Transcription

Question 0

Explain the term genetic code

Answer 0

• the sequence of nucleotide bases on a gene provides a code with instructions for the construction of a polypeptide or protein
• it is a triplet code (known as a codon) –> 3 bases code for 1 amino acid
• there are 4 bases arranged in groups of 3 so the number of different triplet sequences is 64 (4x4x4)
• it is a degenerate code –> some amino acids have more than 1 codon that codes for them

Question 1

What is a gene?

Answer 1

• A gene is a length of DNA (sequence of nucleotide bases) that codes for one or more polypeptides
• genes code for polypeptides such as enzymes

Question 2

Explain the process of DNA replication

Answer 2

• DNA helicase breaks the hydrogen bonds between the bases
• DNA polymerase binds, and activated free nucleotides will form hydrogen bonds with their complementary bases using the original strand as a template
• DNA polymerase joins the sugar of one nucleotide with the phosphate of the next
• DNA ligase seals the gaps in the sugar phosphate backbone

Question 3

Explain the process of transcription (how a nucleotide sequence codes for the amino acid sequence in a polypeptide)

Answer 3

• double helix uncoils in the region of the gene
• DNA helicase breaks the hydrogen bonds between the bases in the region of the gene
• - RNA polymerase binds to the template strand, activated RNA nucleotides will form hydrogen bonds with the complementary base pairs
-RNA polymerase moves in a 5’ to 3’ direction joining the phosphate of one nucleotide to C3 of the sugar on the next, forming an mRNA copy of the gene
• mRNA is the same as the coding strand (except it has U instead of T)
• mRNA is complementary to the template strand
• the mRNA then leaves the nucleus through the nuclear pore and travels to a ribosome