Enzymes Review Day

Biology, Sixth Edition Chapter 6, Energy and Metabolism

“gonic” Reactions

• Reactions that require energy input are called endergonic• if they need heat, they are endothermic • If a reaction releases energy it is exergonic• if the energy is released as heat, it’s exothermic.

Biology, Sixth Edition

Chapter 6, Energy and Metabolism

ATP • Adenosine triphosphate• It is a nucleotide• 3 parts

– Nitrogen base (adenine)– Ribose (5C sugar)– 3 phosphate groups

• Energy of ATP is in these bonds

• Hydrolysis (adding water) breaks this bond making ADP + Pi– This is called phosphorylation

Biology, Sixth Edition

Chapter 6, Energy and Metabolism

Energy Released by the Hydrolysis of ATP is Coupled to Other Reactions

Biology, Sixth Edition

Chapter 6, Energy and Metabolism

NAD+ / NADH & Oxidation / Reduction Reactions

• Reduction is the addition of electrons.– Results in increased energy content– Very common in metabolism– e.g., NAD+ NADH– e.g., FAD FADH2

• Oxidation is the loss of electrons.– e.g., NADH NAD+

– e.g., FADH2 FAD– Oxidation and reduction are often coupled

as redox reactions.

Biology, Sixth Edition

Chapter 6, Energy and Metabolism

Enzymes Lower EA

Activation energy (Ea) is the energy required to break the bonds to begin the reaction

Catalase• Example of an enzyme (all enzymes end in

ASE)• Is found in all living things• Used to break down toxins in the body• For example, Catalase breaks down hydrogen

peroxide in the body (it is a byproduct of metabolism)

3.4 Notes!

• Having too little of an enzyme or having too much of an enzyme can have major consequences– Sucrase (lack of it causes diarrhea, cramps &

possibly slower growth in kids)– Too much of an enzyme is wasteful for the cell

• So in order to maintain homeostasis, we need to regulate enzymes!

Inhibitors

• Chemicals• Some naturally occur in cells (can regulate

metabolism)• Others are made in laboratories (used to treat

diseases)• Inhibitors bind to enzymes, which has an

effect on the function of an enzyme.

Competitive Inhibition• Inhibitor binds to the

active site of an enzyme

• Induced fit occurs and enzyme is unable to bind to substrate.

• Reversible– When inhibitor is in

low amounts, it will leave the active site and then the substrate can bind.

Allosteric inhibition• Inhibitor binds to an alternate site on the

enzyme (not the active site), called the allosteric site.

• Still changes shape of enzyme, so substrate cannot bind to active site

• Also called noncompetitive inhibition

What can affect an enzyme?

• pH• Temperature• All enzymes have optimal conditions for

optimal performance• Remember enzymes are proteins, so if the

tertiary level is changed, the enzyme loses its function