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Enzymes: “Helper” Protein molecules

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Presentation on theme: "Enzymes: “Helper” Protein molecules"— Presentation transcript:

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! +

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?

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