Regulatory strategies

Question 1

How can allosteric proteins activity be regulated?

Answer 1

Specific regulatory molecules modulate allosteric protein activity by binding to distinct regulatory sites, separate from functional sites.

Question 2

What does Aspartate transcarbamoylase (ATCase), an allosteric enzyme, catalyze the synthesis of?

Answer 2

N-carbamoylaspartate, which is the first intermediate in the synthesis of pyrimidines.

Question 3

How is ATCase feedback inhibited?

Answer 3

By CTP, the final product of the pathway

Question 4

What reverses ATCase inhibition?

Answer 4

ATP

Question 5

What does ATCase consist of and what does that bind?

Answer 5

Separable catalytic subunits, which bind the substrates, and regulatory subunits, which bind CTP and ATP.

Question 6

What 3 things do large changes in the quaternary structure of ATCase mediate?

Answer 6

1. Inhibitory effect of CTP
2. stimulatory effect of ATP
3. coop binding of substrates

Question 7

What do all subunits of ATCase do simultaneously?

Answer 7

Interconvert from T to R state

Question 8

How are isozymes similar and different from eachother?

Answer 8

Differ in structure

Catalyze the same reaction

Question 9

What do isozymes do?

Answer 9

Provide a way of fine-tuning metabolism to meet the needs of a given tissue or development stage

Question 10

Covalent modification of proteins

Answer 10

Is a means of controlling the activity of enzymes and other proteins.

Question 11

What is a common type of reversible covalent modification?

Answer 11

Phosphorylation

Question 12

How can signals be highly amplified by phosphorylation

Answer 12

Because a single kinase can act on many target molecules.

Question 13

Protein phosphatases

Answer 13

Reverse regulatory actions of protein kinases by

Catalyzing the hydrolysis of attached phosphoryl groups

Question 14

Cyclic AMP

Answer 14

Serves as intracellular messenger in the transduction of many hormonal and sensory stimuli

Question 15

How does cyclic AMP switch on protein kinase A (which is a major multifunctional kinase)

Answer 15

By binding to the regulatory subunit of the enzyme, thus releasing the active catalytic subunits of PKA.

Question 16

What occupies the catalytic sites of PKA in the absence of cAMP?

Answer 16

Pseudosubstrate sequences of the regulatory subunit

Question 17

Specific proteolytic cleavage (of one or a few peptide bonds)

Answer 17

Activates many enzymes. Control measure seen in processes such as activation of digestive enzymes and blood clotting.

Question 18

What is a zymogen (proenzyme)?

Answer 18

An inactive precursor protein

Question 19

How are digestive enzymes activated by proteolytic cleavage?

Answer 19

Trypsinogen activated by enteropeptidase or trypsin, trypsin then activates host of other zymogens, leading to digestion.

Question 20

How is blood clotting activated by proteolytic cleavage?

Answer 20

By a cascade of zymogen conversions. Activated form of one clotting factor catalyzes activation of next precursor.

Question 21

What is the final step of the clotting process?

Answer 21

Fibrinogen converted to fibrin by thrombin by hydrolysis of 4 arginine-glycine bonds. Fibrin monomer spontaneously forms long, insoluble fibers called fibrin..

Question 22

How is zymogen activation essential in the lysis of clots?

Answer 22

Plasminogen converted to plasmin (a serine protease that cleaves fibrin) by tissue-type plasminogen activator.