CHAPTER 7

Question 1

A non-allosteric protein that binds oxygen independently.

Answer 1

Myoglobin

Question 2

An allosteric protein that binds oxygen cooperatively.

Answer 2

Hemoglobin

Question 3

An allosteric enzyme that exhibits cooperative binding similar to hemoglobin.

Answer 3

Aspartate transcarbamoylase (ATCase)

Question 4

Proteins that change their shape in response to a signal, leading to changes in function. Examples include hemoglobin and ATCas

Answer 4

Allosteric proteins

Question 5

Myoglobin
Hemoglobin
Aspartate transcarbamoylase (ATCase)
Allosteric proteins

Question 6

Catalyzes the first step in the biosynthesis of cytidine triphosphate (CTP), a nucleotide needed for RNA and DNA synthesis.

Answer 6

ATCase function

Question 7

An energy-intensive process involving multiple steps.

Answer 7

Pathway producing nucleotides

Question 8

This is an excellent example of how metabolic pathways are controlled to prevent overproduction of essential compounds.

Answer 8

ATCase regulation

Question 9

A regulatory mechanism that shuts down an entire metabolic pathway when the final product is in excess.

A regulatory mechanism where the end product of a pathway inhibits the first enzyme in the pathway, preventing overproduction.

Answer 9

Feedback inhibition

Question 10

An allosteric enzyme that catalyzes the first step in the biosynthesis of cytidine triphosphate (CTP).

Answer 10

ATCase

Question 11

An inhibitor of ATCase, demonstrating feedback inhibition.

Answer 11

CTP
cytidine triphosphate

Question 12

An oligomer whose biological activity is affected by other substances binding to it changes the enzymes activity by altering its quaternary structure.

Answer 12

Allosteric enzyme

Question 13

A substance that modifies the behavior of an allosteric enzyme.

Answer 13

Allosteric effector

Question 14

A type of allosteric effector that increases the enzyme’s activity.

Answer 14

Allosteric activator

Question 15

A type of allosteric effector that decreases the enzyme’s activity.

Answer 15

Allosteric inhibitor

Question 16

Indicates allosteric behavior in enzyme kinetics.

Answer 16

Sigmoidal curve

Question 17

Both CTP and ATP bind to the same site on ATCase, but CTP is an inhibitor while ATP is an activator

Answer 17

ATCase regulation by CTP and ATP

Question 18

When CTP is in short supply, ATP binding ______ ATCase activity of the enzyme.

Answer 18

ATP effect on ATCase
Increases

Question 19

Models for allosteric enzymes

Answer 19

The two main models are the Concerted Model (1965) and the Sequential Model (1966).

Question 20

A model that assumes all subunits of an allosteric enzyme exist in either a T (tense) or R (relaxed) state, and the transition between these states is concerted.

Answer 20

Concerted Model

Question 21

A model that allows for individual subunits to change conformation independently, leading to a more gradual transition between the T and R states.

Answer 21

Sequential Model

Question 22

Comparative simplicity.

Answer 22

Concerted Model

Question 23

Provides a more realistic picture of protein structure and behavior.

Answer 23

Advantage of the Sequential Model

Question 24

The enzyme exists in two conformations: R (relaxed) and T (tight or taut). The R state binds substrate tightly, while the T state binds substrate less tightly.

Answer 24

Enzyme conformations in the Concerted Model

Question 25

A model proposed by Wyman, Monod, and Changeux in 1965 to explain allosteric behavior.

Answer 25

Concerted Model

Question 26

Conformational changes in the Concerted Model All subunits of the enzyme change conformation simultaneously when transitioning between the T and R states.

Answer 26

Conformational changes in the Concerted Model

Question 27

In the absence of substrate, most enzyme molecules are in the __________ form. The binding of substrate shifts the equilibrium towards the _______ form.

Answer 27

Substrate binding in the Concerted Model T(Inactive) R (active)

Question 28

A model that explains allosteric behavior by proposing that the binding of substrate to one subunit induces a conformational change that is passed along to other subunits.

Answer 28

Sequential Model

Question 29

Substrate binding induces a conformational change from the T to the R form. The conformational change is induced by the fit of the substrate to the enzyme (induced-fit model). The model represents cooperativity.

