Ch 6 A Tour of the Cell
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Microscopes
Light microscope­ uses light
resolving power­measure of clarity of image (min. distance
two points can be separated
and still seen as two points)
Electron­beam of electrons, instead of light
Scanning electron­looks at surface of organism, film of gold, beam excites electrons of gold and collected
to show image
transmission electron­ looks inside cell,beam aimed at thin section, uses magnets to bend and focus electrons
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rabbit trachea
Transmission electron micrograph scanning electron micrograph
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How do you think scientists study the components of cells?
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Cell Fractionation­ takes cells apart
uses ultracentrifuge ­ 130,000 rpm
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Prokaryotic cell
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Escherichia coli (E. coli)­ gram negative rod
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At a minimum, what structures or components must a cell contain to be considered alive?
Out of the cells living today, which types of cells have the above components?
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Prokaryotic
circular DNA
Eukaryotic
DNA in strands
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Surface Area to volume Ratio
higher the ratio, the easier it is for cells to exchange materials
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Plasma membrane
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Animal Cell
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Plant Cell
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Importance of membranes
• partition cell into compartments
• help in cell metabolism
­have enzymes in membranes
­specific metabolic reactions happen here
• allows for many reactions to happen at once in cell
• each membrane has unique make­up of lipids, proteins depending on the function
ex. mitochondria for cell respiration
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• double membrane (each a lipid bilayer) ­ separated by space
• at pore, membranes are fused
• pore complex­lines pores and regulates what goes in and out (large molecules)
• nuclear lamina­ net­like protein filaments, keeps shape of nucleus
Nucleus
• chromatin ­ DNA strands, uncoiled
• nucleolus ­ where ribosomes made
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Ribosomes­ ribosomal RNA and protein
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The Endomembrane system
­made up of many internal membranes
­the membranes are connected to each other or via vessicles (sacs of membrane)
­Each membrane is unique in function
­Includes
nuclear envelope
endoplasmic reticulum
Golgi Apparatus
lysosomes
vacuoles
plasma membrane
Inside cell
outside cell
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Endoplasmic reticulum
­is half of all membranes in eukaryotic cell
­includes tubules and cisternae (fluid filled spaces)
­continuous with nuclear envelope
­cisternae is continuous with nuclear envelope space
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Smooth ER
­no ribosomes attached
­lots of enzymes located here ­synthesize lipids (oils, phospholipids, steroids)
­catalyzes a key step in moving glucose from stored glycogen in liver
­allows glucose to leave cell
­other enzymes of liver detoxify drugs/poisons
­muscles cells rely on these enzymes to move calcium for a contraction
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Rough ER
­contains ribosomes attached to it
­found in cells that secrete proteins
­polypeptides made by ribosomes go into cisternal space ­makes membranes by making the membrane proteins and then inserting them directly into the membrane
­has enzymes that make phospholipids from materials in cytosol
­when membrane gets larger, part can become vesicles and travel to other parts of the endomembrane system
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Golgi apparatus
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­ "packaging and shipping part of a factory"
­flattened membranous cisternae
­cis side = receives material (fusing of vesicle)
­trans side = giving off side, vesicles leave from this side
­going from cis to trans sides ­ products get modified due to enzymes
­manufactures pectin, and other noncellulose polysaccharides
­packages materials into vesicles to go to other places
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Lysosomes
­membrane bound sac filled with digestive enzymes
­hydrolyzes all organic compounds
­enzymes work at pH 5
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­"Suicide sac" ­ if many ruptured, can kill cell (autodigestion)
­lysosomal enzymes and its membrane are made by the rough ER and then moved to Golgi
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­fuse to food vacuoles (from phagocytosis) to digest the food
­monomers then pass to cytosol to be used by cell
­can also fuse to other parts of cell (orgnanelles/cytosol)
­helps keep cell new
­some inherited diseases affect lysosomal metabolism
­Tay­Sachs in brain
­Pompe's disease in liver
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Vacuoles
= large vesicles
­membrane bound
Types:
food vacuoles ­ from phagocytosis
contractile vacuoles ­ in freshwater protists, pump water out of cell
Central vacuoles­ in plant cells
tonoplast = membrane around central vacuole (selective)
stores proteins, ions, stores pigments, defense compounds against herbivores
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Review of endomembrane system
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Mitochondria
• sites of cellular respiration, make ATP from sugars, fats, and other fuels • not part of the endomembrane system ­ their proteins come from free ribosomes and their own ribosomes
