2.1 Enzymes as Biological Catalysts [HY]

Question 1

Zymogen

Answer 1

• enzymes in an inactivated form

Question 2

What’re some key features of enzymes?

Answer 2

• Lower the activation energy
• Increase the rate of the reaction
• Do not alter the equilibrium constant
• Are not changed or consumed in the reaction (which means that they will appear in both the reactants and products)
• Are pH- and temperature sensitive, with optimal activity at specific pH ranges and temperatures
• Do not affect the overall ΔG of the reaction
• Are specific for a particular reaction or class of reactions

Question 3

Substrates

Answer 3

• The molecules upon which an enzyme acts
• one enzyme can act on many, many molecules of substrate over time

Question 4

Enzyme specificity

Answer 4

• a given enzyme will only catalyze a single reaction or class of reactions with these substrates

Question 5

What’re 6 categories of enzymes? (with Mneumonic)

Answer 5

LI’L HOT
-Ligase
- Isomerase
- Lyase
- Hydrolase
- Oxidoreductase
- Transferase

Question 6

What is the ending for an enzyme?

Answer 6

-ase

Question 7

Oxidoreductases

Answer 7

• catalyze oxidation–reduction reactions; that is, the transfer
  of electrons between biological molecules.
• They often have a cofactor that acts as an electron carrier

Question 8

Reductant (of oxidoreductases)

Answer 8

• the electron donor

Question 9

Oxidant (of oxidoreductases)

Answer 9

• the electron acceptor

Question 10

Transferases

Answer 10

• catalyze the movement of a functional group from one
  molecule to another
• Ex. Kinases

Question 11

Kinases

Answer 11

• catalyze the transfer of a phosphate group, generally from ATP, to another molecule

Question 12

Hydrolases

Answer 12

• catalyze the breaking of a compound into two molecules using the addition of water.
• many hydrolases are named only for their substrate
• Ex. phosphatase, peptidases,
  nucleases, and lipases,

Question 13

Lyases

Answer 13

• catalyze the cleavage of a single molecule into two products
• Because most enzymes can also catalyze the reverse of their specific reactions, the
  synthesis of two molecules into a single molecule may also be catalyzed by a lyase

Question 14

Isomerases

Answer 14

• catalyze the rearrangement of bonds within a molecule
• catalyze reactions between stereoisomers as well as constitutional isomers
• Some isomerases can also be classified as oxidoreductases, transferases, or lyases, depending on the mechanism of the enzyme

Question 15

Ligases

Answer 15

• catalyze addition or synthesis reactions, generally between large similar molecules, and often require ATP
• Synthesis reactions with smaller molecules are generally accomplished by lyases
  *Lig means to bind

Question 16

Endergonic

Answer 16

requires energy input (ΔG > 0)

Question 17

Exergonic

Answer 17

energy is given off (ΔG < 0)

Question 18

How do catalysts work?

Answer 18

• exert their effect by lowering the activation energy of a reaction
• making it easier for the substrate to reach the transition state

Question 19

Are enzyme catalyzed rxn’s reversible?

Answer 19

Most rxns catalyzed by enzymes are technically reversible, although that reversal may be extremely energetically unfavorable and therefore essentially nonexistent