Cell Metabolism: Anabolism & Catabolism

Metabolism

• Metabolism encompasses all biochemical reactions within a cell.
• Metabolic pathways are a sequence of enzyme-catalyzed chemical reactions.
• Enzymes, encoded by genes, determine the metabolic pathways.

Catabolism

• Catabolism involves the breakdown of complex molecules.
• It provides energy and building blocks for anabolism.
• Catabolic reactions are exergonic.
• They are also hydrolytic.

Anabolism

• Anabolism utilizes energy and building blocks to synthesize complex molecules.
• Anabolic reactions are endergonic.
• They are dehydration reactions.

Collision Theory

• Atoms, ions, and molecules must collide for chemical reactions to occur.
• Activation energy is required to disrupt electronic configurations.
• Reaction rate describes how frequently collisions occur with sufficient energy for a reaction.
• Enzymes, increasing temperature or pressure can increase reaction rate.

Enzymes

• Enzymes are biological catalysts.
• They are specific to chemical reactions, acting on a specific substrate.
• Enzymes are not consumed during the reaction.
• Enzymes accelerate reactions by lowering activation energy.

Enzyme Components

• An apoenzyme is the protein portion of an enzyme and is inactive on its own.
• A cofactor is a non-protein component that acts as an activator.
• A coenzyme is an organic molecule that acts as a cofactor.
• A holoenzyme is the combination of an apoenzyme and a cofactor, making it active.

Important Coenzymes

• Important coenzymes include NAD+, NADP+, FAD, and Coenzyme A.

Enzyme Activity

• Temperature can denature enzymes.
• pH can denature enzymes.
• Osmotic pressure can denature enzymes.

Enzyme Inhibitors

• Competitive inhibitors compete with the substrate for the enzyme's active site, with similar shapes to the substrate.
• Noncompetitive inhibitors bind to the allosteric site, which is another part of the enzyme, altering the active site's shape.

Feedback Inhibition

• The end-product of a reaction inhibits one of the enzymes in the pathway allosterically.

Cellular Respiration

• In Cellular respiration, molecules are oxidized with an inorganic molecule serving as the final electron acceptor, to generate ATP.
• Aerobic respiration's final electron acceptor is $\ce{O2}$.
• Anaerobic respiration's final electron acceptor is an inorganic molecule other than $\ce{O2}$.

Fermentation

• Fermentation is an ATP-generating process where molecules are oxidized, and an organic molecule is the final electron acceptor.

Glycolysis

• Glycolysis is the process of oxidizing glucose to pyruvic acid.
• Glycolysis yields 2 ATP, 2 NADH, and 2 pyruvic acid molecules.

Pentose Phosphate Pathway

• The Pentose Phosphate Pathway uses pentoses and NADPH.
• It runs alongside glycolysis.
• The Pentose Phosphate Pathway provides synthesis intermediates.

Entner-Doudoroff Pathway

• The Entner-Doudoroff Pathway yields 1 ATP, 1 NADPH, and 1 NADH.
• It occurs in Pseudomonas, Rhizobium, and Agrobacterium, among others.

Intermediate Step

• Pyruvic acid is oxidized and decarboxylated to form acetyl CoA.
• The intermediate step yields 2 NADH, 2 Acetyl CoA, and 2 $\ce{CO2}$.

Krebs Cycle

• Oxidation of acetyl CoA produces 6 NADH, 2 FADH2, 2 ATP, and 4 $\ce{CO2}$.

Electron Transport Chain (ETC)

• The ETC is a sequence of carrier molecules oxidized and reduced as electrons pass down the chain.
• The energy released during electron transfer is used to produce ATP via chemiosmosis.
• The ETC is located in the plasma membrane of prokaryotes and the inner mitochondrial membrane of eukaryotes.

Chemiosmosis

• Electrons pass down the ETC while protons (H+) are pumped across the membrane.
• A proton gradient is established, with more H+ on one side of the membrane.
• H+ diffuses through ATP synthase, using the proton motive force's energy to synthesize ATP.

Aerobic Respiration

• The final electron acceptor in aerobic respiration is $\ce{O2}$.
• $\ce{O2}$ combines with 2H+ to produce $\ce{H2O}$.

Anaerobic Respiration

• The final electron acceptor in anaerobic respiration is not $\ce{O2}$.
• Anaerobic respiration yields less energy than aerobic respiration.
• Nitrate (NO3-) and sulfate (SO4 2-) are examples of final electron acceptors.

Summary of Respiration

Fermentation

• Fermentation releases energy through the oxidation of organic molecules.
• Fermentation does not require oxygen.
• Fermentation does not utilize the Krebs cycle or ETC.
• Fermentation uses an organic molecule as the final electron acceptor.
• Fermentation generates only a small amount of ATP.

Types of Fermentation

• Lactic acid fermentation produces lactic acid.
• Alcohol fermentation produces ethanol and $\ce{CO2}$.

Lactic Acid Fermentation

• Homolactic fermentation exclusively produces lactic acid.
  • Examples include Streptococcus, Lactobacillus, Bacillus.
• Heterolactic fermentation produces lactic acid and other products.
  • Example: Leuconostoc

Alcohol Fermentation

• Glucose is converted to 2 pyruvic acid, which is then converted to 2 acetaldehyde, then to 2 ethanol
  • Example: Saccharomyces

Fermentation Test

• Fermentation tests are used to identify if a microorganism can ferment a carbohydrate.
• The test medium typically contains protein, a carbohydrate, a pH indicator, and a Durham tube.
• Acid production changes the color of the pH indicator.
• Gas production is visible in the Durham tube.