Question

- Put the mark (√) for the correct sentence and mark (X) for the wrong sentence with correction of wrong.

1- A mutation is a change in the DNA sequence. The change is always harmful.               (      ).

2- The mutation in the following DNA (AGTTACCAGGC to AGTTTACCAGGC) corresponds to a deletion                                                                                                       (      ).

3- A 3′ cap is formed by adding a G to the terminal base of the transcript via a 5′–5′ Link (      ).

4- The GU-AG rule describes the requirement for these constant dinucleotides at the first two and last two positions of introns in pre-mRNAs                                                                   (      ).

5- mRNA synthesis occurs in the nucleus region of prokaryotes                                      (      ).

6- Okazaki fragments are made in a 3’ à 5’ direction                                                        (      ).                                                           

Answer 1

Solution 1- False.

Mutation is not always harmful

Eg. Silent mutation do not have any effect on the phenotype. Change of the codon AAG to AAA code the same amino acid Lysine

Solution 2- False

Mutation from AGTTACCAGGC to AGTTTACCAGGC corresponds to a insertion ( highlighted). A Thymine is inserted at the 5th position from left in AGTTACCAGGC sequence. Insertion mutation may lead to frameshift mutation also

Solution 3- False

Cap is formed at the 5' end not at the 3' end. A 5' cap is formed by adding modified GTP at the 5' end and Poly A tail is formed by adding many Adenine molecules (Poly A) at the 3'end of the mRNA

Solution 4- True

The GU-AG rule( GT-AG rule in DNA) describes the requirement for these constant dinucleotides at the first two and last two positions of introns in pre-mRNAs . To identify the ends of introns, this rule can be used. These nucleotides are splicing sites

Solution 5- False

There is no true nucleus present in Prokoryotes. Howerve, mRNA synthesis (transcription) and protein synthesis (translation) occurs simultaneously (coupled) in prokaryotes

Solution 6- False

Okazagi fragments are made in 5'-3' direction. Replication always takes place in the 5'-3' direction and Okazagi fragments are also made in 5'-3' direction. DNA polymerse extent these Okazagi fragments. Okazagi fragments are 150 to 200 bp long short sequences.