Question

12-16

LUIS 15 12. What are the 3 types of RNA? What is the role of each of them in translation? 13. Briefly describe what happens during the steps of translation 1. Initiation of translation 2. Elongation 3. Termination of translation 14. The base sequence of the gene coding for a short polypeptide is the following: TA CGC TAGGCGATTGACT A. What would be the base sequence of the mRNA transcribed from this gene? B. Using the genetic code given out in class, give the amino acid sequence of the polypeptide translated from this mRNA 15. What is the difference between a silent mutation and a missense mutation? 16. Explain why deletions and insertions almost always produce a nonfunctional polypeptide, HOC

Answer 1

12. Answer:

Types of RNA and their functions:

mRNA or Messenger RNA

mRNA transcribes the genetic code from DNA into a form that can be read and used to make proteins. mRNA carries genetic information from the nucleus to the cytoplasm of a cell.

rRNA or Ribosomal RNA

rRNA is located in the cytoplasm of a cell, where ribosomes are found. rRNA directs the translation of mRNA into proteins.

tRNA or Transfer RNA

Like rRNA, tRNA is located in the cellular cytoplasm and is involved in protein synthesis. Transfer RNA brings or transfers amino acids to the ribosome that corresponds to each three-nucleotide codon of rRNA. The amino acids then can be joined together and processed to make polypeptides and proteins.

13.Answer

Steps of translation:

INITIATION U AC பட்டப்பட்ட mRna ribosome

Initiation:

During initiation, the mRNA, the tRNA, and the first amino acid all come together within the ribosome.
The mRNA strand remains continuous, but the true initiation point is the start codon, AUG.
The start codon is the set of three nucleotides that begins the coded sequence of a gene.
The start codon specifies the amino acid methionine.
So, methionine is the name of the amino acid that is brought into the ribosome first.
The methionine get itself to the ribosome by attaching to the tRNA that contains the right anticodon.
The anticodon for AUG is UAC. Because of the rules of complementary base pairing the tRNA with the anticodon UAC will automatically match to the codon AUG, bringing the methionine along for the ride.
So, mRNA is attached to tRNA, and tRNA is attached to methionine. This is initiation.

Elongation:

Growing peptide chain Incoming RNA bound to Amino Acid Outgoing empty RNA TRNA TRNA wuyu Jadweg MessengerRNA Ribosome Peptide Synthesis

While Met-tRNA occupies the P site, another aminoacyl-tRNA with an anticodon complementary to the next codon comes to occupy the A site. This process requires GTP. The enzyme peptidyl-transferase forms a peptide bond between methionine and the next aminoacyl-tRNA.

The tRNA molecule in the P site becomes uncharged and leaves the ribosome. The ribosome then translocates along the mRNA molecule to the next codon. This opens up the A site for the next aminoacyl-tRNA. The polypeptide chain is built up in the direction from the N terminal to the C terminal.

Termination:

new protein peptidyl transferase amino acid charged tRNA new protein Release factor

One of the three stop codons enters the A site. No tRNA molecules bind to these codons so the peptide and tRNA in the P site become hydrolysed releasing the polypeptide into the cytoplasm.

The small and large subunits of the ribosome dissociate ready for the next round of translation. The polypeptide produced undergoes post-translational modification before becoming the fully active protein.

15. Answer:

Diffenece between a silent mutation and a missense mutation:

Silent mutations are mutated codon codes for the same amino acid. In this case there is no amino acid change and no effect on the organism.

Missense mutations are mutated codon codes for a different amino acid. In this type of mutation there is one amino acid change and can have a variety ofeffects on the organism.

16.Answer:

Genes can also be mutated by the deletion or insertion of a number of nucleotide bases. There are different types of deletions or insertions.

Frameshift mutations occur when the number of deleted or inserted base pairs is NOT a multiple of three. Since codons consist of three base pairs, if, for example, only one or two base pairs are deleted, then the way the DNA is read is shifted at the place of the deletion or insertion. After the place of the mutation, ALL of the amino acids that follow will be different. In this case, either an abnormal protein is made or no protein is made at all.

In-frame mutations occur when the number of deleted or inserted base pairs IS a multiple of three. This results in a change in only a few amino acids; it may still be possible for the protein to function, even though its sequence may be slightly different.