C.CellsMet071 - Cell Theory Cell Structure &...

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Unformatted text preview: Cell Theory Cell Structure & Metabolism • The cell is the basic unit of life • All living organisms are made of cells • All cells arise from previously existing cells The basics of life What does a cell need? • Selective isolation from environment (plasma membrane) • Energy (ATP) • Instructions (DNA) • Machinery to carry out instructions and regulate processes (proteins) • Compartmentalization of incompatible or specialized activities (organelles) Smaller cells have more total surface area • Increased surface area makes it easier for nutrients to enter a cell Types of Cells a) Prokaryotic — Bacteria • No organelles b) Eukaryotic — Plant • Organelles present, including chloroplasts • Cell wall outside of plasma membrane c) Eukaryotic — Animal • Organelles present, but no chloroplasts nor cell wall d) Eukaryotic — Protists & Fungi • Organelles present • Cell types variations of plant/animal models Cells & Metabolism Phospholipid Bilayer & Plasma Membranes Isolated activity compartments • Cell’s plasma membrane is its boundary. • Phospho-lipid bilayer forms the essential backbone of cellular membranes. • Cell membrane • Organelle membranes Cell & organelle membranes Plasma Membrane Proteins Cell & organelle membranes • Lipid bilayer has proteins embedded in it. Passive & Active Transport Plasma Membrane Proteins Cell Function & Homeostasis Hormonal System Controls Cell Activity Immune System Cells & Metabolism Bulk Transport: Endo- and Exocytosis Active Transport • Transport against conc. gradient. • Proteins are pumps & use ATP Active Transport (Requires energy) Food V acuole (endocytosis ) Cells Eat and Spit Out: Endo- and Exocytosis Paramecium ( endocytosis ) Cytoplasm • Fills cell; contains – fluids and more – membrane-bound organelles • working as do our organs • carry out cell function. – cytoskeleton • maintain and alter cell shape • hold and move organelles, etc. White blood cell Nucleus • Membrane-bound • Contains DNA of chromosomes • Controls cell – structure – function • Blueprints for new cells Mitochondria • Membrane-bound • Powerhouse of cell • Converts chemical energy from catabolism into ATP: (adenosine triphosphate) • Have own DNA to maintain activity when nucleus is unavailable Cells & Metabolism Disassembly of Proteins & Assembly of Amino Acids Organisms & Energy •Dietary polymers are not directly assimilated! •Polymers hydrolyzed into monomers — monomers absorbed — monomers condensed into new polymers. Molecular motors: Structure of cilia & flagella Using Mitochondrial Energy: Flagella and Cilia • Cilia are numerous & short • Flagella are few & long • Few cells in our body are flagellated: ciliated cells are more common. Fig. 4.19 Cell Metabolism Organisms & Energy • Big animals use more energy than smaller do - but their metabolic rate is lower. – catabolism: energy producing breaking down of foods, and – anabolism: energy-requiring synthesis of compounds. • Heart rate is inversely related to body size. Metabolic Rate Elephant = 30 Human = 70 Cat = 125 Mouse = 400 Shrew = 800 Body Mass • Metabolism: sum of cell's chemical reactions, composed of Cells & Metabolism Enzymes • They’re proteins. • Catalyze (speed up) rates of reaction. – Some maybe 1,000,000x faster! • Vital to metabolism. – Regulate pathways. • Activity depends on environment. • May need vitamins (coenzymes) and/or minerals (cofactors) to function. Metabolic Pathways Sequence of enzymatic reactions that begins with initial substrate, progresses through intermediates and ends with a final product. Naming of Enzymes • Enzyme name ends with suffix “-ase.” • Name = substrate – action – “-ase” – E.g., glucose phosphory lase is an enzyme that adds a phosphate to glucose. – If the “action ” is left out of the name, assume the action is hydrolysis. E.g., a protease catalyzes the hydrolysis of proteins into oligopeptides or amino acids. Different organs may make different enzymes (isoenzymes) that have the same activity. – Differences in structure do not affect the active sites. Branched Pathways • End-Product Inhibition. • One of the final products in a divergent pathway inhibits the activity of the branch-point enzyme. – Prevents final product accumulation. – Results in shift to product in alternate pathway. Inborn Errors of Metabolism • Inherited defect in a gene for enzyme synthesis. • Quantity of intermediates formed prior to the defect increases. • Final product formed after the defect decreases, producing a deficiency. Inborn Errors of Metabolism Example: phenylalanine metabolism • Defective enzyme1 È phenylyketonuria [PKU] • Defective enzyme5 È alcaptonuria • Defective enzyme6 È albino Coupled Reactions: Bioenergetics • Energy transfer from one molecule to another