1. An Introduction to Metabolism
Chapter 8

2. Metabolism What is metabolism?
The sum total of all chemical reactions in an organism
How do catabolic and anabolic pathways differ?
Catabolism - breaks down complex molecules
Anabolism - builds complex molecules

3. Energy Energy is the capacity to cause change or do work
Kinetic Energy
Associated with the relative motion of objects
Heat or thermal energy is kinetic energy associated with the random movement of atoms
Potential Energy
Chemical energy is potential energy available for release in a chemical reaction

4. The Laws of Thermodynamics
The first Law = Energy can be transformed, but is never lost, or created
The second law = With every energy transfer, entropy is increased
Entropy is a measure of disorder

5. How does a cell maintain its high level of order if with every energy transfer entropy is increased?
Life demands a constant input of energy

6. What is free energy?
Free energy is the portion of a system’s energy that is available to perform work
The term free does not mean that there is no cost to using this energy
It means that the energy is available

7. How Do Reactions Occur? Spontaneous reactions may occur very slowly
All reactions require free energy of activation (EA)
Uphill portion represents the EA required to start the reaction
Downhill portion represents the loss of free energy by the molecules in the reaction
DG is the difference in free energy of products and reactants

8. Exergonic and Endergonic Reactions
Less free energy in products than reactants
Energetically downhill
DG is negative
More free energy in products than reactants
Energetically uphill
DG is positive
Give an example of the coupling of exergonic and endergonic
reactions in living organisms

9. Is this reaction exergonic or endergonic?

10. How can the EA barrier be overcome?
Temperature
Temperatures that are too high denature organic molecules, so what else is there?
ENZYMES
Enzymes lower the EA barrier so that reactions can occur at lower temperatures

12. What are Enzymes?
Catalysts change the rate of the reaction without being altered themselves
Enzymes are biological catalysts
Enzymes are proteins, whose three dimensional shape allows for their ability to react specifically

13. Enzyme / Substrate Relationship
What is the substrate?
It is the reactant upon which an enzyme reacts
Enzymes are substrate specific
Only the active site of the enzyme actually binds the substrate

15. The Active Site
The active site is where the enzyme-substrate interaction occurs
Most enzyme-substrate interactions are the result of weak bonds
The active site may cause the enzyme to hold onto the substrate in a very specific way
The active site may provide a micro-environment (e.g. low pH) which enhances a reaction

16. Enzyme Activity Temperature pH Enzyme Concentration
Substrate Concentration

17. Cofactors Non-protein molecules that help enzymes function
Bind to active site to enhance enzymatic reactions
Cofactors may be inorganic metals such as zinc, iron, or copper
Coenzymes are organic cofactors (e.g. vitamins)

18. Enzyme Inhibition
Competitive inhibitors - mimic the substrate and compete for the active site
Non-competitive inhibitors bind to the enzyme away from the active site, and indirectly cause a change in the active site

19. Competitive and Noncompetitive Inhibition

20. Allosteric Regulation
Regulatory molecules that bind to the enzyme’s allosteric site changing the shape of the enzyme
Allosterically regulated enzymes have a quaternary protein structure
Each subunit of the enzyme has an active site and an allosteric site
Allosteric activators stabilizes the active site
Allosteric inhibitors deactivates the active site

22. Feedback Inhibition

23. Cooperativity