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Biology – The Search for Better Health Section 1: What is a healthy organism? Discuss the difficulties in defining the terms ‘health’ and ‘disease’. Health is more than merely the absence of disease. The World Health Organisation (WHO) defines health as ‘a state of complete physical, mental and social well-being, and not merely the absence of disease or infirmity’. This definition allows the ‘whole’ person to be taken into account rather than just whether they have a disease or not. An individual who does not have a disease may still not be considered healthy. On the other hand, an individual who suffers from disease could be still classed as healthy. Physical health refers to the physical state of the body and includes such things as our level of fitness, body weight, amount of energy and the proper functioning of the systems in the body. Mental health is related to our ability to function effectively in society and to cope with changing situations in our lives. Social health is our ability to interact, communicate and socialise effectively. One problem with the WHO definition of health is that is very broad, and if taken literally it would be very difficult to achieve a healthy status. The concept of health for individuals is very subjective and depends on their life circumstances. What is healthy for one may not be regarded as healthy for another. Different people have different ideas about what is considered an appropriate level of physical social and mental health. Health is a constantly changing state and is relative to others and ourselves over a period of time. Disease can be defined in many ways, but the most common is ‘any condition that adversely affects the normal functioning of any part of a living thing.’ A problem with most definitions of disease is that they are quite broad and imprecise. Conditions that would not be normally classed as diseases could be if the above definition of disease were to be taken literally. It could mean that a broken arm would be classed as a disease because it adversely affects the normal functioning of the body. Another difficulty in defining both ‘health’ and ‘disease’ is caused by the different ways the terms are used. Terms used by the general public usually have different meanings to the scientific definitions. Outline how the function of genes, mitosis, cell differentiation and specialisation assist in the maintenance of health. Cell Differentiation: Cells mature and take on different structural features, so that they become structurally suited to perform a specific function in the body. Cell Specialisation: Specific genes are switched on in order to perform a particular function for the body. For example: Nerve cells – have a particular structure and specific genes that are switched on that allow the transfer of electrochemical messages. Differentiation and specialisation enable cells to work together in a healthy body to carry out complex functions in a controlled way in order to maintain and repair tissues. If differentiation and specialisation of cells do not occur, the cells would not be able to function effectively and processes in the body would not be co-ordinated. Genes and Mitosis: The maintenance of health is dependent on the information stored in the DNA of each cell. A gene is a hereditary unit that controls the production of polypeptides that make up proteins in the cell. These proteins are responsible for normal cell functioning, growth and repair. A malfunction in a particular gene may result in the inability of the cells to function properly and lead to the onset of disease. The information contained in genes also prescribes how and when an organism’s body tissues are maintained and repaired, so any malfunction in these genes would be detrimental to healthy cells. Mitosis is the process of cell division by which identical body cells are produced for growth, repair of damaged tissue, replacement of worn out cells, and genetic stability. This results in precise and equal distribution of chromosomes to each daughter nucleus, so that all resulting cells contain the same number and kind of chromosomes as each other and the parent cell. This allows all cells to function normally and tissues in the body to be repaired and maintained. If cells are damaged through injury or disease, the division of healthy cells close to the injury or disease site replaces them. Genes code for the proteins that are responsible for the regulation of the cell cycle and mitosis in healthy cells. The types of genes responsible for the regulation of the cell cycle and mitosis are: - DNA repair gene: This codes for proteins that are responsible for the stopping of the cell cycle while other proteins remove the damaged regions of DNA and replace them with a new correct sequence. If these genes mutate they will no longer function correctly, the DNA is not repaired and the damaged DNA will replicate. As a result the correct proteins necessary for normal cell functioning growth and repair will not be produced and disease will occur. - Proto-oncogenes: These code for proteins that stimulate cell growth and mitosis. - Tumour suppressor genes: these code for proteins that slow down or stop cell growth and mitosis. These genes also code for proteins that induce cell death if there is an uncontrolled increase in cell numbers In a healthy cell, these genes tightly regulate cell growth and mitosis. If these genes are damaged or mutated this regulation is disrupted. Mutations to proto-oncogenes lead to the expression of oncogenes that would be normally silent. This cause uncontrolled production of cells and prevents cell death. Mutations to tumour suppressor genes halt the production of proteins that control cell division and cell death. This disruption of the normally regulated cell cycle leads to uncontrolled cell replication which: - does not allow cells to differentiate, so they cannot perform the specialised functions necessary for normal body functioning. - causes the formation of tumours. If the tumour spreads to other tissues, cancer