Biochemistry 3rd Lecture - Intermediary Metabolism - Cell Biochemistry

Intermediary metabolism – cell biochemistry Metabolism – the process of building and breaking up of organic compounds. Every living system is regulated by other processes. A(substrate) --(E1)--> B --(E2)--> C --(E3)--> D(product) B, C – intermediates. A --> B --> C --> D --> A Energy in living system is conserved in chemical bonds and compounds. The dominant source of energy for all living systems is solar energy. Phototrophs convert solar energy to the chemical energy of organic molecules. Heterotrophs recover this energy by metabolizing the organic substances. The power that drives the cycle is light energy. Metabolism outline All organisms have the same basic set of metabolism pathways; Metabolism is composed of many coupled interconnecting reactions; Metabolism consists of catabolism (degradative pathways) and anabolism (biosynthetic pathways) The oxidation of carbon fuels is an important source of cellular energy; Metabolic pathways contain reccuring motifs Redox Reaction in Metabolism NAD+ collects electrons released in catabolism Catabolism is oxidative – substrates lose reducting equivalents, usually H- ions Anabolism is reductive – NADPH provides the reducting power (electrons) for anabolic processes. Human Nutrition – Carbonhydrates and lipids Carbonhydrates yield metabolic energy; Carbonhydrates are also essential components of nucleic acids, glycoproteins and glycolipids; Brain activity requires glucose for fuel; Excess carbonhydrates are stored as triglycerols and glycogen; Fatty acids can be used as fuel by many tissue in the human body; Phospholipids are membrane components; Excessive or insufficient fatty acids intake present disadvantage; Proteins Proteins yield amino acids Essential amino acids: can't be synthesized by animals and can only be obtained from food. Glucogenic amino acids: can be converted from glucose (e.g, Asp to Oxaloacetate, Phe to fumarate) Ketogenic amino acids: can be converted to fatty acids or keto acids RQ = CO2 /O2

Energy relationship between catabolism and anabolism Catabolism oxidates energy yielding nutriens to energy poor end products such as H2O, CO2, NH3 From this chemical energy is created – ATP, NADPH The energy created triggers anabolism – reductive reaction. Precursor molecules (amino acids, sugars, fatty acids, nitrogenous bases) –> Cell macromolecules (proteins, lipids, polysaccharides, nucleic acids). Transport processes Active transport is strictly regulated. 1. A sodium ion is bound 2. Bound Na+ stimulates glucose binding and a subsequent formation 3. b 4. b 5. Loss of Na+ allows glucose release to inside 6. Release of glucose stimulates return to initial state Na+/K+ pump 1. 2. 3. 4. 5. 6.

3 Na+ are taken from inside ATP phosphorylases (alpha) subunit A formation change following phosphorylation expels 3 Na+ into surroundings Two K+ accepted from outside Dephosphorylation stimulates formation change b

Stages of catabolism 1. 2. 3. 4.

Proteins, polysaccharides, lipids Amino acids, sugars, fatty acids, glycerols Pyruvate, CoA, Citric acid cycle, intermediates CO2, H2O