Energy and enzymes

First law of thermodynamics

Energy can be transferred or transformed but not created or destroyed

Second law of thermodynamics

• The entropy of the universe increases overtime

• The cell keeps its entropy low but transformation of energy increases entropy via removal of heat & waste products

Molecules only react if..

They have more energy than the product energy

ΔG < 0

• Exergonic reaction

• Favourable

ΔG > 0

Endergonic reaction

Enzymes

• Proteins, RNA, or a mix of both

• Lower the activation energy of a reaction

Glutamine synthesis

• Glutamic acid + NH3 → ΔG= +14.2 kJ/mol

• Products have more energy than the reactants

Can endergonic reactions take place, even with enzymes?

No. We need to couple the reactions with ATP so they become exergonic, eventually we can get the same products as the endergonic reaction

Electron “shuttles”

• Coenzymes involved in redox reactions

• NAD(H), NADP(H), FAD(H2)

Redox of NAD(H) and NADP(H)

NAD+ + H+ + 2e- → NADH

NAD+ redox reaction

NAD+ + 2e- + H+ → NADH

NADP+ redox reaction

NADP+ + 2e- + H+ → NADPH

FAD redox reaction

FAD + 2e- + 2H+ → FADH2

Alcohol dehydrogenase (ADH)

Uses NAD+ as a cofactor so instead of acetalaldehyde (poison that causes hangover) acetic acid will be the product

Allosteric regulator

Can be positive (activator) or negative (inhibitor)

Inhibitor

Acts as a fasle substrate and fits in the active site of the enzyme

Penicillin with a broken B-lactam ring

Non-competitive inhibitors

• Use a binding site on the enzyme different from the substrate binding site

• Work independent of [enzyme] & can saturate enzyme

• Used to regulate reactions

Non-competitive inhibition reaction regulation example

• Alanine (ALA) synthesis regulation

• Inhibits pyruvate kinase (makes pyruvate)

• Less pyruvate available to ALT

ALT

• Cytosolic enzyme

• ALT in the blood means trouble with liver

Do enzymes make reactions kinetically favourable?

Yes, but they don’t change ΔG

Does ATP hydrolysis have a lot of energy?

No, it’s useless on it’s own. However coupling it with reactions is what makes it useful!

Do bonds store energy?

NO! The configuration of the molecule is what has energy