Question

1. In terms of codon recognition, how is termination fundamentally different than elongation in protein synthesis?

2. How might splicing increase the versatility of eukaryotic genes? Provide an example of a gene that undergoes splicing.

3. Describe the process in which rho dependent termination occurs.

Answer 1

Question: 1

In terms of codon recognition, how is termination fundamentally different than elongation in protein synthesis?

Translation is the process by which triplet Codes present on mRNA is translated to protein, and this process is called as protein synthesis.

• There number of triplet code each coding for a amino acid.
• AUG is the start codon and it codes for methione.
• UAA, UGA, UAG is the stop codon, it does not code for any amino acid.
• Translation starts when small and large subunit of rRNA binds to the mRNA start site.
• Large rRNA has A site and P site. At A site the tRNA brings the amino acid and its anticodon arm has sequence complementary to mRNA triplet code.
• The rRNA moves forward to the next codon the Amino acid on the A site is moved to P site. A site is empty again the new tRNA brings amino acid based on the triplet code of mRNA.
• The two amino acids at A and P site forms a peptide bond between them, the rRNA moves forward to the next codon the Elongation process continues.
• Temination is the process at which the rRNA when it reaches the site of stop codon, the triplet codon which does not code for any amino acid, no tRNA will be there to involve in the elongation process, and the protein synthesis stops.

Elongation is protein synthesis continues and the protein grows, Termination is protein synthesis stops and the protein is released.

Question: 2

Splicing of introns:

mRNA is made of introns – non coding regions and exons – coding regions.

For the mRNA to be functional it has to be processed by the removal of introns, and exons has to be joined together.

Splicing by spliceosomes:

• Spliceosomes are SnRNPs with proteins.
• The SnRNP are U1, U2, U4, U5, U6.
• These spliceosomes bind to the introns at the 5’ and 3’ end of introns and break the bonds and remove them the adajacent exons are joined by covalent bonding.
• Different exons are joined to form different mRNA transcripts this is called as alternative splicing.
• mRNA resulting from alternative splicing codes for different proteins.

Question: 3

Transcription:

Transcription is the printed version of DNA.

• Transcription is the process by which the code in the DNA to synthesize a protein is produced as mRNA.
• DNA has nucleotides Adenine, Guanine, cytosine, and Thymine.
• When DNA produce mRNA through the process of transcription the Thymine is replaced with Uracil.

Rho dependent termination:

• In prokaryotes Rho protein is the factor based on which the termination of transcription occurs.
• It is the homohexameric protein which recognises and binds to C-rich sites in the transcribed mRNA.
• After binding to mRNA it undergoes ATPase activity and subsequent ATPase helicase activity to unwind RNA-DNA hybrids and release RNA from the transcribing elongation complex.