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Summary Biology A Level Essay: Receptors
Extended and high scoring essay example for AQA A Level Biology on the question 'The Importance of Receptors in Biology'.
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By: dougieharries • 2 year ago
By: rosaiye • 2 year ago
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The importance of receptors in living organismsReceptors are an integral aspect of almost all biological processes as they allow both cells
and organs to recognise and identify specific biological molecules, such as hormones and
potentially deadly pathogens. Receptors also allow endothermic organisms to undergo
complex homeostatic processes which allow them to adapt to a wide range of disparate
environments and thus colonise extremely hostile habitats.
Perhaps one of the more obvious instances where receptors are crucial in living
organisms, comes in the form of coordinated immune response. In humans, T helper cells
have receptors on their cell surface membrane which are complementary to epitopes
present on the surface of antigen presenting phagocytes. When these receptors bind to
their complementary antigen, the T helper cells signal other immune cells, such as
cytotoxic T cells and B plasma cells, to divide using chemical messengers known as
cytokines. This process results in a powerful immune response that can often annihilate
the pathogen before the organism itself begins to exhibit any indications of infection.
However, the prolific lentivirus known as HIV (Human Immunodeficiency Virus) further
highlights the importance of receptors in maintaining the health of organisms, as this virus
infects and destroys T helper cells with CD4 co-transport proteins on their cell surface
membrane, resulting in the disease known as AIDS and a decimated immune system with
severe and often fatal vulnerability to even minor infections. The damage caused by this
virus demonstrates how crucial receptors are to the survival of many organisms and also
how the exploitation of such structures can cause irreparable harm and even death.
Another very pertinent example of the use and importance of receptors in living
organisms is the endocrine system and the massive effect that this system of chemical
messengers has on the function and health of organisms. Many organisms utilise hormonal
messengers to manage and maintain homeostatic conditions, an example of this is the
human hormone ADH (AntiDiuretic Hormone) which is made by the hypothalamus and
secreted by the pituitary gland. When the water concentration of the blood is too low,
osmoreceptors in the hypothalamus detect this change and signal the pituitary gland to
secrete ADH into the blood stream. The ADH has a complementary 3D structure to
receptors on the cell surface membrane of epithelial cells found in the collecting duct of
the nephron in the kidney. Once ADH has bound to the receptors on the epithelial cells, it
activates a second-messenger pathway and the enzyme adenylate cyclase, which converts
ATP to cyclic AMP (the second messenger). The cyclic AMP then causes vesicles containing
aquaporins to bind with the membrane of the epithelial cells, increasing their
permeability to water and therefore the amount of water reabsorbed from the glomerular
filtrate. This process serves to raise the blood water concentration and to maintain
sufficient levels of water in the body. Another example of the important function that
receptors perform in maintaining homeostatic conditions is the action of insulin and
glucagon in relation to blood glucose concentration. Insulin and glucagon are peptide
hormones produced by cells in the Islets of Langerhans in the pancreas. Insulin is the
hormone concerned with lowering blood glucose concentration and causes GLUT4
transporter proteins to fuse with the membrane of its target cells. This process is caused
when insulin binds to complementary receptors on the surface of liver cells and reduces
the levels of glucose in the blood by increasing the rate of its uptake into hepatic cells,
whilst also stimulating glycogenesis and the conversion of glucose to triglycerides. In a
similar manner to the immune system, a deficiency in the receptors responsible for
detection of insulin on the cell surface membrane of liver cells can cause type 2 diabetes,
as the cells become desensitised to the crucial homeostatic hormone and therefore do not
take up the extra glucose in the bloodstream, resulting in polyuria and significant
detrimental symptoms.
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