results. In some cases, mutations to certain genes could cause uncontrolled cell death, which leads to degenerative conditions such as Alzheimer’s disease. Process / Definition Structure Cell Cells mature and take on different Differentiation structural features so that they become suited to perform a specific function in the body. Cell Specific genes are ‘switched on’ in Specialisation order to perform a particular function in the body. Genes These are hereditary units that control the production of polypeptides that make up the proteins in the cell Mitosis Explanation Differentiation and specialisation enable cells to work together to carry out complex functions in a controlled and co-ordinated way in order to maintain and repair tissues. If differentiation and specialisation of cells do not occur the cells would not be able to function effectively and processes in the body will not be co-ordinated. The maintenance of health is dependant upon the information stored in the genes. The genes control the production of proteins that are responsible for normal cell functioning, growth and repair. Genes code for the proteins that are responsible for the regulation of the cell cycle and mitosis. The info contained in the genes prescribes how/when an organism’s body tissues are maintained/ repaired. Mitosis is the process of cell division by It allows all cells to function normally and tissues in which identical body cells are produced the body to be repaired and maintained. If cells are to allow for: damaged through injury or disease, the division of - Growth healthy cells close to the injury or disease site - Repair of damaged tissue, replaces them. replacement of worn out cells Genetic stability - precise and equal distribution of chromosome to each daughter nucleus. Use available evidence to analyse the links between gene expression and maintenance and repair of body tissues. Gene expression involves the ‘switching on’ of genes so that the relevant proteins that they code for are produced. Many genes code for proteins that are responsible for the control of the maintenance and repair of body tissues. If these genes are expressed properly then the maintenance and repair of body tissues occurs as it should. Problems with the normal maintenance and repair processes will occur if the relevant genes are not expressed properly due to such things as the mutation of genes. For example, one particular type of breast cancer is a ‘basal-like’ cancer that is particularly aggressive and more difficult to control and harder to treat than most forms of disease. Mutations to the BRCA1 gene put women at a much higher risk of developing this form of breast cancer. The BRCA1 mutations are inherited and are carried by one woman in 800. The presence of these mutated genes increases the risk of developing this cancer by 85%. BRCA1 is a tumour suppressor gene found on chromosome 17. It is believed to be responsible for the coding of proteins involved in the repair of PTEN gene. The PTEN gene is another tumour suppressor gene that limits the amount of cell division and encourages cell death. This regulates the cell cycle and prevents the excessive proliferation of cells that lead to tumours and cancer. In a normal cell, if there is damage to the PTEN gene, proteins that have been coded for by the BRCA1 gene would repair it. This repaired PTEN gene would then be expressed properly and cell division and differentiation would occur to maintain and repair body tissues. Mutations to the BRCA1 gene would mean that the proteins that are necessary for the repair of the damaged PTEN gene would not be produces, and the PTEN would not be repaired and therefore would not be expressed. This results in a lack of control of the cell cycle and runaway cell division leading to the formation of tumours. Outline how the function of genes, mitosis, cell differentiation and specialisation assist in the maintenance of health. (6 Marks) A gene is a segment of DNA on a chromosome that specifies a particular characteristic. One’s DNA is the most integral part of their existence. The genes coded on this DNA allow for protein synthesis which is essential in ensuring the maintenance of health. When cells are struck by disease, proteins need to be produced in order to repair the tissue, or to generate new substances. Genes on the DNA strand code for the production of these proteins. If a mutation occurs on these genes, the protein formed may be ineffective in achieving its role, hence it will be unable to prevent damage to the cell, and hence disease will be likely to onset. An example of this is when bacterial infections occur. Cells within the bone marrow have their genes specially designed such that they produce red/white blood cells. The extra white blood cells produced will then counteract the disease, thereby assisting in the maintenance of health. Mitosis is the process in which somatic cells duplicate. This is essential in the replacement of old and damaged cells, in the generation of new cells for growth and in the repair of body tissue. As health depends on constant repair within the body, mitosis serves this role by replacing old cells with new ones. This keeps the body healthy by removing damaged and old cells. For example, when a person is cut, new cells will regenerate from older ones via mitosis in order to repair the body tissue and maintain the health of the organism. Cell differentiation is when somatic cells have a number of genes on their chromosomes permanently switched on while others are switched off. This allows the cell to develop into one with a unique use in the body – ie cell specialization. Cell differentiation and specialization ensure that the body can perform complex tasks in a coordinated manner, with different cells taking on different responsibilities. This creates an efficient system within the body, thereby ensuring the maintenance of health. For example, the digestive villi in the small intestine are specialized to absorb nutrients thoroughly – this ensures that the body remains well nourished – an important and integral aspect of human health.