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Metabolism – chemical reactions in cells required by organisms to assimilate energy and use it to grow and reproduce.
Types of metabolic reactions based on rearrangement of molecules and energy transfer processes
- Energy is released from the break down of complex organic compounds into simpler substances.
- energy is required to combine simpler substances to form more molecules.
Note: Energy released from catabolic reactions is stored by ATP for use in anabolic reactions (i.e., concept of coupled chemical reactions in cells)
Enzymes – proteins produced by cells to catalyze chemical reactions by “lowering the activation energy”
When enzymes and substrates combine, substrate is transformed, enzyme is recovered.
Most enzymes consist of a protein portion and a cofactor (can be a metal or a complex organic, coenzyme).
Enzyme specificity to its substrate is a function of the 3D shape of the enzyme’s active site.
Names end with – ase; based on substrate’s name, e.g., urease & lipase; based on type of reaction, e.g., oxidase & hydrolase
4 Types of enzymes:
Exoenzymes (extracellular) vs. endoenzymes (intracellular)
Constitutive (constant amounts) or inducible (only produced when substrates are present) enzymes.
Sensitivity of enzyme activity to environment
- enzymes function optimally under conditions in an organism’s natural habitat (a direct consequence of natural selection); changes in these normal conditions may denature them, preventing substrates from attaching to their active sites; e.g., high temperature, extreme pH, presence of certain chemicals as alcohol or heavy metals
Regulation of enzyme activity
- competitive inhibition of enzyme activity results from the presence of other molecules that have similar structure as the substrate, e.g., sulfa drugs mimicking PABA competing for enzyme’s active site
- feedback inhibition* – product of a reaction inhibits enzyme activity in the pathway, e.g., allosteric enzymes with active site and regulatory site
- repression vs. induction of enzyme synthesis by regulating the way genes are “expressed”
Carbohydrate catabolism –
- converting chemical energy in carbohydrate molecules into available chemical energy in ATP
- Glycolysis (EMP)– oxidation of glucose (6C) to produce pyruvate (3C); ATP & NADH (ecarrier) are released
- Aerobic respiration: O2 as the ultimate oxidizing agent, triggers the “complete” oxidation of glucose (fuel molecule) into water & CO2.
- Krebs Cycle (TCA) – further oxidation of fuel molecules that yield ATP, NADH, FADH2 & CO2
- Electron transport chain – electrons transported through a series of carriers in membrane, generate energy used by ADP & phosphate to produce ATP (oxidative phosphorylation
Other examples of fermentation in bacteria & their products
Acetic acid fermentation produces acetic acid (vinegar)
Mixed acid fermentation produces a complex & variable mixture of acids
Butanediol fermentation produces mostly butanediol (glycol, toxic substance in antifreeze)
Lipid catabolism – lipases hydrolyze fats into glycerol & fatty acids, oxidation of fatty acids yields products that enter part of glycolysis or Krebs cycle
Protein catabolism – amino acids are converted to products that enter the Krebs cycle
Anabolism (Biosynthesis) & amphibolism – most catabolic pathways contain strategic molecular intermediates that can be diverted into anabolic pathways; this property is called amphibolism.
Photosynthesis – conversion of light energy into chemical energy (stored in carbohydrates) through carbon fixation; biosynthesis of carbohydrates
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1. Introduction to Microbiology