Chp 20 Enzymes

Question 1

are globular proteins with a unique three-dimensional shape that recognizes and binds a small group of reacting molecules, called substrates

Answer 1

enzymes

Question 2

have a tertiary structure that includes a region called the active site where one or more small groups of substrates bind to create a chemical reaction.

Answer 2

enzymes

Question 3

have specific amino acid residues within the active site that interact with functional groups of the substrate to form hydrogen bonds, salt bridges, and hydrophobic interactions

Answer 3

enzymes

Question 4

has a rigid substrate binding to a rigid enzyme, much like a key fitting into a lock

Answer 4

lock-and-key model

Question 5

more dynamic model of enzyme action, states that the active site is flexible enough to adapt to the shape of the substrate

Answer 5

induced-fit model

The induced-fit model has the substrate and enzyme working together to acquire a geometrical arrangement that lowers the activation energy

Question 6

Enzymes like lactase have an ____ where the substrate fits for catalysis to occur. The quaternary structure of lactase consists of four subunits. The substrate, lactose (gray), is held in place in the active site by hydrogen bonds with amino acid R groups.

Answer 6

active site

Question 7

Some enzymes show absolute specificity by catalyzing ___ reaction for one specific substrate

Answer 7

only one

Question 8

The combination of an enzyme and a substrate forms a

Answer 8

enzyme–substrate (ES) complex

Question 9

The ES provides an alternative pathway for the reaction with

Answer 9

lower activation energy

Question 10

Within the active site, amino acid R groups catalyze the reaction to form an

Answer 10

enzyme–product (EP) complex

Question 11

oxidoreductases

Answer 11

catalyze redox rxns

Oxidases catalyze oxidation of a substrate

Dehydrogenases catalyze removal or addition of two H atoms

Question 12

Transferase

Answer 12

catalyzes the transfer of a functional group between two compounds

Question 13

Hydrolases

Answer 13

catalyzes hydrolysis (adds H20) rxn that split into two producs

Question 14

Lyases

Answer 14

catalyze the addition or removal of a gruop without hydrolyssi

Question 15

isomerases

Answer 15

catalyze the rearrangement of atoms within a substrate

Question 16

Ligases

Answer 16

joiing of two substrates, using ATP

Question 17

The activity of an enzyme describes how fast an enzyme catalyzes the reaction and is strongly affected by reaction conditions, such as

Answer 17

temperature.
pH.
concentration of the enzyme and substrate.

Question 18

lose activity at ___ temperatures as denaturation occurs

Answer 18

high

Question 19

most active at an ___temperature (usually 37°C in humans).

show little activity at low temperatures.

Answer 19

optimum

Question 20

most active at optimum pH, where proper ___ structure of the protein is maintained

Answer 20

tertiary

Question 21

An increase in enzyme concentration

Answer 21

increases the rate of reaction (at constant substrate concentration).
binds more substrate with enzyme

Question 22

An increase in substrate

concentration

Answer 22

increases the rate of reaction (at constant enzyme concentration).
eventually saturates an enzyme with substrate to give maximum activity

Question 23

type of covalent modification that activates or deactivates an enzyme.

Answer 23

Phosphorylation

Question 24

A kinase activates an inactive enzyme by

Answer 24

phosphorylation

Question 25

A phosphatase activates an inactive enzyme by ___ of a phosphate

Answer 25

removal

Question 26

bind with a regulator molecule at the allosteric site that is different from the active site. change the shape of the enzyme, which causes a change in the shape of the active site

Answer 26

Allosteric enzymes

Question 27

can be a___ that changes the shape of the active site to allow the substrate to bind more effectively

Answer 27

positive regulator allosteric enzymes

Question 28

can be a ____ that changes the shape of the active site to prevent the proper binding of the substrate, which decreases the rate of the catalyzed reaction.

Answer 28

negative regulator allosteric enzyme

Question 29

Enzyme activity can be regulated by allosteric enzymes, feedback control, and

Answer 29

covalent modifications

Question 30

In feedback control, when the end product level is high

Answer 30

the end product of a series of reactions acts as a negative regulator and binds to the allosteric site. the substrate cannot bind to the active site, and production of all of the intermediate compounds in the subsequent reaction sequence stops

Question 31

when the level of end product is low

Answer 31

the regulator dissociates from the allosteric site on the enzyme, unblocking the active site. the initial substrate is allowed to bind to the active site again.

Question 32

Enzyme activity is modified by covalent bonds to a group on the polypeptide chain that are formed or broken. Covalent modification is reversible.

Answer 32

Zymogens, or proenzymes, are produced in their inactive form and can be activated at a later time when they are needed

Question 33

Once a zymogen is formed, it is

Answer 33

transported to where the active form is needed. | converted to its active form by a covalent modification.

