Download CELLULAR RESPIRATION

CELLULAR RESPIRATION
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.
ATP – adenosine triphosphate
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
ATP
Transport Work:
ATP Phosphorylates Transport Proteins
Mechanical Work:
ATP Phosphorylates Motor Proteins
ADP + P
Chemical Work:
ATP Phosphorylates Key Reactants
Phosphate groups are removed and recycled as work is
performed
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
• Final electron acceptor is O2
• 2H+ (from FADH2 and NADH)
• 2e- (from FADH2 and NADH)
• ½ O2
H2O!
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!
Fermentation
• Process whereby cells produce ATP without O2
• Alcohol fermentation – pyruvate is converted to
ethanol
• CO2 released
• Lactic acid fermentation – pyruvate is reduced
directly by NADH to form lactate
• No CO2 released