Translation

Question 1

What is an enhancer?

Answer 1

Short (50-1500 bp) region of DNA that can be bound by proteins - activators - to start the transcription of a particular gene.

Question 2

What is the Promoter?

Answer 2

A promoter is a regulatory region of DNA located upstream (5’ region) of a gene, providing a control point for regulated gene transcription.

Question 3

What is the TATA box?

Answer 3

The TATA box is a sequence of DNA, consisting of nucleobases TATAA.
It is located in the promoter region about 25-30 bases pairs before the site of transcription.

Question 4

What do genes do without TATA boxes?

Answer 4

Most promoter regions of genes do not contain a TATA box.
In TATA-less genes, transcription factors recognise other promoter sequences and RNA polymerase binds to these instead.

Question 5

Where are enhancers?

Answer 5

Upstream enhancers can be several thousand kilobase pairs away from the promoter.
The double helix structure of DNA folds and twists which brings the enhancer closer to the promoter.

Question 6

What is the UTR?

Answer 6

UnTranscribed Region - it is part of DNA and the gene, but is not transcribed.
It is a protector of the genome.
At the 5’ and 3’ end.
3’ end is an insulator.

Question 7

What are the molecular components of mRNA?

Answer 7

The leader at 5’ end - UTR - anything before the start codon.
Reading Frame - translated.
Trailer at 3’ end - UTR - anything after the stop codon.

Question 8

Why does mRNA vary?

Answer 8

mRNAs vary in length.
Sequences of mRNA vary because amino acid coding sequences (reading frames) differ, and because leader and trailer sequences differ.

Question 9

What are ribosomes?

Answer 9

The organelles on which the mRNA is translated.
Consist of two subunits, each of which contains rRNA and ribosomal proteins.
Total 80S

Question 10

What is the large subunit of ribosomes?

Answer 10

60S
28S rRNA
5.8S rRNA
5S rRNA
50 ribosomal proteins.

Question 11

What is the small subunit of ribosomes?

Answer 11

40S
18S rRNA
30 ribosomal proteins

Question 12

What is the P site of ribosomes?

Answer 12

Peptidyl site - tRNA binding site

Question 13

What is the A site of ribosomes?

Answer 13

Aminoacetyle - tRNA binding site

Question 14

What is the simple outline of translation?

Answer 14

In translation, the mRNA passes through the ribosome, where the codons are recognised by tRNAs carrying the specified amino acids.

Question 15

What do tRNA do?

Answer 15

Transfer RNA bring amino acids to the ribosomes during translation to be assembled into polypeptide chains.
tRNAs are encoded by tRNA genes.
All tRNA molecules are similiar in size and shape.

Question 16

How is the structure of tRNA used for translation?

Answer 16

All tRNAs have CCA at the 3’ end to which the amino acid attaches - the acceptor stem.
At the 5’ end, the anticodon reads the matching codon on the mRNA.

Question 17

What is aminoacylation?

Answer 17

Or charging:
An enzyme called aminoacyl-tRNA synthetase adds the correct amino acid to its tRNA.
There are 20 aminoacyl-tRNA synthetases.

Question 18

Which enzymes charge which tRNA?

Answer 18

All tRNAs with the same amino acid are charged by the same enzyme, even though the tRNA sequences and anticodons differ.

Question 19

How do synthetases identify tRNAs?

Answer 19

Contacts on synthetases recognise a small number of bases in the acceptor stem - from 1-5.
It recognises tRNA not because of the anticodon but because there are specific recognition sites on the tRNA.

Question 20

What is the process of charging tRNA?

Answer 20

Amino acid and ATP bind to active site of specific enzyme for amino acid.
ATP loses two phosphate groups and binds to amino acid as AMP.
The enzyme changes shape, and cannot accept another amino acid.
The tRNA anticodon binds to a different part of the enzyme and AMP is released.
This binding charges the amino acid, and the enzyme returns to the original shape.
The enzyme can then charge another tRNA.

Question 21

What do synthetases do after recognising the tRNA?

Answer 21

The enzyme forms a covalent bond between the carboxyl group of the amino acid and the hydroxyl groups of the pentose sugar of the tRNA.

Question 22

What is the initiation of translation?

Answer 22

The GTP cap is a signal to go to the ribosome.
The polyAtail ensures stability until it gets to the ribosome.
The 40S subunit of ribosome binds the first charged Met, using ATP.
The 60S unit comes in and completes the ribosome.

Question 23

What happens after initiation of translation with Met?

Answer 23

Met is in the P site of the ribosome.
The next 3 bases are read, and the tRNA with the anticodon sits in the A site, and the two amino acids are close and able to form a peptide bond.
Once the bond is formed, the amino acid moves into the P site, so the A site is free for another tRNA to move in with another amino acid.

Question 24

What happens once the amino acid is added to the polypeptide chain?

Answer 24

The polyAtail is released, and the tRNA is released, uncharged, and ready to be recharged in the same process.

Question 25

What is the termination of translation?

Answer 25

At a stop codon, a release factor reads the triplet, and polypeptide synthesis ends.
The polypeptide is released from the tRNA.
The tRNA is released from the ribosome, and the two ribosomal subunits separate from the mRNA.

Question 26

What are polysomes?

Answer 26

Several ribosomes can translate an mRNA at the same time - forms a polysome.
So, many polypeptides can be produced simultaneously from a single mRNA.