Biochemistry Ch. 10

Front 1

CTP is able to influence the activity of ATCase. This is an example of:

Back 1

Inhibition by an eventual product of the enzymatic pathway

Front 2

Part 1: This is a profile of the ATCase (Aspartate transcarbamolyase). What does this profile indicate?

Back 2

Cooperativity

Front 3

Part 2: How is this different from allosteric substrate stimulation.

Back 3

Allosteric stimulation involves a second site, whereas with ATCase the substrate stimulation targets the active site. This is an example of unexpected kinetics as the result of a complex multi-protein complex.

Front 4

The regulatory subunits of ATCase:

Back 4

Front 5

If you were to find a molecule that could mimic the binding of CTP to the ATCase enzyme in an irreversible way, what would the result be?

Back 5

ATP would no longer be an inducer

Front 6

In the T state, ATCase:

Back 6

Binds substrate which promotes transition to the R state.

Front 7

You have isolated the inhibitory subunit of ATCase. What would the activity be?

Back 7

It would bind ATP

Front 8

The regulatory subunit of PKA:

Back 8

Binds as a pseudosubstrate to the active enzyme

Front 9

What is an isozyme.

Back 9

Distinct enzymes that have the same catalytic functions.

Front 10

What is the nature of inhibition of protein kinase A by its regulatory subunit?

Back 10

Competitive inhibition

Front 11

How does cAMP overcome this inhibition?

Back 11

By inducing a conformational change through direct binding to the enzyme

Front 12

How is a G-protein normally inactivated?

Back 12

By hydrolysis of GTP

Front 13

The ATCase enzyme is designed to:

Back 13

Increase in activity within a narrow range of substrate concentrations

Front 14

In the ATCase enzyme complex, CTP binds:

Back 14

To the regulatory subunit only

Front 15

In ATCase, there are multiple catalytic subunits. How do they associate together?

Back 15

They form two separate trimers

Front 16

Cooperativity in an enzyme indicates:

Back 16

That separate enzyme subunits in a complex influence one another.

Front 17

Why does ATP stimulate ATCase?

Back 17

Because if ATP is able to stimulate it must be in concentration excess over CTP. It is in the interest of the cell to keep these two molecules in general equilibrium because both are used in near equal proportions during nucleotide biosynthesis.

Front 18

If the concentration of CTP increases, what is the effect upon ATCase activity?

Back 18

It induces inhibition which can be overcome by substrate

Front 19

Tyrosine kinases tend to be involved in:

Back 19

Growth control

Front 20

The regulatory subunit of PKA

Back 20

Binds as a pseudosubstrate to the active enzyme

Front 21

Cyclic AMP

Back 21

Front 22

Histones are commonly modified by:

Back 22

Acetylation

Front 23

What is unique about different types of G-protein coupled receptors (G-protein receptors) compared to other types of cell surface receptors.

Back 23

They have seven transmembrane regions.

Front 24

When epinephrine binds its receptor:

Back 24

Front 25

When bound to GTP the G alpha subunit:

Back 25

Hydrolyzes GTP to become inactivated.

Front 26

G alpha DIRECTLY does which of the following:

Back 26

Promotes formation of cAMP

Front 27

What would happen if GTP hydrolysis by G proteins were eliminated?

Back 27

They would remain continuously active.

Front 28

Cyclic AMP does which of the following?

Back 28

Front 29

Tyrosine kinases:

Back 29

Front 30

When bound to EGF, the EGF receptor:

Back 30

Front 31

When bound to EGF the EGF receptor

Back 31

Initiates a cascade that results in cell growth

Front 32

If the ability of Ras to hydrolyze GTP were reduced, what would most often happen?

Back 32

Uncontrolled cell proliferation

Front 33

According to our discussion in class, why do you think CTP should not be able to completely inhibit ATCase? (Be brief!)

Back 33

A healthy cell needs CTP constantly for mRNA synthesis. It is constantly needed and should constantly be synthesized. The rate of synthesis should be regulated, not the overall synthesis itself.

Front 34

Why are mutations that reduce the GTPase activity of Ras often seen in human tumors?

Back 34

GTPase activity naturally limits the activity of Ras. Without this activity the signaling of Ras would be excessive, commonly participating in tumor formation.

Front 35

Why should ATP stimulate ATCase activity? Where does it bind?

Back 35

It binds to the regulatory site in the regulatory subunit, the same site to which CTP binds. ATP stimulates in order to:

1) Keep the concentration of CTP near that of ATP, since both are used in equivalent proportions for nucleotide synthesis.

2) Because high ATP concentration indicates that there is sufficient energy for the cell to continue active metabolism, which would require CTP.