Lecture 6: Gene Expression 1

Question 1

what are the stages of DNA translation

Answer 1

1: transcription and transcriptional control
2: RNA transcript makes mRNA
3: RNA transport and localisation
4: translation and translational control
5: protein modification, eg phosphorylation
6: RNA degradation

Question 2

what does RNA polymerase I do

Answer 2

transcribes most ribosomal RNA genes

Question 3

what does RNA polymerase II do

Answer 3

transcribes protein-coding genes, some microRNA genes and some for small RNAs, eg those in spliceosomes

Question 4

what does RNA polymerase III do

Answer 4

• transcribes tRNA genes and 5s RNA genes

- too much RNA polymerase III causes excess tRNAs, which increases cancer progression

Question 5

how do we know most mRNAs require RNA polymerase II

Answer 5

amanita phalloid inhibits RNA polymerase II and causes death by massive liver failure

Question 6

what is required for transcription to begin

Answer 6

1: basal transcription factors bind to promoter region
2: RNA polymerase binds to TATA box of promoter region
3: C-terminal domain on RNA polymerase is phosphorylated and complexes of proteins bind in the right order

Question 7

what are enhancers

Answer 7

• binding sites for activator proteins, that can be a long way from promoter region
• DNA loops round, so biding sites can be far away from the gene they activate

Question 8

what is fragile X syndrome caused by

Answer 8

• expansion of CGG repeats, resulting in methylation of DNA in promoter region so RNA polymerase can’t bind properly
• normal allele has 6-54 repeats
• premutated has 55-200
• full mutation has >200

Question 9

what are symptoms of fragile X syndrome

Answer 9

• large protruding ears
• hyperextensible finger joints
• double-jointed thumbs
• macro-orchidism (large testes)
• learning difficulties
• autism

Question 10

what is alpha-thalassemia caused by

Answer 10

• mutation of ATRX genes
• ATRX is a protein that unwinds DNA, and when ATRX is mutated, the genes for multiprotein complexes don;t get transcribed

Question 11

how are RNAs modified

Answer 11

• capping, where a structure is added to the RNA to prevent it from degrading
• splicing, where spliceosomes (guided by splicing RNAs) remove introns. Removed introns are called lariats
• polyadenylation

Question 12

effects of incorrect splicing

Answer 12

• beta thalassemia, resulting from aberrant processing
• mild cystic fibrosis where an exon is removed as an intron
• familial isolated growth hormone deficiency type II due to exon skipping

Question 13

how does polyadenylation work

Answer 13

• when RNA is almost transcribed, a specific polyadenylation sequence is recognised by a protein complex which bind to it
• RNA is cleaved and a poly A tail is added onto the 3’ untranslated region
• the poly A chain is important for translation and transportation of RNA