METABOLISME SEL

1. METABOLISME SEL

2. Microbial Metabolism: The Chemical Crossroads of Life Chapter 8

3. Metabolism The sum total of all chemical reactions & physical workings occurring in a cell

4. 2 types of metabolism • Anabolism - biosynthesis • building complex molecules from simple ones • requires energy (ATP) • Catabolism - degradation • breaking down complex molecules into simple ones • generates energy (ATP)

8. Enzyme structure • Simple enzymes – consist of protein alone • Conjugated enzymes or holoenzymes – contain protein and nonprotein molecules • apoenzyme –protein portion • cofactors – nonprotein portion • metallic cofactors – iron, copper, magnesium • coenzymes -organic molecules - vitamins

10. Enzyme-substrate interactions

11. Exoenzymes – transported extracellularly, where they break down large food molecules or harmful chemicals; cellulase, amylase, penicillinase • Endoenzymes – retained intracellularly & function there

13. Constitutive enzymes – always present, always produced in equal amounts or at equal rates, regardless of amount of substrate; enzymes involved in glucose metabolism • Induced enzymes – not constantly present, produced only when substrate is present, prevents cell from wasting resources

15. Synthesis or condensation reactions – anabolic reactions to form covalent bonds between smaller substrate molecules, require ATP, release one molecule of water for each bond • Hydrolysis reactions– catabolic reactions that break down substrates into small molecules, requires the input of water

17. Transfer reactions by enzymes • Oxidation-reduction reactions – transfer of electrons • Aminotransferases – convert one type of amino acid to another by transferring an amino group • Phosphotransferases – transfer phosphate groups, involved in energy transfer • Methyltransferases – move methyl groups from one molecule to another • Decarboxylases – remove carbon dioxide from organic acids

18. Metabolic pathways

19. Control of enzyme activity • Competitive inhibition – substance that resembles normal substrate competes with substrate for active site • Feedback inhibition – concentration of product at the end of a pathway blocks the action of a key enzyme • Feedback repression – inhibits at the genetic level by controlling synthesis of key enzymes • Enzyme induction – enzymes are made only when suitable substrates are present

20. Competitive inhibition

21. Energy –capacity to do work or cause change • Endergonic reactions – consume energy • Exergonic reactions – release energy

22. Redox reactions • always occur in pairs • There is an electron donor and electron acceptor which constitute a redox pair • The process salvages electrons & their energy. • released energy can be captured to phosphorylate ADP or another compound

23. Electron carriers • resemble shuttles that are loaded and unloaded with electrons and hydrogen • most carriers are coenzymes, NAD, FAD, NADP, coenzyme A & compounds of the respiratory chain

24. NAD reduction

25. Electron carriers

26. ATP • 3 part molecule consisting of • adenine – a nitrogenous base • ribose – a 5-carbon sugar • 3 phosphate groups • Removal of the terminal phosphate releases energy

27. ATP

28. Phosphorylation of glucose by ATP

29. Formation of ATP • substrate-level phosphorylation • oxidative phosphorylation • photophosphorylation

30. substrate-level phosphorylation

31. Catabolism of glucose • Glycolysis • Tricarboxylic acid cycle, Kreb’s cycle • Respiratory chain, electron transport

32. Metabolic strategies

33. Overview of aerobic respiration

34. Overview of aerobic respiration • Glycolysis – glucose (6C) is oxidized and split into 2 molecules of pyruvic acid (3C) • TCA – processes pyruvic acid and generates 3 CO2 molecules • Electron transport chain – accepts electrons NADH & FADH, generates energy through sequential redox reactions called oxidative phosphorylation

35. Glycolysis

36. TCA cycle

37. Electron transport system

38. Chemiosmosis

39. Fermentation • Incomplete oxidation of glucose or other carbohydrates in the absence of oxygen • Uses organic compounds as terminal electron acceptors • Yields a small amount of ATP • Production of ethyl alcohol by yeasts acting on glucose • Formation of acid, gas & other products by the action of various bacteria on pyruvic acid

40. Fermentation

41. Products of fermentation

42. Many pathways of metabolism are bi-directional or amphibolic • Metabolites can serve as building blocks or sources of energy • Pyruvic acid can be converted into amino acids through amination • Amino acids can be converted into energy sources through deamination • Glyceraldehyde-3-phosphate can be converted into precursors for amino acids, carbohydrates and fats