CHAPTER 7: CELLULAR RESPIRATION
 7-1:
Glycolysis + Fermentation
 7-2: Aerobic Respiration
Cellular Respiration
 Most
foods contain usable energy, stored
in complex organic compounds such as:



Proteins
Carbohydrates
Fats
 All
cells break down organic compounds
into simpler molecules, a process that
releases energy to power cellular
activities
Harvesting Chemical Energy
 Cellular

Respiration
Complex process in which cells make ATP by
breaking down organic compounds
• Both autotrophs + heterotrophs undergo cell
respiration
• Some of the energy is used to make ATP; then
energy used by cells to do work
Overview of Cellular Respiration
 Biochemical
pathway with Photosynthesis

Products + Reactants

Redox reactions (‘OILRIG’: e- = energy)
 Equation

C6H12O6 + 6 O2
 Two


Stages:
Glycolysis
Aerobic Respiration
6 CO2 + 6 H2O + NRG
Glycolysis
 Biochemical
pathway in which one 6C molecule of glucose is oxidized to
produce two 3-C molecules of pyruvic
acid



Catalyzed by specific enzymes
Reactions occur within cytosol of cells
Anaerobic process
4 Major Steps of Glycolysis
1.
2.
Two phosphate groups are attached to
one molecule of glucose, forming a new
6-C compound. ATP supplies the
phosphate groups
The 6-C compound splits into 2 3-C
compounds called G3P
Glycolysis (cont.)
The 2 G3P molecules are oxidized and each
receives a phosphate group creating two new
3-C compounds. During the oxidation, NAD+
picks up electrons lost by the oxidation of each
G3P compound (redox) - NADH
4. All phosphate groups are removed which
makes 2 new 3-C compounds called pyruvic
acid. Each phosphate groups is added to ADP
to make four molecules of ATP
3.
Net Yield of NRG?
 Glycolysis
only produces 2 ATP molecules
to be used by the cell from one molecule
of glucose

*Even though 4 ATP are produced at Step
4, 2 ATP were used in Step 1*
Recap of Glycolysis
Video Recap…
 Glycolysis
Fermentation

If oxygen is present after glycolysis, pyruvic acid
enters Aerobic Respiration
In anaerobic conditions, some cells can convert
pyruvic acid into other compounds through
additional biochemical pathways

Glycolysis + additional pathways = Fermentation






Takes place in the cytosol of cells
Does not produce any ATP
Helps regenerate NAD+, which is used throughout
cellular respiration
Differs in enzymes used and compounds made
Two most common: Lactic Acid + Alcoholic
Lactic Acid Fermentation
 Pyruvic
acid converted into lactic acid
 L.A.F. involves the transfer of one H atom
and one free proton (H+)

In the process, NAD+ is regenerated and can
be used again in glycolysis
Lactic Acid Fermentation
L.A.F. (cont.)
 L.A.F.
used by microorganisms in
manufacturing dairy products such as
yogurt and cheese
L.A.F. (cont.)
 L.A.F.
also occurs in your muscle during
strenuous exercise




During this type of exercise, muscle cells use
up O2 much more quickly than it can be
delivered to them
As O2 depletes, aerobic respiration is
changed to L.A.F.
The cytosol more acidic and muscles become
fatigued or sore
Eventually lactic acid gets converted back to
pyruvic acid by the liver
Alcoholic Fermentation
 Pyruvic
CO2
acid converted into ethyl alcohol +
Alc. Fermentation (cont.)
1.
2.
A CO2 molecule is removed from pyruvic
acid, leaving a 2-C compound
Two Hydrogen atoms are added to the 2C compound to form ethyl alcohol
(ethanol)

H atoms transferred from NADH and H+,
regenerating NAD+ for use in glycolysis
Alc. Fermentation (cont.)
Alc. Fermentation (cont.)



AF by yeast cells to make beer +
wine
These microorganisms eat the
SUGAR in fruit or grains which
cause fermentation to take place
AF also used in making bread.
Rises due to loss of CO2
Fermentation (anaerobic pathways)
Efficiency of Glycolysis
Glycolysis alone is only 2% efficient at
extracting energy from glucose
 So where is the rest of the energy?
 PYRUVIC ACID!!!!!!!
 Early Earth + Glycolysis?



Some early unicellular organisms, such as bacteria,
might have been able to survive on using glycolysis
for energy production
Most organisms need more energy (>2 ATP), so
they needed to find a better energy-producing
mechanism
• AEROBIC RESPIRATION!!!