• contain a small amount of DNA (circular like prokaryotes)
• can grow and reproduce by themselves
• eukaryotic cells may have one large mitochondria or many small mitochondria
• move around in cell on tracks of cytoskeleton
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• have smooth outer membrane and a folded inner membrane (cristae)
• cristae increase surface area for cell respiration to happen
• fluid is between the membranes
• inside inner membrane = mitochondrial matrix ­ contains DNA, ribosomes, enzymes, fluid
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Chloroplasts
• found in plants and eukaryotic algae
• sites of photosynthesis
• not part of endomembrane system
• has own DNA (circular), ribosomes
• its protein comes from free ribosomes and from their own ribosomes
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• type of plastid amyloplasts store starch in roots and tubers
chromoplasts store pigments for fruits and flowers
chloroplasts contain green pigment chlorophyll ­ produce sugar via photosynthesis
• has two membranes
inside inner membrane fluid = stroma (Contains DNA, ribosomes & enzymes)
also contains membranous sacs = thylakoids (stacked as grana ­ where light reactions happen)
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Peroxisomes
• contain enzymes to transfer hydrogen from substrates to oxygen
­intermediate = hydrogen peroxide (poisonous)
­has another enzyme that converts hydrogen peroxide to water
and oxygen gas
• functions:
­breakdown fatty acids used in mitochondria for fuel
­detoxify alcohol and other harmful compounds
­glyoxysomes ­ convert fatty acid in seeds to sugars
• have a single membrane
• not from endomembrane system
• divide when get to a certain size
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Cytoskeleton
= network of fibers throughout cytoplasm
function ­ organizes structures and activities of cell
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Cytoskeleton Support
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provides anchorage for organelles and cytosolic enzymes
can come apart in one part of cell and reassemble in another part helps to change shape of cell
Cell motility
• interacts with motor proteins
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­cilia/flagella motor proteins pull cytoskeleton past each other
­happens in muscle cells too
motor molecules also act like "monorails" carrying vesicles or organelles
cytoskeleton and motor proteins move materials via streaming
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How motor proteins and cytoskeleton move other things in cell
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Three types of fibers of cytoskeleton
1. microtubules
­thickest fibers, hollow rods
­made of globular protein ­ tubulin ­ can grow or shrink based on # or tubulin molecules
­function: a. move chromosomes during cell division
b. guide motor proteins that carry organelles to different places in cell
c. structural support for cilia and flagella
cilia ­ hairlike structures, move like oars, many
flagella ­ one or few, long, whiplike structure
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­grow out of a centrosome near nucleus
­ in animals cells has pair of centrioles with 9 triplets of microtubules in a ring
­during cell division centrioles replicate 40
Flagella vs. cilia
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­Both cilia and flagella have same structure
­core of microtubules covered in plasma membrane
­nine doublets of microtubules around a pair at center
= "9 + 2"pattern
­anchored by basal body ­ structure is like centriole
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­cilia and flagella are driven by motor protein called dynein
­dynein grabs, moves and releases the outer microtubules
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II. Microfilaments
• =thinnest of cytoskeletal fibers
• made of solid rods of actin
• designed to resist tension
• form a network just inside membrane
• actin is also found in muscle tissue with myosin, myosin walks along actin so contraction can happen
• actin/myosin divides cytoplasm of animal cells in cell division
• also causes amoeboid movement (pseudopodia)
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Actin and myosin in plants cause cytoplasmic streaming
=circular flow of cytoplasm, helps move materials
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III. Intermediate filaments
function: bear tension
made from keratins
reinforce cell shape and fix organelle position
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Cell Surfaces and Junctions
Cell walls ­ prokaryotes, fungi, some protists
­protects cell, maintains shape, prevents lots of water from coming into cell
­support against gravity
composition changes depending on species
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Extracellular matrix
function: support, adhesion, movement and regulation
­made of glycoproteins (collagen fibers), proteoglycans
­integrin proteins connect extracelluar matrix to plasma membrane
cell behavior ­
can influence genes via signaling pathways
helps embryonic tissue orient its microfilaments with ECM
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Types of Cell Junctions
Plasmodesmata
­channels between adjacent plant cells
­cytosol goes through here
In animals
tight junctions ­ membranes of adjacent cells are fused
­form "belts'
prevent leakage of extracellular fluid
Desmosomes ­ anchoring junctions, fasten cells together
­keratin reinforces desmosomes
Gap Junctions­ communicating junctions
­membrane proteins surround pores
­salt ions, sugar, amino acids, small molecules pass through here
­ in embryos ­ communication for development here
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Animal junctions
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