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Cellular Respiration:
Energy for Life!
A. Introduction


Living is work.
To perform their many
tasks, cells require
transfusions of energy
from outside sources.


In most ecosystems,
energy enters as
sunlight which is
trapped and converted
to organic molecules by
photosynthesis.
Respiration converts
the energy of organic
molecules into usable
energy (ATP).



There are two types of metabolic pathways
that release the energy stored in complex
organic molecules:
Fermentation (aka anaerobic
respiration), leads to the partial
breakdown of sugars in the absence of
oxygen. Occurs in the cytoplasm.
A more efficient and widespread catabolic
process, cellular respiration (aka
aerobic respiration) uses oxygen as a
reactant to complete the breakdown of a
variety of organic molecules.

Most of the processes in cellular respiration
occur in mitochondria.
Comparing Fermentation and
Aerobic Cellular Respiration
Fermentation
Aerobic Cellular
Respiration
Use
oxygen?
No
Level of
breakdown
of sugar?
Partial
- Less efficent
Complete
- More efficient
Location in
cell?
Cytoplasm
Cytoplasm &
Mitochondria
Yes


Cellular respiration is similar to the
combustion of gasoline in an
automobile engine.
The overall process is:


Carbohydrates, fats, and proteins can all be
used as the fuel, but it is traditional to start
learning with glucose.


Organic compounds + O2 -> CO2 + H2O + Energy
C6H12O6 + 6O2 -> 6CO2 + 6H2O + Energy (ATP +
heat)
The catabolism of glucose is exergonic with a
delta G of - 686 kcal per mole of glucose.

Some of this energy is used to produce ATP that
will perform cellular work.
B. ATP powers cellular work !

A cell does three main kinds of work:




Mechanical work, beating of cilia, contraction
of muscle cells, and movement of chromosomes
Transport work, pumping substances across
membranes against the gradient (ie.
Na+K+pump)
Chemical work, driving reactions like
dehydration synthesis of DNA, RNA and proteins.
In most cases, the immediate source of
energy that powers cellular work is ATP.

The transfer of the terminal
phosphate group from ATP to another
molecule is called phosphorylation.
 This changes the shape of the
receiving molecule, performing
work (transport, mechanical, or
chemical).
 When the phosphate groups leaves
the molecule, the molecule returns
to its alternate shape.

ATP (adenosine triphosphate) is a type
of nucleotide consisting of the nitrogenous
base adenine, the sugar ribose, and a chain
of three phosphate groups.
What does ATP look likesimply…
PO4-
PO4-
PO4-
ribose
high-energy bonds
adenine base

The bonds between phosphate groups
can be broken by hydrolysis.

Hydrolysis of the end phosphate group forms
adenosine diphosphate [ATP -> ADP + Pi] and
releases 7.3 kcal of energy per mole of ATP
under standard conditions.

ATP is a renewable resource that is
continually regenerated by adding a
phosphate group to ADP.

In a working muscle cell the entire pool of ATP
is recycled once each minute, over 10 million
ATP consumed and regenerated per second
per cell.
C. Cells recycle the ATP they
use for work



ATP, adenosine triphosphate, is the chemical
equivalent of a loaded spring.
 The close packing of three negatively-charged
phosphate groups is an unstable, energy-storing
arrangement.
 Loss of the end phosphate group “relaxes” the
“spring”.
The price of most cellular work is the conversion of
ATP to ADP and inorganic phosphate (Pi).
An animal cell regenerates ATP from ADP and Pi by
the catabolism of organic molecules like glucose.
Click here for animation
D. Respiration is a “redox” reaction


Respiratory pathways relocate the electrons
stored in food molecules, releasing energy
that is used to synthesize ATP.
Reactions that result in the transfer of one or
more electrons from one reactant to another
are oxidation-reduction reactions, or redox
reactions.


