Introduction to Metabolism

metabolism - sum total of all chemical reactions in living cells
catabolic reactions - degrade macromolecules and other molecules to release energy
anabolic reactions - used to synthesize macromolecules for cell growth, repair, and reproduction

Can divide metabolism into 4 groups: carbohydrates, lipids, amino acids, nucleotides.
• within each group are a set of pathways
• arbitrarily set start and end points for ease of learning and reference
• pathways can take different forms:
1) linear - product of one reaction is substrate for another
e.g. glycolysis
2) cyclic - regeneration of intermediates
e.g. Krebs cycle
3) spiral - same set of enzymes is used repeatedly
e.g. fatty acid synthesis, B-oxidation
• each pathway may have branch points for metabolites to enter or leave

Why have metabolic reactions with so many steps?
1) energy input and output can be controlled
- energy transfer occurs in discrete steps as it it transferred to acceptors a little at a time
2) enzymes can catalyze only a single step of a pathway
3) provides opportunities to establish control points, which are essential for cell function