Review Sesh Flashcards
- True or false. The binding of CTP to ATCase stabilizes the R-state.
a) True
b) False
b) False
The binding of CTP (cytidine triphosphate) to ATCase (aspartate carbamoyltransferase) does not stabilize the R-state; it stabilizes the T-state (tense state). CTP acts as a feedback inhibitor for ATCase. Since ATCase is involved in the synthesis of pyrimidine nucleotides, the presence of CTP (a pyrimidine nucleotide) indicates that there is sufficient pyrimidine in the cell, and hence, further synthesis should be slowed down or halted.
CTP binds to the regulatory subunits of ATCase and stabilizes the T-state, making the enzyme less active. This means that the enzyme has a lower affinity for its substrates, thus slowing down the catalytic reaction that leads to the synthesis of more pyrimidine nucleotides. In contrast, ATP (adenosine triphosphate), as an effector molecule, binds to the same sites but stabilizes the R-state (relaxed state), which has higher catalytic activity, reflecting the need for more nucleotide synthesis under conditions where ATP (energy) is abundant.
Therefore, the correct answer is false regarding the effect of CTP on the conformational states of ATCase.
What is CTP?
- The Threshold Effect:
a) Is observed in enzymes with a small value of T
b) Is observed in enzymes with a large value of T
c) observed when a substrate concentration out-competes the competitive inhibitor d) When allostery enables precise control of enzyme activity with minimal ▲[S]
e) None of the above
The answer is d).
The threshold effect means you need only a very small amount of substrate to pass the threshold.
Define the Threshold Effect, and explain the difference between the term in BIOCHEMISTY vs in Neurophysoiology (like action potentials).
In biochemistry, it would be refering to enzyme regulation, so like allosteric enzymes who have an inhibitor bind to something other than the active site.
In Neurophysiology, it means that the depolarization just has to reach a threshold before it can trigger the action potential.
So i guess the similarity here is just that they both have to reach a small threshold first, but for BIOCHEMISTRY, it just means only a small amount of substrate is required.
Critical Point: Both scenarios involve reaching a critical point or threshold that causes a dramatic shift in activity — in biochemistry, it changes enzyme activity; in neurons, it triggers an action potential.
Define Protyolitic Activation
Proteolytic activation refers to the process in which an inactive precursor of a protein, known as a proenzyme or zymogen, is converted into its active form through the selective cleavage of specific peptide bonds by a protease. This enzymatic cleavage removes a segment of the precursor, which often acts as a regulatory cap or an inhibitory sequence, thereby activating the enzyme.
Define zwitterion in the context of amino acids
a Zwitterion is a NEUTRAL net charge amino acid. It’t not just uncharged, it must have positive AND negative charges that cancel each other out.
