Causes of Mutations
- A mutation is a change in the sequence of base pairs in a DNA molecule
- They occur randomly and continuously to create new alleles of a gene
- Often only with a very small number of differences in the base sequence
- As the DNA base sequence determines the sequence of amino acids that make up a polypeptide, mutations in a gene can sometimes lead to a change in the polypeptide that the gene codes for
- If the change is significant, this could be harmful for the organism (mutations are rarely beneficial). It may affect the ability of the protein to perform its function
- For example:
- If the shape of the active site on an enzyme changes, the substrate may no longer be able to bind to the active site
- A structural protein (like collagen) may lose its strength if its shape changes
- Most mutations are neutral because they do not alter the polypeptide or only alter it slightly so that its structure or function is not changed
- This is because the genetic code is degenerate
- Mutations in body cells can lead to cancer. These mutations are often eradicated when the individuals dies
- Mutations of cells which are involved in gamete production can be inherited by the next generation
Mutagenic agents
- There are natural mechanisms that take place within cells to ensure the accuracy of DNA replication
- These mechanisms involve proofreading and repairing damaged DNA
- When the mutation rate of a cell rises to above a normal (usually low) rate then these mechanisms have become ineffective
- Mutagenic agents are environmental factors that increase the mutation rate of cells
- Radiation can cause chemical changes in DNA, this includes:
- High-energy radiation such as UV light
- Ionising radiation such as X-rays, gamma rays and alpha particles
- Chemical substances can also caused changes to DNA, examples include
- Benzo[a]pyrene and nitrosamines found in tobacco smoke
- Mustard gas used as a chemical weapon in World War I
Ionising radiation can cause mutations in DNA