answer 25 ,26, 27, 28 29 please. Thank you so much. 25. At a specific area of wh

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answer 25 ,26, 27, 28 29 please. Thank you so much.

25. At a specific area of where the double-strand formed starting at t represents the primer sequence? a chromosome, the sequence of nucleotides below is present he underlined T of the template. Which of the following ed helix opens to form a replication fork. An RNA primer is 3'.. C CT A G G CT G C A ATCC-S a. 5'--AGCCTAGG--3' b. 5'- ACGTTAGG--3' 5-A CGUUAGG--3 d. 5 A G C C U A G G-3' 26 Which of the following would you expect of an organism lacking telomerase? a high probability of somatic cells becoming cancerous b. a. an inability to produce Okazaki fragments an inability to repair single-nucleotide mutations ? a reduction in chromosome length in gametes 27. How is template DNA exposed during the process of replication? a.) The origin of replication starts a bubble in the double stranded DNA b. The DNA base pairs separate at the TATA box. An RNA primer is placed at the origin of replication. Topoisomerase unwinds double stranded DNA. c. d. 28. A particular triplet of bases in the template strand of DNA is 5'-AGT-3. The corresponding codon for the mRNA transcribed is a. 5'-ACU-3 b) 5-UCA-3 c. 5'-ACT-3 d. 5'-TCA-3 29. A student researcher inserts an mRNA molecule into a eukaryotic cell's cytoplasm after she has removed the 5' cap and poly-A tail. Which of the following would you expect her to find? The mRNA is translated normally into a protein. The molecule is digested by enzymes because it is not protected. The cell adds a new poly-A tail to the mRNA. The mRNA attaches to a ribosome and is translated, but more slowly. a. c. d.

Explanation / Answer

Ans. #25. Primase synthesizes the complementary RNA primer in 5’-3- direction from the 3’-5’ template DNA strand. Note that RNA has U in place of T.

Given-            Template DNA = 3’- TGCAATCC-5’

            So,            RNA Primer = 5’-ACGUUAGG-3’

So, correct option is- C. 5’-ACGUUAGG-3’

#26. Correct option- D.

Telomerase facilitate telomere synthesis during DNA synthesis. Most somatic cells lack telomerase enzyme that replicate telomere- the end of linear chromosome. Naturally, most somatic cells lose a bit of telomere (end of chromosome) at each round of DNA replication, the process being called telomere shortening. The somatic cells don’t require telomere replication and are perfectly functions like the cells exhibiting telomere replication. In summary, most somatic cells don’t replicate telomere because they don’t require it.

# Telomerase does not mediate the synthesis of Okazaki fragments, or repairing single-nucleotide mutations or inhibits mutagenesis. So, options A, B and C are incorrect.

#27.

# Strand separation, thus exposing the template strands, is mediated by topoisomerases to remove supercoils and strains produced ahead of replication fork during replication. Topoisomerase I do not require ATP for its activity. Topoisomerase II requires 2 ATP for each event of activity.

Note that the first strand separation occurs at the Ori of Replication (marking Initiation of replication) which is initiated by Dna A proteins, and further assisted by Dna B helicase (a type II topoisomerase). However, topoisomerase exposes the template strands throughout the process of replication. Therefore, topoisomerase (option D) is more appropriate option that option A.

# TATA box has roles during transcription (mRNA synthesis).

# RNA primer is placed at the origin of replication, as well as at both the template strands at specified interval. So, placing a RNA primer at OriC does not signifies the exposure of template DNA strands during replication.

#29. Correct option- A. 5’-ACU-3’

RNA pol binds to 3’- end of template DNA and synthesizes complementary mRNA in 5’-3’ direction. The sequence of mRNA is complementary to that of template DNA with opposite polarity. RNA has U instead of T.

Given-             Template DNA = 5’-AGT-3’

            So,                     mRNA = 3’-UCA-5’            or        5’-ACU-3’

#30. Correct option- B.

# Presence of 5’-cap prevents the mature mRNA from being acted upon by exonucleases in cytoplasm. So, an mRNA lacking the 5’-cap would be digested and degraded in cytoplasm.

# Option- A. Incorrect. The 5’-cap helps ribosomes identify and bind mature mRNA. So, ribosomes can bind only to mRNA but no other types of RNA. So, an mRNA lacking 5’-cap is generally NOT translated into proteins.

## Option- C. Incorrect. Polyadenylation machinery is present in nucleus but not in cytoplasm. So, no poly-A tail would be added to the mRNA.

# # Option- D. Incorrect. See #A

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