6.1.5 Gene Control: Post-Transcriptional modification

Question 1

What types of sequences of DNA are found in eukaryotic cells?

Answer 1

Non coding and coding sequences of DNA

Question 2

What are coding sequences of DNA called?

Answer 2

Exons

Question 3

What do exons do?

Answer 3

They are coding sequences of DNA and these are the sequences that will eventually be translated into the amino acids that will form the final polypeptide

Question 4

What are the non coding sequences of DNA called?

Answer 4

Introns

Question 5

What are introns

Answer 5

They are non coding sequences of DNA and are not translated (do not code for any amino acids)

Question 6

What happens to introns and exons when the transcription of a gene occurs?

Answer 6

Both the exons and introns are transcribed - meaning the mRNA molecule formed also contains exons and introns (pre-mRNA)

Question 7

What happens to the pre-mRNA molecule?

Answer 7

As the introns are not to be translated, they must be removed from the pre-mRNA molecule

Question 8

What happens to exons in a pre-mRNA molecule?

Answer 8

Exons are all fused together to form a continuous mRNA molecule called mature mRNA that is ready to be translated

Question 9

What is splicing?

Answer 9

Introns are removed from the pre-mRNA molecule as they are not to be translated
Exons are then all fused together to form a continuous mRNA molecule called mature mRNA that is ready to be translated

Question 10

What is splicing part of?

Answer 10

Post transcriptional modification (after transcription but before translation)

Question 11

What does splicing ensure?

Answer 11

Only the coding sections of mRNA are used to form proteins by translation (if any introns were included in the mature mRNA, the resulting protein would not be formed properly and may not function as it should)

Question 12

What happens after polypeptides are formed by translation?

Answer 12

They undergo modifications in the Golgi apparatus or the cytosol
Some polypeptides may then require activation by cyclic AMP (cAMP)

Question 13

What is cAMP derived from?

Answer 13

ATP and is formed by the action of the enzyme adenyl cyclase

Question 14

What is one important role carried out by cAMP

Answer 14

Activation of protein kinases:
- eukaryotic cells = cAMP activates protein kinase A
- PKA is an inactive precursor enzyme
- Once it is activated, it can activate other proteins (e.g. other enzymes)

Question 15

What is released when muscle cells require energy?

Answer 15

Glycogen phosphorylase - releases glucose from glycogen
This enzyme is activated by cAMP, which changes the shape of the enzyme to expose its active site