Question 34

different forms of an enzyme that catalyze the same reaction in different cells or tissues of the body. have quaternary structures with slight variations in the amino acids in the polypeptide subunits

Answer 34

Isoenzymes

Question 35

are molecules that cause a loss of catalytic activity. | prevent substrates from fitting into the active sites

Answer 35

Inhibitors can be classified as either reversible inhibitors or irreversible inhibitors.

Question 36

cause a loss of enzyme activity that can be restored. | can act in different ways but do not form covalent bonds with the enzyme

Answer 36

Reversible inhibitors

Question 37

Reversible inhibition can be competitive or noncompetitive.

Answer 37

Competitive inhibitors compete for the active site. Noncompetitive inhibitors act on another site that is not the active site.

Question 38

chemical structure and polarity similar to the substrate

Answer 38

competitive inhibitor competes with the substrate for the active site. has its effect reversed by increasing substrate concentration

Question 39

has a structure that is much different from that of the substrate. does not compete for the active site. distorts the shape of the enzyme, which prevents the catalyzing of the substrate at the active site. cannot have its effect reversed by adding more substrate

Answer 39

noncompetitive inhibitor

Question 40

the inhibitor covalently bonds with R groups of an amino acid that may be near the active site the inhibitor changes the shape of the enzyme, which prevents the substrate from entering the active site

Answer 40

irreversible inhibition

Question 41

an active enzyme that consists only of protein

Answer 41

simple enzyme

Question 42

Many enzymes are active only when they combine with __ such as metal ions or small molecules

Answer 42

cofactors

Question 43

A ___ is a cofactor that is a small organic molecule such as a vitamin

Answer 43

coenzyme

Question 44

organic molecules that are essential for normal health and growth. are required in trace amounts. need to be obtained from the diet

Answer 44

Vitamins

Question 45

Water-soluble vitamins

Answer 45

are soluble in aqueous solutions and cannot be stored in the body. are cofactors for many enzymes. are excreted in urine each day. are easily destroyed by heat, oxygen, and ultraviolet light, so care must be taken in food preparation

Question 46

B1 - thiamine

Answer 46

beriberi, fatigue, poor appetite, weight loss

Question 47

B2 - riboflavin

Answer 47

dermatitis, dry skin, sore tongue, cataracts

Question 48

b3 - niacin

Answer 48

pellagra, muscle fatigue, loss of appetite, diarrhea, mouth sores

Question 49

b5 pantothenic acid

Answer 49

fatigue, retarded growth, muscle cramps, anemia

Question 50

b6 pyridoxine

Answer 50

demratitis, fatigue, anemia, retarded growth

Question 51

b9 folic acid

Answer 51

abnormal RBCs, anema, GI issues, loss of hair, growth impairment, depression

Question 52

b12 cobalamin

Answer 52

pernicious anemia, malformed RBCs, nerve damage

Question 53

Vit C ascorbic acid

Answer 53

scurvy, bleeding gums, weakened connective tissues, slowe healing wounds, anemia

Question 54

Biotin H

Answer 54

dermatitis, loss of hair, fatigue, depression

Question 55

Retinol Vit A

Answer 55

necessary to avoid blindness, immune system repression, slowed growth

Question 56

Cholecalciferol - VIt D

Answer 56

necessary to avoid weakened bones

Question 57

Vit E tocopherol

Answer 57

necessary to avoid hemolysis, anemia

Question 58

Vit k menaquinone

Answer 58

necessary to avoid prolnged bleeding time & bruising

Question 59

catalyzes the oxidation of a substrate

Answer 59

oxidase | oxidoreductase

Question 60

catalyzes removal or addition of two H atomss and utilizes a coenzyme

Answer 60

dehydrogenase | oxidoreductase

Question 61

transfer of an amino acid from one substrate to another

Answer 61

transaminase | transferase

Question 62

transfer of phosphate gruops from one substrate to another

Answer 62

kinase | transferase

Question 63

hydrolysis of peptide bond in proteins

Answer 63

proteases | hydrolase

Question 64

hydrolysis of ester bonds in lipids

Answer 64

lipases | hydrolase

Question 65

hydrolysis of phosphate ester bonds in nucleic acids

Answer 65

nucleases | hydrolase

Question 66

removal of CO2 from a substrate

Answer 66

decarboxylase | lyase

Question 67

removal of NH3 from a substrate

Answer 67

deaminases | lyase

Question 68

removal of H20 from a substrate

Answer 68

dehydratases | lyase

Question 69

catalyze the addition of H20 to a substrate

Answer 69

hydratases | lyase

Question 70

rearrangment of carbohydrates

Answer 70

epimerases | type of isomerase

Question 71

formation of a bond between two substrates utilizing ATP

Answer 71

synthestases | ligases

Question 72

formaiton of a bond between CO2 and a substrate using ATP

Answer 72

carboxylases | ligase