Exam Two: Ch 7 Learning Objectives

Question 1

Define an allosteric enzyme

Answer 1

oligomers whose biological activity is affected by other substances binding to it

Question 2

How do allosteric enzymes function?

Answer 2

change the enzymes activity by altering the conformation(s) of the quaternary structure

Question 3

Relate allosteric enzymes with ATCase

Answer 3

ATCase allosterically inhibited by cytidine triphosphate
allosterically activated by adenosine triphosphate

Question 4

Define feedback inhibitor

Answer 4

final product blocks an early reaction and shuts down the whole series

Question 5

What is the feedback inhibitor of ATCase

Answer 5

cytidine triphosphate (CTP) shuts down the production f ATCase

Question 6

T/F: Allosteric enzymes exhibit cooperative behavior

Answer 6

True; when they are positive allosteric effectors

Question 7

Allosteric enzymes can be __ or __

Answer 7

activators
inhibitors

Question 8

What is the main difference between the sequential and concerted model?

Answer 8

sequential - step wise, more detailed
concerted - one motion

Question 9

Describe the concerted model of allosteric enzymes

Answer 9

in the presence of substrates, all subunits change conformations simultaneously

Question 10

If T does not bind to substrate, __ = 0 where __ is equal to K(R)/K(T)

Answer 10

c

Question 11

Lower c means higher __ between S and R formation and more __ effects

Answer 11

affinity; sigmoidal

Question 12

In the concerted model when a protein binds to a substrate there is a __ effect only in the __ state

Answer 12

positive; R

Question 13

In the concerted model when a protein binds to an activator there is a __ effect only in the __ state

Answer 13

positive; R

Question 14

In the concerted model when a protein binds to an inhibitor there is a __ effect only in the __ state

Answer 14

negative; T

Question 15

Describe the sequential model

Answer 15

binding induces a conformational change from T to form R based on cooperative binding of substrate to allosteric enzyme
T binds to substrate; conforms to R

Question 16

In the sequential model, allosteric inhibition occurs by __ __ mechanism

Answer 16

induced-fit

Question 17

What are the three most commonly phosphorylated amino acids?

Answer 17

Ser, Thr, and Tyr

Question 18

Define a protein kinease

Answer 18

enzymes that transfer phosphate onto a substrate, usually from ATP as a donor

Question 19

Define protein phosphates

Answer 19

enzymes that remove phosphate via hydrolysis of the phosphate ester bond

Question 20

Describe the sodium potassium pump with phosphorlyation

Answer 20

Na binds outside the cell making an aspartyl phosphate intermediate which transfers sodium inside the cell
potassium inside the cell helps phosphate hydrolysis where potassium transports outside and ATP binds

Question 21

What does glycogen phosphorlyase do?

Answer 21

catalyzes bond cleavage by substitution of a phosphate group on glycogen which is the Rate determining step

Question 22

What is the allosteric interaction in glycogen phophorylase

Answer 22

glycogen-binding (storage) site

Question 23

What is the phosphorlyation of glycogen phosphorylase?

Answer 23

phosphorylase a - Ser 14

Question 24

What is the function of phosphorylase a

Answer 24

promotes T to R

Question 25

___ is the only allosteric effector and binds to __ state which inactivates the __

Answer 25

glucose; T; enzyme

Question 26

What is the dephosphorlation of glycogen phosphorylation?

Answer 26

phorsphorylase b

Question 27

What is the function of phosphorylase b?

Answer 27

ATP and G6P bind to T state, inactivating enzyme
AMP binds to R state, activating the enzyme

Question 28

Define zygomens

Answer 28

inactive precursor of an enzyme that can be activated by specific hydrolysis of peptide bonds

Question 29

How are zygomens activated?

Answer 29

irreversible covalent modification

Question 30

What are the amino acids in the catalytic triad of serine protease?

Answer 30

Asp, His, and Ser

Question 31

What are the three amino acids involved with chymotrypsin?

Answer 31

Phe, Gly, Ser

Question 32

What are the three amino acids involved with trypsin?

Answer 32

Gly, Lys, Asp

Question 33

What are the three amino acids associated with elastase?

Answer 33

Val, Ala, Thr

Question 34

Define transition state analogs and how they are inhibited

Answer 34

enzyme inhibitors; inhibited by planar analogs of Pro; like in proline racemase

Question 35

Define a coenzyme

Answer 35

function as cosubstrates; transiently associated with a given enzyme

Question 36

Define a cofactor

Answer 36

metal ions that act as catalysts

Question 37

What is an example of a coenzyme?

Answer 37

NAD+ and NADP+

Question 38

What are examples of metal ion cofactors?

Answer 38

Mg, Zn, Fe, Cu, Mn, and Co

Question 39

Describe acid-base catalysis

Answer 39

proton transfer; influence by pH changes

Question 40

What are amino acids involved in acid-base catalysis?

Answer 40

Asp, Glu, His, Cys, Tyr, and Lys

Question 41

The more stable the ___ bond formed, the harder to break.

Answer 41

covalent

Question 42

A good covalent catalyst must be a good __ or a good __, i.e. highly ___

Answer 42

Nucleophile
LG
polarizable

Question 43

What are amino acids involved in covalent catalysis?

Answer 43

Asp, His, Lys, Ser, Cys

Question 44

Describe four benefits of metal ion cofactors

Answer 44

binding substrates and orient them for reaction
mediate redox reactions
electrostatic stabilization of negative charges
charge of ionic increasing acidity, generating OH-