couples chemical reactions • Exergonic reaction: reaction releases energy • Endergonic reaction: reaction requires energy • Coupled bioenergetic reactions: the energy released by the exergonic reaction is used to power the endergonic reaction. Cellular Respiration: ATP is the cell’s rechargable battery • Breaking down complex glucose molecule releases energy. • That energy is used to convert ADP into ATP. ADP + P + energy —› ATP • Energy is released as ATP breaks down into ADP and AMP. ATP —› energy + ADP + P Why Make ATP? Cellular Metabolism • Cellular Respiration provides ATP • Cellular “Work” requires ATP • Universal energy source for the cell. • Many different fuels can be used by power plants to make one kind of electricity to power all the appliances in your home. • Many different fuel types may be used by the cell to make one rechargeable energy molecule (ATP) to power all the endergonic reactions of the cell. ATP drives cellular processes Coupled Reactions: ATP • The three types of cellular work a re powered by the hydrolysis of ATP P i P Motor protein (a) Protein moved Mechanical work : ATP phosphorylates motor proteins Membrane protein ADP + ATP P P Solute (b ) i Solute transported Transport work : ATP phosphorylates transport proteins P Glu + NH 3 Reactants: Glutamic acid and ammonia (c) P NH 2 Glu + P i Product (glutamine) made Chemical work : ATP phosphorylates key reactants i Coupled Pathways: Bioenergetics • Energy transfer from one metabolic pathway to another by means of ATP. • Catabolic pathway (catabolism): breaking down of macromolecules. Releases energy which may be used to produce ATP. • Anabolic pathway (anabolism): building up of macromolecules. Requires energy from ATP. • Metabolism: the balance of catabolism and anabolism in the body. Energy Organelles • chloroplasts for photosynthesis • mitochondria for aerobic respiration Fig. 4.14a — Plant cell Animal cells rely upon chemical energy produced by plants Photosynthesis In the chloroplast… Fig. 6.18 Cellular Respiration (making ATP) • “OXIDIZED COENZYME ” = B-vitamin molecule capable of picking up high-energy electrons from fuel molecules ( “empty ”) • “REDUCED COENZYME ” = the B-vitamin molecule with the high-energy electrons ( “full ”) * if all the coenzymes get “full”, no more electrons can be picked up fi the whole process grinds to a stop! Anaerobic Respiration Anaerobic Respiration = “fermentation” Aerobic Respiration OXIDIZED COENZYMES REDUCED COENZYMES OXIDIZED COENZYMES Yeasts and some bacteria Aerobic Respiration REDUCED COENZYMES Aerobic Respiration Aerobic Respiration Cellular Respiration • Anaerobic Respiration “without air ” • Aerobic Respiration “with air ” • = glycolysis + pyruvate reduction • • Produce ATP in absence of O 2 (or absence of mitochondria) = glycolysis + pyruvate oxidation * + Krebs cycle * + electron transport system * • Produces much more ATP per sugar molecule • Non-toxic waste product (CO 2) • Allows use of fats and protein for fuel • * requires mitochondria Cells & Metabolism Uses of Different Energy Sources Cellular Respiration = glycolysis + pyruvate reduction • Produce ATP in absence of O2 Aerobic Respiration “with air” • = glycolysis + pyruvate oxidation + Krebs cycle + electron transport system • Produces much more ATP per sugar molecule Non-toxic waste product (CO 2 ) • • • • • Anaerobic Respiration “without air ” Allows use of fats and protein for fuel Gluconeogenesis & the Cori Cycle Glycogenesis and Glycogenolysis 4) • Glucose-6-phosphate cannot leak out of the cell. • Skeletal muscles generate glucose-6-phosphate for own glycolytic needs. • Only Liver contains the enzyme glucose-6phosphatase that can remove the phosphate group and produce free glucose. Muscle Fuel Consumption During Exercise 1. 2. 3. 4. 5. At rest: mostly from aerobic resp . of plama fatty acids. Start exercise: anaerobic resp . of plasma glucose; start muscle glycogenolysis . È blood flow & O 2 delivery ‡ aerobic resp . of muscle triglycerides. Gluconeogenesis È plasma glucose for Cori Cycle. Lipolysis in adipose tissue È plama fatty acids for continued aerobic resp . 5) 6) • Lactic acid produced by anaerobic respiration in muscle is released into the bloodstream and delivered to the liver. LDH converts lactic acid to pyruvic acid. Gluconeogenesis : (“creating new glucose”) Pyruvic acid converted to glucose-6-phosphate: G-6-P can be used either for A. liver glycogenesis or B. can be converted to free glucose and released into the bloodstream. 7A 7B 6 & 7B 6 only occur in liver! Oxygen Debt Following anaerobic respiration, increased O 2 consumption continues to support aerobic oxidation of lactate back to pyruvate . (Reverse of pyruvate reduction. — Uses same LDH enzyme.) Krebs Cycle Lactate Oxidation Lipogenesis Gluconeogenesis ...
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