Please help with those questions, thanks Rour tulors 2 questions for FREE Midto

Question

Please help with those questions, thanks

Rour tulors 2 questions for FREE Midto es in water to fom en present in the DNA ered base ia refemed to as a and is repaired by mutation, at h repai Animal vine lil e smallpox, carry double-stranded DNA in their viral paul others carry single stranded DNA. Mutation rates are higher in viruses with single stranded rather than in double stranded geri omes. This is probably because is more accurate in a double stranded DNA replicatie genome b. Transcription is more accurate in a double-stranded genome c, Excision repair is possible only in double stranded DNA d Excision repair is more accurate in double stranded DNA dod DNA genome

Explanation / Answer

Ans. 1. Correct option. C. DNA damage product, excision repair.

Under physiological conditions, cytosine spontaneously undergoes deamination to form uracil and ammonia as follow-

                        Cytosine + H2O ----- deamination-----> Uracil + NH3

So, C is replaced by U due to deamination. Therefore, G=C base pairing becomes: G=U.

The process of change in nucleotide sequence is called mutation.

However, the chemically altered base (Uracil is NOT a process of mutation, it’s the product of mutation) is a DNA damage product.

Such DNA damage is corrected through base- excision repair pathway.

#2. Correct option C. Excision repair is possible only ds DNA.

All types of excision-repair mechanism share fundamental similarities-

            Identification and excision of the mutated base lesion.

            Addition of the correct base on the damaged strand using the complementarity of the other normal strand.

            Ligation of the newly added base by DNA ligase.

Since the replacement of mutated base is based on “complementary DNA strand”, the mechanism works only on dsDNA where the complementary strand is present along with the damaged strand.

In ssDNA, there is no complementary DNA strand. So, any mutation (say, C à U) can’t be corrected using excision repair pathway. Instead, any base (G, C, A, G) can randomly be substituted at place of U. Therefore, mutation rates are abnormally high in ssDNA.

#26. Correct option. A. 1   

Note that the second codon (UAG) on the mRNA (5’ –3’) is a STOP codon.

Thus, translation starts at first codon (UGG) and terminates at second codon (UAG).

Therefore, the only amino acid encoded by the polypeptide is the one by UGG.

#30. In ABC model of flower development, the normal function of genes are as follow-

            Gene A = forms sepals (whorl 1, from outermost to innermost whorl)

            Gene B = forms petal (whorl 2) and stamen (whorl 3)

            Gene C = forms Carpel (whorl 4)

Given, B class function is expanded into whorl 4

That is class B genes expression is extended to whorl 4 (carpel). Or, gene B expression extends into whorl 4 replacing it. Since whorl 4 is replaced by gene B product (petals or stamen), whorl 4 (carpel) is NOT observed in such flowers. Instead, either petal or stamen (here, stamen) is present at the place of carpel.

Therefore, correct option is – C. Sepal, Petal, Stamen, Stamen (Note: Carpel must NOT be present in such flower).   

Related Questions

Navigate

• Browse (All)
• Browse P
• Subjects

---