Cell Metabolism and Enzyme Control in Physiology

1. Cell Physiology: Metabolism Biology 346 General PhysiologyDr. Tony Serino

2. 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

3. Energy Flow in Reactions

4. 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

5. 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)

6. Pathway Map of Cell Metabolism Note: Kreb Cycle

7. 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)

8. Energy flow in a reaction • Every reactions must overcome an energy barrier to begin. • Energy of Activation (EA)

9. Energy Flow with Enzyme Present • Enzymes increase reaction rates by lowering the EA

10. 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

11. 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

12. Enzyme Control • Enzyme activity can be modified by changes in both enzyme and substrate concentrations • Excess substrate eventually hits a maximum or saturation point

13. 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

14. 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)

15. Central Dogma

16. Protein Synthesis Overview

17. ATP cycle

18. Utilization of ATP

19. ATP Synthesis • Two ways to produce ATP • Substrate Phosphorylation • Oxidative Phosphorylation

20. Substrate Phosphorylation • An ATPase binds a substrate that can be stripped of a high energy phosphate to synthesize ATP

21. 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

22. 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.

24. Glycolysis

25. Kreb Cycle

26. Electron Transport Chain

27. Glycolysis: Overview 2 PGAL

31. Transition Reaction: Acetyl-CoA For one molecule of glu, 2 pyruvates will be processed.

32. Kreb Cycle

33. 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

34. 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

35. Chemiosmosis Generates a high H+ concentration in the intermembrane space

36. 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

37. Cellular Respiration Overview

38. Aerobic vs. Anaerobic Respiration

39. Anaerobic Respiration

40. Food Processing

41. 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

45. Fat Metabolism Triglyceride  3 fatty acids + glycerol ( a sugar)

46. 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)