Transcription and Translation

Question 1

What is transcription?

Answer 1

Where a DNA provides instruction for a sequence of bases to be copied in the form of a codon.

Question 2

Transcription
1. Where does it take place?

Answer 2

Nucleus

Question 3

Transcription
2. What enzyme unwinds the double helix?
What bonds are broken?

Answer 3

DNA helicase. Breaks hydrogen bonds between bases so the helix unwinds.

Question 4

Transcription
3. Unwinding of the DNA helix exposes what?

Answer 4

Exposes the gene to be transcribed.

Question 5

Transcription
4. The exposed nucleotides on one side of the DNA strand act as what?

Answer 5

Template

Question 6

Transcription
5. What binds to exposed bases on the DNA strand and where do they come from?

Answer 6

Free nucleotides from the nucleus bind to the exposed DNA

Question 7

Transcription
6. What enzyme is used to join the free nucleotides together?
What molecule is this forming?

Answer 7

RNA polymerase.
This forms pre mRNA

Question 8

Transcription
7. As pre mRNA is produced, what enzyme re joins the original DNA strand behind it?

Answer 8

DNA polymerase.

Question 9

Transcription
8. Once the pre mRNA has been formed, what is reached that terminates the production of the pre mRNA?

Answer 9

Stop codon.

Question 10

What is splicing?

Answer 10

Removal of introns from pre mRNA leaving exons only (only the coding regions). This forms the mRNA molecule.

Question 11

Why does splicing not occur in prokaryotes?

Answer 11

They do not have introns.

Question 12

What is alternative splicing?
How do the size of the genome and proteome compare as a result?

Answer 12

Exons of a gene are spliced and arranged in a different order.
This means the proteome is much bigger than the genome.

Question 13

What is translation?

Answer 13

Production of the polypeptide.

Question 14

Translation
1. What does mRNA leave the nucleus though?

Answer 14

Nuclear pores

Question 15

Translation
2. What type of codon on the mRNA attaches to the ribosome first?

Answer 15

Start codon

Question 16

Translation
3. What part of the tRNA pairs with the mRNA codon?
What does the tRNA carry?

Answer 16

Anticodon
Carries the amino acid

Question 17

Translation
4. What does the next tRNA molecule do?

Answer 17

The next tRNA carries another amino acid towards the sequence and the anticodon binds the mRNA.

Question 18

Translation
5. How many tRNA molecules are brought to a ribosome at one time?
How do they know what amino acid to bring next?

Answer 18

2 amino acids at a time.
The mRNA molecule moves along the ribosome and once each codon has been read, this tells what amino acid should be brought to the ribosome.

Question 19

Translation
6. Once 2 amino acids have been brought to the ribosome, what happens?

Answer 19

Amino acids join in a condensation reaction to form a peptide bond. This starts to form the polypeptide.

Question 20

Translation
7. What happens when the 3rd codon on the mRNA is read by the ribosome?

Answer 20

The ribosome reads the 3rd codon and this signals what the next amino acid to be brought over should be. The tRNA binds to the ribosome and releases the amino acid to be added to the polypeptide chain.

Question 21

Translation
8. Once at least 3 amino acids are in the polypeptide chain, what happens to the 1st tRNA molecule that bound to the amino acid?

Answer 21

The first tRNA molecule that bound is released.

Question 22

Translation
9. When will polypeptide production be terminated?

Answer 22

Once a stop codon is reached.