Topic 8A - Mutations and Gene Expression Flashcards
Define mutation
A mutation is any change to a base sequence of DNA, caused by errors during DNA replication
Define the 6 different types of mutations.
(SADDIT)
- Substitution: when 1+ bases are swapped for another.
- Addition: 1+ bases are added
- Deletion: 1+ bases are removed
- Duplication: 1+ bases are repeated
- Inversion: A sequence of bases is reversed.
- Translocation: A sequence of bases is moved from one location in genome to another. This could be movement within same chromosome or movement to a different chromosome.
Why can mutations affect proteins/characteristics?
The order of DNA sequences determine the order of amino acids in a polypeptide, which determines shape of a protein
- If there is a mutation, order of amino acid may change, which could change the shape of the protein, so it no longer works. (e.g. enzyme active site would change, so substrate will no longer be able to fit into it, and it is denatured)
What type of things can mutations lead to?
give 3 points and some examples
- Genetic disorders e.g. cystic fibrosis
- Increased likelihood of developing cancer e.g mutations on the gene BRCA1 can increase the chances of developing breast cancer.
What are hereditary mutations?
They are mutations that will be present in a fetus when a gamete, containing a mutation for a genetic disorder/type of cancer, is fertilised.
Are all hereditary mutations harmful?
No, some drive evolution
Do all mutations affect the order of amino acids?
No as the degenerate nature of the genetic code means that some amino acids are coded for by more than one triplet code. This means that not all mutations will result in a different amino acid sequence
- THESE ARE CALLED SILENT MUTATIONS
What 2 types of mutations may not lead to a change in amino acid sequence?
look at examples on page 194
- (SOME) Substitution
2. (SOME) Inversion
What type of mutations lead to a change in amino acid sequence and why?
look at examples on page 195
- Additions
- Duplications
- Deletions
As they change the number of bases in the DNA code.
- This causes a shift (called a frameshift) in the base triplets that follow, so that the triplet code is read in a different way
Do mutations occur randomly or systematically?
Randomly
What are mutagenic agents (and give examples of some)
Mutagenic agents are things that increase the rate of mutations e.g. ultraviolet radiation, ionising radiation, some chemicals and some viruses
How do mutagenic agents increase the rate of mutations?
- Acting as a base
- Altering bases
- Changing the structure of DNA
How does the ‘acting as a base’ increase the rate of mutation?
Acting as a base - Chemicals called base analogs can substitute for a base during DNA replication, changing the base sequence in the new DNA (E.g. 5-bromouracil is a base analog that can substitute for thymine, it can pair with guanine (instead of adenine), causing a substitution mutation in the new DNA
How does ‘altering bases’ increase the rate of mutations?
Altering bases - some chemicals can delete or alter bases (e.g. alkylating agents can add an alkyl group to guanine, which changes the structure so that it pairs to thymine instead of cytosine.
How does ‘changing the structure of DNA’ increase the rate of mutations?
Changing the structure of DNA - Some types of radiation can change the structure of DNA, which causes problems during DNA replication. (e.g. UV radiation can cause adjacent thymine bases to pair up together)
What are acquired mutations?
They are mutations that occur in the individual cells after fertilisation
What can happen if acquired mutations occur in genes that control the rate of cell division?
It can cause UNCONTROLLED cell division, which can form a tumour. Tumours can invade and destroy surrounding tissues, and turn into cancers.
What is a tumour?
A mass of abnormal cells
Name the 2 types of genes that control cell division
- Tumour suppressor genes
2. proto-oncogenes
What effect do mutations have on tumour suppressor genes?
Tumour suppressor genes can be inactivated if a mutation occurs in the DNA sequence
- when dividing normally, tumour suppressor genes slow cell division by producing proteins that stop cells dividing or cause them to self-destruct (apoptosis)
- If a mutation occurs in tumour suppressor gene, the protein isn’t produced. The cells divide uncontrollably, resulting in a tumour —-> cancer
What effect do mutations have on proto-oncogene?
The effect of a proto-oncogene can be increased if a mutation occurs in a DNA sequence. A mutated proto-oncogene is called an oncogene.
- When functioning normally, proto-oncogenes stimulate cell division by producing proteins that make cells divide
- If mutation occurs in proto-oncogene, gene can become overactive and produce more proteins, so that cells divide uncontrollably and result in a tumour –> cancer
Name the two different types of tumours.
Benign and malignant tumours
What are benign tumours?
Non-cancerous tumours.
- they grow slower than malignant tumours and are often covered in fibrous tissue to stop cells invading other tissues. They are often harmless, but they can cause blockages and put pressure on organs
- some benign tumours can become malignant
What are malignant tumours?
Cancerous tumours
- They grow rapidly and invade and destroy surrounding tissues. Cells can break off the tumours and spread to other parts of the body in the bloodstream or lymphatic system