Answer 29

Main features of the Sequential Model

Question 30

The binding of substrate to one subunit triggers a conformational change that is transmitted to other subunits, leading to a cooperative effect.

Answer 30

Substrate binding in the Sequential Model

Question 31

An enzyme whose activity is ________ by molecules binding at sites other than the active site.

Answer 31

modulated Allosteric enzyme

Question 32

____, the pathway's end product involving ATCase, inhibits ______ activity through feedback inhibition.

Answer 32

CTP, ATCase

Question 33

The regulation of an enzyme's activity by the binding of molecules at sites other than the active site.

Answer 33

Allosteric regulation

Question 34

A molecule that binds to allosteric sites on ATCase and inhibits its catalytic activity.

Answer 34

CTP

Question 34

A non-allosteric enzyme that does not exhibit allosteric regulation.

Answer 34

Chymotrypsin

Question 35

An inactive precursor of an enzyme that requires proteolytic activation to become the active enzyme.

Answer 35

Zymogen

Question 36

A single-chain of polypeptide composed of ____ amino acid residues cross-linked by __ disulfide bonds.

Answer 36

245, 5 Chymotrypsinogen structure

Question 36

A zymogen ______ and _____ in the pancreas, destined for secretion into the small intestine.

Answer 36

synthesized, stored Chymotrypsinogen

Question 37

Non-protein chemical compounds or metallic ions that help enzymes perform their catalytic functions.

Answer 37

Cofactors

Question 37

___________ molecules that assist enzymes in their catalytic activities.

Answer 37

Non Protein Cofactors and Coenzymes

Question 37

Cleavage of a __-amino acid peptide of trypsin from the N-terminus gives Pi - chymotrypsin that removes ___ dipeptide fragments leading to the formation of fully _________-chymotrypsin.

Answer 37

15, 2 active α Activation of chymotrypsinogen

Question 38

Organic molecules that are a _____ of cofactors.

Answer 38

subset Coenzymes

Question 39

Cofactors can ______ enzyme structure, _______ in the actual catalytic reaction, or____ in substrate binding

Answer 39

stabilize, participate, assist Role of cofactors

Question 39

Examples of cofactors:

Answer 39

Mg2+ for DNA polymerase, Zn2+ for alcohol dehydrogenase. and Fe2+ they are also inorganic ions

Question 39

Organic cofactors that assist enzymes in catalyzing reactions by acting as carriers for _________ or electrons. Often derived from vitamins.

Answer 39

chemical groups Coenzymes Nature of coenzymes: Organic Molecules

Question 40

Participate in reactions by _______ accepting or donating atoms, ions, or functional groups.

Answer 40

temporarily Role of coenzymes

Question 41

often regenerated after the reaction, allowing for their repeated use.

Answer 41

Coenzymes

Question 42

Biotin Back: A coenzyme involved in carboxylation reactions. Vitamin precursor: _____ Coenzyme A A coenzyme involved in acyl transfer reactions. Vitamin precursor: ________ Flavin coenzymes Coenzymes involved in oxidation-reduction reactions. Vitamin precursor: _________. Lipoic acid A coenzyme involved in acyl transfer reactions. Vitamin precursor: None. Nicotinamide adenine coenzymes Coenzymes involved in oxidation-reduction reactions. Vitamin precursor: _______ Pyridoxal phosphate A coenzyme involved in transamination reactions. Vitamin precursor:_________ Front: Tetrahydrofolic acid Back: A coenzyme involved in the transfer of one-carbon units. Vitamin precursor: _______ Front: Thiamine pyrophosphate Back: A coenzyme involved in aldehyde transfer reactions. Vitamin precursor: _______

Answer 42

Biotin Pantothenic acid. Riboflavin (B2) Niacin Pyridoxine (B6). Folic acid. Thiamin (B1).

Question 42

Cofactors Non-protein chemical compounds or metallic ions that assist enzymes in their catalytic functions. Coenzymes Organic molecules that are a subset of cofactors. Difference between cofactors and coenzymes Cofactors can be inorganic (metal ions) or organic, while coenzymes are always organic. Relationship between cofactors and coenzymes All coenzymes are cofactors, but not all cofactors are coenzymes. Role of coenzymes in enzymatic reactions Coenzymes often participate directly in the enzymatic reaction. Role of cofactors in enzymes Some cofactors may play more structural or stabilizing roles.

Answer 42

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