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Transcript
Cells Prokaryotic and Eukaryotic Prokaryotes • Prokaryotic cells have no “true” nucleus but rather a nuclear “region” • Typical prokaryotic components are: – Capsule – Cell wall – Plasma membrane – Cytoplasm (alt. cytosol) – Pili (fimbriae) – Flagella – Ribosomes – Nucleoid (nuclear region) Prokaryotic Cell Escherichia coli (E. coli) Result of Binary Fission Eukaryotic Cells • More “evolved” cells • Composed of: – Nucleus – Nucleolus – Chromatin – Nuclear Envelope – Plasma Membrane – Golgi Apparatus – Lysosome - Peroxisome - Mitochondria - Endoplasmic Reticulum - Ribosomes - Microvilli - Cytoskeleton - Centrosome Eukaryotic Cells Organelle Structure & Function • Nucleus – Contains the genetic information of the cell – Surrounded by the nuclear envelope – Nuclear pores lined with pore complex protein – Nuclear lamina maintains shape of envelope – Chromosomes contain chromatin; DNA mixed with proteins – Nucleolus synthesizes rRNA • Proteins and rRNA make subunits of ribosomes • May function in cell division Structure & Function • Ribosomes – Complex of rRNA and protein – Present abundantly in cells active in protein synthesis (i.e., pancreas, muscle, etc.) – Sight of polypeptide assemblage – Free and bound – 70S and 80S ribosomes • 70S in prokaryotes • 80S in eukaryotes – Mitochondria/Chloroplast 70S Endoplasmic Reticulum • Approximately ½ of total membrane in eukaryotic cells • Composed of cisternae or lumen • Both smooth and rough endoplasmic reticulum Smooth Endoplasmic Reticulum • Functions include – Synthesis of lipids • Oils, phospholipds and steriods – Cells that secrete sex hormones are rich in smooth ER (ovaries and testicles) – Metabolism of carbohydrates – Detoxification of drugs and poisons • Liver cells add hydroxyl group for water solubility • Proliferation occurs with consistent exposure – Calcium storage in muscle tissue Rough Endoplasmic Reticulum • Studded with Ribosomes – Pancreatic cells synthesize insulin on the ER – Polypeptide chains enter lumen of ER • Bound to carbohydrates to form glycoproteins • Considered “Secretory Proteins” • Secretory Proteins separated from cytosol via transport vessicles Golgi Apparatus • Receiving center for vesicles from ER • Plentiful in cells specialized for secretion • Cis face and trans face to “stack” due to polarity difference – Cis is receiving side of Golgi; trans is shipping side • ER products are enzymatically modified between cis and trans sides – Glycoproteins – Monomers are removed and substituted for large variety of carbs – Membrane phospholipids also altered in Golgi • Polysaccharides (pectin and other cell wall materials) synthesized directly by the Golgi • Targeting of products takes place between cis and trans face via molecular tags Lysosome • Sack of hydrolytic enzymes – Enzymes made at Rough ER and refined at Golgi • Lysosomes form from trans face of Golgi Apparatus • Engage in phagocytosis • Lysosomes merge with food vacuoles in cells and digest food – Products then passed onto the cytosol • Autophagy – Damaged organelle surrounded by double membrane – Lysosome fuses with membrane and digests organelles – Recycles raw materials back into cytosol Vacuoles • Food, contractile and central vacuoles • Certain plants have vacuoles that act as disposal sites for “toxic” metabolic byproducts • Others hold pigments that determine the petal color of flowers • Defense mechanism to make plant unpalatable to animals Mitochondria • Site of cellular respiration • Found in nearly all eukaryotic cells: plants, animals, fungi and most protists – Human parasites have organelles that may have evolved from mitochondria • Number of mitochondria correlates to level of metabolic acitivty • Mitochondria move, alter shape and divide • Double phospholipid bilayer encases mitochondria – Outside smooth; inside convoluted and forms “cristae” – More folds create more efficiency • Mitochondrial matrix is inside inner membrane – Enzymes, mitochondrial DNA and ribosomes present here • Some enzymes aid in cellular respiration Chloroplasts • Member of the plastid family – Amyloplasts • Contain chlorophyll and photosynthetic enzymes • Double membrane bound • Three major components – Thylakoids – Granum – Stroma (DNA and ribosomes) Peroxisome • Single membrane • Transfers hydrogen to various molecules to create H2O2 (some conversions are for mitochondria) – Enzymes within lysosome convert H202 to water for expulsion from cell • Glyoxysomes found in plant seed fat tissue – Converts fatty acids to sugar Cytoskeleton • Mechanical support and maintenance of shape • “Monorail” theory for movement within cell • Three components of cytoskeleton – Microtubles – Micorfilaments – Intermediate filaments Microtubules • Hollow tube 25 nm in diameter • Composed of tubulin protein – Dimer: composed of two subunits • Growth occurs by adding tubulin dimers • “Plus end” is the more active of two microtubule ends • Functions include – Guiding secretory vesicles from Golgi – “Beating” of cilia and flagella – Separate chromosomes during cell division • Form from centrosome (near nucleus) – Centrioles located here Microfilaments • Composed of actin (globular protein) – Twisted chain with branching ability • Function in specialized cells that pull materials across plasma membrane (microvilli) • Play a major role in cell motility (think muscle cells and clevage furrows) Intermediate Fibers • Form the “permanent” framework for the cell • Much more of a structural molecule than microtubules and microfilaments – Nuclear lamina – Nucleus – Nerve cell strength