1. Enzymes: “Helper” Protein molecules

2. Enzymes Catalysts for biological reactions Most are proteins
Lower the activation energy
Increase the rate of reaction
Activity lost if denatured
May be simple proteins
May contain cofactors such as metal ions or organic (vitamins)

3. Flow of energy through life
Life is built on chemical reactions

4. Chemical reactions of life
Processes of life
building molecules
synthesis
breaking down molecules
digestion + +

5. Nothing works without enzymes!
How important are enzymes?
all chemical reactions in living organisms require enzymes to work
building molecules
synthesis enzymes
breaking down molecules
digestive enzymes
enzymes speed up reactions
“catalysts”
enzyme +
enzyme
We can’t live without enzymes! +

6. CATALYST – A SUBSTANCE THAT CAUSES A CHEMICAL REACTION TO HAPPEN MORE QUICKLY.
Enzymes work by weakening bonds which lowers activation energy

7. Progress of the reaction Free energy of activation
Enzymes
Without Enzyme
With Enzyme
Free
Energy
Progress of the reaction
Reactants
Products
Free energy of activation

8. Enzymes are proteins
Each enzyme is the specific helper to a specific reaction
each enzyme needs to be the right shape for the job
enzymes are named for the reaction they help
sucrase breaks down sucrose
proteases breakdown proteins
lipases breakdown lipids
DNA polymerase builds DNA

9. Enzymes aren’t used up Enzymes are not changed by the reaction
used only temporarily
re-used again for the same reaction with other molecules
very little enzyme needed to help in many reactions
substrate
product
active site
enzyme

10. Enzyme vocabulary Enzyme Substrate Products Active site
helper protein molecule; catalyst
Substrate
molecule that enzymes work on
Products
what the enzyme helps produce from the reaction
Active site
part of enzyme that substrate molecule fits into

11. It’s shape that matters!
Lock & Key model
shape of protein allows enzyme & substrate to fit
specific enzyme for each specific reaction

12. Lock and Key Model
E S ES complex E P P S S P

13. 2 1 3

14. Enzyme Action: Induced Fit Model
Enzyme structure flexible, not rigid
Enzyme and active site adjust shape to bind substrate
Increases range of substrate specificity
Shape changes also improve catalysis during reaction

15. Enzyme Action: Induced Fit Model
E S ES complex E P P S S S P

16. Factors Affecting Enzyme Action: Temperature
Little activity at low temperature
Rate increases with temperature
Most active at optimum temperatures (usually 37°C in humans)
Activity lost with denaturation at high temperatures

17. Factors Affecting Enzyme Action
Optimum temperature
Reaction
Rate
Low High
Temperature

18. What affects enzyme action
Correct protein structure
correct order of amino acids
why? enzyme has to be right shape
Temperature
pH (acids & bases)

19. Order of amino acids Wrong order = wrong shape = can’t do its job! DNA
folded protein
chain of amino acids
DNA
right shape!
folded protein
chain of amino acids
DNA
wrong shape!

20. Factors Affecting Enzyme Action: Substrate Concentration
Increasing substrate concentration increases the rate of reaction (enzyme concentration is constant)
Maximum activity reached when all of enzyme combines with substrate

21. Factors Affecting Enzyme Action
Maximum activity
Reaction
Rate
substrate concentration

22. Temperature Effect on rates of enzyme activity Optimum temperature
greatest number of collisions between enzyme & substrate
human enzymes
35°- 40°C (body temp = 37°C)
Raise temperature (boiling)
denature protein = unfold = lose shape
Lower temperature T°
molecules move slower
fewer collisions between enzyme & substrate

23. Temperature
human enzymes
37°
reaction rate
temperature

24. How do cold-blooded creatures do it?
Enzymes work within narrow temperature ranges. Ectotherms, like snakes, do not use their metabolism extensively to regulate body temperature. Their body temperature is significantly influenced by environmental temperature. Desert reptiles can experience body temperature fluctuations of ~40°C (that’s a ~100°F span!).
What mechanism has evolved to allow their metabolic pathways to continue to function across that wide temperature span?

25. pH Effect on rates of enzyme activity
changes in pH changes protein shape
most human enzymes = pH 6-8
depends on where in body
pepsin (stomach) = pH 3
trypsin (small intestines) = pH 8

26. pH stomach pepsin intestines trypsin reaction rate pH 1 2 3 4 5 6 7 8
What’s happening here?!
reaction rate 1 2 3 4 5 6 7 8 9 10 11 12 13 14 pH

27. Enzyme Inhibition Inhibitors cause a loss of catalytic activity
Change the protein structure of an enzyme
May be competitive or noncompetitive
Some effects are irreversible

28. Competitive Inhibition
A competitive inhibitor
Has a structure similar to substrate
Occupies active site
Competes with substrate for active site
Has effect reversed by increasing substrate concentration

29. Noncompetitive Inhibition
A noncompetitive inhibitor
Does not have a structure like substrate
Binds to the enzyme but not active site
Changes the shape of enzyme and active site
Substrate cannot fit altered active site
No reaction occurs
Effect is not reversed by adding substrate

31. Allosteric Site – undergoing a change in the shape and activity of a protein (as an enzyme) that results from the combination with another substance at a point other than the chemically active site.

32. For enzymes… What matters?
SHAPE!