1. In allosteric enzyme inhibition, the active site is blocked by another molecu
ID: 204102 • Letter: 1
Question
1. In allosteric enzyme inhibition, the active site is blocked by another molecule
a. True
b. False
2. In the second-messenger system of hormonal action,
a. The presence of a small amount of one hormone (the second messenger) is essential to permit another hormone (the first messenger) to exert its full effect.
b. A tropic hormone (the first messenger) stimulates secretion of another hormone (the second messenger).
c. The hormone first binds to a specific surface receptor (the first messenger), whereupon the hormone-receptor complex moves into the cell to combine with a specific intracellular receptor (the second messenger).
d. Releasing hormones (the first messenger) from the hypothalamus regulate the release of many anterior pituitary hormones (the second messenger).
e. The combination of a hormone (the first messenger) with membrane surface receptors activates adenylyl cyclase, which catalyzes the transformation of cellular ATP to cyclic AMP, which in turn acts as a “second messenger” to produce alteration of cell function associated with that hormone.
3. Which is NOT a product at the completion of Kreb’s Cycle?
a. NADH
b. FADH2
c. Pyruvate
d. Carbon Dioxide
e. ATP
4. In many second messenger mechanisms calcium binds to ______ and together they form a complex which activates various enzyme systems.
a. Adenylyl cyclase
b. G proteins
c. Calmodulin
d. IP3
e. All of the above
5. ________ is the principle enzyme that is responsible for the synthesis of an RNA transcript that ultimately becomes part of a ribosome?
a. RNA Polymerase II
b. RNA polymerase III
c. DNA Polymerase
d. RNA Polymerase I
e. DNA Primase
Explanation / Answer
1. False
The regulatory enzymes that posses an additional site other than active site are called allosteric site and the enzymes are called allosteric enzymes. The molecules called modulators will bind to the allosteric site and inhibit the enzyme activity
2. e. The combination of a hormone (the first messenger) with membrane surface receptors activates adenylyl cyclase, which catalyzes the transformation of cellular ATP to the cyclic AMP, which in turn acts as a “second messenger” to produce an alteration of cell function associated with that hormone.
Many hormones like epinephrine act as first messenger and bind to the G protein-coupled receptors. The GTP bound G alpha subunit of the G protein activates the adenylyl cyclase which converts the cellular ATP to the cyclic AMP. The cyclic AMP acts as “the second messenger” and mediates the effects of epinephrine.
3. c. Pyruvate
The Pyruvate is the end product of glycolysis. One glucose molecule (6 Carbon compound) enters into glycolysis produces two molecules of pyruvate (3 Carbon compound).
Krebs cycle is also called citric acid cycle or tricarboxylic acid cycle. The acetyl coenzyme A combine with one oxaloacetate molecule produces citrate. The citrate molecule degraded and oxaloacetate molecule is regenerated. During Krebs cycle, two GTP, two FADH2, six NADH2 and 2 Co2 are produced from two molecules of private.
Oxaloacetate + Acetyl CoA -> Citrate -> Isocitrate -> Oxalosuccinate -> -Ketoglutarate -> Succinyl-CoA -> Succinate Fumarate -> L-Malate -> Oxaloacetate
4. c. Calmodulin
The calcium act as a second messenger and its concentrations in the cell can be increased by the Ryanodine receptors. The increased calcium concentrations can activate a protein kinase called calmodulin. The calmodulin is calcium binding protein and it regulates the ion channels, myosin light chain kinase, and CAM kinases.
5. d. RNA Polymerase I
It is found in the nucleolus and responsible for expression of all types of ribosomal RNA (rRNA) except 5S rRNA in eukaryotes. It is insensitive to the action of alpha-amanitin a cyclic octapeptide.
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