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Proteins have many functions in the human body and these include transport, catalysis, protection, storage, sensitivity, structure and co-ordination.

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Introduction

Proteins Introduction Protein accounts for about three-fourths of the dry matter in human tissues other than fat and bone. It is a major structural component of hair, skin, nails, connective tissues, and body organs. It is required for practically every essential function in the body. Proteins are made from the following elements; carbon, hydrogen, oxygen, nitrogen and often sulphur and phosphorus. Proteins cannot be stored except in eggs and seeds and they form the body's main structural elements and are found in every cell and tissue. The human body uses proteins for growth and to build and repair bones, muscles, tissue, skin, internal organs and blood. Hormones, antibodies and the enzymes that regulate the body's chemical reactions are all made of protein. Without the right proteins, blood won't clot properly and cuts won't heal and if carbohydrates and fat can't meet your energy needs, proteins can be broken down and used as a source of emergency energy. ...read more.

Middle

Transport Proteins are also used as transport molecules, such protein is haemoglobin which transports oxygen in red blood cells all around the body. The main haemoglobin in adult humans is Haemoglobin A and it contains two alpha and two beta subunits. Haemoglobin also transports carbon dioxide away from the tissues to the lungs where it is exhaled. Haemoglobins are a chain of polypeptide which is held in position by three types of bonds; disulphide bond, ionic bond and hydrogen bond. Haemoglobins are formed when four Globin molecules link together. Hormones Regulatory proteins such as insulin which are hormones regulate blood sugar levels. These kinds of proteins are used by people who have diabetes. Vasopressin is another kind of hormone of the posterior pituitary gland which controls blood pressure and controls the amount of urine secreted by the kidneys. Storage Proteins cannot be stored except in seeds and eggs, Ferritin is a storage protein which holds iron in egg yolk, spleen and liver. ...read more.

Conclusion

When forces cause the molecule to become even more compact, as in globular proteins, a tertiary protein structure is formed. When a protein is made up of more than one polypeptide chain for example haemoglobin it is said to have a quaternary structure. Collagen, which makes up bone, skin, tendons, and cartilage, is the most abundant protein found in humans. The molecule usually contains three very long polypeptide chains, each with about 1,000 amino acids that twist into a regularly repeating triple helix and give tendons and skin their great tensile strength. When long collagen fibrils are denatured by boiling, their chains are shortened to form gelatine. Keratin, this protein gives mechanical support to the body. It makes up the outermost layer of human skin, hair, and nails, and the scales, hooves, and feathers of animals. It twists into a regularly repeating coil called an alpha helix. Serving to protect the body against the environment, keratin is completely insoluble in water. Its many contains disulphide bonds which make it an extremely stable protein. ...read more.

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Here's what a teacher thought of this essay

3 star(s)

***This is an average essay that explores a number of points but seldom explores them in enough depth. It covers a number of examples of the biological use of proteins but the structure of proteins is described rather superficially.
To improve:
To gain high marks the essay should cover all the main areas relevant to the topic and must include discussion of each area with suitable examples. All the material must be relevant to the topic and the essay should only contain very few factual errors. In a biology examination the title would probably be either "The function of proteins " or " The structure of proteins" so that the essay could be completed in the time available.
Scientific content:
To improve this essay needs to widen its scope to include more relevant examples of protein use from all of the five kingdoms. For example locomotion could include the proteins within cilia and flagella in Kingdom Protoctista and enzymes could include extracellular digestion by cellulases made by Fungi. The number of key A level terms should be increased as the essay does not demonstrate comprehensive knowledge of A level standard.
Breadth:
The essay is a little unbalanced as it concentrates for the most part on aspects of human biology. Candidates should always try to include as much factual material as they can from different areas of the specification to demonstrate breadth. The section on the structure of protein was a little brief and would have benefited from some clear annotated diagrams.
Relevance:
This essay contains only material relevant to the title.
Quality of written communication:
The essay is fairly logical and generally presented in clear scientific English. It could be improved by describing protein structure first and then relating the structure to the differing functional roles. Technical terminology has been used effectively and is usually accurate.

Marked by teacher Stevie Fleming 29/05/2013

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