1. An Introduction to Metabolism
Chapter 8 notes
An Introduction to Metabolism

2. Concept 8.1
Metabolism: the totality of an organism’s chemical reactions
A metabolic pathway begins with a specific molecule and is altered into a product
- each step is catalyzed by an enzyme

3. Concept 8.1
Catabolic pathway: release energy in the breaking down of complex molecules into simpler compounds
- ex. glucose  CO2 + H2O
Anabolic pathway: consume energy to build complicated molecules from simpler ones
- ex. amino acids  proteins

4. Concept 8.1 Energy: the capacity to do work
Reactions (Rxns.) are either exergonic (energy outward) or endergonic (energy inward)

5. Concept 8.2 Exergonic rxns. proceed with a net release of energy
- occur spontaneously
Endergonic rxns. absorb free energy from their surroundings
- nonspontaneous

6. Concept 8.2

7. Concept 8.2 Cells do three kinds of work:
- mechanical work (ex. contraction of a muscle cell)
- transport work (ex. pumping of substances across a memebrance)
- chemical work (ex. synthesis of polymers from monomers)

8. Concept 8.3
Energy coupling: the use of an exergonic process to drive an endergonic one
ATP is the energy source used in most rxns.
- contains a ribose (sugar), adenine (base), and 3 phosphate molecules

9. Concept 8.3

10. Concept 8.3
Energy is released from ATP when the terminal phosphate bond is broken
ATP  ADP + Pi + Energy
- work is accomplished by phosphorylation
- the transferring of the Pi to another molecule (ex. channel protein)

11. Concept 8.3

12. Concept 8.3
ATP is regenerated in the cell by phosphorylating ADP through an exergonic rxn. in the cell
- in a muscle cell 10 million ATP are consumed and regenerated per second per cell

13. Concept 8.3

14. Concept 8.4 Spontaneous rxns. May occur at very slow rates
- sucrose  glucose + fructose
- if an enzyme is added, the same rxn. can completed in seconds
Catalyst: a chemical agent that speeds up reaction w/out being consumed

15. Concept 8.4 Enzyme: a biological catalyst
Activation energy, the energy needed to begin a rxn, prevents many rxns from occurring quickly
Heat is used to speed up rxns b/c it increases the speed of reactant molecules (to collide more often)

16. Concept 8.4

17. Concept 8.4 In biological systems heat alone would not work
- too much heat denatures proteins and kills cells
An enzyme (catalyst) lowers the amt. of activation energy needed
- enzymes are very selective

18. Concept 8.4

19. Concept 8.4

20. Concept 8.4 The reactant an enzyme binds to is called the substrate
- binds to the active site of the enzyme
- the enzyme converts the substrate to product
- the product is released
Enzyme animation

21. Concept 8.4
Up to a point, the rate of an enzymatic reaction will increase with temperature
- eventually it will drop because of thermal agitation and protein denaturing

22. Concept 8.4 Most human enzymes function best at 35-40 oC.
- some bacteria that live in hot springs have proteins that work best at 70 oC.
Most human enzymes also work best at 6-8 pH.
- pepsin in the stomach work best at PH 2

23. Concept 8.4

24. Concept 8.4
Certain chemicals can selectively inhibit the activity of specific enzymes
Competitive inhibitors: reduce enzyme activity by blocking the substrate from binding to the active site
- can be overcome by increasing [substrate]

25. Concept 8.4
Noncompetitive inhibitors: impede the reaction by attaching to another part of the enzyme, thus changing its shape
- ex. toxins and poisons