1. How does the first nucleotide at the 5 end of a new mRNA chain differ from th
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Question
1. How does the first nucleotide at the 5 end of a new mRNA chain differ from the other nucleotides in the chain?
The first nucleotide is always a uracil.
The first nucleotide does not retain its triphosphate group, while the others in the chain do.
The first nucleotide retains its triphosphate group, while the others do not.
The first nucleotide is always a modified cytosine.
The first nucleotide is always a cytosine.
2. In the tricarboxylic acid cycle, oxaloacetate reacts with acetyl CoA forming citrate.
__________________
True
False
3. How does anaerobic respiration differ from aerobic respiration?
Anaerobic respiration produces CO2.
Anaerobic respiration utilizes NO3 as the terminal electron acceptor.
Anaerobic respiration produces ATP.
Anaerobic respiration utilizes O2 as the terminal electron acceptor.
Anaerobic respiration involves an electron transport chain.
4. Homologous pairs of chromosomes separate during meiosis I.
__________________
True
False
5. During signal transduction of a G protein, the first messenger binds to the receptor, and the G protein is activated. What happens next?
activation of adenylyl cyclase
formation of cAMP
phosphorylation of the G protein
cellular response
activation of protein kinase
a.The first nucleotide is always a uracil.
b.The first nucleotide does not retain its triphosphate group, while the others in the chain do.
c.The first nucleotide retains its triphosphate group, while the others do not.
d.The first nucleotide is always a modified cytosine.
e.The first nucleotide is always a cytosine.
Explanation / Answer
Ans. 1. Correct option. C. The residue at 5’-end of new mRNA in prokaryotes is a triphosphate. [Note: In eukaryotes, a 7-Methylguanosine cap is added at 5’ end. None of the options provided here are specific to eukaryotes.]
During polymerization in 5’-3’ direction, two terminal phosphate groups of the second incoming nucleotide is removed to form a phosphodiester bond between the first nucleotide (at 5’end) and second nucleotide (at 3’-end). So, all residues in a mRNA, except the one at 5’-end lack two phosphate groups. So, option B is incorrect.
Option A- Incorrect. Methionine is the generally the first amino acid encoded by an mRNA. Methionine is encoded by “AUG” codon. From this perspective, adenine is always the first nucleotide.
Option. D and E- Incorrect. The first nucleotide in new mRNA (not mature mRNA) is generally adenine (of AUG codon).
#2. True.
OAA + Acetyl-CoA ----Citrate synthase------> Citrate
#3. Aerobic respiration uses O2 as terminal electron acceptor. CO2 is produced during TCA cycle- a pathway involved in aerobic respiration. Aerobic respiration uses ETC to harvest energy of NADH and FADH2. Both aerobic and anaerobic respiration produce ATP- 2 ATP in anaerobic respiration and 30 ATP in aerobic respiration.
Use of NO3 or other inorganic molecules/ atoms (ex- S, sulfate, NH3, etc.) other than O2 is exclusive to anaerobic respiration.
So, correct option is B. Anaerobic respiration utilizes NO3- as terminal electron acceptor.
#4. True.
Homologous chromosomes separate during meiosis I whereas the sister chromatids segregate during meiosis II.
#5. After activation, G-protein releases GDP, and bind to GTP. In due sequence of events, adenylate cyclase is activated. Later, cAMP (secondary messenger) is formed. cAMP subsequently binds to protein kinase A; and triggers cellular response through further events in the signaling cascade.
Correct option. A. Activation of adenylate cyclase.
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