There may not be so much protein as lipid in plasma membrane but it still has great biological importance.
Within a cell membrane,
“Protein functions as:
1. Carriers-water soluble material (glucose).
2. Channels-for ions (sodium and chloride).
3. Pumps-using energy to move the above.
4. Receptors-enables hormones, nerve transmitters to pass between specific cells.
5. Recognition sites-identifies cells.
6. Adhesion sites-helps some cells stick together.
7. Enzymes-speeds up chemical reactions at the edge of membrane.”
Ribonuclease is an enzyme which hydrolyses ribonucleic acid. This enzyme breaks RNA into smaller components.
“It is a globular protein so it has a distinctive tertiary structure. Like all enzymes, it functions because part of its molecule forms what is called an active site. RNA molecules will fit into this site where they are broken down into their components.”
The structure of an enzyme is key to its efficiency. Without the chemical bonds between amino acids that maintain this structure, the protein would be denatured and useless. The structure and shape of an enzyme has to be just right; if the enzyme molecule is deformed, even slightly, it will not function. Only a few amino acids are actually involved in the active site the others then make up the correct bulk and structure of the enzyme.
Collagen is a fibrous protein, which is insoluble and has important structural functions. Collagen is the basic structure of connective tissue, tendons and sheath of muscle, but also the organic structure of bone.
Haemoglobin is the red coloured pigment in red blood cells. It is a globular protein and its structure allows oxygen to dock in an active site and be carried around the body. This makes haemoglobin a transport protein. Transport proteins like haemoglobin; carry substances from one place in the body to another. Other transport proteins are located in the cell membranes. These proteins shuttle nutrient and waste from one side of the membrane to another. They are again able to do this due to their active sites.
Regulatory proteins are similar - they help prevent the depletion of nutrients in tissues or the harmful accumulation of the products of respiration.
Protein is also involved in processes of growth, movement, reproduction, repair and aging, as many different enzyme compounds that accelerate chemical reactions in and around cells acting as a catalyst. Protein does this, as it is a supportive element that provides biological structures with strength and protection and also they catalyse the hundreds of reactions that together constitute cellular metabolism. Through these enzymatic reactions, cells are able to generate, conserve and transform chemical energy for other processes such as nutrient metabolism and the production of large molecules from smaller ones.
Immunoglobulins or antibodies make up perhaps the largest category of globular proteins. They help animals disarm potentially harmful foreign materials that enter the body. This is done in two different ways. One way is that the foreign body targeted and bonded with a protein’s active site identifying it to structures on the cell surface as something to be digested and destroyed. The second is when a protein engulfs the foreign body and as an enzyme breaks it down digesting it.
Glycogen is the primary animal storage form of carbohydrates, and starch is the primary storage for plants.
“In most animals, carbohydrates provide a quickly available reservoir of energy. Glycogen is stored in the liver and muscles as a stable chain of glucose and is then broken down when energy is needed.”
Monosaccharides are an important source of energy in respiration but also are an immediate product in the biochemical pathways of respiration and photosynthesis. This is because a monosaccharide is so simple it makes energy transference easy.
For structural purposes polysaccharides may be used. Cellulose is very important to the rigid yet flexible structure of a plant cell wall. The cellulose’s properties allow the plant cell wall to keep it shape.
Bibliography
- Compton’ interactive encyclopedia, 1998 edition.
-
http://chemlearn.chem.indiana.edu/facrsh/oakley.htm
- AS – AQA Biology specification A – A New Introduction to Biology.
- Gray’s Anatomy - thirty fifth edition.
Appendix
“Some proteins, called transport proteins, carry substances from one place in the body to another. Hemoglobin, for example, is a transport protein in red blood cells that picks up oxygen as it circulates through lung tissue and then carries it to the body's cells. Other transport proteins are located in cell membranes. These proteins shuttle nutrients and waste products from one side of the membrane to the other. Many proteins make up the supportive elements that provide biological structures with strength and protection. Regulatory proteins help to prevent the depletion of nutrients in tissues or the harmful accumulation of the products of respiration.”
“Immunoglobulins, or antibodies, make up perhaps the largest category of globular proteins. They help animals disarm potentially harmful foreign materials that enter their bodies. Most enzymes are globular proteins. They catalyze the hundreds of reactions that together constitute cellular metabolism. Through these enzymatic reactions, cells are able to generate, conserve, and transform chemical energy for other processes, such as nutrient metabolism and the production of large molecules from smaller ones.”
“Lipids are crucial components of many signal transduction pathways, specifically binding to target proteins and modulating their functions. In spite of the biological importance of these interactions, the origin of specificity in protein-lipid interactions is not well understood.”
- http://chemlearn.chem.indiana.edu/facrsh/oakley.htm.
“Both external and internal membranes (cytomembranes) have many features in common. They are all composed chemically of phospholipids and proteins with a small amount of carbohydrate; they also have a similar ultra-structural appearance”.
- Gray’s Anatomy, thirty fifth edition.
