Some Diffficult exam questions

Question 1

Describe the process of Translation in detail ?

Answer 1

Initiation :

Smaller subunits begin to bind to the start codon of the mRNA . Specific initiation tRNA carrying a methionine
Large subunits of a ribosome binds to this complex in which the tRNA occupies the P site .

Elongation :
The complementary anti codon of the tRNA bonds to the mRNA occupying the A site the ribosome. They both form polypeptide bonds. In addition the ribosome will move one codon futher away mRNAA translocation in the 5-3 direction A-P site .Empty tRNA will move from p site to the E site .In which the A sie becomes empty and is ready for another tRNA . The tRNA is rleased from the E site

Termination :

1. Ribsome reaches the stop codon (UAG, UAA and UGA ).Leading the polypetide to be released from the ribosome and the tRNA is released from the ribosome .

Question 2

Describe the process of transcription in detail ?

Answer 2

Initiation :

1. DNA molecule unwinds , separates to form a small open complex , RNA polymerase binds to the promoter . Sit down on the DNA and begin transcribing .

Elongation :
RNA polymerase move along the template strand 5-3 synthesis on mRNA molecule

Eukaryotes , there are about three RNA polymerase 1, 2, 3 including the PRE mRNA which is spliced and modified producing mRNA.

The RNA transcript carries the same information as the non-template (coding) strand of DNA, but it contains the base uracil (U) instead of thymine (T).

Termination :
Sequences called terminators signal that the RNA transcript is complete. Once they are transcribed, they cause the transcript to be released from the RNA polymerase. An example of a termination mechanism involving formation of a hairpin in the RNA is shown below.

Question 3

What do Hairpins specifically do ?

Answer 3

In transcription termination, the hairpin causes the RNA polymerase to stall and the transcript to separate from the DNA.

In a tRNA, multiple hairpins form and give the tRNA molecule the 3D shape it needs to perform its job of delivering amino acids.

Question 4

Which is the First step in gene expression ?

Answer 4

Transcription is the first step in gene expression. It involves copying a gene’s DNA sequence to make an RNA molecule.

Question 5

What do Bacteria do ?

Answer 5

RNA transcripts can act as messenger RNAs (mRNAs) right away.

In eukaryotes, the transcript of a protein-coding gene is called a pre-mRNA and must go through extra processing before it can direct translation.

Question 6

How is a Hairpin Loop created ?

Answer 6

A hairpin loop is an unpaired loop of messenger RNA (mRNA) that is created when an mRNA strand folds and forms base pairs with another section of the same strand. The resulting structure looks like a loop or a U-shape.

Question 7

Where does the 5 cap and the 3 added ?

Answer 7

A 5’ cap is added to the beginning of the RNA transcript, and a 3’ poly-A tail is added to the end.

Question 8

What happens during splicing ?

Answer 8

In splicing, some sections of the RNA transcript (introns) are removed, and the remaining sections (exons) are stuck back together.

Question 9

What do the gene splicing lead to ?

Answer 9

leading to the production of different mature mRNA molecules from the same initial transcript.

Question 10

5
′
AAAAUGAGUAAG3
′
Which of the following DNA strands could have been the template for this RNA?

Answer 10

RNA
DNA
​

5
′
AAAAUGAGUAAG3
′

3
′
TTTTACTCATTC5
′
​

Each nucleotide is appropriately paired according to the A-U/T-A and C-G pairing rules, so these are complementary strands.