Comprehensive Notes on Carbohydrates and Cellular Respiration

Carbohydrates

• Carbohydrates are represented by the general formula \text{CH}_{2}\\text{OH}.

Introduction to Biochemistry: Carbohydrates (2)

• Relates proteins, amino acids, CO2, lipids, glycerol, fatty acids, ATP, polysaccharides, monosaccharides, H2O, aerobic respiration, and cellular respiration.

Aerobic Respiration of Glucose

• The chemical equation for aerobic respiration of glucose is: \text{C}{6}\text{H}{12}\text{O}{6} + 6 \text{O}{2} \rightarrow 6 \text{CO}{2} + 6 \text{H}{2}\text{O} + \text{energy} (in the chemical bonds of ATP).
• Reduction and oxidation processes are involved.

Cellular Respiration

• Aerobic respiration: Breaking down food molecules to CO2 and H2O with the production of ATP and by consuming oxygen. Requires the use of an electron transport chain; occurs in some prokaryotes and most eukaryotes.
• Anaerobic respiration: Similar to aerobic respiration but occurs in the absence of oxygen. Requires the use of an electron transport chain; occurs in some prokaryotes.
• Fermentation: Breaking down food molecules without an electron transport chain but with the production of ATP. Occurs in some prokaryotes and fungi, and also in muscle cells of animals.

Energy and Stepwise Harvest

• Total energy E is the sum of individual energy increments: E = e1 + e2 + e3 + e4 + e_5
• In cellular respiration, glucose and other organic molecules are broken down in a series of steps.
• Electrons from organic compounds are usually first transferred to NAD+, a coenzyme.
• As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration.
• Each NADH (the reduced form of NAD+) represents stored energy that is used to synthesize ATP.

Nicotinamide Adenine Dinucleotide (NAD)

• NAD+ is reduced to NADH, involving the acceptance of 2 electrons and 1 proton:
  • NAD^+ + 2e^- + H^+ \rightarrow NADH
• Dehydrogenase enzymes facilitate the reduction of NAD+ and oxidation of NADH.
• The reaction:
  • H-C-OH + NAD^+ \rightarrow C=O + NADH + H^+

Cellular Respiration Stages

• Cellular respiration has four stages:
  • Glycolysis: Breaks down glucose into two molecules of pyruvate.
  • Formation of Acetyl-CoA: Further breakdown of glucose and release of CO2.
  • The citric acid cycle: Completes the breakdown of glucose.
  • Electron transport: Accounts for most of the ATP synthesis.

Aerobic Respiration Overview

• A simplified illustration of aerobic respiration shows the involvement of Glycolysis, Formation of acetyl coenzyme A, Citric acid cycle, and Electron transport and chemiosmosis.
• Glycolysis occurs in the cytoplasm, while the remaining stages occur in the mitochondrion.
• ATP production: Glycolysis (2 ATP), Formation of acetyl coenzyme A (2 ATP), Citric acid cycle and Electron transport and chemiosmosis (32 ATP).

STEP 1: Glycolysis

• Glycolysis:
  • Involves glucose phosphorylation and cleavage.
  • Generates Glyceraldehyde 3-phosphate, NADH, ATP, and Pyruvate.
  • Requires 2 ATP to start.

Glycolysis - Detailed Steps

• Step 1: Glucose to Glucose-6-phosphate
  • Enzyme: Hexokinase
  • Reactants: Glucose, ATP
  • Products: Glucose-6-phosphate, ADP
• Step 2: Glucose-6-phosphate to Fructose-6-phosphate
  • Enzyme: Phosphoglucoisomerase
  • Reactants: Glucose-6-phosphate
  • Products: Fructose-6-phosphate

Glycolysis Enzymes and Products

• Key Enzymes:
  • Hexokinase (1)
  • Phosphoglucoisomerase (2)
  • Phosphofructokinase (3)
• Key Reactants and Products:
  • Glucose → Glucose-6-phosphate (1)
  • Glucose-6-phosphate → Fructose-6-phosphate (2)
  • Fructose-6-phosphate → Fructose-1,6-bisphosphate (3)