The loss of electrons is called oxidation.
The addition of electrons is called reduction.
“Redox” can be defined in
many ways…
Reduction Oxidation
Electrons
Gain of
electrons
Loss of
electrons
Hydrogen
Gain of
hydrogen
Loss of
hydrogen
Oxygen
Loss of
oxygen
Gain of
oxygen
Energy?
Storage of
energy
Release of
energy
Remember:
GER!!
GER!!!
“LEO” the lion says
“GER”
Lost electrons
means oxidized
Gained electrons
means reduced
E. Electrons get transferred from organic
molecules to oxygen during cellular respiration



In cellular respiration, glucose and
other fuel molecules are oxidized,
releasing energy.
In the summary equation of cellular
respiration:
C6H12O6 + 6O2 + 6 H2O-> 6CO2 +
12H2O + 36 ATP
Glucose is oxidized, oxygen is reduced,
and electrons lose potential energy.
F. NAD and FAD are important electron
carrier molecules in respiration.

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Cellular respiration does not oxidize glucose
in a single step.
Rather, glucose and other organic molecules
are broken down gradually in a series of
steps, each catalyzed by a specific enzyme.
At key steps, hydrogen atoms are stripped
from glucose and passed first to a coenzyme,
like NAD+ (nicotinamide adenine
dinucleotide).
• This changes the oxidized form, NAD+, to the
reduced form NADH.
•NAD + functions as the oxidizing agent in
many of the redox steps during the
breakdown of glucose.
Glucose  NADH and FADH2  O2
Therefore, NADH which is reduced
is a temporary electron-energy
storage molecule.
 FADH2 is another reduced
coenzyme.
 This energy is tapped to
synthesize ATP as electrons “fall”
from NADH to oxygen.



Cellular respiration uses an electron
transport chain to break the fall of
electrons to O2 into several steps.
Otherwise, if all of the energy were
released from glucose at once, the cell
would explode!
G. Respiration -an overview

Respiration occurs in five metabolic
stages:
1.
2.
3.
4.
5.
Glycolysis
The oxidation of pyruvic acid to acetyl
CoA (The Link Reaction)
The Krebs-citric acid cycle
The electron transport chain
The chemiosmotic synthesis of ATP.
H. Glycolysis is the first stage of any kind
of respiration (both anerobic and
aerobic)

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During glycolysis, glucose, a six carbonsugar, is split into two, three-carbon
sugars.(Lysis means to split)
These smaller sugars are oxidized and
rearranged to form two molecules of
pyruvate.(3 carbons compounds)
Each of the ten steps in glycolysis is
catalyzed by a specific enzyme.

In the energy investment phase, ATP
provides activation energy by
phosphorylating glucose.



This requires 2 ATP per glucose.
In the energy payoff phase, ATP is
produced by substrate-level
phosphorylation and NAD+ is
reduced to NADH.
2 ATP (net) and 2 NADH are produced
per glucose.
• The ATP produced in
glycolysis is an example
of substrate-level
phosphorylation.
•Here, an enzyme
transfers a phosphate
group from an organic
molecule
(the substrate) directly
to ADP, forming
ATP.
What Do You Really Need to Remember
About Glycolysis?


The process starts with 1 glucose.
The net yield from glycolysis is 2 ATP
and 2 NADH per glucose.



No CO2 is produced during glycolysis.
Glycolysis occurs whether O2 is
present or not.
Glycolysis takes place in the
cytoplasm of the cells (this makes
sense since all cells have cytoplasm)
I. Types of Cellular Respiration


Cellular respiration can occur in the
presence or absence of OXYGEN (O2)
With oxygen =
Without oxygen =
AEROBIC
ANAEROBIC
Overall reaction for aerobic respiration
C6H12O6

+ 6 O + 12 H2O
2
6 CO2 + 6 H2O + energy
NOTE: the reverse of this equation is the
equation for PHOTOSYNTHESIS
Which came first: aerobic or anaerobic
respiration?

ANAEROBIC- starting with
glycolysis
 Why?

Because there was no free oxygen present in
the early earth’s atmosphere when organisms
first evolved.
FREE
OXYGEN
AEROBIC & ANAEROBIC RESPIRATION
ANAEROBIC PHASE
AEROBIC PHASE
2 ATP
GLUCOSE
(C6H12O6)
2 ADP
Glycolysis2 NAD+
4 ADP
2 NADH
4 ATP
O2
2 PYRUVIC ACID
( 2 C3H4O3 )
2NAD+
2 ALCOHOL +2 CO2
( 2 C2H3OH +2CO2)
CO2 + H2O
2NAD+
2 LACTIC ACID
( 2 CH3CHOHCOOH)
34 ADP
Anaerobic net gain = 2 ATP
 Aerobic overall net gain = 36 ATP

