The Various Roles Played By Proteins

Stephanie Ashton 11/11/07

An Essay On ‘The Various Roles Played By Proteins

In The Cell Membrane.’

Throughout this essay I am going to be investigating the different types of proteins found in the cell membrane, and why their functions are important in everyday life. Proteins make up about half of the mass of the cell membrane and are responsible for most of the membrane’s properties. On average a cell has about ten thousand different types of proteins within it, therefore each of these different types need to be localised to a specific area in order for them to do the job at hand adequately.

Proteins which are known as membrane proteins can be split into two groups; the first of these groups is known as the ‘extrinsic proteins’ and the second is called the ‘intrinsic proteins’. Extrinsic proteins can only be found on one side of the phospholipid bilayer, they do not alter the movement of substances and combine with specific substances which have a complimentary shape to their own; therefore act as receptor site. Intrinsic proteins lie across the whole membrane. They help ions and molecules which are water soluble to cross the membrane at this point, therefore controlling what goes into and what comes out of the cell.

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Another function of proteins in the cell membrane is to ‘detect signals from the outside of cells and relay them to the inside’ (Phillipallan,nov 1999); these are known as receptor proteins (sometimes with sugars attached) and their job is to alter a cells behaviour to enable signal molecules like hormones to bind specifically to their own receptor. This enables them to respond to tasks which need completing, very quickly. These proteins are also important for keeping us healthy. For example diabetics need receptors to bind the insulin; which they have to inject, to receptors on adipose tissue cells in order for the cells to take up glucose from the blood. (Phillipallan,nov1999). When a receptor is activated the response given depends upon the ‘relay machinery’ which it is connected to inside the cell. (Phillipallan,nov,1999) . On occasions the binding leads to other events in the cell being triggered like cell recognition. However cells do not always respond to the signals which are being given positively and this may result in the cells committing suicide.

Throughout the cell membrane there are low density lipoproteins which have the job of binding the bad cholesterol from the cell and removing it from the circulation. It has also been proven that these proteins also contribute a lot to carrying the cholesterol from the membrane to other cells in the body which may need it. (Science Daily, Apr. 13, 2000).

Similar to the intrinsic proteins trans-membrane protein molecules also help to control what passes through into the cell. These proteins are of specific shape and size (similar to the lock and key method in enzymes) and therefore only substances which match this are allowed to cross. Transport proteins can also be broken up into two groups; the channel proteins and the carrier proteins. Channel proteins allow charged substances and water soluble molecules to diffuse across the membranes through water filled pores, the majority of these pores can be opened or closed which allows the cells to control what is entering or leaving. Carrier proteins are constantly switching between two states so that the opposite sides of the membrane have alternate chances to enter the site. The substances involved will bind to the side where there is a higher concentration and automatically be released once in the lower concentration.(Biologymad.com).

Glycoprotein’s are formed when proteins are attached to carbohydrates and perform a variety of roles in the cell. Some of these are; that they help in interaction with other cells and are used to recognize foreign molecules in order to keep them out of the cell. They assist in cell adhesion; which is when cells are bound with other cells. For example; the egg cells and sperm cells bind together in reproduction. Situated on the outside of cells there are also numerous identification proteins used in cells such as; antigen proteins which are found in parts of some bacteria’s.

Proteins in the membrane work together with the cytoskeleton; which is found in the cytoplasm of the membrane and provides structure and support for the proteins to attach themselves to. These work together to form appendage like organelles which extend from the cell such as; cilias. The majority of the cilia are covered by the cell membrane but do stick out slightly from the cell with little hair like structures called microvilli. Therefore the proteins help the membrane to act as a protecting body. The anchoring proteins are also the ones which restrict themselves to a particular cell surface. For example; ‘the apical surface of epithelial cells that line the vertebrate gut’ (www. wikipedia.org) and puts a limit on how far the organelles can diffuse within the bilayer.

. Anchoring proteins restricts them to a particular cell surface — for example, the apical surface of that line the — and limits how far they may diffuse within the bilayer.

like projections, called , which increase cell surface area and thereby increase the absorption rate of nutrients. The cell membrane acts as a protecting body.

Peer Reviews

Here's what a star student thought of this essay

skatealexia

28th of Mar 2012

Quality of writing

Spelling, punctuation and grammar are all adequate and correct but the essay could be organised better, and references should be included in their own separate section at the end of the text.

Level of analysis

Introduction is good, but could set out the main examination basis of the essay better rather than concentrating on broad points about proteins. Language used is basic scientific A level terms that from the beginning stick to the syllabus and the basic sciences used at A level rather than scoping above and beyond. Link structure to function vaguely and makes a few points although they could make a few more real life examples. Do not include a conclusion for the essay and could include a lot more in depth analysis.

Response to question

Overall a mediocre essay that outlines all the basic A level facts for this level of syllabus. Introduction could be more centered around the question, and the main analytical body of the text could be a lot more in depth and explore topics of proteins around the a level syllabus to gain a higher mark. No conclusion. Response to the question is very scientifically accurate although basic.

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