Mod 6- RNA Structure & Function

Question 1

What is Ribonucleic Acid (RNA)?

Answer 1

RNA is the product of transcription from a DNA template.

There is 10x more RNA than DNA in a cell.

Question 2

What are the key differences between RNA and DNA?

Answer 2

Differences include:
* Chemical structure
* Physical properties
* Biological role

Question 3

What sugar is used in RNA instead of Deoxyribose?

Answer 3

Ribose

Ribose contains 2’-OH (hydroxyl), whereas Deoxyribose lacks an oxygen.

This makes RNA less stable than DNA

Question 4

What base is used in RNA in place of Thymine?

Answer 4

Uracil

Uracil does not have a -CH3 (methyl) group.

Question 5

What are the biological roles of RNA?

Answer 5

Roles include:
* Transfer of information from DNA to protein (messenger RNA (mRNA) codes for proteins)
* Synthesis of proteins (rRNA and tRNA)
* Processing of mRNA (snRNA)
* Processing and modification of rRNA (snoRNA)
* Catalytic RNA (self-splicing introns & natural and artificially created ribozymes)

Question 6

What percentage of a single cell’s RNA content is ribosomal RNA?

Answer 6

80-85%

Other RNA types include 10-15% low m/w species and 1-5% mRNAs.

Question 7

What is a key physical property of RNA?

Answer 7

RNA is generally single stranded.

Question 8

How can RNA base-pair with itself?

Answer 8

RNA can fold into complex structures due to self-complementary base pairing

Has hydrophobic and hydrophilic sides and folds into itself to produce secondary structure via palindromic sequences

Question 9

What regulates the amount or usage of certain RNAs?

Answer 9

Regulated by:

• Synthesis (transcription can be turned on and off rapidly) = i.e. lac operon
• Regulated degradation = i.e. transferrin receptor mRNA
• Translation efficiency (proteins can control the usage of certain RNAs) = i.e. ferritin (picks up iron) mRNA

Regulated degradation & Translation efficiency are properties of the UTRs

Question 10

What are the components of Eukaryotic Class II (mRNA-encoding) genes?

Answer 10

Components include:
* Enhancer
* Promoter
* Exons
* Introns
* 5’-UTR
* 3’-UTR

Question 11

What happens to transferrin receptor mRNA when there is enough intracellular Fe2+?

Answer 11

Transferrin receptor mRNA is degraded.

Question 12

What is the role of Iron Response Element-binding protein (IRE-BP) under low iron conditions?

Answer 12

IRE-BP binds to IRE and prevents translation initiation.

Question 13

Fill in the blank: RNA secondary structure regulates _______ receptor mRNA degradation.

Answer 13

transferrin

Question 14

What is the role of the ferritin gene in the cell?

Answer 14

Ferritin binds Fe2+ within the cell.

Low iron = IRE-BP binds to IRE and prevents translation initiation

Question 15

What is the importance of RNA secondary structure?

Answer 15

Important for:
* Catalysis
* Organisation
* Recognition

Consequences:
* Stability (transferrin)
* Translation (ferritin)

Question 16

What is the role of the transferrin receptor?

Answer 16

Iron in blood binds to transferrin - transported into cells via a receptor

If there is enough intracellular Fe2+, transferrin receptor mRNA is degraded (not needed anymore)

Question 17

How does the RNA secondary structure regulate transferrin receptor mRNA degradation?

Answer 17

• No Fe2+ (intracellular iron) = IRE-BP (iron response element-binding protein) bound to 3’-UTR
• So RNA is stable and receptor is made
• Presence of Fe2+ = IRE-BP binds Fe2+
• So dissociates from 3’-UTR and RNA is degraded so receptor is not made