Cellular Respiration

• Autotrophs


  Organisms that make their own food
• Heterotrophs


  Organisms that eat other organisms for food
• Cellular Respiration


  Process where organisms get energy from carbs, fats, and proteins by releasing energy while O2 oxidizes food molecules
• Metabolism


  1. Synthesis (combines small molecules to form more complex molecules for cell growth + maintenance, consumes energy)

  2. Decomposition (breaks down organic molecules to simpler forms, releases energy used to make ATP)
• ATP


  Mediates the transfer of energy in metabolism
• How we get energy from food

  1. Respiration breaks down food and releases energy

  2. This energy is then used to make ATP
• Cellular Respiration


  • Decomposition pathway that provides the energy for cells to function
  • Releases free energy by oxidizing sugars into CO2 and H2O
  • Some energy is converted to ATP
  • Occurs in the presence or absence of oxygen
• Chemical equation for cellular respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
• Aerobic Respiration


  Requires O2 to receive e- from decomposed substrates
• Anaerobic Respiration


  Substrate may be partly decomposed, releasing less energy with nitrogen or sulfur replacing oxygen
• Aerobic Respiration


  Process where carbs, fats, and proteins are used as raw materials
• Substrates


  Glucose + glucose-phosphate (C6H12O6 - H3PO3)
• Glycolysis


  1. Occurs in cytoplasm

  2. Anaerobic

  3. Enzymes split glucose into two 3-carbon molecules

  4. Small amount of ATP
• Krebs Cycle


  1. Occurs in mitochondrial matrix

  2. Aerobic

  3. Carbon molecules oxidize to CO2

  4. More ATP
• ETC (Electron Transport Chain)

  1. Occurs in inner mitochondrial membrane

  2. Aerobic

  3. Most ATP

  4. Regenerates NAD+

  5. Protons and electrons transferred to O2, forming water
• Glucose is oxidized during aerobic respiration
• NAD+ is reduced to NADH
• FAD is reduced to FADH2
• Hydrogen carriers in cells

  • NADH
  • NADPH
  • FADH2
• At the end of the ETC, NADH+FADH2 reduce oxygen to form water
• In the Krebs cycle, 2 hydrogen atoms from glucose reduce FAD to FADH2
• NADH, NADPH, FADH all carry hydrogen in cells
• Glycolysis


  1. Glucose is converted into glucose-6-phosphate by using 1 ATP molecule

  2. Glucose-6-phosphate is converted into fructose 1, 6-bisphosphate by using 1 ATP molecule

  3. Fructose 1, 6-bisphosphate is converted into (2) PGAL

  4. The (2) PGAL are oxidized to form pyruvate. This reduces 2 NAD+ into 2 NADH and 4ADP+P into 4 ATP
• Products of Glycolysis per 1 molecule of glucose

  • pyruvate=2
  • NADH=2
  • ATP=2
• Role of glycolysis


  Synthesis of ATP, NADH, and pyruvate. Used to form carbon skeletons for biosynthesis
• If oxygen is low or not present


  1. Cells reverse the oxidation that produced the pyruvate (NADH+pyruvate-->NAD+Lactate)

  2. Lactate= 3 carbon acid molecule

  3. NAD+ cycles back to glycolysis which continues to provide a small amount of energy

  4. Anaerobic pathway= lactic fermentation
• If oxygen is present


  Pyruvate enters the krebs cycle
• ETC


  Embedded in mitochondria
• Mitochondria


  • Cell organelle where the krebs cycle and ETC occur
  • Have inner and outer membrane
  • Outer membrane regulates movement of molecules in+out of mitochondrion
  • Inner membrane contains more proteins than lipids
  • Inner membrane has folds that are called cristae
• Matrix


  Inside fluid-filled space
• Grooming


  1. Pyruvate from glycolysis is transported into the mitochondria

  2. A CO2 is removed, resulting in a 2 carbon molecule (acetate)

  3. NAD+ is reduced to NADH, and CoA bonds to acetate, forming acetyl CoA

  4. CoA acts as a carrier molecule to bring acetate into the cycle
• Krebs Steps


  1. Acetyl CoA combines the acetate with a 4 C acid (oxolacetate) to form citrate. CoA is released to carry more acetate

  2. A carbon atom from citrate is oxidized and released as CO2

  3. A molecule of NAD+ is reduced, resulting in a 5 C sugar (ketoglutarate)

  4. A carbon atom from ketoglutarate is oxidized and released as CO2

  5. A molecule of NAD+ is reduced again, resulting in a 4 C sugar

  6. The 4 C sugar is rearranged + oxidized, reducing NAD+, a FAD, and creates a molecule of ATP to form oxolacetate
• NADH and FADH2


  • Carry H+ to the ETC and reduce oxygen
• ETC


  1. H atoms separate into e- and p+

  2. transfers through cytochromes

  3. At each transfer, some energy is released

  4. Some p+ diffuses back into matrix through ATP synthase

  5. p+ transfers some energy to the ATPase, which synthesizes ATP from ADP+P

  6. The final cytochrome combines the e- and p+ with O2 to form water
• Once reduced, NADH and FADH2 form water and synthesize ATP
• ETC


  • Has enzymes and cytochromes
• The H from NADH has enough energy to synthesize 2 ATP molecules
• Bacteria don't have mitochondria, their ETC is in cell membranes
• Facultative Anaerobes


  Can survive with or without O2, can switch between fermentation and anaerobic respiration
• Obligate Anaerobes


  Can't survive with O2, only performs fermentation or anaerobic respiration