Gene regulation and protein synthesis

Question 1

What are the three main types of RNA?

Answer 1

Ribosomal RNA (rRNA), Transfer RNA (tRNA) and Messenger RNA (mRNA).

Question 2

General definition of rRNA.

Answer 2

RNA which combines with proteins to form ribosomes

Question 3

General definition of tRNA.

Answer 3

RNA which carries amino acids to be incorporated into a protein

Question 4

General definition of mRNA.

Answer 4

RNA which carries genetic information for protein synthesis

Question 5

What are the local stretches of intramolecular base-pairing called in RNA?

Answer 5

Stem loops.

Question 6

General description of RNA.

Answer 6

• Ribose sugar
• contains uracil
• single stranded

Question 7

What are the three types of RNA polymerase?

Answer 7

Pol I, Pol II and Pol III.

Question 8

What does Pol II synthesise?

Answer 8

mRNA.

Question 9

How can the three types of RNA polymerase be distinguished?

Answer 9

By their sensitivity to toxins like α-amanitin

Question 10

RNA polymerase can start transcription without needing a primer. True or false?

Answer 10

True

Question 11

What are the 5 steps of transcription?

Answer 11

1. RNA polymerase binds to promoters
2. DNA unwinds and chains separate
3. Initiation
4. Elongation
5. Termination

Question 12

What are promoters?

Answer 12

Specific DNA sequences that RNA polymerase binds to, indicating where transcription is going to start.

Question 13

What is the TATA box?

Answer 13

Part of a general transcription factor called TFIID and is bound by a specific protein called TATA box binding protein. Found on promoter.

Question 14

What is TFIID?

Answer 14

A general transcription factor which determines transcriptional start and its direction and provides a landing platform for further transcription factors and for RNA polymerase.

Question 15

What happens at the initiation step of transcription?

Answer 15

Pol II and TFIIF extend the transcript while TFIID remains in one place at the promoter and a new initiation complex can assemble. It requires additional general transcription factors.

Question 16

What is the difference between the coding strand and the template strand?

Answer 16

The coding strand is not being read/copied whereas the template strand is being read/copied.

Question 17

What happens at the elongation step of transcription?

Answer 17

A transcription bubble moves along the DNA which is unwound then rewound. The RNA chain is synthesised in a 5’ to 3’ direction.

Question 18

What happens at the termination step of transcription?

Answer 18

The new RNA makes a stem-loop structure, followed by a stretch of Us. A specific enzyme cleaves the finished RNA and the RNA is released. The polymerase dissociates.

Question 19

What are coding regions called?

Answer 19

Exons

Question 20

What are non-coding regions called?

Answer 20

Introns

Question 21

What happens to the primary mRNA strand to make it the mature mRNA strand?

Answer 21

Splicing, addition of poly(A) tail and addition of 5’ cap

Question 22

What are transcription factors and their function?

Answer 22

Transcription factors are DNA-binding proteins which bind to specific DNA sequences called enhancers in the vicinity of a promoter.

Question 23

What are the two domains of transcription factors?

Answer 23

A DNA binding domain and a transcriptional activation domain

Question 24

Transcription factors can regulate transcription positively or negatively. True or false?

Answer 24

True.

Question 25

Where are steroid receptors found?

Answer 25

Cytoplasm

Question 26

Pathway of steroids as an example of gene regulation.

Answer 26

Steroids in blood enter cells by diffusion and bind to the inactive steroid receptor to activate it. Then moves to nucleus to bind to Steroid- response-elements (SREs) on DNA to regulate gene expression

Question 27

How many reading frames can an RNA molecule be translated from?

Answer 27

3

Question 28

What are the 3 tRNA binding sites of ribosomes called?

Answer 28

E site (exit), P site (peptidyl), A site (aminoacyl)

Question 29

what are aminoacyl-tRNA synthetases?

Answer 29

Enzymes which bind the amino acid to its corresponding tRNA molecule. ATP is supplied to break the covalent bond.

Question 30

What happens in the initiation step of translation?

Answer 30

Small ribosomal unit with initiation factors and energy from GTP binds to 5’ end of mRNA and moves along until finds a start codon. A special initiator tRNA carrying methionine with the anticodon pairs with the start codon. The Large subunit joins and the tRNA is in the P site.

Question 31

Describe free VS bound ribosomes.

Answer 31

Free ribosomes make proteins for the cytosol, nucleus, mitochondria and are translocated post-translationally.

Bound Ribosomes in RER make proteins for gold apparatus, secretion, plasma membrane and are translocated co-translationally

Question 32

Describe free VS bound ribosomes.

Answer 32

Free ribosomes make proteins for the cytosol, nucleus, mitochondria and are translocated post-translationally.

Bound Ribosomes in RER make proteins for gold apparatus, secretion, plasma membrane and are translocated co-translationally.

Question 33

What is targeting?

Answer 33

Moving of a finished protein to its final cellular destination.

Question 34

What happens in the elongation step of translation?

Answer 34

An elongation factor brings an aminoacyl-tRNA to the A site. Anticodon and codon pair up. GTP is hydrolysed and the elongation factor is released from tRNA. Another elongation factor regenerates to pick up the next aminoacyl-tRNA.

Question 35

Describe the direction of the tRNA in terms of the different binding sites.

Answer 35

P—> A—->E

Question 36

What happens in the termination step of translation?

Answer 36

Stops when the A site encounters a stop codon. There are no anticodons to pair with the stop codon.GTP hydrolysis cirrus and a release factor binds to the stop codon. The finished protein is cleaved off.