Chapter 6: Enzymes

Question 1

Biological catalysts

Answer 1

Enzymes

Question 2

catalytic activity depends on the

Answer 2

integrity of their native protein conformation

Question 3

Enzymes are modified covalently by

Answer 3

phosphorylation, glycosylation, and other processes

Question 4

Enzymes are protein molecules and are made up of

Answer 4

long chains of amino acids

Question 5

Transfer of hydrogen and oxygen atoms or electrons from one substrate to another

Answer 5

Oxidoreductases

Question 6

Transfer of a specific group (a phosphate or methyl etc.) from one substrate to another

Answer 6

Transferases

Question 7

Hydrolysis of a substrate

Answer 7

Hydrolases

Question 8

Change of the molecular form of the substrate

Answer 8

Isomerases

Question 9

Nonhydrolytic removal of a group or addition of a group to a substrate

Answer 9

Lyases

Question 10

Joining of two molecules by the formation of new bonds

Answer 10

Ligases (Synthetases)

Question 11

When several steps occur in a reaction the overall rate is determined by the step ( or steps) with the highest activation energy

Answer 11

Rate-limiting step

Question 12

Rate of reaction determined by

Answer 12

Alignment of reacting groups Formation of transient unstable charges Bond rearrangements Other transformations required for the reaction to proceed in either direction

Question 13

the relationship between the rate constant k and activation energy Gt is

Answer 13

inverse and exponential.

Question 14

First-ordered reaction

Answer 14

V=k[S]

Question 15

Second order reaction

Answer 15

V=k[S1][S2]

Question 16

The energy derived from enzyme-substrate interaction

Answer 16

binding energy, DeltaG_B

Question 17

Derived from the free energy released in forming many weak bonds and interactions between an enzyme and its substrate

Answer 17

catalytic power

This binding energy contributes to specificity as well as to catalysis

Question 18

What needs to occur for a reaction to take place?

Answer 18

1. a reduction in entropy, in the form of decreased freedom of motion of two molecules in solution
2. the solvation shell of hydrogen-bonded water that surrounds and helps to stabilize most biomolecules in aqueous solution
3. the distortion of substrates
4. the need for proper catalytic functional groups on the enzyme.

Question 19

Enzyme active sites are ________ to the transition states through which ______ pass as they are converted to products during enzymatic reaction.

Answer 19

complementary; substrates

Question 20

Derived from the formation of many weak interaction between the enzyme and its specific substrate molecule

Answer 20

specificity

Question 21

transfer of protons to or from the substrate

Answer 21

specific acid-base catalysis

Question 22

the functional groups of some enzyme cofactors can serve as nucleophiles, activate a substrate for further reaction

Answer 22

Covalent catalysis

Question 23

Why study enzyme kinetics?

Answer 23

• Quantitative description of biocatalysis
• Determin the order of binding of substrates
• Elucidate acid-base catalysis
• Understand catalytic menchanism
• Find effective inhibitors
• Understand regulation of activity

Question 24

parallel lines on a Lineweaver-Burk plot represent

Answer 24

a ping-pong (double-displacement) pathway

Question 25

Reversible: called competitive inhibitor resemble the substrate form an

Answer 25

EI complex

competes with substrate for binding

does not affect catalysis

Lines intersect at the y-axis

Question 26

requires that an enzyme-substrate complex must be formed

Answer 26

Uncompetitve inhibition

Question 27

can bind either free enzyme or the enzyme-substrate complex thereby preventing the reaction from occuring.

Answer 27

noncompetitive inhibitor

Question 28

cannot be overcome by increasing the concentration of the substrate (lower Vmax)

Answer 28

noncompetitive inhibition

do not interfere with the binding or substrate to enzyme (same Km)

Question 29

A mixed inhibitor usually affects:

Answer 29

both Km and Vmax

Question 30

Inhibitors that bind covalently with or destroy a functional group on an enzyme that is essential for the enzyme’s activity.

Answer 30

Irreversible inhibitors

Question 31

The enolase reaction mechanism requires

Answer 31

metal ions

Question 32

a natural antibacterial agent found in tears and egg whites, is a monomer with 129 amino acid resides

Answer 32

Lysozymes

Question 33

hyperbolic curve

Answer 33

Enzymes following Michaelis-Menten kinetics show

Question 34

Show sigmoid curve

Answer 34

alllosteric enzymes

Question 35

The reaction velocity _______ with temperature

Answer 35

increases

Question 36

Increased Km=

Answer 36

Low affinity of the enzyme to its substrate

Question 37

Reduced Km =

Answer 37

High affinity of the enzyme to its substrate

Question 38

Phosphate groups are cleaved from phosphorylated enzymes by the action of

Answer 38

phosphoprotein, phoshatases

Question 39

An enzyme can be regulated by colavent addition or removal of phosphate groups from specific…

Answer 39

serine, threonine, or tyrosine residues of the enzyme.

Question 40

commonly determined in the diagnosis of myocardial infarction

Answer 40

creatine kinase (CK)

Question 41

Isoenzymes of Creatine kinase (CK)

Answer 41

CK1= BB → common in brain

CK2= MB → common in caridiac muscles

CK3 = MM → common in skeletal and cardiac muscles

Question 42

regulatory proteins involved in myocardial contractility

Answer 42

Troponin T and troponin I

Question 43

Troponins are released into the plasma in response to

Answer 43

cardiac damage