Chapter 8: An Introduction To Metabolism

1. Chapter 8: An Introduction To Metabolism

2. Essential Knowledge • 2.a.1 – All living systems require constant input of free energy (8.1-8.3). • 4.b.1 – Interactions between molecules affect their structure and function (8.4 & 8.5).

3. Metabolism • The totality of an organism’s chemical processes • Concerned with managing the material and energy resources of the cell

4. Catabolic Pathways • Pathways that break down complex molecules into smaller ones, releasing energy • Example: Cellular respiration • DOWNHILL!

5. Anabolic Pathways • Pathways that consume energy, building complex molecules from smaller ones • Example: Photosynthesis, condensation synthesis • UPHILL!

6. 1st Law of Thermodynamics • Energy cannot be created or destroyed • It can be converted from one form to another • The sum of the energy before the conversion is equal to the sum of the energy after the conversion

7. 2nd Law of Thermodynamics • Some usable energy dissipates during transformations and is lost • During changes from one form of energy to another, some usable energy dissipates, usually as heat • The amount of usable energy therefore decreases

8. Energy • Ability to do work • The ability to rearrange a collection of matter • Forms of energy: • Kinetic • Potential • Activation

9. Kinetic and Potential Energy • Kinetic: • Energy of action or motion • Ex: heat/thermal energy • Potential: • Stored energy or the capacity to do work • Ex: chemical energy

10. Activation Energy • Energy needed to convert potential energy into kinetic energy Activation Energy Potential Energy

11. Free Energy • The portion of a system's energy that can perform work • Known as ΔG

12. Free Energy ΔG = Δ H - T Δ S Δ = change (final-initial) ΔG = free energy of a system ΔH = total energy of a system (enthalpy) T = temperature in oK ΔS = entropy of a system

13. Free Energy of a System • If the system has: • more free energy=less stable (greater work capacity) • less free energy=more stable (less work capacity) • As rxn moves towards equilibrium, ΔG will decrease

14. Chemical Reactions • These are the source of energy for living systems • They are based on free energy changes • Two types: exergonic and endergonic

15. Reaction Types • Exergonic: • chemical reactions with a net release of free energy • Ex: cellular respiration • - ΔG , energy out, spontaneous • Endergonic: • chemical reactions that absorb free energy from the surroundings • Ex: Photosynthesis • + ΔG , energy in, non-spontaneous

16. Exergonic/Endergonic • - ΔG • +ΔG

17. Cell Energy • Couples an exergonic process to drive an endergonic one • ATP is used to couple the reactions together • Types:mechanical, transport, chemical

18. ATP Description • Adenosine Triphosphate • Made of: • Adenine (nitrogenous base) • Ribose (pentose sugar) • 3 phosphate groups* *bonds can be broken to make ADP

20. Keys to ATP • Three phosphate groups and the energy they contain • Negative charges repel each other and makes the phosphates unstable • Tail is unstable = more free energy = more instability • Works by energizing other molecules by transferring phosphate groups • Hydrolysis of ATP = free energy is released as heat (can be adv or not adv)

21. ATP Cycle • Energy released from ATP drives anabolic reactions • Energy from catabolic reactions “recharges” ATP • Very fast cycle • 10 million made per second Coupled RXN

22. ATP Cycle

23. ATP is Made • Takes place in cytoplasm and mitochondria • Using special process called substrate-level phosphorylation • Energy from a high-energy substrate is used to transfer a phosphate group to ADP to form ATP

24. Enzymes • Biological catalysts made of protein • Speeds up rxn without being consumed • Cause the speed/rate of a chemical rxn to increase • By lowering activation energy

25. Basic Chemical Reaction AB + CD AC + BD *AB and CD are “reactants” *AC and BD are “products” *Involves bond forming/breaking *Transition state: can be unstable

26. Unstable state Energy is released as heat

27. Enzymes Intro to Enzymes movie • Lower the activation energy for a chemical reaction to take place • Why do we need enzymes? • Cells can’t rely on heat to kick start rxns • Why? Denaturation, heat can’t decipher between rxns • Enzymes are selective! Can only operate on a given chemical rxn

29. Enzyme Terms • Substrate – • the material the enzyme works on • Enzyme names: • Ex. Sucrase • “- ase” name of an enzyme • 1st part tells what the substrate is (i.e. Sucrose)

30. Enzyme Name • Some older known enzymes don't fit this naming pattern • Examples: pepsin, trypsin

31. Active Site • The area of an enzyme that binds to the substrate • Structure is designed to fit the molecular shape of the substrate • Therefore, each enzyme is substrate specific

33. Enzyme equation Enzyme + Enzyme- Enzyme + Subtrate Sub complex Product Notice: Complex becomes product, but enzyme stays the same! Enzyme is NOT CONSUMED!

34. Models of How Enzymes Work • Lock and Key model • Induced Fit model Reminder:Enzymes and substrates are usually held together by weak chemical interactions (H/ionic bonds)

36. Lock and Key Model • Substrate (key) fits to the active site (lock) which provides a microenvironment for the specific reaction

37. Induced Fit Model • Substrate “almost” fits into the active site, causing a strain on the chemical bonds, allowing the reaction

38. Enzymes • Usually specific to one substrate • Each chemical reaction in a cell requires its own enzyme • Don’t change during rxn • Always catalyze in direction towards equilibrium

39. Four Mechanisms to Lower EA • Active site is template for enzyme • Enzymes may break/stretch bonds needed to be broken/stretched • Active site is microenvironment • Active site directly participates in chemical rxn

40. Factors that Affect Enzymes • Environment • Cofactors • Coenzymes • Inhibitors • Allosteric Sites

41. Environment • Factors that change protein structure will affect an enzyme. • Examples: • pH shifts (6-8 optimal) • Temperature (up, inc activity) • Salt concentrations

42. Cofactors & Coenzymes • Cofactors: • Non-protein helpers for catalytic activity • Examples: Iron, Zinc, Copper • Coenzymes: • Organic molecules that affect catalytic activity • Examples: Vitamins, Minerals, usually proteins

43. Enzyme Inhibitors Inhibitor video • Competitive • mimic the substrate and bind to the active site (compete for active site) • Toxins/poisons – Ex: DDT • Can be used in medicine – painkillers, antibiotics • Noncompetitive • bind to some other part of the enzyme • Causes active site to change shape

45. Summary • Identify forms of energy and energy transformations. • Recognize the Laws of Thermodynamics. • Recognize that organisms live at the expense of free energy. • Relate free-energy to metabolism. • Identify exergonic and endergonic reactions. • Identify the structure and hydrolysis of ATP. • Recognize how ATP works and is coupled to metabolism. • Recognize the ATP cycle • Relate enzymes and activation energy. • Recognize factors that affect enzymes specificity and enzyme activity.. • Recognize factors that control metabolism.