Chem 161 ch 6 review

What are enzymes

• responsible for catalyzing reactions

• almost all made up of proteins (except for catalytic RNA)

Cofactor

A metal ion or organic compound that is necessary for function

Coenzyme

A complex organic compound

• Specific kind of cofactor

List the 7 enzyme classes

1. oxidoreductase

2. transferase

3. hydrolases

4. lyases

5. isomerases

6. ligases

7. translocases

Oxidoreductase

• Transfer of electrons between molecules

• 1 bond to oxygen → two bonds to oxygen and vice versa

Transferase

• Involved in group transfer reactions

Hydrolase

• Hydrolysis reaction

• involves water

Lyase

• cleavage of C-C, C-O, C-N or other bonds through elimination reactions that leaves rings or double bonds in product

• can also have addition of groups across a double bond

Isomerase

• Transfer groups within the same molecule to yield isomeric form

Ligase

• Form C-C, C-O, C-N, C-S or any single bond between two different atoms

• done by condensation reactions using ATP

Translocase

• Catalyzes movement of ions or molecules across membranes

What are the three catalytic strategies of enzymes

1. acid base

2. covalent

3. metal ion

General acid base catalysis

• proton transfer mediates by amino acids (just moving around protons)

• usually done by glu, asp, lys, arg, cys, his, tyr, ser (have ionizable protons)

• h2o usually not found in active site

Covalent catalysis

• A transient covalent bond that is formed between a amino acid & substrate

• usually done by glu, asp, lys, arg, cys, his, tyr, ser

• done to activate substrate via nucleophilic attack

Metal ion catalysis

• ionic interactions between a metal ion & substrate can help orient or stabilize substrate for reaction & mediate redox reactions

Transition state

• bonds being broken and formed

• usually very short lived

Intermediates

• The valleys between the steps of a multistep reaction

Catalyzed vs uncatalyzed reaction graph

Uncatalyzed:

• Without enzyme, activation energy is higher

Catalyzed:

Enzyme lowers activation energy, but doesn’t change the ΔG of the reaction

Activation energy

speed of the reaction (low AE = fast reaction)