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Overall Process
C6H12O6 + 6O2 6CO2 + 6H2O + ENERGY
Purpose: Organisms routinely break down complex molecules in controlled steps and use energy released (in the form of ATP) from this catabolic process to do work.
Phosphate bonds• PO4 bonds are high energy bonds
– Require energy to make– Release energy when broken
Phosphorylation• Adding a phosphate group to any molecule
– Ex: ADP + Pi ATP
• Oxidative phosphorylation – phosphorylation results from redox reactions
• Substrate-level phosphorylation – phosphate group transfers from a molecule (“substrate”) instead of ADP + Pi ADP
How ATP Drives Cellular Work
Transport Work:
ATP Phosphorylates Transport Proteins
Mechanical Work:
ATP Phosphorylates Motor Proteins
Chemical Work:
ATP Phosphorylates Key Reactants
Phosphate groups are removed and recycled as work is performed
ATP ADP + P
Cellular Respiration
• Divided into 3 parts:1. Glycolysis
2. Krebs Cycle (aka Citric Acid Cycle) or Fermentation
3. Oxidative phosphorylation (ETC & Chemiosmosis)
1. Glycolysis• Breakdown of glucose into pyruvate in cytoplasm w/
or w/o presence of O2
• 2 phases:– Investment phase: use 2 ATP to break up glucose into 2
PGAL (C-C-C-p)– Payoff phase: each PGAL turns into pyruvate (C-C-C)
• Each PGAL pyruvate change makes 2 ATPs via substrate level phosphorylation and 1 NADH via redox
2. Krebs Cycle (aka citric acid cycle)
• Occurs in presence of O2
• Occurs in inner space or
matrix of mitochondria
• Complete oxidation of
glucose to CO2 occurs here
1. Pyruvate is oxidized into Acetyl CoA reducing NAD+ into NADH on the way
• CO2 is formed
2. Acetyl CoA + oxaloacetic acid → citric acid
3. Citric acid is oxidized forming 2 CO2 as waste
• This becomes oxaloacetic acid again @ end of cycle
• This oxidation powers the reduction of 3 NAD+ 3 NADH and 1 FAD+ FADH2 as well as the phosphorylation of ADP ATP.
• Also get e-’s and protons (H+) for ETC/Chemiosomosis
ETC• Occurs in the inner membrane of mitochondrial
matrix
• Energy released as e- travels down
ETC is used to establish a proton
gradient
Key Points
• No ATP is generated during ETC; ATP comes from chemiosmosis!
• Source of e- = NADH and FADH2 reduction
• Source of H+ = same as above!
Phosphorylation…
1. Photophosphorylation – plants use energy from sun to drive phosphorylation of ADP ATP
2. Substrate-level phosphorylation – glycolysis and Krebs cycle use proteins (substrates) to phosphorylate ADP ATP
3. Oxidative phosphorylation – in ETC, redox reactions drive production of ATP• This is where most of ATP generated from cell
respiration comes from!
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