Cells How Release
Stored Energy
Chapter 8
ATP Is Universal
Energy Source
Photo synthesizers get energy from the
sun
Animals get energy 2nd or 3rd hand
from plants or other organisms
Regardless, the energy is converted to
the chemical bond energy of ATP
Making ATP
Plants make ATP during photosynthesis
Cells of all organisms
Main Types of
Energy-Releasing Pathways
Anaerobic pathways
Evolved first
Dont require
oxygen
Start w/ glycolysis
in cytoplasm
Completed in
cytoplasm
Aerobic pathways
Evolved later
Require Oxygen
Start w/ glycolysis
in cytoplasm
Completed in
mitochondria
Summary Equation for Aerobic
Respiration
C6H12O6+6O2
6CO2+6H2O
Overview of Aerobic Respiration
glucose
2
ATP
Glycolysis
e- + H+
8 NADH
2 FADH2
e-
ATP
(2 ATP net)
2 pyruvate
2 NADH
2 NADH
*
4
e- + H+
2 CO2
*
e- + H+
e- + H+
Krebs
Cycle
Electron
Transfer
Phosphorylation
*
H+
4 CO2
2
32
ATP
ATP
water
e- + oxygen
Typical Energy Yield: 36 ATP
(cytoplasm)
CCCCCC
glucose
Glycolysis
2 ATP
2CCC
lactate
or
2C CC
pyruvate
2 C C +2 C
ethanol CO2
Fermentation
C 2 CO2
Cellular respiration
CC
2 acetyl CoA
Krebs
cycle
4 C CO2
2 ATP
electron
carriers
Electron
transport chain
H2O
O2
(mitochondrion)
32 or 34 ATP
intermembrane
compartment
Overview of Aerobic Respiration
The Role of Coenzymes
Small molecules associated w/ an enzyme
that participates in enzymatic catalysis
NAD+, FAD, NAD, FADH2 are examples
NAD+ and FAD accept electrons and
hydrogen to become NADH and FADH2
Deliver electrons and hydrogen to the
electron transfer chain
Glucose
A simple sugar
(C6H12O6)
Atoms held
together by
covalent bonds
Glycolysis Occurs
in Two Stages
Energy-requiring steps
ATP energy activates glucose and its 6-carbon
derivatives
Energy-releasing steps
The products of the first part are split into 3carbon pyruvate molecules
ATP and NADH form
Energy-Requiring Steps of Glycolysis
2 ATP invested
Energy-Requiring
Sglucose
teps
ATP
ADP
P
glucose-6-phosphate
P
fructose-6-phosphate
ATP
ADP
P
P
fructose1,6-bisphosphate
P
PGAL
P
PGAL
P
NAD+
Pi
P
PGAL
NADH
P
P
1,3-bisphosphoglycerate
ADP
ATP
P
3-phosphoglycerate
P
ADP
NADH
P
P
1,3-bisphosphoglycerate
2-phosphoglycerate
H2
O
PEP
ATP
pyruvate
PGAL
EnergyADP
ATP
P
Releasing
3-phosphoglycerate
Steps P
2-phosphoglycerate
P
NAD+
Pi
P
ADP
H2
O
PEP
ATP
pyruvate
2 3-carbon sugars
2 NADH
Glycolysis: Net Energy Yield
Energy requiring steps:
- 2 ATP invested
Energy releasing steps
- 2 NADH formed
- 4 ATP formed
Net yield is 2 ATP and 2 NADH
Second Stage Reactions
Preparatory reactions
Pyruvate is oxidized into 3-carbon acetyl
units and CO2
NAD+ is reduced
Krebs cycle
Acetyl units are oxidized to form CO2
Nad+ and FAD are reduced
Preparatory Reactions
pyruvate
coenzyme A (CoA)
NAD+
NADH
O
acetyl-CoA
CoA
O carbon dioxide
=CoA
acetyl-CoA
Krebs
Cycle
CoA
oxaloacetate
citrate
malate
isocitrate
NADH
NAD+
NAD+
H2
O
NADH
FADH2
fumarate
H2
O
H2
O
O
+
phosphate -ketoglutarate
FAD
NAD+
succinate
CoA
NADH
O
succinyl-CoA
ATP
O
ADP group
O
The Krebs Cycle
Overall Reactants
Acetyl-CoA
Overall Products
3 NAD+
FAD
ADP/ Pi
Coenzyme A
2 CO2
3 NADH
FADH 2
ATP
Results of the Second Stage
All of the carbon molecules in pyruvate
end up in CO2
Coenzymes are reduced (they pick up
electrons and hydrogen)
One molecule of ATP forms
Four-carbon oxaloacetate regenerates
Coenzyme Reductions during
First Two Stages
Glycolosis
2 NADH
Preparatory reactions
2 NADH
Krebs cycle
2 FADH2 + 6 NADH
Total
2 FADH2 + 10 NADH
Electron Transfer
Phosphorylation
Occurs in the mitochondria
Coenzymes are responsible for
delivering electrons to electron transfer
chains
Electron transfer sets up H+ ion
gradients
Flow of H+ down gradient powers ATP
formation
Creating a H+ Gradient
OUTER COMPARTMENT
NADH
INNER COMPARTMENT
Making ATP:
Chemiosmotic Model
ATP
INNER
COMPARTMENT
ADP
+
Pi
Importance of Oxygen
Electron transport phosphorylation
requires the presence of oxygen
Oxygen withdraw spent electrons from
electron transfer chain, then combines
w/ H+ to form water
Oxygen is the final electron acceptor
molecule
Summary of Energy Harvest
(per molecule of glucose)
Glycolosis
Krebs cycle and preparatory reactions
2 ATP formed by substrate level
phosphorylation
2 ATP formed by substrate level
phosphorylation
Electron transfer phosphorylation
32 ATP formed
Energy Harvest Varies
NADH formed in cytoplasm cant enter
mitochondrion
It delivers electrons to mitochondrial
membrane
Membrane proteins shuttle electrons to
NAD+ or FAD inside mitochondrion
Electrons given to FAD yield less ATP
than those given to NAD+
Efficiency of
Aerobic Respiration
Efficiency is only 39%
Sounds low but it really is not
Most energy is lost as heat
Anaerobic Pathways
Dont use oxygen
Produces less ATP than aerobic
pathways
Two types
Fermentation pathways
Anaerobic electron transport
Fermentation Pathways
Begins w/ glycolosis
Doesnt break glucose down completely to CO2
and H2O
Yields only the 2 ATP from glycolosis
Steps that follow glycolosis serve to
regenerate NAD+. 2 types are lactate and
Pickles
Kimchi
Anaerobic Electron Transport
Carried out by certain bacteria
Electron transfer chain is in bacterial plasma
membrane
Final electron acceptor is compound from
environment (such as nitrate), not oxygen
ATP yield is low
Evolution of Metabolic
Pathways
When life originated, atmosphere had little
O2
Earliest organisms used anaerobic pathways
Later, non-cyclic pathway of photosynthesis
increased atmospheric oxygen
Cells arose that used oxygen as final acceptor
in electron transport
Processes Are Linked
sunlight energy
PHOTOSYNTHESIS
water
+
carbon
dioxide
sugar
molecules
AEROBIC
RESPIRATION
oxygen