Transcription And Translation

Question 1

What is the initiator in Transcription?

Answer 1

Promoter recognition.

Question 2

What is the enzyme which builds RNA in transcription?

Answer 2

RNA polymerase.

Question 3

In which direction on the DNA double strand do promoters go?

Answer 3

Promoters can go in either direction on the strand, but they always go from 5 prime towards 3 prime so on the complementary strand this is in the opposite direction.

Question 4

Define upstream and downstream on DNA in relation to a gene to be transcripted.

Answer 4

Downstream is in the same direction as the gene faces, and upstream is in the opposite direction.

Question 5

What is a TATA box?

Answer 5

In eukaryotes this is found 30 base pairs before the sequence to be transcripted begins. It is the promoter sequence.

Question 6

What is the promoter for transcription found in prokaryotes?

Answer 6

It is a pribnow box which is found 10 base pairs before the sequence with other regulation upstream at -35.

Question 7

How do sequences a long way upstream have an impact on transcription?

Answer 7

DNA is a flexible molecule and so these two parts of the sequence may be very close together spacially.

Question 8

In transcription, which strand of DNA is used as a template?

Answer 8

The opposite strand to the one which has the required sequence. This strand is called the template strand and the other the coding strand.

Question 9

Name three ways in which RNA is processed following transcription.

Answer 9

Capping, polyadenation (tailing), splicing.

Question 10

Where on an RNA molecule does capping occur?

Answer 10

Capping occurs at the 5’ end. A 5’ 5’ linkage is created with another nucleotide, which provides protection and plays a role in translation.

Question 11

What is added to the 3’ end of an mRNA molecule for protection?

Answer 11

A poly-A tail is added which prevents against degradation.

Question 12

What does the sequence AAUAA indicate on RNA during transcription?

Answer 12

This sequence is recognised by a specific endonuclease which then cleaves the sequence and stops transcription. After this point many Adenine nucleotides are added.

Question 13

What is the difference between an endonuclease and an exonuclease?

Answer 13

An endonuclease cleaves somewhere in the middle of a polynucleotide whilst an exonuclease degrades a polynucleotide at one end or the other.

Question 14

In splicing, what sections are removed?

Answer 14

Introns are removed leaving just the exons. This converts pre mRNA to mRNA which is then ready for translation. This is the template.

Question 15

What is meant by the open reading frame?

Answer 15

The open reading frame is the section of the molecule just made up from exons which will be used as the template for translation.

Question 16

Where does translation take place?

Answer 16

Translation occurs on ribosomes found on the rough Endoplasmic Recticulum.

Question 17

What is meant by the triplet code?

Answer 17

This is the code which is used to identify amino acids. This is used because 4 possible bases in DNA must be converted to code for 20 different amino acids.

Question 18

In translation, what is the role of tRNA?

Answer 18

tRNA is the Adaptor molecule which is required to convert a polynucleotide chain into a N-C polypeptide chain.

Question 19

What does the codon AUG mean?

Answer 19

This is the initiation codon.

Question 20

Give three examples of a termination codon for translation.

Answer 20

UAA, UAG, UGA.

Question 21

In translation, how are amino acids activated?

Answer 21

Amino acids are activated when they bind to tRNA molecules.

Question 22

What is an anticodon?

Answer 22

This is the three base pairs found on the tRNA molecule. They are the complementary to what is found on mRNA

Question 23

What is the wobble position?

Answer 23

This is a base which doesn’t matter what it is in most cases. It is found on the 3’ base of a codon.

Question 24

Name the enzyme involved in the activation of amino acids, and state what other molecules are required.

Answer 24

tRNA synthase. This process uses up ATP –> AMP + PPi

Question 25

In translation, what substances recognise the cap at the end of mRNA?

Answer 25

Cap binding proteins, initiation factors, met-tRNA, GTP.

Question 26

Describe elongation in translation.

Answer 26

The met-tRNA moves along the mRNA until it find AUG. This is then in the P position. The next aminoacyl-tRNA binds to the A position and this uses GTP –> GDP + Pi. A peptide bond (with another use of GTP) forms leaving the A site empty and P sit occupied by the chain.

Question 27

Name the enzyme which is responsible for the reaction in translation which adds amino acids to the polypeptide.

Answer 27

Peptidyl transferase.

Question 28

What happens at termination in translation?

Answer 28

When the stop codon is reached there is no amino acid to be added to the chain. The reaction involves water and give a tRNA-OH and the completed polypeptide chain.

Question 29

Define transcription.

Answer 29

Transcription is the copying of DNA into RNA which occurs in the nucleus.