8.4 Polypeptide synthesis- transcription and splicing

Question 1

Describe the basic process of protein synthesis.

Answer 1

• DNA provides the instructions in the form of a long sequence of bases
• a complimentary section of part of this sequence is made in the form of a pre-RNA molecule (transcription)
• pre-RNA is spliced to form mRNA
• mRNA is used as a template to which complimentary tRNA molecules attach and the amino acids they carry are linked to form a polypeptide (translation)

Question 2

Describe the process of transcription.

Answer 2

1) An enzyme acts on a region of DNA causing the 2 strands to separate and expose the nucleotide bases
2) the bases on 1 of the DNA strands (template strand) pair with the complimentary nucleotides from the pool present in the nucleus. RNA polymerase then moves along the strand and joins the nucleotides together to form a pre-RNA molecule.
3) as the RNA polymerase goes along the strand, the DNA strand rejoins behind it so only around 12 base pairs are left exposed.
4) when it reaches the stop code the production is complete.

Question 3

Why is splicing necessary in eukaryotic cells?

Answer 3

• Eukaryotes produce pre-RNA which has to be spliced to form mRNA
• this is because the DNA is made up of exons which code for proteins and in introns that do not.
• the introns would prevent polypeptide synthesis.

Question 4

What is splicing?

Answer 4

the removal of introns and the joining together of exons in pre-RNA to make mRNA.