6.1 - Cellular control Flashcards
What is a mutation?
A random change to the genetic material.
What is a mutagenic chemical?
A chemical that can induce DNA mutation.
Will mutations associated with mitotic division (replication) and somatic mutations be passed to offspring?
NO.
They may be associated with the development of cancerous tumours.
What type of mutations may be inherited by offspring?
Mutations that are associated meiosis and gamete formation. (as these involve the sex cells & chromosomes etc.)
What may gene mutations affect?
Protein production and function
What are the two main classes of DNA mutation?
- Point mutation
2. Insertion or deletion (indel) mutation
What is point mutation?
One base pair replaces (is substituted for) another
What is indel mutation?
What might this type of mutation cause?
One or more nucleotides are inserted or deleted from a length of DNA.
These may cause a FRAMESHIFT
What are the three types of point mutation?
- silent
- missense
- nonsense
Why is the ‘degeneracy’ or ‘redundancy’ of the genetic code so important?
Because the majority of amino acids involved in protein synthesis have more than one base triplet code.
- this reduces the effect of point mutations
What is a silent mutation?
Does it have an affect on the primary structure of the protein?
A point mutation involving a change to the base triplet, where that triplet still codes for the same amino acid.
- the primary structure of the protein, and therefore the secondary and tertiary structure, is not altered.
What is a missense mutation?
A change to the base triplet sequence that leads to a change in the amino acid sequence in a protein.
What effect might a missense mutation have on the protein produced?
The alteration to the primary structure leads to a change to the tertiary structure of the protein, altering its shape and preventing it from carrying out its usual function.
State a condition that is caused by a missense mutation?
Sickle cell anaemia.
- results from a missense mutation on the sixth base triplet of the gene for the β-polypeptide chains of haemoglobin.
- the amino acid valine, instead of glutamic acid, is inserted at this position.
- this results in deoxygenated haemoglobin crystallising within erythrocytes, causing them to become sickle shaped, blocking capillaries and depriving tissues of oxygen.
What is a nonsense mutation? Why is it so disruptive?
A point mutation may alter a base triplet, so that it becomes a termination (STOP) triplet.
- this results in a truncated protein that will not function.
This abnormal protein will most likely be degraded within the cell.
State a condition which is caused by a nonsense mutation?
Duchenne muscular dystrophy is the result of a nonsense mutation.
What is a frameshift?
If nucleotide base pairs, (not in multiples of three!!) are inserted in the gene or deleted from the gene, because the code is non-overlapping and read in groups of three bases, ALL the subsequent base triplets are altered.
Why is a frameshift so disruptive?
When the mRNA from such a mutated gene is translate, the amino acid sequence after the frameshift is severely disrupted.
- the primary sequence of the protein and subsequently the tertiary structure, is much altered.
- therefore, the protein cannot carry out its normal function.
- if the protein is very abnormal, it will be rapidly degraded within the cell.
What is thalassaemia caused by?
Some forms of thalassaemia, a haemoglobin disorder, result from frameshift due to the deletions of nucleotide bases.
What do insertions or deletions of a triplet of base pairs result in?
The addition or loss of an amino acid, and not in a frameshift.
