Structure and properties of RNA

Question 1

Why is RNA less stable than DNA?

Answer 1

Ribose sugar instead of 2-deoxyribose sugar. RNA has a hydroxyl group where DNA has a hydrogen

Question 2

What are the main features of RNA?

Answer 2

Single-stranded
Written in 5' to 3'
Shorter than DNA
Can form a hairpin structure
Carries genetic information

Question 3

What is the role of the hairpin loop?

Answer 3

Gives stability (so that enzymes have more time)

Question 4

What are the features of tRNA

Answer 4

3 hairpin loops
Variable loop
Stable due to H bonds

Question 5

What are the features of mRNA?

Answer 5

Complex but single-stranded

4 major domains

Question 6

What is transcription?

Answer 6

Synthesis of RNA under the direction of DNA

Question 7

What is translation?

Answer 7

Actual synthesis of a protein which occurs under the direction of mRNA

Question 8

What is mRNA?

Answer 8

messenger RNA which encodes the amino acid sequence of a polypeptide

Question 9

What is tRNA?

Answer 9

Transfer RNA brings amino acids to ribosomes during translations

Question 10

What is rRNA

Answer 10

Ribosomal RNA. With ribosomal proteins, makes up the ribosomes, the organelles that translate the mRNA

Question 11

What is sRNA?

Answer 11

Small nuclear RNA. with proteins forms the complex that are used in RNA processing in eukaryotes (not found in prokaryotes)

Question 12

What 3 sections does a protein containing gene have?

Answer 12

Promotor
Coding sequence
Terminator

Question 13

How does transcription occur?

Answer 13

1. RNA polymerase recognises the promotor and begins transcription (synthesised in a 5’ to 3’ direction
2. As the polymerase moves long the template the RNA is released and the DNA helix reforms
3. Once the polymerase hits the terminator sequence it stops and the full pre-mRNA transcript is released

Question 14

How can you work out the mRNA sequence from DNA?

Answer 14

The template strand is used to make the mRNA but you can use the coding strand and swap the Ts for Us

Question 15

What is the difference between mRNA in prokaryotes and eukaryotes?

Answer 15

In prokaryotes protein-coding is collinear with the translated mRNA. The transcript of the gene is the molecule that is translated into the polypeptide. Whereas in eukaryotes the protein-coding gene is typically NOT COLLINEAR with the translated mRNA. The transcript has to be spliced to remove the introns

Question 16

How are the ends of pre mRNA modified in transcription?

Answer 16

At the 5’ end a cap is added containing a modified GTP (occurs at the beginning of transcription.)
At the 3’ end a poly(A) tail of 150 or more adenine nucleotides is added.

Question 17

What is the role of the cap added during transcription?

Answer 17

Used as a recognition signal for ribosomes to bind to the mRNA

Question 18

What is the role of the poly(A) tail added during transcription?

Answer 18

Stability

Question 19

How does splicing occur?

Answer 19

1. The intron loops out as snRNPs (small nuclear ribonucleoprotein particles, complexes of snRNAs and proteins) bind to form the SPLICESOME
2. The intron is removed and the exons are spliced together
3. The resulting mature mRNA may then exit the nucleus and be translated in the cytoplasm.

Question 20

What is tissue specific gene expression?

Answer 20

every cell expresses genes depending on the tissue in which to resides

Question 21

What are housekeeping genes?

Answer 21

The genes that are expressed in every cell e.g actin for the cytoskeleton