Genetic Control Of Protein Structure And Function

Question 1

What is a codon?

Answer 1

The sequence of three bases on mRNA that codes for a single amino acid

Question 2

Why is RNA required?

Answer 2

In order to transfer the DNA code from the nucleus into the cytoplasm where protein synthesis occurs.

mRNA is small enough to leave the nucleus and enter the cytoplasm

Question 3

What are some of the main features of the genetic code?

Answer 3

It’s degenerate- most amino acids have more than one codon
Three codons don’t code for an amino acid - stop codons
There’s no overlap of codes
It’s a universal code - the same codon codes for the same amino acid in all organisms

Question 4

What is a stop codon and why is it needed?

Answer 4

A codon that doesn’t code for an amino acid.

They mark the end of a polypeptide chain and so stop translation

Question 5

tRNA

Answer 5

Clover shaped
Single stranded 
One end extended which attaches the amino acids 
At the other end is the anticodon 
RNA pairs adenine to uracil

Question 6

What is an anticodon?

Answer 6

A sequence of three organic bases on tRNA that is complimentary to a codon on an mRNA

Question 7

mRNA

Answer 7

A long strand
Single helix
It is manufactured when DNA forms a mirror copy of part of one of its strands
Formed in the nucleus and leaves through nuclear pores
Acts as a template upon which proteins are built

Question 8

What is transcription?

Answer 8

The process of making pre-mRNA using part of the DNA as a template

Question 9

DNA helicase in the process of transcription

Answer 9

DNA helicase breaks the hydrogen bonds between bases of the DNA cussing the two strands to separate.

Question 10

RNA polymerase in the process of transcription

Answer 10

The enzyme RNA polymerase moves along one of the DNA strands (the template strand) causing the nucleotides to join free, individual nucleotides

Question 11

Stop codons in the process of transcription

Answer 11

When the RNA polymerase reaches a particular sequence of bases in the DNA that it recognises as a stop triplet code, it detaches and pre-mRNA is complete

Question 12

The process of splicing

Answer 12

When the introns are removed so only the functional exons are left and they join together

Question 13

Ribosomes in the process of translation

Answer 13

The ribosome becomes attached to the start codon at one end of the mRNA molecule
Move along the mRNA bringing two tRNA molecules at any one time

Question 14

Where does translation occur?

Answer 14

In the cytoplasm

Question 15

tRNA in the process of translation

Answer 15

tRNA has the complementary anticodon sequence and moves to the ribosome, pairing up with the sequence on the mRNA.
The tRNA carries an amino acid

Question 16

Peptide bonds in the process of translation

Answer 16

An enzyme and ATP join the two amino acids on the tRNA by a peptide bond

Question 17

What happens after the peptide bond is formed in translation?

Answer 17

The ribosome moves on to the next codon and so releases the first tRNA which is now free to collect another amino acid

Question 18

When does translation stop?

Answer 18

Synthesis of a polypeptide continues until a ribosome reaches a stop codon

Question 19

Nonsense mutation

Answer 19

Change in bases results in the formation of a stop codon

So the production of a polypeptide would stop prematurely

Question 20

Mis sense mutation

Answer 20

Base change results in a different amino acid being coded for
The protein may be a different shape or not function properly

Question 21

Silent mutation

Answer 21

The substitute base is different but still codes for the same amino acid as before

Question 22

What causes mutations?

Answer 22

Spontaneous gene mutation during DNA replication
Basic mutation rate is increase by mutagenic agents:
High energy radiation that the disrupts DNA
Chemicals that alter the DNA structure

Question 23

The role of Proto-oncogenes

Answer 23

Stimulate cell division
Growth factors attach to a receptor on the cell surface
Switch on the genes for DNA replication
Gene mutation can cause Proto-oncogenes to mutate into oncogenes:
- receptors can even permanently activated
- oncogenes may code for a growth factor that is produced in excessive amounts
Cells divide too rapidly developing a tumour

Question 24

Role of tumour suppressor genes

Answer 24

Inhibit cell division
Maintain normal rates of division
If it mutates, it becomes inactive
Cell division therefore increases