Metabolism - all of the chemical reactions in an organism.
Metabolic rate varies between different species: temperature and size are the main factors.
Catabolism - breaking down large molecules to small molecules ( usually releases energy ).
Anabolism - building up large molecules from small ones (usually requires energy).
Types of energy : chemical ( eg. in food )
light
heat
electrical ( nerves )
kinetic ( energy of movement )
ATP ( Adenosine Tri Phosphate ) : stores chemical energy. It has three phosphate groups attached to adenine and ribose (the same sugar as in RNA). ATP is mainly produced in mitochondria.
First Law of Thermodynamics : energy can be changed from one form to another, it cannot be destroyed or created.
Second Law of Thermodynamics : entropy ( disorder ) is always increasing. So things fall apart and break down, because the general trend is towards disorder.
Second law
In living things, chemical energy ( ATP ) is used for :
1) Mechanical work eg muscles
2) Chemical work eg anabolism
3) Active transport eg sodium/potassium pump
Enzymes
Enzymes control chemical reactions in the cell.
Enzymes are proteins. They act as catalysts ( speed up chemical reactions by lowering the activation energy Fig 7-10).
Enzymes are specific ( each affects a particular substrate ).
They have an active site that the substrate molecule fits. Fig 7-11.
Enzymes work very rapidly (up to 100,000 chemical reactions per minute) so are only needed in tiny quantities.
Enzymes
The speed of enzymes can be affected by :
- Environmental conditions ( temp, pH ). Fig 7-12.
Human enzymes work best at about 37o C ( body temp). Above about 40o C enzymes become denatured.
Cold temperatures slow enzymes.
Siberian surgery : by cooling down a patient's body, surgeons can do heart surgery without a heart/lung machine.
Most human enzymes work best close to pH 7 (for example trypsin in the intestines works best around pH 8). There are a few exceptions: pepsin in the stomach works best around pH 2.
Generally, however, acids act as preservatives, as they slow or stop enzymes. Bog bodies
- Coenzymes ( vitamins ).
Vitamins are needed in very small amounts. Large amounts of vitamins can actually be toxic:
Vitamin A toxicity.
Vitamin E supplements may increase death risk. New Scientist
Recently folate (folic acid) was added to flour and other basic foods, because it was the only vitamin that people generally were deficient in. During pregnancy, a folate deficiency increases the risk of birth defects.
Some vitamins are antioxidants, that protect cells from damage. Drinks like coffee also contain antioxidants.
Antioxidants
The law on marketing vitamins and other nutritional supplements is very lax: companies do not have to prove the supplements are effective, or even safe.
Supplements
- Inhibitors ( toxins ) Fig 7-17 : Competitive and non-competitive inhibitors.
Competitive inhibitors attach to the active site of the enzyme.
Non-competitive inhibitors attach away from the active site.
Commercially, enzyme inhibitors are important in pesticides, and some medications, such as HIV drugs and aspirin, are inhibitors.