Enzymes - Biochemistry

Question 1

What is an enzyme? what is the function?

Answer 1

• a biological catalyst, usually a protein
• function as catalyst (lower activation energy and provide alternate pathway but does not change delta G or free energy difference between substrate and product)
• enhances speed of forward and reverse reactions

Question 2

what is a substrate?

Answer 2

the reactant that is acted upon by the enzyme

Question 3

Enzyme characteristics

Answer 3

• effective catalyst
• high specificity
• domains. active site where catalysis occurs. have potential control functions.

Question 4

What are isozymes?

Answer 4

Different structural forms of an enzyme that have the same function. Different kinetics.

Question 5

What are zero order reactions?

Answer 5

reaction rate is independent of substrate concentration. V=K

Question 6

What are first order reactions?

Answer 6

reactions rate depends on the concentration of one substrate. V=k (A)

Question 7

what are second order reactions?

Answer 7

Reaction rate depends on the concentrations of two substrates. V=K (A*B)

Question 8

What are pseudo first order reactions?

Answer 8

There are two substrates but only one of them is rate limiting, for example, hydrolysis reactions in aqueous solution. A + H2O C + D

V= K(A)

Question 9

What are the classes of enzymes? what do they do?

Answer 9

1) Oxidoreductases = catalyze oxidation-reduction reactions (NADH)
2) transferases
3) Hydrolases
4) Lyases
5) Isomerases
6) ligases

Question 10

Describe exergonic and endergonic reactions in thermodynamics.

Answer 10

Exergonic reactions (negative delta G), reaction is spontaneous.

Endergonic reactions (positive delta G), reaction is non spontaneous.

When delta G is zero, the reaction is at equilibrium.

possible test question: that exergonic reactions drive endergonic reactions. Therefore the overall free energy change for the reaction in negative (spontaneous)

Question 11

Why are coupled processes important to living things?

Answer 11

many important cellular reactions must run against their thermodynamic potential, that is in direction of positive delta G. for example, hydrolysis of ATP coupled for the reaction of glucose and inorganic Phosphate to occur spontaneously.

Question 12

What are the difference between “delta G” and “delta G zero”?

Answer 12

delta G is an actual value at a cellular level, depends on the actual concentration of reactants and products.

delta G zero is the biochemical standard free energy change value that you can calculate

Question 13

what are simple enzymes?

Answer 13

contain only the polypeptide portion

Question 14

what are conjugated enzyme?

Answer 14

enzyme that contains the polypeptide portion and a non-polypeptide portion.

Question 15

What are apoenzyme?

Answer 15

the protein portion of a conjugated enzyme

Question 16

what are cofactor (prosthetic group)

Answer 16

the nonprotein (commonly metal ions: Fe, Mg, Zn) portion of a conjugated enzyme.

Question 17

what are coenzymes?

Answer 17

an organic cofactor, commonly vitamins

Question 18

what are Holoenzyme?

Answer 18

the complete, native enzyme

Question 19

what are proenzyme?

Answer 19

also known as zymogen. its an inactive precursor of a native enzyme. for example, pepsinogen is a proenzyme which is not active in its present form. needs a part of it cleaved to be the active form of pepsin.

Question 20

what are the functions of coenzymes?

Answer 20

accomplish goals amino acide side chain can not, such as in reductions and oxidations

Question 21

what are the characteristic of high energy molecules?

Answer 21

energy transfer! 2 classes of biomolecules do this: (1) reduced coenzyme (NADH, FADH2)
(2) high energy phosphate compounds (ATP)

Question 22

give 2 examples of phosphoric acid anhydrides.

Answer 22

ADP and ATP

Question 23

why does ATP have a large negative free energy change?

Answer 23

The hydrolysis of ATP to ADP (and ADP to AMP) leads to relief of electrostatic repulsion, and stabilization of products by ionization and resonance.