BCEM 393 Lecture Notes - Lecture 10: Acetyl-Coa, Vitamin Deficiency, Oxidative Phosphorylation
9 Jun 2018
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Metabolism Part 1
GENERATION OF ENERGY FROM FOOD
- Occurs in 3 stages:
- Digestion
- Conversion of simple digestion units (sugars, fatty acids, glycerol, and many amino acids)
to Acetyl CoA
- Some ATP is already generated in this stage
- Complete oxidation of acetyl CoA to yield ATP
- Consists of the citric acid cycle and oxidative phosphorylation
- Acetyl CoA is completely oxidized to CO2
WHY DO WE NEED FOOD?
- Difference between phototrophs and chemotrophs (humans)
- Phototrophs (photosynthetic animals): An organism that can meet its energy needs by
converting light energy into chemical energy
- Chemotrophs: An organism that obtains energy by the oxidation of food
WHY DO WE EAT? VITAMINS AND COFACTORS
- Almost all coenzymes are derived from vitamins — organic molecules needed in small
amounts in the diets of many higher animals
- In all cases, the vitamin must be modified before it can serve its function
- Lower organism don’t need vitamins to be modified in order to be consumes
- Higher animals lost the capacity to synthesize vitamins in the course of evolution —> it is
biologically more efficient to ingest vitamins than to synthesize the enzymes required to
construct them from simple molecules
- This efficiency comes at the cost of:
- Dependence on other organisms for chemicals essential for life
- Vitamin deficiency can generate diseases —> scurvy (weakness, anemia, gum disease,
and skin problems) = lack of Vitamin C
WHY DO WE NEED ENERGY?
- Energy fuels:
- Muscle contraction and movement
- Active transport of ions and molecules
- The synthesis of biomolecules from precursors
- Homeostasis
- Metabolism refers to the highly integrated network of chemical pathways that enables a cell to
extract energy from the environment and use this energy for biosynthetic purposes
METABOLISM CONSISTS OF ENERGY-YIELDING REACTIONS AND ENERGY-REQUIRING
REACTIONS
- Metabolic pathways can be divided into two types:
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- Catabolic pathways convert fuels (glucose, fatty acids) into useful energy forms (ATP, ion
gradients)
- Fuel (carbohydrates, fats) —> CO2 + H2O + useful energy
- Anabolic pathways use ATP and reducing power to synthesize large biomolecules
- Useful energy + simple precursors —> complex molecules
- Although anabolic and catabolic pathways may have reactions in common, the regulated,
irreversible reactions are always distinct
METABOLISM IS COMPOSED OF MANY INTERCONNECTING REACTIONS
- In order to construct a metabolic pathway, two criteria must be met:
- The individual reactions must be specific:
- A reaction that will yield only one particular product or set of products from its reactants
- The pathway in total must be thermodynamically favourable
- Question: how are unfavourable reactions completed?
- Use products quickly, so that the reaction equilibrium proceeds forward
- Couple favourable reactions with unfavourable reactions
PHOSPHORYL-TRANSFER
POTENTIAL
- Measures the tendency of a
phosphorylated compound to
transfer a phosphoryl group to
another compound
- Presented as the ∆G°’ of
hydrolysis of the
phosphorylated compound
- The more negative the ∆G°’ of
hydrolysis, the greater the
phosphoryl-group-transfer
potential
DO ANY MOLECULES HAVE A
PHOSPHORYL-TRANSFER
POTENTIAL GREATER THAN
ATP?
- YES
- Phosphoenolpyruvate (PEP), 1,3-BPG, and creatine phosphate all have higher phosphoryl-
transfer potential than ATP
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Document Summary
Conversion of simple digestion units (sugars, fatty acids, glycerol, and many amino acids) to acetyl coa. Some atp is already generated in this stage. Complete oxidation of acetyl coa to yield atp. Consists of the citric acid cycle and oxidative phosphorylation. Acetyl coa is completely oxidized to co2. Phototrophs (photosynthetic animals): an organism that can meet its energy needs by converting light energy into chemical energy. Chemotrophs: an organism that obtains energy by the oxidation of food. Almost all coenzymes are derived from vitamins organic molecules needed in small amounts in the diets of many higher animals. In all cases, the vitamin must be modified before it can serve its function. Lower organism don"t need vitamins to be modified in order to be consumes. Higher animals lost the capacity to synthesize vitamins in the course of evolution > it is biologically more efficient to ingest vitamins than to synthesize the enzymes required to construct them from simple molecules.
