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Cell Physiology: Metabolism. Biology 346 General Physiology Dr. Tony Serino. Metabolism. Refers to all of the reactions that occur in the cell Each reactions requires a specific enzyme Energy may be released or consumed in the reactions. Energy Flow in Reactions.
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Cell Physiology: Metabolism Biology 346 General PhysiologyDr. Tony Serino
Metabolism • Refers to all of the reactions that occur in the cell • Each reactions requires a specific enzyme • Energy may be released or consumed in the reactions
Metabolic Reactions (R P) • Most reactions are reversible • All reactions try to proceed to a dynamic equilibrium. Therefore, one way to favor a reaction is to manipulate the amount of reactants or products present. A + B C + D
Metabolic Pathways • A series of reactions in the body. • Most are linked with other sets, so that the products of one reaction become the reactants of the next. • Two Kinds: • Degradative (Catabolism) • Biosynthetic (Anabolism)
Pathway Map of Cell Metabolism Note: Kreb Cycle
Enzymes • Catalyze reactions • Reactants = substrates (S) • S bind to active site on E • S bound non-covalently • 3D structure give E specificity • # of bonds formed gives affinity • May use co-factors (co-enzymes) • May bind other chemicals that act as modulators (change 3D shape of active site)
Energy flow in a reaction • Every reactions must overcome an energy barrier to begin. • Energy of Activation (EA)
Energy Flow with Enzyme Present • Enzymes increase reaction rates by lowering the EA
Enzymes Lower EA • Bring reactants into close proximity • Produce bond strain in substrates Both of these characteristics allows the enzyme to lower the reaction’s EA
Control of Enzyme Function • Proteins remain functional in a narrow range of pH and temp. • Radical changes in these values can cause proteins to denature; that is, change its 3D shape
Enzyme Control • Enzyme activity can be modified by changes in both enzyme and substrate concentrations • Excess substrate eventually hits a maximum or saturation point
Enzyme Control • Other substances may bind to the enzyme and modify its behavior; either as an activator or inhibitor • If the substance competes with the substrate for the active site; it is a competitive inhibitor
Enzyme Modulation:non-competitive inhibition and activation • Binding of a molecule to a site other than the active site may result in an enzyme conformational change that either turns the enzyme “on or off” • If the modulator is bound by non-covalent forces; it is allosteric modulation (the most common type); if bound covalently, it is covalent modulation (which is more difficult to change)
ATP Synthesis • Two ways to produce ATP • Substrate Phosphorylation • Oxidative Phosphorylation
Substrate Phosphorylation • An ATPase binds a substrate that can be stripped of a high energy phosphate to synthesize ATP
Oxidative Phosphorylation • High energy electrons are scavenged from the breakdown of food molecules and used to power an electron transport chain which allows the cell to synthesize ATP • Uses a series of Redox reactions to power pumps • Note: the PO4- is an ion of the environment and contains no extra energy
Co-enzymes: NADH & FADH2 Oxidized ReducedNAD+ NADHFAD+ FADH2 The co-enzymes pick up high energy electrons and transport them to where they are needed, such as, the electron transport chain.
Glycolysis: Overview 2 PGAL
Transition Reaction: Acetyl-CoA For one molecule of glu, 2 pyruvates will be processed.
Kreb Cycle Transition reaction • For one molecule of glucose, 2 acetyl-CoAs will be processed, so the Kreb cycle will make 2 complete turns • All of the carbon atoms of the sugar have now been converted to CO2 • After the co-enzymes are processed, the total amount of ATP produced per turn of the wheel will be 12 ATP
Electron Transport Chain (Respiratory Chain) • NADH unloads its electrons at the start of the chain; yielding the maximum energy release per electron pair • FADH2 unloads further down the line, thereby diminishing its energy return • Oxygen is the final electron acceptor, it combines with hydrogen to form water
Chemiosmosis Generates a high H+ concentration in the intermembrane space
ATP synthase complex • H+ are pushed through the channel due to their electro-chemical gradient • This spins the rotor molecules which produces the energy needed to convert ADP to ATP
Protein Metabolism • Proteins Amino Acids • Amino Acids • Deamination –removes NH forming a keto-acid • Transamination –transfers NH to other keto-acid • Keto-acids can be fed into Kreb Cycle • Amino group may form ammonia which can be converted to urea and excreted by kidney
Fat Metabolism Triglyceride 3 fatty acids + glycerol ( a sugar)
Fat Metabolism • Fatty acids broken down 2 C’s at one time = Beta-oxidation of fat • 8 C fatty acid would yield 62 ATP molecules((12 * 4); -1 initial ATP used; -5 for last two carbons do not generate extra co enzymes)