Hello everyone and welcome to this blog post. This week's article is the second in a series about DNA. In last week's article, I explained what DNA is and how it controls the proteins our cells produce. I also outlined some of the ways in which DNA can get damaged. This week, I will be exploring some of the diseases associated with DNA.
There are many inherited diseases associated with damage or mutations associated with the DNA structure. As I mentioned in last week's article, the order of bases in the DNA is very important as it dictates the order of amino acids in the protein the gene codes for. Due to the reasons discussed in last week's article, mutations can occur. This is when a base in changed for another (a point mutation), or a base is removed from or added to the structure (frameshift mutations).
When a mutation changes the sequence of bases in the gene, it forms an allele - a new version of a gene. If these alleles are formed in the gametes, then these versions of the gene can be passed on to offspring. Consequently, if these alleles are faulty, then they can cause genetic diseases in the offspring. Thes alleles can either be recessive (in which case the sufferer needs to inherit two copies of the allele to cause the disease) or dominant (in which case inheriting one copy of the disease will be sufficient to cause disease.
Sickle cell anaemia
One of these inherited diseases is sickle cell anaemia. Sickle cell anaemia is caused by a point mutation on chromosome 11, in the gene that codes for haemoglobin. In the faulty allele, one of the adenine bases has been changed to a thymine base. As a result, the haemoglobin produced contains the amino acid 'valine' instead of 'glutamic acid'.
Consequently, since the new amino acid is non-polar, the haemoglobin produced is more fibrous. This causes the haemoglobin molecule to be much less soluble. In addition, the haemoglobin molecules also form long strands inside the red blood cell, causing the cell to become deformed (or 'sickle-shaped'). These defective cells are much worse at carrying oxygen. Additionally, these cells can also get stuck in capillaries, stopping healthy red blood cells from getting through and oxygenating the area.
Interestingly, carriers of the faulty sickle cell allele have increased resistance to malaria. This has resulted in the disease is more common than expected in tropical regions at high risk of contracting malaria, such as the Democratic Republic of the Congo and Nigeria. There are many different theories behind why this allele gives the sufferer increased resistance to malaria. To read more able these theories, feel free to read my blog post here.
Albinism
In addition, albinism is also a disease caused by mutations in the genetic code. Albinism is caused by a mutation in any one of seven genes. The most common form of albinism is a mutation in an autosomal chromosome that affects the enzyme tyrosinase. If this mutation occurs, then the tyrosinase is either not produced or not produced correctly.
Tyrosinase is an essential enzyme in the production of melanin. Melanin is a skin pigment that is produced by specialist cells in the skin (called melanocytes). This pigment is responsible for making the hair, skin and eyes appear darker. In sufferers of albinism, the melanocytes lack functioning tyrosinase, so melanin can't be produced.
As a result, suffered from albinism have pale pink irises in the eyes and very light skin and hair. In addition, sufferers may also have problems with their eyes, causing poor vision and their eyes to make rapid, jerky movements. Furthermore, melanin also has a role in protecting the body from the harmful effects of UV radiation. Consequently, sufferers of albinism also have an increased risk of skin cancer.
Moreover, ocular albinism can also occur. Ocular albinism is a recessive, genetic condition that primarily affects the iris and the retina in the eyes. This disease is more common in men, as it is a sex-linked disease. This is because the mutation that causes ocular albinism occurs on the X chromosome. Since men have one X chromosome and one Y chromosome, they only need to inherit one copy of the allele to have the disease. In contrast, women need to inherit the allele on both X chromosomes to suffer from the disease.
Haemophilia
Furthermore, haemophilia is another example of a sex-linked, genetic disease. Haemophilia is caused by a mutation on the X chromosome, which prevents clotting factors from being produced. There are three main types of haemophilia - the most common type is haemophilia A, which is caused by a lack of clotting factor VIII. In addition, there is also haemophilia B (a deficiency of clotting factor IX) and haemophilia C (the absence of clotting factor XI).
Haemophilia is a very dangerous disease as it reduces the effectiveness of the bodies response to injuries to blood vessels, causing clots to form more slowly. This is because clotting factors (which are mainly produced by the liver) are essential in helping the platelets to form a clot to plug the hole in the vessel.
Consequently, those who suffer from haemophilia have to be careful not to get cut, as it is harder for the body to stop the bleeding (as the clots that form are weak and break easily). In addition, sufferers also bruise easily and may bleed into their joints, which causes swelling and is very painful.
Huntington's disease
Additionally, dominant genetic conditions can also be inherited. These conditions are those that only need the sufferer to inherit one copy of the faulty allele. One example of this disease is Huntington's disease. Huntington's disease is caused by a defect in chromosome 4 in the gene that codes for the protein huntingtin. Whilst the exact function of this protein is unknown, it is thought that the protein has an important role in nerve cells.
The defect occurs due to a 'stutter'. This is where there is an error in the creation of this DNA, that causes a large number of repeats of the bases CAG. It is thought that having more of these repeats is associated with having the symptoms of Huntington's earlier in life.
One of the common symptoms of Huntington's disease is a series of movement disorders. This includes having muscle problems, impaired gait, jerky movements and difficulties in speaking. In addition, sufferers can also have cognitive disorders (including difficulties in learning new information) and psychiatric disorders (including feelings of sadness and social withdrawal). Additionally, sufferers are also at a higher risk of having OCD and bipolar disorder.
Cancers
So far in this article, we have discussed some diseases that can be inherited and passed on between generations. However, there are also some diseases that are caused by new mutations in the offspring themselves. Whilst the risk of contracting these diseases can be impacted by genetic factors, environmental factors have a significant impact on them.
One of these types of diseases is cancer. There are many different types of cancers, which are caused by different mutations in different genes. These mutations can occur by chance when the cell divides. Additionally, genes can also get damaged while they remain in the nucleus. Whilst the body can repair some of this damage, eventually, this damage builds up, and cancers form.
These damaged genes can cause cancer in many different ways. For example, the cell could produce abnormal proteins that work differently. Furthermore, they could also cause the cell to make proteins (e.g. enzymes) that cause the cell to divide rapidly or cause the cell to stop producing proteins that prevent cell division.
If the cells start dividing rapidly by mitosis, then they are often removed by the immune system or self-destruct. However, sometimes this doesn't occur. In these cases, the cells continue to divide, forming tumours. These tumours then start to invade the surrounding tissue, causing problems for your health. In addition, they can also cause blood vessels and lymph vessels to supply nutrients to them, depriving the rest of your body of these materials. Tumours can also break apart and spread to other parts of the body causing secondary growths.
Final remarks
I hope you have enjoyed this week's article, which has provided a summary of some of the diseases caused by damaged DNA. Make sure to subscribe to the mailing list below so that you get notified every time I publish a new article.
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