Cellular Respiration and
Fermentation
Review

The purpose of photosynthesis is to take
kinetic light energy and convert it into
potential chemical energy in the form of
GLUCOSE

In order to build glucose, low energy CO2 and
H20 molecules are built up using light energy.
Chloroplasts 
fix carbon
which requires
energy input
Mitochondria 
release energy
from organic
molecules
Cellular Respiration
Goal – To BREAK DOWN glucose and use energy
to produce ATP

Can happen WITH oxygen present  Aerobic

Can happen WITHOUT oxygen present 
Anaerobic
Two Routes an organism can release
energy

Fermentation (aka anaerobic respiration)




Aerobic Cellular Respiration




Takes place entirely in the cytoplasm (no mitochondria
necessary)
Only nets 2 ATP (inefficient) per glucose
No oxygen necessary!
Takes place mostly in mitochondria
Nets 36 ATP per glucose
Oxygen necessary!
Either way, both start with the same process,
Glycolysis, which means “glucose splitting”
Overview of Cell Respiration and
Fermentation
Glucose
Glycolysis
Krebs
cycle
Fermentation
(without oxygen)
IT ALL STARTS WITH GLYCOLYSIS!!!!
Electron
transport
Alcohol or
lactic acid
Glycolysis
Glucose
To the electron
transport chain
Glycolysis Summary
• One molecule of glucose split in half  two
molecules of pyruvic acid
• Uses 2 ATP to start the process but gets 4 ATP
back in the end. (Net 2 ATP!)
• 4 high energy electrons are removed from the
carbon compounds and passed to an electron
carrier
– 2 NAD+  2 NADH
– Electrons carriers will take high energy electrons to
the electron transport chain for later use!
What happens after glycolysis?
• Depends on who you are and what your oxygen
availability is.
• In order to move forward with cell respiration, you
must have the following;
– Mitochondria
– Available Oxygen
• If an organism does not have one or more of these,
big problem as all available NAD+ molecules will be
used-up. Without available NAD+, glycolysis shuts
down and now not even 2 ATP generated from
glucose via glycolysis
• Enter fermentation AKA anaerobic respiration.
Fermentation
• Release of energy from food molecules in
the absence of oxygen
• AKA: Anaerobic respiration
– Two forms:
• Alcoholic fermentation
• Lactic acid fermentation
– NADH reverts back to NAD+ in both types by
dropping back off their electrons and H ions.
– With NAD+ freed up again, ATP production
can continue via glycolysis
Lactic Acid Fermentation

Occurs in many cells


Both eukaryotic and prokaryotic
Pyruvic acid + NADH  lactic acid + NAD+

In foods, production of acid results in characteristic
flavors of cheeses and yogurt

This is what happens in our muscles when we exercise
heavily “feel the burn”
Lactic Acid Fermentation

Point of this happening is so the NADH can
go back to NAD+ and keep glycolysis going!
Glucose
Pyruvic acid
Lactic acid
Alcoholic Fermentation

Occurs in yeast and a few other
microorganisms

Pyruvic acid + NADH  alcohol + CO2 +
NAD+


Bread dough rising
Wine and Beer fermentation
Alcohol Fermentation
(same as pyruvate)
Uses – producing alcohol
Uses – producing CO2 Bubbles
3 Possible Pathways
Fermentation
Aerobic Cellular
Respiration
Aerobic Cellular Respiration
THE PROCESS BY WHICH CELLS UTILIZE
OXYGEN TO BREAK DOWN ORGANIC
MOLECULES INTO WASTE PRODUCTS,
WITH THE RELEASE OF ENERGY THAT
CAN BE USED FOR BIOLOGICAL WORK.
Using energy from glucose into ATP!
Equation
6O2 + C6H1206  6CO2 + 6H20 + Energy (ATP)
Cellular Respiration - 3 Main Steps

1.Glycolysis (same process as in fermentation)



2. Krebs Cycle



Occurs in cytoplasm of cell
Net 2 ATP per glucose
Occurs in mitochondria
Net 2 ATP per glucose
3. Electron Transport Chain


Occurs in mitochondria
Net 32 ATP per glucose
Cellular Respiration
Glucose
(C6H1206)
+
Oxygen
(02)
Glycolysis
Krebs
Cycle
Electron
Transport
Chain
Carbon
Dioxide
(CO2)
+
Water
(H2O)
Cellular Respiration
Electrons carried in NADH
Pyruvic
acid
Glucose
Glycolysis
Krebs
Cycle
Electrons
carried in
NADH and
FADH2
Electron
Transport
Chain
Mitochondrion
Cytoplasm
Overview of Aerobic Respiration
2
2
32
Glucose
Glycolysis
2 NADH
Acetyl
CoA
2 NADH
Krebs
cycle
6 NADH
Electron
transport
2 FADH2
Fermentation
(without oxygen)
Alcohol or
lactic acid
After Glycolysis…….

