Structure and Function of RNA - Lecture 14

Question 1

What are the three differences between RNA and DNA?

Answer 1

○ Chemical structure
○ Physical properties
○ Biological role

Question 2

How is the chemical structure of RNA different to DNA?

Answer 2

○ In DNA: 2’ C has a H atom
○ In RNA: 2’ C has a OH group
○ This makes RNA less stable than DNA

Question 3

How is uracil different to thymine?

Answer 3

Uracil does not have a methyl group

Question 4

What are the biological roles of RNA?

Answer 4

○ Transfer of information from DNA to protein:
- mRNA to code for proteins
○ Synthesis of proteins:
- rRNA and tRNA
○ Processing mRNA:
- snRNA involved in splicing introns from pre-mRNA
○ Processing and modification of rRNA: - snoRNA which processes and modifies rRNA
○ Catalytic RNA:
- Self-splicing introns
- Natural and artificially created ribozymes

Question 5

What is the RNA content of a cell?

Answer 5

○ 10pg of RNA
○ 80-85% = rRNA
○ 10-15% = low m/w species
○ 1-5% = mRNAs

Question 6

What are the physical properties of RNA?

Answer 6

○ RNA is generally single stranded
○ RNA can base-pair with itself to fold into complex structures (not mRNA)
○ Secondary structures: stem loop structures
○ Tertiary structures

Question 7

How does RNA secondary structure form?

Answer 7

○ Palindromic sequences (same in both directions)
○ Self-complementary base pairing

Question 8

How is the RNA regulated?

Answer 8

○ Synthesis - transcription can be turned on and off rapidly e.g. lac operon
- Once RNA stops being made it disappears as it is unstable
○ Regulated degradation e.g. transferrin receptor mRNA
○ Translation efficiency - proteins can control the usage of certain RNA’s e.g. Ferritin mRNA

Question 9

What do the UTRs do?

Answer 9

Control the availability of that RNA

Question 10

How does the transferrin receptor work?

Answer 10

○ TfR mRNA makes transferrin receptor
○ Iron in blood binds to transferrin and is transported into cells via transferrin receptor
○ If there is enough intracellular Fe2+ -> TfR mRNA is degraded

Question 11

How does the RNA structure regulate transferrin receptor?

Answer 11

When there is no Fe2+:
○ Iron Response Element - binding protein (IRE-BP) is bound to stem loop structure (AU rich) at 3’ UTR and stabilises RNA
In presence of Fe2+:
○ IRE-BP binds to Fe2+ and dissociates from 3’ UTR so RNA degrades

Question 12

What is ferritin?

Answer 12

Protein made in the prescence of iron

Question 13

How does the RNA secondary structure regulate the ferritin gene?

Answer 13

High iron:
○ IRE-BP does not bind to IRE at the 5’ UTR so ferritin is made
Low iron:
○ IRE-BP binds to IRE at 5’ UTR which prevents translation of ferritin