Untitled

• Glucose is a key source of energy in both Prokaryotes and Eukaryotes

Metabolism Overview

• Metabolism involves the buildup and breakdown of nutrients within a cell
• These chemical reactions furnish energy and generate substances to sustain life
• Catabolism breaks down complex molecules, providing energy and building blocks for anabolism; it's exergonic
• Anabolism utilizes energy and building blocks to construct complex molecules; it's endergonic
• Metabolic pathways are sequential, enzymatically catalyzed chemical reactions
• Enzymes dictate metabolic pathways, accelerating chemical reactions by converting substrates into products

Catabolic and Anabolic Reactions

• The collision theory posits that chemical reactions occur when atoms, ions, and molecules collide
• Activation energy is required for a chemical reaction to occur
• Reaction rate is the frequency of collisions with sufficient energy to initiate a reaction
• Reaction rate can be elevated by enzymes or by increasing temperature, pressure, or concentration

Enzymes

• Catalysts accelerate chemical reactions without being altered themselves
• Enzymes are biological catalysts
• Enzymes act on a specific substrate and lower the activation energy

Enzyme Components

• Apoenzyme is the protein portion of an enzyme
• Cofactor is the nonprotein component
• Coenzyme is an organic cofactor
• Holoenzyme comprises the apoenzyme and the cofactor

Factors Influencing Enzyme Activity

• Temperature can affect enzymes
• pH affects how enzymes function
• Substrate concentration plays a role in enzyme funstion
• Inhibitors can stop enzymes functioning
• High temperature and extreme pH denature proteins
• Enzyme catalysis reaches its maximum rate when substrate concentration is high (saturation)

Inhibitors

• Competitive inhibitors occupy the active site of an enzyme, competing with the substrate
• Noncompetitive inhibitors interact with another part of the enzyme (allosteric site), leading to allosteric inhibition

Metabolic Pathways

• Metabolic pathways are sequences of chemical reactions where the product of one reaction serves as the substrate for the next, with each reaction catalyzed by different or sometimes the same enzymes

Feedback Inhibition

• End-product allosterically inhibits enzymes from earlier in the pathway

Oxidation-Reduction Reactions

• Oxidation involves the removal of electrons
• Reduction involves the gain of electrons
• Redox reaction pairs an oxidation reaction with a reduction reaction
• Biological oxidations are often dehydrogenations, removing electrons and protons simultaneously

ATP Generation

• ATP is generated through the phosphorylation of ADP, requiring energy input

Substrate-Level Phosphorylation

• ATP is generated when high-energy PO4- is transferred from a phosphorylated compound to ADP

Oxidative Phosphorylation

• Electrons are transferred from one carrier to another along an electron transport chain on a membrane, releasing energy to generate ATP

Components Assisting Enzymes

• Nicotinamide adenine dinucleotide (NAD+) is a coenzyme that assists enzymes
• Nicotinamide adenine dinucleotide phosphate (NADP+) is also a coenzyme
• Flavin adenine dinucleotide (FAD) is another coenzyme
• Coenzyme A assists reactions

ATP Production from Coenzymes

• Each NADH oxidized in the electron transport chain can produce 3 molecules of ATP
• Each FADH₂ can produce 2 molecules of ATP

Photophosphorylation

• Photophosphorylation occurs in light-trapping photosynthetic cells
• Light energy is converted to ATP as electrons from chlorophyll pass through a system of carrier molecules

Metabolic Pathways

• A series of enzymatically catalyzed chemical reactions that extracts energy from organic compounds and stores it as ATP

Carbohydrate Catabolism

• A process that breaks down carbohydrates to release energy via glycolysis, the Krebs cycle, and the electron transport chain

Glycolysis

• Glycolysis involves the oxidation of glucose to pyruvic acid, producing ATP and NADH
• Preparatory stage uses 2 ATP to split glucose into two molecules of glyceraldehyde 3-phosphate
• Energy-conserving stage oxidizes two glyceraldehyde 3-phosphate molecules to 2 pyruvic acid molecules, producing 4 ATP and 2 NADH

Glycolysis Products

• Net gain of two ATP molecules for each molecule of glucose oxidized

Additional Pathways to Glycolysis

• Uses pentoses, producing NADPH and important pentose intermediates and operates simultaneously with glycolysis
• The Entner-Doudoroff pathway produces NADPH and ATP but does not involve glycolysis, occurring in Pseudomonas, Rhizobium, and Agrobacterium

Cellular Respiration

• Operates an electron transport chain
• The final electron acceptor is inorganic and comes from outside the cell
• ATP is generated by oxidative phosphorylation

Aerobic Respiration

• Pyruvic acid (from glycolysis) is oxidized, undergoing decarboxylation, where CO2 us lost

Krebs Cycle

• Results in a two-carbon compound that attaches to coenzyme A, forming acetyl CoA and NADH
• Oxidation of acetyl CoA produces NADH, FADH2, and ATP, releasing CO₂ as waste

Electron Transport Chain (ETC)

• The electron transport chain (system) occurs in the plasma membrane of prokaryotes and the inner mitochondrial membrane of eukaryotes
• Series of carrier molecules (flavoproteins, cytochromes, and ubiquinones) are oxidized and reduced as electrons pass
• Energy released is used to produce ATP by chemiosmosis

Chemiosmosis

• Electrons pass down the electron transport chain while protons are pumped across the membrane, establishing a proton gradient (proton-motive force)
• H+ diffuses through ATP synthase, releasing energy to synthesize ATP
• • Molecular oxygen (O2) is the final electron acceptor