1) Pyrimidines are synthesized through a long series of reactions beginning with
ID: 215954 • Letter: 1
Question
1)
Pyrimidines are synthesized through a long series of reactions beginning with the amino acid aspartate (wow!). The ribonucleotide CTP is one of the final compounds in this reaction pathway, and when the cell has enough CTP, it binds to and inhibits the enzyme that catalyzes the first reaction in the pathway, aspartate transcarbamoylase (ATCase). This is most likely an example of:
Competitive inhibition
Allosteric activation
Allosteric inhibition
Direct feedback inhibition
End-product inhibition
Both allosteric inhibition and end-product inhibition
Both competitive inhibition and direct feedback inhibition
2)
The enzyme phosphofructokinase-1 (PFK-1) catalyzes the 3rd reaction in glycolysis. ATP is a substrate for this reaction and therefore must bind in the active site in order for the enzyme to catalyze the reaction. However, when ATP concentrations get very high, ATP also binds to a separate site on PFK-1, inhibiting its activity, even if some ATP is bound to the active site. Inhibition of PFK-1 by ATP is an example of:
Competitive inhibition
Allosteric activation
Allosteric inhibition
Covalent modification
Two of the above
3)
The active and inactive forms of a hypothetical enzyme are shown below. What type of enzyme is it?
Phosphorylase
Zymogen
ATPase
GTPase
4)
The reaction shown below is a/an ______________ reaction.
NADH NAD+ + H+ + 2e-
Oxidation
Reduction
5)
The last product in a reaction pathway often regulates the activity of the first enzyme in the branch of the pathway that is unique to its production when the concentration of the product gets very high. Because the structure of the product is very likely to differ substantially from that of the the enzyme's normal substrate, this type of regulation is most likely:
Competitive inhibition
Competitive activation
Allosteric inhibition
Allosteric activation
Covalent modification
Competitive inhibition
Allosteric activation
Allosteric inhibition
Direct feedback inhibition
End-product inhibition
Both allosteric inhibition and end-product inhibition
Both competitive inhibition and direct feedback inhibition
2)
The enzyme phosphofructokinase-1 (PFK-1) catalyzes the 3rd reaction in glycolysis. ATP is a substrate for this reaction and therefore must bind in the active site in order for the enzyme to catalyze the reaction. However, when ATP concentrations get very high, ATP also binds to a separate site on PFK-1, inhibiting its activity, even if some ATP is bound to the active site. Inhibition of PFK-1 by ATP is an example of:
Competitive inhibition
Allosteric activation
Allosteric inhibition
Covalent modification
Two of the above
3)
The active and inactive forms of a hypothetical enzyme are shown below. What type of enzyme is it?
Phosphorylase
Zymogen
ATPase
GTPase
4)
The reaction shown below is a/an ______________ reaction.
NADH NAD+ + H+ + 2e-
Oxidation
Reduction
5)
The last product in a reaction pathway often regulates the activity of the first enzyme in the branch of the pathway that is unique to its production when the concentration of the product gets very high. Because the structure of the product is very likely to differ substantially from that of the the enzyme's normal substrate, this type of regulation is most likely:
Competitive inhibition
Competitive activation
Allosteric inhibition
Allosteric activation
Covalent modification
Explanation / Answer
1.
Correct: the given example is both allosteric inhibition and end-product inhibition. This is because allosteric inhibition is said when the higher concentration of end product is responsible to give the signal to stop the synthesis. As the end product is inhibiting the synthesis of its own so it can also be called an end product inhibition.
Hence, the correct option is (5).
Incorrect: all the other options do not justify the given situation. Hence, the options (1), (2), (3), (4), and (6) are incorrect.
2.
Correct: the given condition is the example of allosteric inhibition. This is because the same substrate is binding to the enzyme to stop the reaction and also this reversible. Hence, the correct option is (3).
Incorrect: all the other options do not justify the given situation. Hence, the options (1), (2), (4), and (5) are incorrect.
3.
Correct: this enzyme is ATPase.
4.
The given reaction is the oxidation reaction as NADH oxidized to NAD+ in the reaction.
5.
Correct: allosteric inhibition is said when the higher concentration of end product is responsible to give the signal to stop the synthesis.
Hence, the correct option is (3).
Incorrect: all the other options do not justify the given situation. Hence, the options (1), (2), (4), and (5) are incorrect.
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.