http://igcse-school.blogspot.com/
Enzymes are biological catalysts. They speed up chemical reactions in all living things, and allow them to occur more easily.
They occur in plant cells and animal cells. Without them we would not be alive.
Although they work powerfully, enzymes are just chemical molecules, made up of proteins. They are too small to be seen either when they are inside cells or after they have been released from them, for example in the digestive system.
Each particular enzyme has a unique, 3-dimensional shape shared by all its molecules. Within this shape there is an area called the active site where the chemical reactions occur.
Some enzymes help to break down large molecules. Others build up large molecules from small ones. While many others help turn one molecule into another.
Probably the fastest enzyme known is called catalase.
It breaks the chemical hydrogen peroxide down to water and oxygen. Catalase is found in all cells and protects them from this dangerous waste chemical.
The substrate (hydrogen peroxide) and the catalase molecules are continuously on the move. Every so often they will collide so that the substrate molecule(s) fits into the enzyme's active site.
Then the substrate is broken down into the two products.
The enzyme is not used up in the reaction. It is ready to work again!
No matter what job an enzyme does it will work in a similar way.
Although they can do fantastic things they are sensitive and work best under specific conditions.
Each type of enzyme has its own specific optimum conditions under which it works best.
Enzymes work best when they have a high enough substrate concentration for the reaction they catalyse. If too little substrate is available the rate of the reaction is slowed and cannot increase any further.
Sometimes, if too much product accumulates, the reaction can also be slowed down. So it is important that the product is removed.
The pH must be correct for each enzyme. If the conditions are too alkaline or acidic then the activity of the enzyme is affected. This happens because the enzyme's shape, especially the active site, is changed. It isdenatured, and cannot hold the substrate molecule.
Temperature is a key factor too. If it is too cold the enzymes will move around too slowly to meet the substrate molecules, so the reaction rate is slowed. Likewise, if it is too warm they do not work properly either. This is because the extra heat energy shakes them around so much that the active sites change shape so, just like with pH, the enzyme molecules are denatured, and can't hold the substrate.
Enzymes control all kinds of reactions in all cells. For example, they help control respiration, photosynthesis, and our digestion, amongst many others.
We also make use of enzymes elsewhere. Protease and lipase enzymes are used in biological washing powders to remove those stubborn stains.
Enzymes are also used in making foods and drinks. The enzyme pectinase helps to break down the cells in fruit to release more of their juice.
[ IGCSE Biology Revision ( Enzymes ) , IGCSE revision , IGCSE Biology , Biology , Enzymes , Enzymes revision , what is enzyme ]
Hiç yorum yok:
Yorum Gönder