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Transcript
Chapter 7 A tour of the Cell What do all cells have in common? Prokaryotic Cells •Pro = before; Karyon = nucleus •Cells w/o nucleus •Circular DNA free in “nucleoid” region •1 – 10 micrometers in size (size of mitochondria) •No membrane organelles •Cell wall •Ex. bacteria Eukaryotic Cells •Eu = true; Karyon = nucleus •Phospholipid plasma membrane •Cytoplasm •Ribosomes •Genetic Material (DNA) •Cells w/ nucleus •Linear DNA contained in nucleus •10 – 100 micrometers in size •With membraneorganelles (endomembrane system) •Cell wall only in plants •Ex. Plants and animal cells Prokaryotic Bacteria Animal Cells Plant Cells Nucleus • Contain DNA of eukaryotic cells • Porous phospholipid membrane • Inner membrane lined with intermediate filaments of the cytoplasm • ER often is an extension of the nuclear membrane Condensation of Eukaryotic Chromosomes Nucleosome = DNA coils around histone proteins Chromatin = supercoiled nucleosomes Looped Domains = supercoiled chromatin Chromosome = supercoiled looped domains Ribosomes •Assembles AA into polypeptide chain, which eventually folds into functional protein •Made of rRNA and protein •2 subunits: large and small Nucleolus •Located inside nucleus •makes ribosomal subunits by combining rRNA and proteins imported from cytoplasm •subunits leaves nuclear pore and assembles into a ribosome in the cytoplasm What is the endomembrane system? • System of membrane-bound organelles in euk. cells that work cooperatively together to create secretory proteins, membrane-bound proteins, or plasma membrane proteins – – – – – – – – Nucleus ER Golgi Transport Vesicles Lysosomes Peroxisomes Vacuoles Plasma Membrane Rough Endoplasmic Reticulum RER w/ bound ribosomes Space w/in ER = cisternae space Fcn: to fold and modify secretory proteins (glycoproteins) within cisternae space - attaches CHO called oligosaccharides to growing and folding polypeptide chain (2o 3o) - vesicles bud off from RER and delivers glycoprotein to Golgi Golgi Apparatus Accepts vesicles from RER (cis side) Adds and removes monomers to oligosach. of glycoproteins Adds “ID” tags (like phosphate groups) and uses these to “sort” proteins into different vesicles Dispatches vesicles w/glyco-proteins for shipping (trans side) 3 destinations for proteins within Golgi vesicles 1) Secreted from cell 2) Remains within vesicles vacuole, lysosome, peroxisome 3) Protein becomes part of plasma membrane Lysosomes • Membrane-bound sac of digestive enzymes • Acidic env’t maintained by pumping H+ ions from cytoplasm • Digests food, worn out cell parts, programmed cell death (webbing b/t fingers, tadpole tails) Peroxisome • Breaks down toxic substances in liver • Breaks down fatty acids into CHO for use in CR • In breakdown process, oxygen and hydrogen combine to create H2O2 • Peroxide = metabolic waste Smooth ER • • • • ER w/o ribosomes Makes lipids, oils, steroids Helps break down CHO Detoxifies drugs by adding –OH groups water soluble toxins flushed from body Vacuoles Contractile vacuole - pumps excess water out for freshwater organisms Central vacuole - Stores water, organic compounds, ions, and helps increase turgor pressure in plant cells Mitochondria and Chloroplasts Mitochondria - CR site - Generates ATP (usable E) from glucose Chloroplasts - PS site - Generates glucose (stored E) from inorganic compounds and light Cytoskeleton Network of fibers in the cytoplasm that a) maintains cell shape/mechanical support b) anchors organelles c) helps w/ cell motility 3 components 1) microtubules 2) microfilaments 3) intermediate filaments Microtubules Structure: Hollow tube made up of α and β tubulin polypeptide 25 nm diameter Compression Resistent supports cell shape Forms spindle fibers for separation of chromosomes, makes up centrioles, and cilia/flagella Microtubule 9 sets of 3 arrangement (ring formation) Ex. Centrioles, spindle fibers, basal body of cilia and flagella 9 + 2 arrangement (9 doublets surrounding a pair in the center) Ex. Cilia and Flagella Radial Spokes and Dynein Arms of Microtubule • Dynein arms “walk” along the microtubules to bend and move flagella, using ATP energy Microfilaments AKA: actin fibers Structure: twisted double chain of actin protein that forms a solid rod 7 nm diameter Tension resistent (protects against “pulling” forces) Makes up microvilli core, contracts muscles, causes cytoplasmic streaming and pseudopod extensions in cells Intermediate Filaments • In btwn microtubules and microfilaments in size (10 nm) • Fixes positions of organelles • Organelles w/motor proteins can move by “walking” along intermediate filaments (as if along a track) • Helps to maintain cell shape Cell Wall and Plasmodesmata • In plants, bacteria, protists, fungi • Maintains shape, prevents excessive water uptake • Cell walls are non-continuous: plasmodesmata connects cytoplasm btwn 2 plant cells and helps them communicate Animal Cell Junctions Desmosomes: AKA “anchoring” junctions -Holds together tissues under stress -Disc-shaped w/ protein fibers extended into cytoplasm Tight Junctions: Gap Junctions: -Fuses cell membranes of Type of neighboring communicati cells; prevents ng junction leakage btwn cellsprovides (ex. that Digestive tract) cytoplasmic channels btwn cells