell
Note: Ribosome, RER, vesicle, Golgi
C. Lysosomes
• membranous sac of enzymes that digest macromolecules
• What do they do?recycle cell components (autophagy)get rid of phagocytosed invadersform food vacuoles
How do they work?
phagocytosis A cell engulfs another cell to form a food vacuole– lysosome fuses with food vacuole and digests
molecules
D. Vacuoles– Food vacuoles formed by phagocytosis– Contractile vacuoles
• freshwater protists• store or/and pump excess water out of cells
– Central vacuoles• found in many plant cells• hold organic compounds and water
4. Mitochondria
• cellular respiration generates ATP (energy)• contain mtDNA• all eukaryotic cells have mt– Some have 1, some 1000sOuter
membrane
Cristae
mitochondrion
Mitochondria
• outer membrane and inner membrane fold into cristae– large surface area for enzymes that synthesize ATP
5. Chloroplasts (plastid)• found in plants and algae• sites of photosynthesis– green pigment chlorophyll, enzymes, other
molecules
6. Peroxisomes
• detoxify
catalase2 H2O2 2H2O + O2
(toxic)
• Bioflix Tour of animal cell – the big picture• Note:– Sticky extracellular matrix– Plasma membrane– Cytoskeleton – Mitochondria- ATP, surface area– Nucleus and nuclear envelope with pores– DNA and protein wrappings, code for protein– Ribosome builds protein– Endomembrane system = RER and SER + Golgi
7. Cytoskeleton
• Network of protein fibers organize structures and activities in cell
• Anchors organelles• Maintains cell shape
Cytoskeleton
• interacts with motor proteins to transport cargo or for movement
10 µm
Column of tubulin dimers
Tubulin dimer
25 nm
Actin subunit
10 µm
7 nm
5 µm
Keratin proteinsFibrous subunit
(keratinscoiled together)
8–12 nm
• Vesicles in a plant cell• Golgi sorting and packaging
8. Centrosomes and Centrioles
• Centrosome– microtubule-
organizing center
Centrosome
Microtubule
Centrioles0.25 µm
Longitudinal section of one centriole
Cross sectionof the other centriole
– centrioles • animal cells only• centrosome has pair • each with 9 triplets of microtubules arranged in a ring
centrosome
9. Cilia and Flagella
• Locomotor appendages of some cells
• Movement pattern controlled by microtubules
• Example: paramecium, algae
10. Extracellular materials
• Cells secrete materials external to plasma membrane
• Harvard life of a cell – 3 min.• Can you find –
– Cell membrane– Cytoskeleton– Microtubule polymerization and depolymerization– A motor protein walking along the cytoskeleton– Lysosomes and mt– A centriole– Nuclear pores with mRNA leaving nucleus– RER– Ribosomes making proteins– Vesicles budding with cis face of Golgi– Proteins leaving the cell
A. Cell Walls of PlantsAlso, prokaryotes, fungi, some protists
• protects, maintains shape, prevents excessive uptake of water
• cellulose fibers + polysaccharides and protein
• Layers of cell wall
– Primary wall: thin – Middle lamella: between primary walls of adjacent
cells– Secondary wall (some cells): between plasma
membrane and primary cell wall
• Plasmodesmata -channels between adjacent plant cells for water, nutrients…..
B. Extracellular Matrix (ECM) of Animal Cells
• No cell walls • Functions :
Support, Adhesion, Movement, Regulation
• Structure– Glycoproteins: bind to receptor proteins in membrane
called integrins• Integrins “glue cytoskeleton to ECM
Collagen
Fibronectin
Plasma membrane
Proteoglycan complex
Integrins
CYTOPLASM
Micro-filaments
EXTRACELLULAR FLUID
Collagen in the ECM Collagen, fibronectin and laminin of cartilage
C. Intercellular Junctions
• Function – Adherance, communication through direct physical contact
• 4 Types:– Plasmodesmata- plant cells– Tight junctions– Desmosomes– Gap junctions
• Tight junction seals against fluid and ions
• Desmosome in cells that experiencemechanical stress (skin)
• Gap junction connects cytoplasm to allow small molecules, ions to pass from cell to cell – connexin protein
Tight junction
0.5 µm
1 µm
Desmosome
Gap junction
Extracellularmatrix 0.1
µm
Plasma membranesof adjacent cellsSpacebetweencells
Gapjunctions
Desmosome
Tight junction
The Cell: Living Unit Greater Than Sum of Its Parts
• integration of structures and organelles to function
• example, a macrophage’s ability to destroy bacteria involves coordinating cytoskeleton, lysosomes, and plasma membrane
5 µ m