1. ENZYMES AND ENERGY
LECTURE 4

2. Each enzyme has a unique conformation
Enzymes as Catalysts
Biological catalysts – may be RNA or protein Globular proteins with 3-D structure (see pic) Properties: 1) increase the rate of the reaction, 2) is not itself changed at the end of the reaction, and 3) specific for its substrate An enzyme catalyzes a reaction that would otherwise happen on its own
Glycogen synthase
Each enzyme has a unique conformation

3. ENZYMES LOWER ACTIVATION ENERGY
Activation energy is the amount of energy required to start the reaction

4. Mechanism of Enzyme Action
Induced – fit model – the enzyme undergoes a slight structural change to better fit the substrate
Lock and key model

5. Naming of Enzymes (use –ase endings, except for the old ones
Pepsin, trypsin, renin are OLD enzymes
More recently classes of enzymes were required to be named for their job category, using –ase.
e.g. hydrolases promote hydrolysis
phosphatases remove phosphate kinases add a phosphate to a molecule
Isoenzymes – subtypes of the enzymes that catalyze the same reactions but are found in different organs
e.g. creatine phosphokinase (CPK) has isoenzymes encoded by different genes on different chromosomes. They can be distinguished using antibodies

6. Effects of Temperature and pH
Enzymes have temperature and pH optima
Enzyme optima reflect where they are active in the living organism
e.g. pepsin is a stomach enzyme, active at pH 2.0
Trypsin is from pancreatic juice
Amylase from saliva is active at pH 8.0

7. Cofactors and Coenzymes
Cofactors include metal ions such as Ca2+, Mg2+, Mn2+, Cu2+, Zn2+ Cofactors may cause the enzyme to undergo a conformational change, shaping its active site. Cofactors and Coenzymes – Vitamins or vitamin derivatives that are needed for the functions of particular enzymes

8. Ways enzymes are activated:
Enzyme Activation
Ways enzymes are activated:
Zymogens such as pepsinogen are cleaved to pepsin to avoid destroying the stomach wall.
A protein kinase must phosphorylate the enzyme that hydrolyzes stored glycogen in the liver at the proper time (between meals). Dephosphorylation inactivates the enzyme.
The enzyme, protein kinase is activated by binding cAMP,
a second messenger molecule.
4) Enzyme turnover – synthesis and degradation can control enzymes.

9. Effect of Substrate Concentration on reaction rate
Enzymatic reaction rate increases with substrate concentration up to the point at which the enzyme is saturated, and then a plateau is observed.

10. Reversible reactions
Sometimes a single enzyme can drive a reaction in two directions, depending on the concentration of substrate/product.
-- When one side gets higher, the reaction proceeds to the other side.
--This is called the law of mass action.
--Example: the enzyme carbonic anhydrase
H2O + CO2 ↔ H2CO3
An anhydrase removes water from a compound

11. Metabolic Pathways
A metabolic pathway is a series of enzyme-catalyzed reactions where the product of one reaction is the substrate for the next reaction.
LIINEAR PATHWAY:
BRANCHED PATHWAY:

12. End-Product Inhibition
A form of negative feedback One of the final products of a divergent pathway inhibits the activity of the branch-point enzyme that began the path.
Allosteric Inhibition – the inhibitor combines with the enzyme at a place different from the active site

13. Inborn Errors of Metabolism
A defect in a single gene results in a defect in the enzyme encoded by that gene.

15. Bioenergetics – the flow of energy in living systems
Thermodynamics: 1st law – energy cannot be created or destroyed 2nd law – the free energy decreases as entropy increases Free energy – amt of energy available for work
Glucose is more available to do work than carbon dioxide and water b/c glucose is more organized

16. Coupled Reactions: ATP
Exergonic and endergonic reactions are often coupled. ENDERGONIC- energy goes in; products are more organized and contain more free energy EXERGONIC - opposite

17. Endergonic and Exergonic Reactions
The combustion of glucose is exergonic because you are going to a more disorganized state.
Little by little, energy spins off and is used to drive other reactions

18. Calories
Calorie – the amount of heat required to raise the temperature of 1 cubic centimeter of water 1 degree Celsius. The energy obtained by the body from the oxidation of a molecule is the same as the amount released when the molecule is combusted (in the lab), so the # of calories in food can be measured by the heat released when the food is combusted. Calories in food are usu. expressed as kilocalories (1 kilocalorie = 1000 calories; AKA “large calories”).

19. adenosine tri-phosphate
ATP carries potential energy. The energy is released when the terminal phosphate is removed:
ATP IS THE “UNIVERSAL ENERGY CARRIER”
Click HERE to learn more about ATP

20. ATP as the Universal Energy Carrier for the Cell’s Work

21. Reduction-Oxidation Reactions (REDOX)
Electrons transfer energy between molecules.
Look at the picture Molecule “A” gives up electrons, and is oxidized. Molecule “B” receives electrons is reduced.

22. Coupled Reactions: Oxidation-Reduction
Remember:
Oxidation does not involve oxygen. The term “oxidation” is used because oxygen has a strong tendency to accept electrons.
REDOX reactions often involve the transfer of hydrogen atoms because 1 H atom contains 1 electron and 1 proton. A molecule that loses a hydrogen is oxidized. A molecule that gains a hydrogen is reduced.

23. Action of NAD
NAD+ and FAD are often used in the cell as electron acceptors or donors. They are derivatives of B vitamins. They are also coenzymes