2. For those protein- or peptide- encoding genes, how many nucleotides encode on

Question

2. For those protein- or peptide- encoding genes, how many nucleotides encode one amino acid? What exactly does codon and anticodon mean? About how many different codons and protein-coding amino acids can we find in organisms? Do different organisms use the same set of genetic codes or largely different sets?

3. What codon is used as start codon, which amino acid does it encode? What codons are used for stop codons?

4. What are the three major steps in transcription? What segments on DNA molecules are critical for transcription to start and to finish? How do you know what base will be added to the newly synthesized RNA strand?

5. What is an mRNA? What sequence will appear in mature mRNA, the introns or the exons? Does prokaryotic cells have introns in general? What does the splicing process do to make the mature mRNA?

6. What modifications will be done for the 5’ head and the 3’ end of mRNA?

Explanation / Answer

2. One amino acid is encoded by 3 nucleotides. Codon is found on DNA , which code for an amino acid and anticodon is found on t-RNA which matches with codon. About 64 codons and 20 amino acids are found. Different organisms use same set of codons.

3. AUG is a start codon , encodes methionine amino acid. UGA, UAG and UAA are stop codon.

4. Initiation, elongation and termination are steps of transcription. On DNA promoter is necessary for start and stop codons to stop the transcription . By knowing the DNA sequence we can know the base added in the RNA.

5. mRNA is the result of transcription by which protein is synthesized . Exons are added to form a mature mRNA. Prokaryotes does not have introns. Splicing process splice out introns from the newly synthesized mRNA to make mature mRNA.

6. At 5' end capping is done by adding 7-methylguavonosine and at 3'end polyadenylation is done by adding multiple residues of Adenine nucleotide .

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