1. An Introduction to Metabolism
Chapter 8
Unit 3

2. Metabolism the totality of an organism’s chemical reactions
Metabolic Pathway: begins with a molecule, goes through a series of steps, results in a product
Each step catalyzed by an enzyme

3. Bioenergetics
Catabolic Pathways: release energy by breaking down molecules
EX: Cellular Respiration
Anabolic Pathways: Absorb energy by building molecules
EX: Photosynthesis

4. Energy: capacity to do work
Kinetic energy (KE): energy associated with motion
Heat (thermal energy)
Potential energy (PE): stored energy as a result of its position or structure
Chemical energy (potential available for release in a chemical reaction)

5. Laws of Thermodynamics
Subject to two laws of thermodynamics:
First Law : energy can be transferred and transformed, but cannot be created or destroyed
Second Law: energy transfer or transformation makes the universe more disordered
Entropy: measurement of disorder

6. Free energy and metabolism
Exergonic
Endergonic
Products have less free energy than reactant molecules
Energetically downhill
spontaneous
Products have more free energy than reactants
Energetically uphill
Requires energy input

7. ATP Powers Cells A cell does three main kinds of work:
Mechanical: beating of cillia, contracting of muscles, and movement of chromosomes
Transport: pumping of substances across memebranes
Chemical: synthesis of polymers from monomers

8. ATP
Consist of: Nitrogenous base adenine, sugar ribose, three phosphates
Formation of ATP from ADP is endergonic
When the bonds between the phosphate groups are broken energy is released

9. Activation Energy EA
Initial investment of energy for a reaction to start
Often supplied as heat that is absorbed by reactants
Accelerates reactants so they collide and break bonds
Transition state: reactants are in unstable condition

10. Enzymes Catalyze reactions by lowering activation energy
Specific to reactions they catalyze

12. Substrate Specificity of Enzymes
The reactant that an enzyme acts on is called the enzyme’s substrate
The enzyme binds to its substrate, forming an enzyme-substrate complex
The active site is the region on the enzyme where the substrate binds

13. Effects of Local Conditions on Enzymes
Temperature and pH
Cofactors
Enzyme Inhibitiors

14. Temp and pH
Optimal Conditions: conditions required for best enzymatic acitivity
Enzymes work increases with temp increase until it goes above optimal temp
Disrupts weak interactions that change the 3D structure of the enzyme

15. Cofactors Nonprotein helpers for catalytic activities
Inorganic molecules: metals
Zinc, iron, and copper
Coenzymes: organic molecules
vitamins

16. Enzyme inhibitors Competitive Inhibitors Noncompetitive Inhibitors
Inhibitor and substrate compete for active site
ex: penicillin blocks enzyme that bacteria use to build cell walls
Noncompetitive Inhibitors
inhibitor binds to site other than active site
causes enzyme to change shape

17. Inhibition of Enzyme Activity

18. Regulation of Enzyme Activity
Allosteric regulation: protein’s function at one site is affected by binding of a regulatory molecule to allosteric site
Activator – stabilizes active form
Inhibitor – stabilizes inactive form
Cooperativity – one substrate triggers shape change in other active sites  increases catalytic activity

20. Feedback Inhibition
Regulation of a metabolic pathway by its end product
final product is inhibitor of earlier step
no unnecessary accumulation of product