34 ATP
AEROBIC & ANAEROBIC RESPIRATION


GLYCOLYSIS (glucose  pyruvic
acid (a.k.a. pyruvate)) IN CYTOSOL
Pyruvate can then pass through
three different pathways:
ANAEROBIC



alcoholic fermentation (in cytosol)
PROCESSES
lactic acid fermentation (in cytosol)
oxidation of pyruvate followed by Krebs cycle
(in matrix of mitochondria) and the electron
transport chain (in inner membrane of
mitochondria)
AEROBIC PROCESS
J.Fermentation enables some cells to
produce ATP without the help of oxygen
In glycolysis, glucose is oxidized to
two pyruvate molecules with NAD+ as
the oxidizing agent, not O2.
 Some energy from this oxidation
produces 2 ATP (net).
Glycolysis generates 2 ATP whether
oxygen is present (aerobic) or not
(anaerobic).

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
Fermentation can generate ATP from
glucose by substrate-level
phosphorylation as long as there is a
supply of NAD+ to accept electrons.
Under anaerobic conditions, various
fermentation pathways generate ATP
by glycolysis and recycle NAD+ by
transferring electrons from NADH to
pyruvate.
Why anaerobic?



When a short burst of ATP is
needed
When oxygen supplies run out in
respiring cells
In environments that are deficient
in oxygen, such as water-logged
soils.

In alcohol fermentation, pyruvate is
converted to ethanol in two steps.
1. Pyruvate is
converted to a
two-carbon
compound,
acetaldehyde, by
the removal of
CO2.
2. Acetaldehyde is
reduced by NADH
to ethanol.
1
2
Alcohol fermentation by yeast is
used in brewing and baking
industries.
Fermentation tanks
producing wine
Bioethanol is a renewable source of
energy using alcoholic fermentation
Pros and Cons of Biofuels?
Positive effect of biofuels
May limit greenhouse
gases compared to burning
petrol sources
(considered carbon neutral
since carbon made and
carbon used is about equal)

May reduce dependence on
foreign sources of fuel

Renewable source of
energy unlike burning
fossil fuels

Negative effect of biofuels




Certain sources of biofuels
can be costly to grow
Growing sources could put
pressure on local water
supplies
Using corn or soybeans for
fuel could put pressure on
food supply availability
Consequences of growing
biofuel plants 
deforestation and use of
fertilizers may hurt the
ecosystem

During lactic acid fermentation,
pyruvate is reduced directly by NADH
to form lactate (ionized form of lactic
acid).


Lactic acid fermentation by some fungi
and bacteria is used to make cheese and
yogurt.
Muscle cells switch from aerobic
respiration to lactic acid fermentation to
generate ATP when O2 is scarce.
 The waste product, lactate, may cause
muscle fatigue, but ultimately it is
converted back to pyruvate in the liver.
Products of lactic acid
fermentation


REVIEW:
Fermentation and cellular respiration
are anaerobic and aerobic
alternatives, respectively, for
producing ATP from sugars.



Both use glycolysis to oxidize sugars to
pyruvate with a net production of 2 ATP
by substrate-level phosphorylation.
Both use NAD+ as an electron acceptor.
In fermentation, the electrons of
NADH are passed to an organic
molecule, regenerating NAD+.
Q: Has NADH been oxidized or reduced? OXIDIZED



In respiration, the electrons of NADH
are ultimately passed to O2,
generating ATP
In addition, even more ATP is
generated from the oxidation of
pyruvate in the Krebs cycle (net
gain=36 ATP)
Without oxygen, the energy still
stored in pyruvate is unavailable to
the cell (Only 2 ATP are made from
glycolysis pathway)

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Some organisms (facultative
anaerobes), including yeast and many
bacteria, can survive using either
fermentation or respiration.
At a cellular level, human muscle cells
can behave as facultative anaerobes,
but nerve cells cannot.
For facultative anaerobes, pyruvate is
a fork in the metabolic road that leads
to two alternative routes.
Review
1.
2.
3.
4.
5.
What waste products do yeast make as a
result of fermentation?
What happens when our muscles are low
in oxygen?
Why do anaerobes need to continue
reactions beyond glycolysis when all of
their ATP that they can make has already
been produced?
What is the net gain of ATP as a result of
lactic acid and alcoholic fermentation?
Why are anaerobes not able to produce
as much ATP as aerobes?
If O2 is present, pyruvate moves to the

