Diseases can be caused in humans in many a way. Some diseases may be pathogenic some may be caused by a lifestyle choice of an individual or an individual surrounding them, or some may be genetic. Pathogens are micro-organisms which cause disease some bacteria, fungi and all viruses are pathogens. Pathogens enter our bodies through various methods such as breaks in the skin, the digestive system, and respiratory system. Pathogens can survive in many conditions such as in the air and in water and can be passed on in this way, examples such as; the common cold virus is airborne and cholera bacteria are waterborne.
Pathogens can thrive in unhygienic conditions, rapidly multiply and can be picked up of surfaces such as a kitchen work surface. Pathogens enter our body produce toxins and damage cells. When a pathogen enters our body it may release a harmful molecule called a toxin which can damage cells or interfere with the bodily functions for example tetanus produces toxins which block the functioning of certain nerve cells causing muscle spasms.
Other pathogens may damage cells physically this can be done in 3 ways; the cell may be ruptured and nutrients released into the cell; the organelles may be damaged by enzymes for example, the cell may be invaded by pathogens which then multiply causing lysis in cells this is common in virus’s. Pathogens may take nutrients from the cell and break them down for their own use this eventually starves the cell and kills it. Diseases can be caused by the lifestyle choice of an individual or the individuals surrounding them.
For example the increased risk of lung cancer caused by smoking or inhaling second hand smoke on a regular basis. While some people develop cancer without ever smoking, there is increased risk of developing lung cancer by smoking. Mutagenic agents in a cigarette can cause a mutation in the DNA of a cell causing it to rapidly multiply uncontrolled. Many other diseases such as heart disease are caused by a poor diet and lack of exercise. Genetics can be another cause of disease.
When parents pass on their genes to their offspring they can pass on genetic diseases as well. These genes can be either recessive or dominant; this can mean that people can carry a disease without showing symptoms. With a recessive disease both recessive genes must be present for the symptoms to show eg cystic fibrosis, However only one dominant gene needs to be present for the symptoms to be present such as Huntington’s disease. Some genetic diseases can be sex linked this means that the genes for the disease are found on the X and Y chromosomes eg haemophilia.
These diseases tend to show symptoms more commonly in men as even if the disease is recessive only one gene needs to be present as the Y chromosome is shorter than the X chromosome. Women will therefore need two recessive genes to show symptoms but only one to be a carrier. Some genetic diseases are not inherited but are caused by a change in the base sequence. These changes can cause a different amino acid to be coded for instead of the correct amino acid, this can majorly alter the structure of the protein like changing the shape of the active site of an enzyme.
If there is a mutation in the proto-oncogenes or the tumour suppressant gene then it may lead to the rapid uncontrolled division of the cell which can lead to the formation of a tumour. However not all changes in the base sequence can have an effect due to the degenerate nature of DNA. For example the code GGA codes for glycine but so does GGC. In conclusion diseases may be caused in many ways however some diseases may be protected against such as pathogenic diseases and diseases caused by a lifestyle choice.