With free 02 and mitochondria, a cell can
release even more energy from pyruvic acid.


Only 10% of total energy of glucose released in
glycolysis!
We already know how glycolysis “splits” a
glucose molecule into 2 pyruvic acid, so lets
pick up with what happens AFTER glycolysis
Structure of the Mitochondria
•
•
•
•
Outer membrane
Inner membrane
Inter-membrane space
Cristae
– Projections of the inner membrane
– Contain the enzymes of the ETS, ATP synthase
• Matrix
– Inside area of the mitochondria
• Cells can contain 10 – 1000s of Mitochondria
Kreb’s Cycle

Big Picture



Further break-down of pyruvic acid molecules
into CO2 via series of energy releasing reactions.
Energy which is released is used to generate ATP
(one per pyruvic acid molecule)
Electrons released during cycles used to make;



NAD+  NADH
FAD  FADH2
Will be used later in electron transport (check to be
cashed!)
Before Pyruvic Acid enters the
Kreb’s cycle, it get modified;
• Carbon removed  C02
• Electrons removed  NADH
• Coenzyme A joins the remaining 2-carbon
molecule  acetyl-CoA
• Acetyl-CoA joins up with a 4-carbon compound
already in the cycle and forms………… Citric Acid
(6 carbon molecule)!
• Equation:
– Pyruvic acid  Acetyl Co A + CO2 + NADH
• Entry into Krebs Cycle
– Acetyl CoA + 4-C (oxaloacetate)  Citric Acid (6-C)
Kreb’s Cycle (aka Citric Acid Cycle
Citric Acid
Production
Mitochondrion
IMPORTANT!
This cycle is
repeated twice for
each glucose
molecule!
Results of Krebs Cycle
• Per Glucose molecule (2 cycles)
– 2 ATP
– 6 NADH  To electron transport chain
– 2 FADH2  To electron transport chain
– 6 CO2 (waste product) (4 in Krebs 2 in shuttle
step)
– Also, 2 NADH were generated just before
Kreb’s Cyles started when pyruvic acid was
converted to Acetyl-CoA!
Electron Transport

Big Idea


All those high energy electrons which have been
saved-up until now can be “cashed-in” for some
big ATP gains!
Electron transport links the movement of
these high-energy electrons with the
formation of ATP!
Electron Transport


Electrons passes along an “electron transport
chain”
Prokaryotes


Chain is a series of carrier proteins on cell
membrane
Eukaryotes (one we really care about)

Chain is a series of carrier proteins located on
inner membrane of mitochondria.
Electron Transport



High Energy electrons passed along transport
chain
At end of chain, electrons passed to H+ and
Oxygen to form H20. Oxygen is final electron
acceptor
Oxygen is important for the main reason that
it accepts the low energy electrons and
hydrogen ions which are wastes of cellular
respiration!
Electron Transport and ATP
production





The movement of electrons down transport chain is
coupled to the movement of hydrogen ions across
inner membrane into the intermembrane space
Hydrogen ion gradient established
Special transport proteins along inner membrane
called ATP synthases.
As hydrogen moves through ATP synthase, ADP
and P joined to form ATP!
CALLED CHEMIOSMOSIS
Electron Transport Chain
Electron Transport
Hydrogen Ion Movement
Channel
ATP synthase
ATP Production
The importance of oxygen
• Must be present to accept electrons and protons
of hydrogen. Becomes WATER!
• Krebs and ETS cannot function without O2
• Photosynthesis and respiration
– Products of Photosynth. are the raw materials for
cellular respiration and vice versa
– Both utilize ETS
– Krebs and Calvin are similar, both involve
rearrangements of carbon compounds
– Krebs forms ATP, NADH and FADH2 while Calvin
uses ATP and NADPH
Grand Totals  Net 36 ATP per glucose
38% efficiency
Exceeds efficiency of
gas combustion in a
car.
Totals:
Step
ATP
NAD
H
Glycolysis
2 (net)
2*
Prep Step
0
Krebs Cycle 2
2
6
FADH2 Total ATP
(net)
0
6
2
6
24
*energy is expended to get NADH (glycolysis) to ETS
Only 2 ATP per NADH from glycolysis
3 ATP per NADH (prep and Krebs); 2 ATP per FADH2
Energy and Exercise

Quick energy


ATP contained in muscles used in a few seconds
After that:

Anaerobic (weight lifting, sprinting – high ATP
demands short term)



Most ATP through lactic acid fermentation (90
seconds)
Lots of oxygen required to get rid of buildup (oxygen
dept)
Sore muscles – caused by tissue damage
(cont.)

Aerobic (jogging, light weights, - med ATP
demands long term)

First use ATP/glucose in blood

Glycogen


Lasts for 15-20 minutes
Body breaks down fats after that