Glycolysis - Continued

• Key Steps:
  • Glucose → Glucose-6-phosphate (Hexokinase)
  • Glucose-6-phosphate → Fructose-6-phosphate (Phosphoglucoisomerase)
  • Fructose-6-phosphate → Fructose-1,6-bisphosphate (Phosphofructokinase)
  • Fructose-1,6-bisphosphate → Dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate (Aldolase)
  • Dihydroxyacetone phosphate ↔ Glyceraldehyde-3-phosphate (Isomerase)

Glycolysis - Glyceraldehyde-3-phosphate Reactions

• Step 6: Glyceraldehyde-3-phosphate to 1,3-Bisphosphoglycerate
  • Enzyme: Triose phosphate dehydrogenase
  • Reactants: Glyceraldehyde-3-phosphate, NAD+, Pi
  • Products: 1,3-Bisphosphoglycerate, NADH + H+

Glycolysis - ATP Generation

• 1,3-Bisphosphoglycerate to 3-Phosphoglycerate
  • Enzyme: Phosphoglycerokinase
  • Reactants: 1,3-Bisphosphoglycerate, ADP
  • Products: 3-Phosphoglycerate, ATP

Glycolysis - Mutase Reaction

• 3-Phosphoglycerate to 2-Phosphoglycerate
  • Enzyme: Phosphoglyceromutase
  • Reactants: 3-Phosphoglycerate
  • Products: 2-Phosphoglycerate

Glycolysis - Enolase Reaction

• 2-Phosphoglycerate to Phosphoenolpyruvate
  • Enzyme: Enolase
  • Reactants: 2-Phosphoglycerate
  • Products: Phosphoenolpyruvate, H2O

Glycolysis - Pyruvate Kinase Reaction

• Phosphoenolpyruvate to Pyruvate
  • Enzyme: Pyruvate kinase
  • Reactants: Phosphoenolpyruvate, ADP
  • Products: Pyruvate, ATP

Glycolysis Summary

• A summary of glycolysis steps, including the energy investment and pay-off phases, key intermediates, and enzymes involved.

Glycolysis - Energy Balance

• Energy Investment Phase:
  • 2 ATP used
• Energy Payoff Phase:
  • 4 ATP formed
  • 2 NADH formed
• Net:
  • 2 Pyruvate + 2 H2O
  • 2 ATP (4 ATP formed - 2 ATP used)
  • 2 NADH + 2 H+

Substrate-Level Phosphorylation

• Substrate-level phosphorylation involves the direct transfer of a phosphate group from an energy-rich intermediate to ADP to form ATP.

Other Sugars in Glycolysis

• Other sugars such as Trehalose, Lactose, Starch, Glycogen, Sucrose, D-Galactose, D-Glucose, D-Fructose, D-Mannose can feed into glycolysis at different steps.

Aerobic Respiration Overview Again

• A simplified illustration of aerobic respiration shows the involvement of Glycolysis, Formation of acetyl coenzyme A, Citric acid cycle, and Electron transport and chemiosmosis.
• Glycolysis occurs in the cytoplasm, while the remaining stages occur in the mitochondrion.
• ATP production: Glycolysis (2 ATP), Formation of acetyl coenzyme A (2 ATP), Citric acid cycle and Electron transport and chemiosmosis (32 ATP).

STEP 2: Formation of Acetyl CoA

• 2 pyruvate + 2 NAD+ + 2 CoA → 2 acetyl CoA + 2 NADH + 2 CO2

Aerobic Respiration - Again

• A simplified illustration of aerobic respiration shows the involvement of Glycolysis, Formation of acetyl coenzyme A, Citric acid cycle, and Electron transport and chemiosmosis.
• Glycolysis occurs in the cytoplasm, while the remaining stages occur in the mitochondrion.
• ATP production: Glycolysis (2 ATP), Formation of acetyl coenzyme A (2 ATP), Citric acid cycle and Electron transport and chemiosmosis (32 ATP).

