B3b - Proteins and Mutations

Proteins
1. Proteins are needed in cells because they are vital components in the construction of membranes. Some proteins are very specialised for particular functions.
  1. Collagen - an important structural protein found in connective tissue
  2. Insulin - is a hormone that helps to control blood sugar levels.
  3. Haemoglobin - is a carrier protein, found in red blood cells, which binds with oxygen
  4. Enzymes - control chemical reactions in the body.
2. Each protein has its own number an sequence of amino acids. This results in different shapes of molecule. It is estimated that there are over 19000 differnent proteins in the human body, each with a particular function
Enzymes
1. Enzymes act as biological catalysts. They speed up chemical reactions, including those that take place in living cells, e.g respiration, photosynthesis and protein synthesis.
2. Enzymes are highly specific; each one will speed up only a particular region. Enzymes have active sites, regions of the enzyme molecule which bind to substrate molecules temporarily and allow the substrate to be changed.
3. Changing temperature and pH will affect the rate of reaction cataylsed by an enzyme.
4. A rise in temperature increases the number of collisions between reactants and enzymes, and will increase the enzyme activity until optimum temperature is reached.
5. Temperatures above the optimum permanently damage the enzyme molecules, decreasing or stopping enzyme activity.
6. Different enzymes have different optimum temperatures. The ones in the human body work best around 37 degrees celsius.
7. There is an optimum pH at which the enzyme works best. As the pH increases or decreases, the enzyme becomes less and less effective.
8. The optimum pH for different enzymes can vary considerably: human saliva 7.3 wheras stomach needs to be very acidic.
9. The rate of an enzyme- controlled reaction can be expressed as a Q10 value by comparing the rate at a temperature 10C lower
Lock & Key mechanism
1. Each enzyme has a different number an sequence of amino acids. This gives it an unique 3-D shape, which includes an active site that only a specific reactant can fit into.
2. Reactant fits into active site -> Reactant is broken down an enzyme can be re-used.
3. Enzyme molecules are denatured by very high temperatures and extreme pH; the bonds in the protein break and the shape of its active site is changed irreversibly, so the lock and key mechanisms no longer works.
4. At lower than optimum temperatures, the enzyme does not collide as often with substrate molecules and so the reaction rate is lowered.
Mutations
1. Different cells and different organisms produce different proteins. If the base sequence changes this might result in the production of different proteins, in which case new forms of genes may arise from mutations in existing genes.
2. Mutations are normally harmful or have no effect whatsoever but can sometimes be beneficial because the new protein could function better. They occur naturally and spontaneously but their frequency is increased by exposure to ultraviolet light, x-rays, radioactive substances and certain chemicals.
3. Mutations are changes to the structure of the DNA molecule. The mutations change or prevent the sequence of amino acids that the genes usually code for, so different proteins are made, which causes the nature of that particular gene to change. The new gene can then be passed on to daughter cells through cell division.

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B3b - Proteins and Mutations

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	Created by Chloe.Sharland almost 11 years ago