Cellular Respiration
This is the process by which animals process
food to obtain the calories needed for energy
to do the cellular processes necessary for life.
Watch this:
http://youtu.be/Gh2P5CmCC0M
Or this: https://www.youtube.com/watch?v=-Gb2EzF_XqA
Photosynthesis vs Cellular
Respiration
• There is an energy trail: producers
(photosynthesizers) consumers
(animals) decomposers (bacteria)
• A cow eating grass is an example of
a consumer eating a producer
• Photosynthesis is carried out by
plants inside of chloroplasts
(organelle)
Plants vs Animals
• Cellular respiration is carried out in
the mitochondria in animals and
plants
• Plants carry out photosynthesis and
therefore have chloroplasts and
mitochondria
• Besides photosynthesis, they also
must break down their products to
make ATP for cellular processes
Food
• The ultimate source of energy in food
is “the sun”
Cellular Respiration
•
•
•
•
•
•
Includes pathways that require oxygen
Glucose directly provides energy for
cellular work through cellular respiration!
Glucose is oxidized and O2 is reduced
Glucose breakdown is therefore an
oxidation-reduction reaction (redox)
Breakdown of one glucose results in 36 to
38 ATP molecules
THE GOAL IS TO MAKE ATP TO RUN THE
PROCESSES OF OUR CELLS.
Cell Respiration Overview
Glucose:
Stores energy in the molecule
Cell respiration:
• Breaks down the molecules
• Extracts the contained energy
• Transfers electrons (from glucose)
• To electron carriers (e.g., NADH, FADH)
•to make ATP
• Giving off waste products (CO2 & H2O)
1st stage:
Cytoplasm
2nd & 3rd stage:
Mitochondria
Overall Equation for
Cellular Respiration
C6H12O6
+ 6O2
YIELDS
6CO2 + 6H20 + 36-38ATP’s
What Type of Process is
Cellular Respiration?
• An Oxidation-Reduction
Process or REDOX Reaction
• Oxidation of GLUCOSE -->
CO2 + H2O (e- removed from
C6H12O6)
• Reduction O2 to H2O (epassed (added) to O2)
•
Electrons are lost from one substance and added to another substance!
Other Cellular
Respiration Facts
• Metabolic Pathway that breaks
down carbohydrates
• Process is Exergonic as Highenergy Glucose is broken into
CO2 and H2O
• Process is also Catabolic
because larger Glucose breaks
into smaller molecules
What are the Stages of
Cellular Respiration?
• 1. Glycolysis
• 2. The Krebs Cycle
• 3. The Electron Transport Chain
(ETC)
• REMEMBER THESE STEPS!
What this process needs to do is to strip the electrons
off of glucose and eventually use them in the electron
transport chain to create a proton gradient which, when
turned on, allows them to flow through an enzyme
(protein) which attaches a high energy phosphate to
ADP to form ATP.
So steps 1 and 2 are just electron collecting processes.
It does take some work.
Cellular Respiration
Glycolysis
Krebs cycle
Electron transport
Where Does Cellular
Respiration Take Place?
• It actually
takes place
in two parts
of the cell:
Glycolysis occurs
in the Cytoplasm
Krebs Cycle &
ETC Take place in
the Mitochondria
Review of Mitochondria
Structure
• Smooth outer
Membrane
• Folded inner
membrane
• Folds called
Cristae
• Space inside
cristae called
the Matrix
Copyright Cmassengale
In A Nutshell…
Diagram of the
Process
Occurs
across
Cristae
Occurs in
Cytoplasm
Occurs in
Matrix
Copyright Cmassengale
1st stage:
Glycolysis
2nd stage:
3rd stage:
Krebs cycle
(or citric
acid)
Electron
transport
Electrons are the stars!
• If we track the transfer of hydrogen
from sugar to oxygen, we also follow
the transfer of electrons. During
cellular respiration, hydrogen and its
bonding electrons change partners
from sugar to oxygen, forming water
as a product. Energy is also
released.
Glycolysis,
occurs in the cytoplasm
Series of steps (but 2 phases)
1. Glucose
2 pyruvic acid molecules
As bonds in glucose are broken
2. Electrons (and H+ ions)
NAD+
NADH
Glucose
Is oxidized
NAD+
Is reduced
Net output is 2 ATP for each glucose molecule
But, most of the released energy carried by NADH
Steps of Glycolysis
• 1. glucose (6 carbon sugar) is broken into
two 3 carbon molecules which requires 2
ATP
• 2. The 3 carbon molecules donate high
energy electrons to NAD+ forming NADH
(reduction)
• 3. 4 ATP are produced. Net, 2 ATP
• The two 3 carbon molecules are pyruvate
and still hold a lot of energy which will be
harvested in step 2. the Kreb’s cycle (citric
acid cycle)
With or Without Oxygen
aerobic means with oxygen
Glucose
Phase one
2 pyruvic acids
3 carbon
6 carbon
3 carbon
Glycolysis,
phase 1
Some ATP is used to start the ‘breakdown’ of glucose
Mitochondria
Cytoplasm
Glycolysis, phase 2
High energy electrons are donated
To
NAD+
Forming
NADH
Glycolysis, phase 2
And, phosphate groups are transferred
ATP is made
Overall Review of Glycolysis
Notice that two ATPs are used and Four are
yielded, resulting in net 2 ATPs produced.
