Human Physiology Enzymes and energy

1. Enzymes and Energy
Human
physiology

2. Enzymes
• Biological catalysts.
• Increase rate of chemical reactions.
• Most enzymes are proteins with
diverse structure.

3. Biological Catalyst
• Chemical that:
▫ Increases the rate of a reaction.
▫ Is not changed at the end of the reaction.
▫ Does not change the nature of the reaction or
final result.
▫ Lowers the activation energy required.
• Activation energy:
▫ Amount of energy required for a reaction to
proceed.

4. Activation Energy

5. Mechanism of Enzyme Action
• Each type of enzyme has has a characteristic
3-dimensional shape (conformation).
• Has ridges, grooves, pockets lined with
specific amino acids.
• Pockets active in catalyzing a reaction are
called the active sites of the enzyme.

6. Mechanism of Enzyme Action
• Lock-and-key model of enzyme activity:
• Reactant molecules (substrates) have specific
shapes to fit into the active sites.
▫ Substrate fits into active sites in enzyme.
▫ Enzyme-substrate complex dissociates.
▫ Products of reaction formed and free enzyme.

8. Naming of Enzymes
• Enzyme name ends with ase.
• Classes of enzymes named according
to activity.
• Enzymes that have the same activity
in different organs may make
different models called isoenzymes.

9. Control of Enzyme Activity
• Rate of enzyme-catalyzed reactions
measured by the rate substrates
are converted to products.

10. Control of Enzyme Activity
• Factors influencing rate:
▫ Temperature
▫ pH
▫ [cofactors and coenzyme]
▫ [enzyme and substrate]
▫ Stimulatory and inhibitory effects of
products

11. Effect of Temperature
• Increase in
temperature
increases rate of
reaction.
• At body
temperature,
plateaus.
• Denature at high
temperatures.

12. pH
• Each enzyme exhibits
peak activity at
narrow pH range
(pH optimum).
• Optimum pH reflects
the pH of the body
fluid in which the
enzyme is found.

13. Cofactors and Coenzymes
• Cofactor:
▫ Attachment of cofactor causes a
conformational change in enzyme.
▫ Participate in temporary bonds between
enzyme and substrate.
• Coenzymes:
▫ Cofactors that are organic molecules derived
from niacin, riboflavin and other H20 soluble
vitamins.

15. Substrate Concentration
• Rate of product
formation will
increase as the
[substrate].
• Plateau of
maximum
velocity occurs
when enzyme is
saturated.

16. Reversible Reactions
• H20 + C02 H2C03
• Direction of reversible reaction
depends on the concentration of
molecules to the left and right of
the arrows.
ca

17. Sequence of enzymatic reactions that begins with
initial substrate, progresses through intermediates
and end with a final product.

18. An intermediate can serve as substrate for 2 different
enzymes, producing 2 different products.

19. Negative feedback inhibition. One of the final
products inhibits the activity of the branch enzyme.
Prevents final product accumulation.

20. Inborn Errors of Metabolism
• Inherited defect in a gene.
• Quantity of intermediates formed
prior to the defect increases.
• Final product decreases, producing a
deficiency.

21. Cannot produce tyrosine, PKU results.
Cannot produce melanin, albinism results.

22. Bioenergetics
• Flow of energy in living systems.
• 1st
law of thermodynamics:
▫ Energy can be transformed, but it cannot be
created or destroyed.
• 2nd
law of thermodynamics:
▫ Energy transformations increase entropy.
▫ Free energy can be used to do work.

23. Endergonic Reactions
• Chemical reactions that require an
input of energy.
• Products must contain more free
energy than reactants.

24. Exergonic Reactions
• Convert molecules with more free energy to
molecules with less.
• Release energy in the form of heat.
• Heat is measured in calories.
• Calorie:
▫ Amount of heat to raise the temperature of one
cubic centimeter of H20 one degree Celsius.

27. Coupled Reactions: ATP
• Cells cannot use heat for energy.
• Require energy released in
exergonic reactions (ATP) to be
directly transferred to chemical-
bond energy in the products of
endergonic reactions.

28. Universal energy carrier of the cell.

29. Oxidation-Reduction
• Reduced:
▫ Molecule/atom gains electrons.
• Reducing agent:
▫ Molecule/atom that donates electrons.
• Oxidized:
▫ Molecule/atom loses electrons.
• Oxidizing agent:
▫ Molecule/atom that accepts electrons.
• May involve the transfer of H+
rather than free
electrons.

30. Reduced form.

31. Oxidized form.