6.1.5 Gene Control: Post-Transcriptional Modification

Question 1

What is an exon

Answer 1

Coding sequence of a gene, translated into amino acid forming final polypeptide eventually

Question 2

What is an intron

Answer 2

Genes which are not translated and do not code for any amino acids

Question 3

Post Transcription

Answer 3

Introns and exons are both transcripted, so primary (pre) mRNA contains both exons and introns.

Introns are not meant to be TRANSLATED, so must be removed from primary (pre) mRNA molecule

Exons then all fuse together to form a continuous mature mRNA molecule ready for translation.

This elimination of introns is called ‘splicing’ and is part of post-transcriptional modification (but before translation)

Splicing essentially ensures only the exons are present so only coding sections of pre mRNA are used to form proteins.

If introns were included in the mature mRNA, the protein would not function as it should.

Question 4

Post translation control

Answer 4

• Golgi apparatus
• Some polypeptides require activation of cyclic AMP (cAMP)
• Derived from ATP, formed by adenyl cyclase enzyme
• cAMP activates protein kinase A, which can activate other proteins and enzymes
• When muscle cells need energy, glycogen phosphorylase hydrolyses glycogen into glucose
• This enzyme is activated by cAMP, changing shape of enzyme to expose its active site