The Effects of Mutations
- Most mutations do not alter the protein or only alter it slightly so that its appearance or function is not changed
- However, a small number of mutations code for a significantly altered protein with a different shape
- This 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
- On rare occasions mutations lead to the development of new alleles and so new phenotypes
- Occasionally, the new allele (and its resulting phenotype) gives the individual a survival advantage over other members of the species
- For example:
- A bird develops a mutation leading to a change in feather colours
- This makes it more attractive to birds of the opposite sex
- Which causes the bird to breed more frequently and have more chances of passing on the mutated phenotype to the next generation
- Mutations can also lead to harmful changes that can have dramatic effects on the body - for example, sickle cell anaemia in humans
Sickle cell anaemia
- Sickle cell anaemia was the first genetic disease to be described in terms of a gene mutation
- A gene mutation is a change in the base sequence of DNA
- The mutation changes the molecule haemoglobin, causing the red blood cells (RBC’s) to become stiff and sometimes sickle-shaped when they release oxygen to the body tissues
- The sickled cells tend to get stuck in narrow blood vessels, blocking the flow of blood
- As a result, those with sickle cell disease suffer painful “crises” in their joints and bones
- They may suffer strokes, blindness, or damage to the lungs, kidneys, or heart. They must often be hospitalized for blood transfusions and are at risk for a life-threatening complication called acute chest syndrome
- Although many sufferers of sickle cell disease die before the age of 20, modern medical treatments can sometimes prolong these individuals’ lives into their 40s and 50s
Sickle cell anaemia is caused by abnormal haemoglobin which changes the shape of red blood cells