Glycolysis
Diagram
Glycolysis
Summary
• Also produces 2 NADH and 4
ATP
• Pyruvate is oxidized to Acetyl
CoA and CO2 is removed
In-between glycolysis & Krebs
Just before (or as) they enter the mitochondria
1. Pyruvic acid molecules are modified. It loses one carbon
And CO2 is released
The altered molecule is acetic acid (…vinegar!)
Acetic acid is attached to a carrier molecule
Called coenzyme A one NADH is produced
And forms acetyl CoA
To the mitochondrion
Prep for Citric Acid Cycle
Krebs cycle,
in the mitochondria
Series of reactions
Continues to break down the sugar
Present as acetic acid
Captures more energy
As NADH & FADH2
And more CO2 is released – the first
electron acceptor of cellular respiration is
NAD+
Net output is 2 ATP for each glucose molecule
But again, most of the released energy carried by NADH
A Little Krebs Cycle History
• Discovered by
Hans Krebs in
1937
• He received the
Nobel Prize in
physiology or
medicine in
1953 for his
discovery
• Forced to leave
Germany prior
to WWII
Krebs Cycle
Summary
• Requires Oxygen (Aerobic)
• Cyclical series of oxidation
reactions that give off CO2 and
produce one ATP per cycle
• Turns twice per glucose molecule
• Produces two ATP
• Takes place in matrix of
mitochondria
Krebs Cycle
Summary
• Each turn of the Krebs Cycle
also produces 3NADH,
1FADH2, and 2CO2
• Therefore, For each Glucose
molecule, the Krebs Cycle
produces 6NADH, 2FADH2,
4CO2, and 2ATP
Krebs Cycle
ATP
NETS: 3NADH, 1ATP, 1FADH , & 2CO
What Carries the
Electrons?
• NAD+
(nicotinadenin
e dinucleotide)
acts as the
energy carrier
• NAD+ is a
coenzyme
• It’s Reduced to
NADH when it
picks up two
electrons and
one hydrogen
ion
Are There Any Other
Electron Carriers?
• YES!
Another
Coenzyme!
• FAD+ (Flavin
adenine
dinucleotide)
• Reduced to
FADH2
Electron Transport,
in the mitochondria
Most of the ATP is produced in the ETC
And, NADH & FADH donate their electrons to the ETC
At the end of the chain of steps
O2 exerts a strong pull on electrons
And combines electrons & H+ ions to form H2O
The ‘downhill’ flow of electrons powers an enzyme
ATP synthase
Which produces ~ 34 ATP
Electron Transport
An array of molecules
(…proteins)
In the inner membrane of the mitochondrion
Electrons move from one member to the next
The energy given up pumps H+ to inner space
Mat
rix
Oxygen captures electrons
Hydrogens are added, water forms
The buildup of H+ ions give up energy
When they diffuse through a special protein
Mat
rix
ATP synthase
ATP synthase captures their energy
To make ATP
ATP Synthase
ATP Synthase – actual
protein
Electron Transport Chain
Summary
• 34 ATP Produced
• H2O Produced
• Occurs Across Inner
Mitochondrial membrane
• Uses coenzymes NAD+ and
FAD+ to accept e- from glucose
• NADH = 3 ATP’s
• FADH2 = 2 ATP’s
• Oxygen is eventually reduced by
the electrons to form water!
What would
happen to the flow
of electrons if
oxygen were not
present?
a. The flow of electrons would continue but at a slower rate.
b. The flow would cease and ATP production would stop.
c. The presence of oxygen would have no effect.
Cyanide binds strongly
with the last electron
carrier in the chain.
How would this affect
the flow of electrons?
a. The flow of electrons would continue but at a slower rate.
b. The flow would cease and ATP production would stop.
c. The presence of cyanide would have no effect.
Learning check
1. Of the 3 stages of cell respiration, which
produces the most ATP per glucose?
2. In glycolysis, _______ is oxidized and _______
is reduced.
3. The final electron acceptor of the electron
transport chains in mitochondria is _______.
Learning check
4. Cells can harvest the most chemical energy
from which of the following?
a. An NADH molecule
b. A glucose molecule
c. Six carbon dioxide molecules
d. Two pyruvic acid molecules
Fermentation
 Occurs when O2 NOT present
(anaerobic)
Called Lactic Acid fermentation in
muscle cells (makes muscles tired)
Called Alcoholic fermentation in
yeast (produces ethanol)
Nets only 2 ATP
Learning check
This figure represents an
overview of the different
processes of cellular
respiration.
Which of the following correctly identifies the
different processes?
a) 1. Glycolysis; 2. Electron transport chain; 3. Krebs cycle
b) 1. Glycolysis; 2. Krebs cycle; 3. Electron transport chain
c) 1. Krebs cycle; 2. Electron transport chain; 3. Glycolysis
d) 1. Electron transport chain; 2. Glycolysis; 3. Krebs cycle