Chapter 9
How Cells Harvest Chemical Energy
Introduction to Cell Metabolism
Glycolysis
Aerobic Cell Respiration
Anaerobic Cell Respiration
Breathing and Cell Respiration are related
O2
BREATHING
CO2
Lungs
CO2
Bloodstream
Muscle cells
O carrying out
2
CELLULAR
RESPIRATION
Sugar + O2  ATP + CO2 + H2O
Cellular Respiration uses oxygen and glucose to produce
Carbon dioxide, water, and ATP.
Glucose
Oxygen gas
Carbon
dioxide
Water
Energy
How efficient is cell respiration?
Energy released
from glucose
(as heat and light)
Energy released
from glucose
banked in ATP
Gasoline energy
converted to
movement
About
40%
25%
100%
Burning glucose
in an experiment
“Burning” glucose
in cellular respiration
Burning gasoline
in an auto engine
Reduction and Oxidation
OILRIG
Oxidation is losing electrons
Reduction is gaining electrons
Loss of hydrogen atoms
Energy
Glucose
Gain of hydrogen atoms
Glucose gives off energy and is oxidized
Reduction and Oxidation
OILRIG
Gain or loss of electrons is often in the form of hydrogen.
The hydrogen is then passed to a coenzyme such as NAD+
Reduction and Oxidation
What are some common co-enzymes?
NAD+ and FAD
NAD+ + 2 H
FAD

+ 2H
Remember that H = 2
NADH

+
H+
FADH2
electrons
and
2H+
Reduction and Oxidation
These co-enzymes are very important for cell
respiration because they transfer high-energy
electrons to electron transport systems (ETS).
Reduction and Oxidation
As the electrons move from carrier to carrier,
energy is released in small quantities.
Electron transport system
(ETS)
Generation of ATP
There are two ways to generate ATP
Chemiosmosis
Substrate-Level Phosphorylation
Generation of ATP
Chemiosmosis
Cells use the energy
released by “falling”
electrons in the ETS to
pump H+ ions across a
membrane
Uses the enzyme ATP
synthase.
Generation of ATP
Chemiosmosis
Generation of ATP
Substrate Level Phosphorylation
Enzyme
ATP can also be
made by transferring
phosphate groups
from organic
molecules to ADP
Adenosine
substrate
Adenosine
product
Figure 6.7B
Generation of ATP
Substrate Level Phosphorylation
Enzyme
ATP can also be
made by transferring
phosphate groups
from organic
molecules to ADP
Adenosine
substrate
Adenosine
product
Figure 6.7B
General Outline
Glucose
Glycolysis
Oxygen
Aerobic
Transition Reaction
Krebs Cycle
ETS
38 ATP
Pyruvic Acid
No Oxygen
Anaerobic
Fermentation
Glycolysis
Where? The cytosol
What? Breaks down glucose to pyruvic acid
Glycolysis
Steps 1 – 3 A fuel
molecule is energized,
using ATP.
Glucose
Step
1
Glucose-6-phosphate
2
Fructose-6-phosphate
3
Energy In: 2 ATP
Fructose-1,6-diphosphate
Step 4 A six-carbon
intermediate splits into
two three-carbon
intermediates.
4
Glyceraldehyde-3-phosphate
(G3P) (TRIOSE PHOSPHATE)
5
Step 5 A redox
reaction generates
NADH.
6
Energy Out: 4 ATP
Steps 6 – 9 ATP
and pyruvic acid
are produced.
1,3-Diphosphoglycerate
(2 molecules)
7
3-Phosphoglycerate
(2 molecules)
8
2-Phosphoglycerate(2
molecules)
2-Phosphoglycerate(2
molecules)
NET 2 ATP
9
Pyruvic acid
(2 molecules
per glucose molecule)
General Outline
Glucose
Glycolysis
Oxygen
Aerobic
Transition Reaction
Krebs Cycle
ETS
36-38 ATP
Pyruvic Acid
No Oxygen
Anaerobic
Fermentation
General Outline of Aerobic Respiration
Glycolysis
Transition Reaction
Krebs Cycle
Electron Transport System
Transition Reaction/Pre-Krebs/Link Reaction:
Occurs in the Matrix
Each pyruvic acid molecule is broken down to form
CO2 and a two-carbon acetyl group, which enters the
Krebs cycle. An Oxidative Decarboxylation Reaction:
Pyruvic Acid
Acetyl CoA
General Outline of Aerobic Respiration
Glycolysis
Transition Reaction
Krebs Cycle
Electron Transport System
Krebs Cycle
Where? In the Mitochondria
What? Uses Acetyl Co-A to generate ATP, NADH,
FADH2, and CO2.
Krebs Cycle
Krebs Cycle
General Outline of Aerobic Respiration
Glycolysis
Krebs Cycle
Electron Transport System
Electron Transport System
Protein
complex
Intermembrane
Electron
space
carrier
Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix
ELECTRON TRANSPORT CHAIN
Figure 6.12
ATP
SYNTHASE
Electron Transport System
CHEMIOSMOSIS
• The coupling of ATP synthesis to electron
transport via a concentration gradient.
• It is the MECHANISM for oxidative
phosphorylation in Aerobic C.R. and
Photosynthesis
Electron Transport System
For each glucose molecule that enters cellular
respiration, chemiosmosis produces up to 38 ATP
molecules
Overview of Aerobic Respiration
General Outline
Glucose
Glycolysis
Oxygen
Aerobic
Transition Reaction
Krebs Cycle
ETS
38 ATP
Pyruvic Acid
No Oxygen
Anaerobic
Fermentation
Fermentation
Requires NADH generated by glycolysis.
Where do you suppose these reactions take place?
Yeast produce carbon dioxide and ethanol
Muscle cells produce lactic acid
Only a 2 ATP are produced per glucose
Fermentation