Sesh 8: Gene Expression

Question 1

DNA to mRNA is _____________, and mRNA to protein is ____________.

Answer 1

1. Transcription

2. Translation

Question 2

Transcription occurs in the _______ and translation occurs in the _________.

Answer 2

1. Nucleus

2. Cytoplasm

Question 3

What is a gene?

Answer 3

A stretch of DNA at a specific chromosomal locus, coding for a specific protein.

Question 4

What direction is a polypeptide elongated in?

Answer 4

N to C terminus.

Question 5

What are the 3 stages of DNA replication, transcription and translation?

Answer 5

1. Initiation
2. Elongation
3. Termination

Question 6

What 3 general components are needed to make DNA, RNA and proteins?

Answer 6

1. Enzymes
2. Activated substrates
3. A template

Question 7

What is a TATA BOX?

Answer 7

A sequence within the promoter sequence of a gene that is recognised by transcription factors, to set the direction of transcription.

Question 8

What do transcription factors do?

Answer 8

Bind the promoter sequence of a gene, to set the direction of transcription, and recruit RNA polymerase.

Question 9

RNA polymerase binds 1 nucleotide __________ of where transcription begins.

Answer 9

Upstream.

Question 10

Pre-mRNA is synthesised from the _________ strand, and made in the __ to __ direction.

Answer 10

1. Template/ non-coding
2. 5’
3. 3’

Question 11

RNA polymerase reads the template DNA strand in the __ to __ direction.

Answer 11

1. 3’
2. 5’
   To make mRNA in 5’ to 3’ direction.

Question 12

What 3 types of RNA processing occur?

Answer 12

1. Capping
2. Polyadenylation
3. Splicing

Question 13

What is RNA capping?

Answer 13

A 7-methylguanosine cap is added to the 5’ end of pre-mRNA via a 5’ to 5’ triphosphate link.
Protects against degradation and has a role in translation.

Question 14

How does polyadenylation of pre-mRNA occur?

Answer 14

• Endonuclease recognises a specific polyA site, which then cleaves the RNA- ‘falls off’ the DNA
• PolyA polymerase then adds ~200 adenylate residues to the 3’ end

Question 15

What subunits make up a eukaryotic ribosome?

Answer 15

40S+60S–> 80S ribosome

Question 16

What is the most abundant type of RNA in the body?

Answer 16

Ribosomal RNA (rRNA)=~80%

Question 17

What is the adaptor molecule for translation?

Answer 17

tRNA

Question 18

What is meant by the degenerate nature of the genetic code?

Answer 18

Some amino acids are coded for by >1 triplet code….due to ‘wobble’ base.

Question 19

What is the start/initiation codon, and what amino acid does it code for?

Answer 19

AUG codes for Methionine. At N-terminus of all proteins unless cleaved off after translation.

Question 20

What are tRNA stem loops?

Answer 20

Loops formed by H bonds between anti-parallel complementary sequences, from a single-stranded structure.

Question 21

Which part of the tRNA does an amino acid bind to?

Answer 21

The 3’OH end.

Question 22

A charged tRNA is referred to as an…….?

Answer 22

Aminoacyl tRNA

Question 23

A tRNA anticodon of 5’CAU would recognise the mRNA codon_____?

Answer 23

5’AUG- Met

Anticodon needs to be in 3’ to 5’ =UAC=complementary to AUG.

Question 24

How is translation initiated?

Answer 24

A ‘special’ methionyl tRNA recognises 5’ cap of mRNA & moves along until reaches start codon (AUG). Ribosome 40S subunit is also associated.
Once the tRNA anticodon has recognised this, the 60S ribosome subunit associates to form a fully functional ribosome.

Question 25

Which ribosome site will the ‘special’ methionyl tRNA move in to?

Answer 25

The P site. Another charged tRNA will then move into the adjacent A site.

Question 26

What enzyme moves an amino acid from the ribosome P site to on top of an amino acid in the A site, allowing the ribosome to translocate?

Answer 26

Peptidyl transferase.

tRNA in P site becomes uncharged, is released, so ribosome can move along.

Question 27

The final tRNA to occupy the P site during translation is called………….?

Answer 27

Peptidyl tRNA (has peptide on top).

Question 28

What breaks the bond between peptidyl tRNA and the polypeptide?

Answer 28

Water and another tRNA.

Allows tRNA, ribosome and polypeptide to be released.