Topic 4 - Genetics

Question 1

What is a gene?

Answer 1

Section of DNA that codes for making a polypeptide and functional RNA

Question 2

Define Locus

Answer 2

Location of a particular gene on a chromosome

Question 3

Define allele

Answer 3

Alternative form of a gene

Question 4

Describe how DNA is stored in eukaryotes

Answer 4

DNA is tightly wound around proteins called histones
Chromosomes are linear in shape

Question 5

Describe how DNA is stored in prokaryotes

Answer 5

DNA is shorter and circular

Question 6

Define homologous pairs

Answer 6

Pairs of matching chromosomes

Question 7

Define transcription

Answer 7

Where one gene on the DNA is copied into mRNA

Question 8

Define translation

Answer 8

Where the mRNA joins with a ribosome, and corresponding tRNA molecules brings the specific amino acid the codon codes for

Question 9

Give the first stage of transcription

Answer 9

DNA helix unwinds - DNA helices breaks hydrogen bonds - one chain of the DNA acts as a template

Question 10

Give the second stage of transcription

Answer 10

Free mRNA nucleotides in the nucleus align opposite exposed complementary DNA bases

Question 11

Give the third stage of transcription

Answer 11

RNA polymerase bonds together the RNA nucleotides to create a new RNA polymer chain. One entire gene is copied

Question 12

What happens to pre-mRNA after transcription?

Answer 12

Pre-mRNA has to be modified to become mRNA that is ready to leave the nucleus and take part in translation.
The introns need to be spliced out

Question 13

What are introns?

Answer 13

Introns don’t code amino acids

Question 14

Describe what happens to the introns after transcription

Answer 14

The introns are spliced out by a protein (splicesome). This just leaves the exons (coding regions)

Question 15

Describe the first stage of translation

Answer 15

Modified mRNA leaves the nucleus and attaches to a chromosome. Ribosome attaches at start codon. tRNA molecule with complementary anticodon to the start codon aligns opposite mRNA, held in place by the ribosome.

Question 16

Describe the second stage of translation

Answer 16

Ribosome will move along the mRNA molecule to allow other complementary tRNA to attach to the next codon on the mRNA.
The two amino acids that have been delivered by the tRNA molecule are joined by a peptide bond. This is catalysed by an enzyme and requires ATP.

Question 17

Describe the third stage of translation

Answer 17

This continues until the ribosome reaches the stop codon at the end of the mRNA molecule. The stop codon doesn’t code for an amino acid and therefore the ribosome detaches and translation ends.