Topic 8A: Mutations and Gene Expression Flashcards
Definition: Mutation
A change in the base sequence of DNA.
What are the different types of mutation?
- Substitution
- Deletion
- Addition
- Duplication
- Inversion - a sequence of bases is reversed.
- Translocation - a sequence of bases is moved from one location in the genome to another
What are the affects of mutations?
1) Base sequence of DNA is changed.
2) The sequence of amino acids in the polypeptide could be changed.
3) The tertiary structure of the protein is changed.
4) Unable to function properly.
What are hereditary mutations?
When a gamete containing a mutation is fertilised, meaning the mutation is present when the foetus forms. Therefore, they are passed on to the offspring.
Why are not all mutations harmful?
1) The degenerate nature of the genetic code means some amino acids are coded for by more than one DNA triplet.
2) Therefore, not all types of mutation will cause a change in the amino acid sequence of a polypeptide.
What are frameshift mutations?
1) Addition, duplication or deletion occurs meaning there is a change in the number of bases in the DNA code.
2) Therefore, there is a shift in the base triplets that follow, so the triplet code is read in a different way.
3) This means you get a completely amino acid sequence.
Definition: Mutagenic agents
Something which increases the rate of mutations by:
• Acting as a base.
• Altering bases.
• Changing the structure of DNA.
Definition: Acquired mutations
Mutations that occur after fertilisation.
Formation of tumours: Mutations in tumour suppressor genes
1) When functioning normally, tumour suppressor genes slow down cell division by producing proteins which stop cells dividing and cause them to self-destruct in a process called apoptosis.
2) If a mutation occurs, the gene will becomes inactive, meaning the protein it codes for isn’t produced.
3) Therefore cells divide uncontrollably, resulting in a tumour.
Formation of tumours: Mutations in proto-oncogenes
1) When functioning normally proto-oncogenes stimulate cell division by producing proteins which make cells divide.
2) If a mutation occurs, the gene becomes overactive, stimulating the cells to divide uncontrollably, resulting in a tumour.
What is an oncogene?
A mutated proto-oncogene.
Tumours: Malignant tumours
- Cancerous tumours which grow rapidly and invade and destroy surrounding tissues.
- Cells can break off the tumour and spread to other parts of the body in the bloodstream or lymphatic system.
Tumours: Benign tumours
- Non-cancerous tumours which grow slower and contain fibrous tissue preventing them from invading other tissues.
- Often harmless, but can cause blockages or put pressure on organs.
Features of tumour cells
- Large, dark nucleus.
- Irregular shape.
- Different surface antigens.
- Don’t respond to growth regulating processes.
- Divide by mitosis more frequently.
Growth of tumours: Abnormal methylation of tumour suppressor genes
1) If tumour suppressor genes are hyper-methylated the proteins they produce to slow cell division aren’t made.
2) Therefore, the cells divide uncontrollably by mitosis and a tumour develops.
Growth of tumours: Abnormal methylation of proto-oncogenes
1) If proto-oncogenes are hyper-methylated they act as oncogenes, causing increased production of the protein that causes cell division.
2) Therefore, the cells divide uncontrollably by mitosis and a tumour develops.
Growth of tumours: Oestrogen
1) Oestrogen stimulates breast cells to divide and replicate, meaning the more oestrogen you have, the higher the rate of cell division and so the chances of a mutation occurring are increased.
2) Also, if cells do become cancerous, their rapid replication could be further assisted by oestrogen, helping tumours to grow quickly.
Definition: Stem cell
An unspecialised cell which has the ability to develop into other types of cell.
Stem cells: Totipotent
Totipotent stem cells are stem cells which are able to develop into any type of body cell.
Stem cells: Pluripotent
Pluripotent stem cells are stem cells which are able to develop into any type of body cell, apart from placental cells.
Stem cells: Multipotent
Multipotent stem cells are only able to divide into a few different types of cell.
Stem cells: Unipotent
Unipotent stem cells are only able to develop into one type of cell.
How do stem cells become specialised?
1) Stem cells become specialised because during their development they only transcribe and translate part of their DNA.
2) This means only certain genes are expressed and the others are switched off.
3) Expressed genes get transcribed into mRNA which is then translated into proteins which modify the cell.
4) This causes the cell to become specialised.
What are cardiomyocytes?
Heart muscle cells which can only be replaced (if damaged) by new cardiomyocytes derived from a small store of unipotent stem cells in the heart.