SPEC POINT 2.6

Question 1

What is the difference between transcription and translation?

Answer 1

Transcription occurs in the nucleus and is when DNA is transcribed and mRNA is produced
Translation occurs in the cytoplasm and is when mRNA is translated and a polypeptide is formed

Question 2

Describe the process of transcription of a gene:

Answer 2

1. Enzyme unwinds DNA molecule, breaking H bonds, and exposing the gene to be transcribed.
2. RNA nucleotides line up and pair with complementary bases on the antisense strand.
3. RNA polymerase bonds the RNA nucelotides together to form the backbone of the mRNA molecule which then leaves via a nuclear pore and DNA reforms

Question 3

Describe the process of translation:

Answer 3

1. Once in cytoplasm, mRNA attaches to a ribosome.
2. Each tRNA molecule has the complementary anticodon to the codon on the mRNA.
3. tRNA molecules then form H bonds with the codons on the mRNA to bring amino acids, which form peptide bonds.
4. 2 tRNA molecules are on the ribosome at a time, the process continues until a stop codon, when the polypeptide chain moves away and translation is complete.

Question 4

What is the role of tRNA in translation?

Answer 4

1. transport amino acids to the ribosome
2. tRNA has an anticodon which binds to/recognises codon on mRNA
3. each tRNA carries a particular amino acid

Question 5

Explain how the sequence of bases in DNA ensures the correct order of amino acids in a polypeptide chain:

Answer 5

1. the sequence of bases is transcribed to produce mRNA
2. the sequence of triplets in DNA determines the sequence of codons in mRNA
3. the mRNA is translated to form the polypeptide chain
4. the sequence of codons determines the sequence of amino acids in a polypeptide chain (primary structure)

Question 6

What is the difference between the antisense/template strand and the sense/coding strand?

Answer 6

The antisense strand is the strand of DNA that RNA nucleotides pair with
The other strand is known as the sense or coding strand as mRNA will have the same base sequence as this strand (T replaced by U)

Question 7

What direction does RNA polymerase move down the template strand, and why?

Answer 7

Moves in 3’ to 5’ direction as mRNA grows in 5’ to 3’ direction