Transcription - Eukaryotes

Question 1

mRNAs in eukaryotes

Answer 1

Are monocistronic

Question 2

How eukaryotic genes are ‘interrupted’

Answer 2

Coding sequences (exons) are split by non-coding sequences (introns)
- 5’ end of the first exons + the 3’ end of the last exons will contain an untranslated sequence
- RNA-P transcribe the introns which are then removed

Question 3

RNA processing

Answer 3

• Initial transcript is modified + spliced
• Modified G residue is added to 5’ end (5’ CAP)
• Introns are spliced out by spliceosome
• A polyA tail added to 3’ end
• Mature RNA is transported from nucleus to cytoplasm for translation

Question 4

Alternative splicing

Answer 4

• pre-mRNA can be spliced to give slightly different versions of same proteins
• > 80% of human genes are alternatively spliced
• Is responsible for morphological + physiological complexity of mammals

Question 5

Alternative splicing + the brain - REST

Answer 5

Plays a role in neurodevelopment + brain function e.g.
- In embryo, REST is differentially spliced in neurons (REST4) vs other tissues (REST)
- REST binds to neuronal genes _ stop transcription
- REST4 cannot bind so neuronal genes are transcribed

Question 6

Alternative splicing + the brain - SnoN

Answer 6

Is differentially spliced to give SnoN1 + SnoN2
- Both found in neurons but in different parts of the brain
- N1 - inner granular layer
- N2 - molecular layer of the cerebellum