BBOL- RNA processing and translation

Question 1

How is eukaryotic mRNA is processed?

Answer 1

• Addition of a 5’ cap
• Addition of poly A tail
• Splicing out of introns

Question 2

What does adding a 5’ cap involve?

Answer 2

• Involves adding methylated G residue to terminal base of a transcript
• Helps cell distinguish mRNAs from other RNAs
• Helps mRNA to be properly processed and exported from nucleus

Question 3

What does adding a poly A tail involve?

Answer 3

• 3’ end polyadenylated
• Addition of a string of A nucleotides to end of transcript
• Signal for poly-A coded in DNA
• Cleavage signal to stop copying
• Proteins bind to poly A tails and help stabilise RNA
• Allows protein binding to protect strand when it leaves nucleus

Question 4

What does splicing involve?

Answer 4

• Introns removed from primary RNA transcript

- Particular signalling features GU and AG beginning and end of intron

Question 5

How does splicing happen?

Answer 5

• Spliceosome removes introns from primary transcript
• Spliceosome- large complex proteins and non-coding RNAs
• Introns removed through formation of lariat

Question 6

What does alternative transcription and processing mean?

Answer 6

We get many proteins from few genes

Question 7

What are alternative promoters?

Answer 7

• Either alternative exon 1 or alternative internal promoters each expressed in different tissue
• Polymerase may only start from a certain point= shorter polypeptide

Question 8

What could alternative promoters result in?

Answer 8

Tissue specificity, developmental stage specificity, differential sub cellular localisation, differential functional capacity, sex-specific gene regulation

Question 9

Describe alternative splicing

Answer 9

• Can result in generation of many different protein isoforms from 1 primary RNA transcript and use of alternative untranslated sequences
• Regulated by RNA binding proteins binding to splicing enhancer sequences encoded in DNA
• Can generate multiple related forms of RNA from a single mRNA transcript
• Different exons, different point of joining, some exons included

Question 10

What is RNA editing?

Answer 10

• Involves enzyme-mediated insertion/deletion of nucleotides or sub of nucleotides at RNA level
• Rare
• No change to DNA
• Leads to stop codon formes- short protein