Regulatory strategies Flashcards
How can allosteric proteins activity be regulated?
Specific regulatory molecules modulate allosteric protein activity by binding to distinct regulatory sites, separate from functional sites.
What does Aspartate transcarbamoylase (ATCase), an allosteric enzyme, catalyze the synthesis of?
N-carbamoylaspartate, which is the first intermediate in the synthesis of pyrimidines.
How is ATCase feedback inhibited?
By CTP, the final product of the pathway
What reverses ATCase inhibition?
ATP
What does ATCase consist of and what does that bind?
Separable catalytic subunits, which bind the substrates, and regulatory subunits, which bind CTP and ATP.
What 3 things do large changes in the quaternary structure of ATCase mediate?
- Inhibitory effect of CTP
- stimulatory effect of ATP
- coop binding of substrates
What do all subunits of ATCase do simultaneously?
Interconvert from T to R state
How are isozymes similar and different from eachother?
Differ in structure
Catalyze the same reaction
What do isozymes do?
Provide a way of fine-tuning metabolism to meet the needs of a given tissue or development stage
Covalent modification of proteins
Is a means of controlling the activity of enzymes and other proteins.
What is a common type of reversible covalent modification?
Phosphorylation
How can signals be highly amplified by phosphorylation
Because a single kinase can act on many target molecules.
Protein phosphatases
Reverse regulatory actions of protein kinases by
Catalyzing the hydrolysis of attached phosphoryl groups
Cyclic AMP
Serves as intracellular messenger in the transduction of many hormonal and sensory stimuli
How does cyclic AMP switch on protein kinase A (which is a major multifunctional kinase)
By binding to the regulatory subunit of the enzyme, thus releasing the active catalytic subunits of PKA.
What occupies the catalytic sites of PKA in the absence of cAMP?
Pseudosubstrate sequences of the regulatory subunit
Specific proteolytic cleavage (of one or a few peptide bonds)
Activates many enzymes. Control measure seen in processes such as activation of digestive enzymes and blood clotting.
What is a zymogen (proenzyme)?
An inactive precursor protein
How are digestive enzymes activated by proteolytic cleavage?
Trypsinogen activated by enteropeptidase or trypsin, trypsin then activates host of other zymogens, leading to digestion.
How is blood clotting activated by proteolytic cleavage?
By a cascade of zymogen conversions. Activated form of one clotting factor catalyzes activation of next precursor.
What is the final step of the clotting process?
Fibrinogen converted to fibrin by thrombin by hydrolysis of 4 arginine-glycine bonds. Fibrin monomer spontaneously forms long, insoluble fibers called fibrin..
How is zymogen activation essential in the lysis of clots?
Plasminogen converted to plasmin (a serine protease that cleaves fibrin) by tissue-type plasminogen activator.
