Download Chapter 9 p. 160-164 and p. 170-172

Chapter 9: p. 160-164 and p. 170-172
Overview of Cell Respiration
- Respiration = 3 metabolic pathways
Pathway
1. Glycolysis
Where it
Happens
cytosol
2. Krebs Cycle
mitochondrial
matrix
3. Electron
Tranport Chain
and oxidative
phosphorylation
mitochondrial
matrix
-
Purpose
Input
Ouput
catabolism of
glucose to 2
pyruvate
decomposes
pyruvate derivative
to CO2
Glucose 
2 NAD+ 
2 ADP + 2 Pi 
2 pyruvate 
2 ADP+2Pi 
6 NAD+ 
2 FAD 
2 pyruvate + 2 H2O
2 NADH + 2H
Net: 2 ATP
4 CO2
2 ATP
6 NADH
2 FADH2
accepts electrons
from steps 1 and 2,
combines with H
ions  H2O and
convert ADP+Pi 
ATP
Glycolysis and Krebs have redox reactions
dehydrogenase transfers electrons from organic/food substrates to NAD+ which forms NADH
2 Mechanisms of Making ATP
- Oxidative Phosphorylation
-powered by redox reactions: transfer electrons from food to O2
- accounts for 90% ATP made via respiration
- Substrate Level Phosphorylation
-enzymatic transfer of phosphate group from organic (catabolized glucose molecules)
 makes ADP
~ For every glucose molecule catabolized  up to 38 ATP
to ADP
Glycolysis oxidizes glucose to pyruvate
-
-
Splits glucose (6C) into two 3-carbon sugar molecules which are then rearranged and oxidized
to 2 pyruvate molecules
Occurs via 10 steps, each catalyzed by a specific enzyme.
2 phases:
- 1. Energy investment phase (ATP used up tp phosphorylate)
- 2. Energy payoff phase
ATP produced by substrate level phosphorylation and NAD+ reduced to NADH.
Glycolysis is anaerobic: BUT with oxygen energy in NADH becomes ATP through Electron
Transport Chain and Oxidative Phosphorylation
Source of ATP + NADH
Net reaction
o glucose  2 pyruvates + 2 H2O
-
o 2ADP + 2Pi  2 ATP
o 2 NAD+  2 NADH + 2H+
Note: all carbons present in glucose still present in pyruvate. Also, glycolysis occurs whether or
not O2 is present.
See Fig 9.9 for exact steps
Krebs cycle Completes energy-yielding oxidation of organic molecules
-
The Krebs Cycle (a.k.a. Citric Acid Cycle) occurs in mitochondrial matrix. Takes derivative of
pyruvate and breaks it down into CO2.
Glycolysis releases less than 25% of chemical energy stored in glucose. Most still stored in 2
molecules of pyruvate.
Krebs cycle completes the energy yielding oxidation stocked in pyruvate
Upon entering mitochondria, pyruvate is first converted to acetylCoA in 3 simultaneous steps
1. carboxyl group of pyruvate removed as CO2, which diffuses out of cell.
2. the 2-carbon molecule is oxidized and NAD+ is reduced to NADH.
3. CoenzymeA (CoA) has S atom, which attaches to acetyl fragment by an unstable bond
(i.e reactive).
-Acetyl CoA then enters the Krebs Cycle.
-
Krebs cycle involves 8 enzymatic steps . See Fig. 9.11
2 carbon molecules enter as a relatively reduced acetylCoA which gets enzymatically added to
oxaloacetate to form citrate (6 carbons)
citrate gets decomposed into oxaloacetate (regenerated) and CO2.
Most energy harvested by oxidation steps of Krebs is conserved as NADH.
For every acetylCoA  3 NADH + 1 FADH2 + 1 ATP are produced.
NADH and FADH2 shuttle electrons into the ETC where ATP is produced by oxidative
phosphorylation.
Fermentation enables some cells to produce ATP without the help of O2
-
When O2 is present, additional ATP is made by oxidative phosphorylation
In anaerobic environments, catabolism of nutrients occurs by fermentation.
Fermentation generates ATP by substrate level phosphorylation as long as there is enough
NAD+ to accept electrons in the oxidative steps of glycolysis.
Fermentation consists of glycolysis + reactions that regenerate NAD+ by transferring electrons
from NADH to pyruvate or derivatives of it  NAD+ oxidizes the sugar (glycolysis)  2 ATP
(substrate phosphorylation )
Alcohol fermentation
pyruvate converted in 2 steps:
pyruvate  acetaldehyde + CO2
2. Acetaldehyde reduced by NADH  ethanol + NAD+
1.
-
Lactic acid fermentation
-
Pyruvate is reduced directly by NADH  lactic acid (No CO2 given off)
Human muscle cells use lactic acid fermentation when oxygen scarce (ie:
strenuous exercise)—ATP produces faster than oxygen is received from blood
Lactate waste causes muscle fatigue/pain
Similarities and Differences: Cellular Respiration vs. Fermentation
CELLULAR RESPIRATION
 aerobic
 Mechanism of oxidizing
NADH to NAD+: final
electron acceptor from
NADH = Oxygen
 ATP Bonus: electron
transport from NADH to
oxygen causes oxidative
phosphorylation
 Krebs Cycle: Big ATP
Payoff – oxidation of
pyruvate
 38 ATP per glucose
molecule
SIMILIARITIES
 -produce ATP from
chem. energy of
food
 -use glycolysis to
oxidize glucose to
pyruvate
 -net production of
2 ATP by substrate
level
phosphorylation
 -NAD+ is oxidizing
agent during
glycolysis
FERMENTATION
 -anaerobic
 -Mechanism of of oxidizing
NADH to NAD+: final electron
acceptor = organic molecule
like…
 pyruvate(lactic acid) or
acetaldehyde(alcohol)

No ATP Bonus

No Krebs Cycle

2 ATP per glucose molecule
(substrate level
phosphorylation)
Facultative Anaerobes- organisms that make enough ATP to survive using fermentation or
respiration
-Aerobic conditions: pyruvate  acetyl CoA  oxidation in Krebs cycle
-Anaerobic conditions: pyruvate as electron acceptor  NAD+ recycled
Evolutionary Significance of Glycolysis
-ancient prokaryotes used glycolysis to make ATP before Oxygen was in Earth’s atmosphere
-1st prokaryotes ATP via glycolysis ONLY (no Oxygen necessary)
-Glycolysis = OLD!!! because …1) most wide spread metabolic pathway 2)cytosolic location