Citric Acid Cycle (Krebs Cycle/TCA Cycle)

• Goal: To generate NADH and FADH2 for the electron transport chain.
• Acetyl-CoA + 3NAD+ + FAD + GDP + Pi → 2CO2 + 3NADH + FADH2 + GTP + CoA

STEP 3: Citric Acid Cycle

• Shows the cyclical process where Acetyl coenzyme A combines with Oxaloacetate to form Citrate.
• The cycle generates NADH, FADH2, ATP, and releases CO2.

Citric Acid Cycle - Steps

• Acetyl CoA + Oxaloacetate → Citrate

Citric Acid Cycle - Isocitrate Formation

• Citrate → Isocitrate

Citric Acid Cycle - Isocitrate Dehydrogenase

• Isocitrate → α-Ketoglutarate

  • Enzyme: Isocitrate dehydrogenase (The rate limiting Enzyme)

Citric Acid Cycle - α-Ketoglutarate Formation

• α-Ketoglutarate → Succinyl CoA

Citric Acid Cycle - Succinyl CoA Formation

• Succinyl CoA → Succinate

Citric Acid Cycle - Succinate Formation

• Succinate → Fumarate

Citric Acid Cycle - Fumarate Formation

• Fumarate → Malate

Citric Acid Cycle - Malate Formation

• Malate → Oxaloacetate

Citric Acid Cycle - Products

• Pyruvate is converted to Acetyl CoA, producing CO2 and NADH.
• The citric acid cycle generates FADH2, ATP, and more NADH.

Energy-Rich Compounds

• Examples of energy-rich compounds:

  • Phosphoenolpyruvate
  • 1,3-Bisphosphoglycerate
  • Acetyl phosphate
  • ATP, ADP
  • Acetyl-CoA
  • Glucose-phosphate
    A summary of the energy values of various compounds:

• Phosphoenolpyruvate: -51.6 \text{kJ/mol}

• 1,3-Bisphosphoglycerate: -52.00\text{kJ/mol}

• Acetyl phosphate: -44.87 \text{kJ/mol}

• ATP/ADP: -31.87 \text{kJ/mol}

• Acetyl-CoA: -35.77 \text{kJ/mol}

• AMP: -14.2 \text{kJ/mol}

• Glucose 6-Phosphate: -13.8 \text{kJ/mol}

Aerobic Respiration - Products per Glucose

• Per glucose:
  • 2 Krebs cycles: 4 CO2, 6 NADH + 6H+, 2 FADH2, 2 ATP
  • Acetyl CoA formation: 2 CO2, 2 NADH
  • Glycolysis: 2 ATP, 2 NADH
• Total: 4 ATP, 10 NADH, 2 FADH2, 6 CO2

Aerobic Respiration Summary

• A simplified illustration of aerobic respiration shows the involvement of Glycolysis, Formation of acetyl coenzyme A, Citric acid cycle, and Electron transport and chemiosmosis.
  • Glycolysis occurs in the cytoplasm, while the remaining stages occur in the mitochondrion.
  • ATP production: Glycolysis (2 ATP), Formation of acetyl coenzyme A (2 ATP), Citric acid cycle and Electron transport and chemiosmosis (32 ATP).

Oxidative Phosphorylation (Electron Transport Chain)

• Electrons from high-energy molecules (NADH and FADH2) are transferred through the protein complex.
• Movement of electrons is coupled with the pumping of protons (H+ ions) across the inner mitochondrial membrane from the matrix to the intermembrane space.
• Pumping of protons creates a concentration gradient.
• Protons moving back across the membrane through ATP synthase.
• Conformational change in ATP-synthase leads to activation of its catalytic site.
• ATP-synthase converts ADP to ATP.

Electron Transport Chain and Chemiosmosis

• Illustrates the electron transport chain within the inner mitochondrial membrane, showing the movement of protons (H+) and the role of ATP synthase.

Electron Transport Chain Detail

• Shows the complexes involved in the electron transport chain, the movement of electrons, and the pumping of protons to create a concentration gradient for ATP synthesis.

Oxidative Phosphorylation Overview

• Protein complexes of electron carriers facilitate the transport of electrons, pumping protons (H+) across the membrane.
• Process involves chemiosmosis and ATP synthase to produce ATP.

