Molecular Basis of Inheritance Test - 100

In the given mRNA sequence there are 15 nucleotide . One amino acid codes  triplet three nucleotide. So, after addition of adenosine residue the total number of nucleotide is 16. So five amino acids will be coded by the mRNA sequence.

In the question, it is mentioned only adenosine and guanosine nucleotides are provided and from them 3 nucleotide codons have to be synthesized. So, the three sites of the codon can be occupied by either A or G. So, the possible combinations can give rise to 2 X 2 X 2 = 8 types of codons.

A primer is a short single strand of RNA or DNA (generally about 18-22 bases) that serves as a starting point for DNA synthesis. It is required for DNA replication because the enzymes that catalyze this process, DNA polymerases, can only add new nucleotides to an existing strand of nucleotides. Since primase produces RNA molecules, the enzyme is a type of RNA polymerase. Primase functions by synthesizing short RNA sequences that are complementary to a single-stranded piece of DNA, which serves as its template. It is critical that primers are synthesized by primase before DNA replication can occur. 

The base complementarity occurs between adenine and thymine/uracil or guanine and cytosine. As from the template strand, RNA has to be transcribed so the growing RNA strand will incorporate uracil in it complementary to adenine. The growing strand can only incorporate thymine complementary to adenine when it is a DNA.

The DNA double helix polymer of nucleic acid held together by nucleotides which base pair together. In B-DNA, the most common double helical structure found in nature, the double helix is right-handed with about 10–10.5 base pairs per turn. The double helix is antiparallel & a linear molecule and uracil are not present in DNA.

A. The leading strand is the DNA strand that DNA polymerase constructs in the 5' → 3' direction. This strand of DNA is made in a continuous manner, moving as the replication fork grows.DNA polymerase is then able to use the free 3'-OH group on the RNA primer to make DNA in the 5' → 3' direction.

B. On the lagging strand, DNA polymerase is moving away from the replication fork, meaning copying is discontinuous. As DNA polymerase is moving away from a helicase, it must constantly return to copy newly separated stretches of DNA. This means the lagging strand is copied as a series of short fragments (Okazaki fragments), each preceded by a primer. The primers are replaced with DNA bases and the fragments joined together by a combination of DNA pol I and DNA ligase

 C. DNA polymerase adds nucleotides to the 3’ end of a primer, extending the new chain in a 5’ → 3’ direction.

D. When an incorrect base pair is recognized, DNA polymerase moves backward by one base pair of DNA. The 3'–5' exonuclease activity of the enzyme allows the incorrect base pair to be excised (this activity is known as proofreading).

So, the incorrect statement is "D".

When one Heavy DNAs is transferred to Light DNAs medium than in the First generation, 2 Hybrid Heavy DNAs are formed, In the second generation again 2 hybrid DNA formed.

• First codon is AUG which is the start codon and also codes for methionine.
• Second codon is UUU which codes for phenylalanine.
• Third codon is CUC which codes for leucine.
• Fourth codon is UAG which is the stop codon and does not code for any amino acid.

Transition in DNA means when a pyrimidine is replaced with another pyrimidine or a purine is replaced with another purine. So here, second and third nucleotide is replaced with Adenine and Cytosine, then the sequence will become AAC CTC GA.