Chapter 9 ENZYMES: Regulation of Activities

Question 1

describe the ability of animals to maintain a constant intracellular environment despite changes in their
external surroundings

Answer 1

homeostasis

Question 2

the causative agent of plague, elaborates a protein-tyrosine phosphatase that hydrolyzes phosphoryl groups on key cytoskeletal proteins.

Answer 2

Yersinia pestis

Question 3

the causative agent of cholera, disables sensor-response pathways in intestinal epithelial cells by ADP-ribosylating the GTP-binding proteins (G-proteins) that link cell surface receptors to adenylyl cyclase

Answer 3

Vibrio cholerae

Question 4

The ability of enzymes to discriminate between the structurally similar coenzymes NAD+ and NADP+ also results in a form of ______

Answer 4

compartmentation

Question 5

Decreasing the catalytic efficiency or the quantity of
the catalyst responsible for the ____ will immediately reduce metabolite flux through the
entire pathway.

Answer 5

“bottleneck” or rate-limiting reaction

Question 6

Schoenheimer deduced that proteins exist in a state of “dynamic equilibrium” within our bodies where they are continuously synthesized and degrade

Answer 6

protein turnover

Question 7

The synthesis of certain enzymes depends upon the presence of ____, typically substrates or structurally related compounds that stimulate the transcription of the gene that encodes them

Answer 7

inducers

Question 8

an excess of a metabolite may curtail synthesis of its cognate enzyme via ____

Answer 8

repression

Question 9

activity is controlled by the interaction of hormones and other extracellular signals with specific cell-surface receptors

Answer 9

transcription factors

Question 10

Proteins are targeted to the interior of the proteasome by _____, the covalent attachment of one or more ubiquitin molecules.

Answer 10

ubiquitination

Question 11

is catalyzed by a large family of enzymes called E3 ligases, which attach ubiquitin to the sidechain amino group of lysyl residues.

Answer 11

Ubiquitination

Question 12

is responsible both for the regulated degradation of selected cellular proteins, for example, cyclins, and for the removal of defective or aberrant protein species.

Answer 12

ubiquitin-proteasome pathway

Question 13

refers to the process by which the end product of a multistep biosynthetic pathway binds to and
inhibits an enzyme catalyzing one of the early steps in that
pathway

Answer 13

Feedback inhibition

Question 14

• bind small, physiologically important molecules to modulate enzymes
• Usually contain multiple subunits and frequently catalyze the committed step early in a pathway

Answer 14

Allosteric Enzymes

Question 15

the catalyst for the first reaction unique to pyrimidine biosynthesis, is a target of feedback regulation by two nucleotide triphosphates: cytidine triphosphate (CTP) and adenosine triphosphate

Answer 15

Aspartate transcarbamoylase (ATCase)

Question 16

are those for which catalysis at the active site may be modulated by the presence of effectors at an allosteric site

Answer 16

Allosteric Enzymes

Question 17

a phenomenologic term devoid of mechanistic implications

Answer 17

feedback regulation

Question 18

a mechanism for regulation of enzyme activity

Answer 18

feedback inhibition

Question 19

Nerve impulses and the binding of many hormones to cell surface receptors elicit changes in the rate of enzyme-catalyzed reactions within target cells by inducing the release or synthesis of specialized allosteric effectors called ____

Answer 19

second messengers

Question 20

is the hormone molecule or nerve impulse

Answer 20

primary or first messenger

Question 21

Those effectors that increase catalytic activity are known as ___

Answer 21

Positive effectors ( Activators)

Question 22

Effectors that reduce or inhibit catalytic activity are ___

Answer 22

Negative effectors (Inhibitors)

Question 23

represents a classic example of epigenetics, the hereditary transmission of information by a means other than the sequence of nucleotides that comprise the genome

Answer 23

Histone code

Question 24

Certain proteins are synthesized as inactive precursor proteins known as ___

Answer 24

proproteins

Question 25

The proprotein forms of enzymes are termed ___

Answer 25

proenzymes or zymogens

Question 26

involves one or more highly specific proteolytic clips that may or may not be accompanied by separation of the resulting peptides

Answer 26

Selective Proteolysis

Question 27

The conformational changes that accompany selective proteolysis of ____ align the three residues of the charge-relay network, forming the catalytic site.

Answer 27

prochymotrypsin (chymotrypsinogen)

Question 28

phosphorylate proteins by catalyzing transfer of the terminal phosphoryl group of ATP to the hydroxyl groups of seryl, threonyl, or tyrosyl residues, forming O-phosphoseryl, O-phosphothreonyl, or O-phosphotyrosyl residues, respectively.

Answer 28

Protein Kinases

Question 29

The unmodified form of the protein can be regenerated by hydrolytic removal of phosphoryl groups, catalyzed by protein ____.

Answer 29

phosphatases

Question 30

permits the functional properties of the affected enzyme to be altered only for as long as it serves a specific need

Answer 30

Phosphorylation-dephosphorylation

Question 31

Types of Allosteric Effectors

Answer 31

1. Heterotropic effectors - effector is different from substrate
2. Homotropic effectors - the substrate itself serve as an effector

Question 32

catalyze the transfer of the acetyl group of acetyl-CoA to the ε-amino groups of lysyl residues, forming N-acetyl lysine

Answer 32

Lysine acetyltransferases

Question 33

catalyze the removal by hydrolysis of acetyl groups, regenerating the unmodified form of the protein and acetate as products

Answer 33

histone deacetylases

Question 34

use NAD+ as substrate, which yields O-acetyl ADP-ribose and nicotinamide as products in addition to the unmodified protein

Answer 34

Sirtuins

Question 35

targets multiple proteins in a pathway

Answer 35

Acetylation-deacetylation

Question 36

A mechanism of regulating enzyme activity is to sequester enzymes in compartments where access to their substrates is limited

Answer 36

Enzyme sequestration

Question 37

Inactive proenzymes are activated by ___

Answer 37

proteolysis

Question 38

• A substance that kills bacteria or inhibits their growth
• Exert their action on bacteria and do not affect the host organism
• Usually inhibits specific enzymes essential to the life process of bacteria

Answer 38

Antibiotics

Question 39

• The first antibiotic discovered by the German Gerhard Domagk
• Inhibits bacterial growth by its competitive inhibition of PABA conversion to folate, which is essential for normal DNA synthesis
• Humans are not affected because we do not use PABA for folate synthesis. We derive folate from our diet

Answer 39

Sulfa Drugs

Question 40

• Discovered by Alexander Fleming while he was working with staphylococci
• inhibits transpeptidase, an enzyme essential for bacterial cell wall synthesis

Answer 40

Penicillin

Question 41

• One of the best broad-spectrum antibiotics

- Inhibits the enzyme DNA gyrase, which is essential for removing “kinks” formed in bacterial DNA during replication

Answer 41

Ciprofloxacin

Question 42

The final product (E) inhibits the step from A to B

Answer 42

Simple feedback inhibition

Question 43

Both final products (D,E) inhibit the first step of their own synthesis together

Answer 43

Cooperative feedback inhibition