Redox Reactions in ETC

• Illustrates the location of the electron transport chain within the mitochondrial membrane, highlighting the redox reactions involved in the transfer of electrons from NADH and FADH2 to oxygen.

Electron Transport Chain and Redox Reactions

• Electron transport chain and redox reactions with protein complexes.

Proton Motive Force

• Depicts the proton gradient across the inner mitochondrial membrane, creating a proton motive force that drives ATP synthesis.

ATP Synthase

• ATP synthase is a key enzyme in oxidative phosphorylation, converting ADP to ATP using the energy from the proton gradient.

Cellular Respiration Overview

• An overview of cellular respiration, showing the locations of glycolysis, the citric acid cycle, and oxidative phosphorylation, as well as the movement of electrons via NADH.

Cellular Respiration Overview - Integrated

• An integrated view of cellular respiration, showing glycolysis in the cytosol, and the citric acid cycle and oxidative phosphorylation in the mitochondrion.

Cellular Respiration - Overall

• An overview of cellular respiration, showing glycolysis in the cytosol, and the citric acid cycle and oxidative phosphorylation in the mitochondrion.

Energy Balance

• Energetics Balance Sheet for Aerobic Respiration
  • Glycolysis: Glucose + 2 NAD+
    • Substrate-level phosphorylation: 2 ADP+ Pi → 2 ATP
    • Oxidative phosphorylation: 2 NADH → 6 ATP
  • CAC: Pyruvate + 4 NAD++ GDP + FAD
    • Substrate-level phosphorylation: GDP + Pi → GTP (ADP → ATP)
    • Oxidative phosphorylation: 4 NADH → 12 ATP; 1 FADH2 → 2 ATP
• Sum: Glycolysis plus CAC: 38 ATP per glucose.

Energy Balance - Details

• Maximum ATP per glucose: About 36 or 38 ATP
• Includes ATP from glycolysis, citric acid cycle, and oxidative phosphorylation.
• Real energy production is lower due to the cost of moving pyruvate, phosphate, and ADP into the mitochondria.

Various Molecules Fuel Respiration

• Deamination of amino acids can feed into respiration:
  • Alanine → Pyruvate
  • Glutamic acid → α-ketoglutarate
  • Asparaginic acid → Oxaloacetate

Various Molecules Fuel Respiration - Pathways

• Shows how different molecules, such as lipids and amino acids, can feed into cellular respiration at various points, including glycolysis and the citric acid cycle.

Fermentation and Anaerobic Respiration

• Most cellular respiration requires O2 to produce ATP.
• Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions).
• In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP

Anaerobic Respiration

• Anaerobic respiration uses the ETC, but with electron acceptors other than O2. Examples:
  • SO4^{2-} , NO3^-, Fe^{3+}, CO2 \rightarrow H2S, NO2^-, N2, Fe^{2+}, CH_4

Fermentation

• Fermentation is an anaerobic process without electron transport.
• Regeneration of NAD+ by reduction of an organic molecule.
• Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP.
• Two common types: alcohol fermentation and lactic acid fermentation

Alcohol Fermentation

• Glucose → 2 Pyruvate (via Glycolysis) → 2 Acetaldehyde → 2 Ethanol
• Involves the regeneration of NAD+.

Lactic Acid Fermentation

• Glucose → 2 Pyruvate (via Glycolysis) → 2 Lactate
• Involves the regeneration of NAD+.

Cori Cycle

• Lactic acid fermentation occurs in muscle cells, producing lactate.
• Lactate is transported to the liver, where it is converted back to glucose via gluconeogenesis.
• Glucose returns to the muscle.

Glycolysis and Fermentation - Detailed

• Illustrates the intermediates and enzymes involved in glycolysis and fermentation, detailing the steps from glucose to pyruvate and then to either ethanol (alcohol fermentation) or lactate (lactic acid fermentation).

Energetics of Fermentation

• Yeast fermentation: Glucose → 2 ethanol + 2 CO2 (-239 kJ)
• Lactic acid bacteria: Glucose → 2 lactate (-196 kJ)