Week 15

• Cellular respiration involves the oxidation of macromolecules e.g. glucose and electron carriers

  
• Redox reactions, oxidation-reduction reactions


  Occur together and are coupled reactions
• In the breakdown of glucose, glucose is oxidized (loss of electrons) to carbon dioxide and oxygen is reduced (gain of electrons) to water

  
• Cellular electron carriers


  Nicotinamide adenine dinucleotide (NAD+/NADH) and flavin adenine dinucleotide (FAD/FADH2)
• Oxidized forms


  NAD+ and FAD
• Reduced forms


  NADH and FADH2
• The reduced form has high potential energy, which is used to synthesize ATP in the final stage of cellular respiration

  
• Aerobic Respiration


  C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
• Metabolism


  The building and breaking down of carbon sources
• Anabolism


  Building of molecules; input of energy
• Catabolism


  Breakdown of molecules; net release of energy e.g. cellular respiration

  
• ATP production


  Substrate-level and oxidative phosphorylation

  
• Electron transport chain (ETC)


  A series of membrane-associated proteins that harness electron energy to produce ATP, in a process called oxidative phosphorylation
• Substrate-level phosphorylation


  An enzyme/substrate complex is used in a hydrolysis reaction that drives the synthesis of ATP
• Glycolysis


  A series of 10 anaerobic chemical reactions that occurs in the cytoplasm
• Glycolysis


  The starting molecule is glucose (C6H12O6); the end products are two three-carbon molecules, each called pyruvate (C3H3O3)

  
• Glycolysis phases


  1. Phase 1: Glucose is prepared for the next 2 phases by the addition of 2 phosphate groups, producing fructose 1,6-bisphosphate

  2. Phase 2: Fructose 1,6-bisphosphate is cleaved into 2 molecules of glyceraldehyde 3-phosphate

  3. Phase 3: 2 pyruvate are formed, 2 NADH are produced and 4 ATP are produced via substrate-level phosphorylation

  
• The net ATP gained from glycolysis is 2 because 2 ATP are used during phase 1

  
• Pyruvate oxidation

  Pyruvate is initially oxidized to form CO2 and an acetyl group. The acetyl group is then transferred to coenzyme A, which carries the acetyl group to the citric acid cycle (acetyl-CoA).

  
• Mitochondrion


  Has an inner membrane and an outer membrane that define two spaces. The space between the two membranes is called the inner membrane space, and the space inside the inner membrane is the mitochondrial matrix.
• Citric acid cycle

  A set of reactions starting with acetyl-CoA that occurs in the mitochondrial matrix and is called a cycle because the starting molecule (oxaloacetate) is regenerated.

  
• Citric acid cycle


  The inputs are 2 acetyl-CoA and the outputs are 2 CO2, 2 ATP, 6 NADH, and 2 FADH2.
• Citric acid cycle intermediates can be used to synthesize other molecules like amino acids, pyrimidine bases, and lipids
• Glucose has been oxidized to 6 CO2, 4 ATP, 10 NADH and 2 FADH2 have been synthesized or reduced

  
• Electron Transport Chain (ETC)


  Oxidizes NADH and FADH2 and uses the net energy released to make a proton gradient
• Proton gradient


  Protons are pumped from the mitochondrial matrix across the inner mitochondrial membrane to the intermembrane space, creating a concentration gradient with high potential energy
• Oxidative Phosphorylation


  Uses the potential energy of the proton gradient to drive ATP synthesis
• Intermembrane space


  This creates a concentration gradient with high potential energy
• Electron Transport Chain (ETC): Mapping the movement of electrons


  1. Electrons are passed from electron donors to acceptors until they reach the final electron acceptor, oxygen

  2. When oxygen accepts the electron, it is reduced to water. In cellular respiration, oxygen is often called the "terminal electron acceptor"

  
• Electrons enter the ETC


  Via either complex I or II, depending on whether they enter as NADH or FADH2
• Energy is released


  As the electrons are passed from the high-energy electron carriers
• Oxidative Phosphorylation: Using the potential energy of the proton gradient to drive ATP synthesis


  1. Protons in the intermembrane space diffuse down their electrical and concentration gradients through a transmembrane protein channel into the mitochondrial matrix

  2. The energy released is used to synthesize ATP
• ATP Synthase


  • Couples the synthesis of ATP to the movement of protons down their concentration gradient
  • Has 2 distinct subunits called F0 and F1
  • F0 forms the channel in the inner mitochondrial membrane through which protons flow
  • F1 is an enzyme that catalyzes the synthesis of ATP from ADP and Pi
• The movement of protons


  Is coupled with the synthesis of ATP
• Fermentation


  1. Allows glycolysis to continue in the absence of oxygen

  2. NADH is oxidized in ethanol (plants and fungi) and lactic acid (animals and bacteria) fermentation

  3. Lactic acid and ethanol receive electrons from NADH (produced in glycolysis)

  4. In the absence of oxygen, pyruvate (produced in glycolysis) is reduced and ethanol and lactic acid are the final electron acceptors

  
• Gibbs free energy (G)


  The amount of energy available to do work
• The difference between the free energy of the reactants and products is delta G
• Topics We'll Go Over


  • Vocab
  • Diffusion + Concentration Gradient (brief overview)
  • Cellular Respiration (glycolysis → pyruvate oxidation → citric acid cycle → oxidative phosphorylation)
  • Photosynthesis
  • Lac Operon
  • Old Content Vocab
  • Old Exam Questions

  
• Kinase


  Assist in phosphorylation, adding a phosphate group (ADP → ATP, GDP → GTP etc)
• Phosphatase


  Assist in dephosphorylation (the other way around)