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Cellular Metabolism

Metabolism is the chemical changes that occur within a cell. Cells go through metabolism in order to maintain life. Enzymes control metabolism.
There are two types of metabolism:

1. Anabolism: The cell creates a larger molecule through the combination of smaller ones. The cell needs outside energy in order to perform this. SMALL → BIG
2. Catabolism: The cell creates smaller molecules by breaking down larger ones. This releases energy. BIG → SMALL

Energy can be in the form of heat, light, sound, electrical, mechanical and chemical energy.

Types of reactions can include:

1. Cellular respiration
- Glycolysis: breakdown of six carbon glucose into 2 three carbon pyruvic acid molecules; anaerobic, no oxygen required
- Aerobic respiration: requires oxygen, occurs after glycolysis. Pyruvic acid molecules go through a reaction to create a product of carbon dioxide, water and energy.

2. Metabolic pathways
- Carbohydrate Pathways: breakdown of carbohydrates into glucose. 
i. Step one: Glycolysis occurs which break glucose into pyruvic acid
ii. Step two: pyruvic acid reacts to form acetyl coenzyme A which then goes through the citric acid cycle to form energy, carbon dioxide and water. The energy then reacts to form ATP and heat.

- Lipid pathways: breakdown of fats into glycerol and fatty acids.
i. Step one: hydrolysis, breakdown of fat into glycerol and fatty acids
ii. Step two: Beta oxidation, fatty acid portions react to form molecules of coenzyme A
iii. Step three: acetyl coenzyme A oxidized in citric acid cycle
- Protein pathways: breakdown of protein to amino acids
i. Step one: Protein hydrolysis to form amino acids
ii. Step two: Amino acid deamination to form its separate components
iii. Step three: Depending on protein involved, can through several pathways: can form acetyl coenzyme A, or go right to citric acid cycle

3. DNA synthesis
- the building of DNA
- DNA is made through the combination of 4 base pairs, and a sugar phosphate backbone

4. Protein synthesis
- the making of protein through amino acids and guided by RNA

5. DNA replication
- the making of a new DNA strand through an old DNA strand

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