Krebs cycle and the energy stored
in NADH can be converted to ATP
by the electron transport system
and oxidative phosphorylation.
K. Stage 2 of Aerobic Respiration:
Oxidation of Pyruvic Acid- The Link
Reaction



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More than three quarters of the original
energy in glucose is still present in two
molecules of pyruvate.
If oxygen is present, pyruvate enters the
aerobic pathway in the mitochondria in
eukaryotes where the oxidation of the
organic fuel to carbon dioxide occurs.
Note: some aerobic bacteria exist. Which organelle
in prokaryotes takes the place of the mitochondria?
ANSWER: The plasma membrane is used for the
necessary enzymatic reactions (ETC)
As pyruvate enters the mitochondrion,
pyruvate is converted to acetyl CoA
which enters the Krebs cycle in the
matrix.



Carboxyl group is
removed as CO2.
A pair of electrons is
transferred from the
remaining two-carbon
fragment to NAD+ to
form NADH.
The oxidized fragment
combines with
coenzyme A to form
acetyl CoA.
What is important to remember about
this stage? Per glucose,
Two 3-carbon pyruvate molecules are the
reactants and are converted to acetyl
compounds.
 2 acetyl-CoA (coenzyme A) molecules are
formed
(two 2 carbon compounds)
 2 carbon dioxide molecules are formed since
pyruvate is decarboxylated.
(How many more are yet to come?)
 2 NADH molecules are formed since pyruvate
is oxidized. (How many so far is that?)

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L. STAGE 3- THE KREBS/CITRIC ACID
CYCLE:
The Krebs cycle is named after Hans Krebs who
was largely responsible for elucidating its
pathways in the 1930’s.
Acetyl-CoA (2 carbon molecule) is the starting
point of the cycle.
Overview of cycle:
Oxidation of acetyl-CoA is coupled with the
reduction of electron carrier molecules, NADH
FADH2
Decarboxylation which liberates carbon dioxide
The production of ATP (substrate-level
phosphorylation.
animation
This cycle begins when acetate from
acetyl CoA combines with oxaloacetate
(OAA) to form citrate.


Ultimately, the oxaloacetate is recycled.
Each cycle produces one ATP by
substrate-level phosphorylation, two
carbon dioxides, three NADH, and one
FADH2 (another electron carrier) per
acetyl CoA.

Since there are 2 acetyl-CoA molecules
produced from stage 2, there are two
turns of the Krebs cycle which doubles the
numbers of the products made.



The conversion
of pyruvate and
the Krebs cycle
produces large
quantities of
electron carriers.
How many do
we have at this
point per
glucose?
NADH? FADH2?

8 from pyruvate
oxidation & Krebs
2 from Krebs
What do you really need to
remember about the Krebs
cycle?





2 acetyl Co-A are the initial reactants
The cycle begins when a 2-carbon
acetyl-CoA joins with a 4 carbon
oxaloacetic acid to form a 6 carbon
citrate.
There are two “spins” of the cycle per
original glucose molecule
With 2 turns…4 carbon dioxide
molecules, 2 ATP, 6 NADH and 2FADH
are made!
The cycle occurs in the mitochondrial
matrix
Draw a picture of the mitochondria and
label where the Krebs Cycle occurs
M. Oxidative Phosphorylation includes
The Electron Transport Chain and
Chemiosmosis



Only 4 of 36 ATP ultimately produced
by respiration of glucose are derived
from substrate-level phosphorylation.
The vast majority of the ATP comes
from the energy in the electrons carried
by NADH and FADH2.
The energy in these electrons is used in
the electron transport system to power
ATP synthesis.
What does oxidative
phosphorylation mean?



The final stages of aerobic respiration:
including the electron transport chain
and the chemiosmosis of ATP. (coupled
reactions)
This is where the most amount of ADP is
phosphorylated to ATP (the phosphate
is added back on to ATP)
Oxygen is used to accept electrons from
NADH and FADH2 in this process.
N. Stage 4 –
The Electron
Transport Chain
• As hydrogens come off
of NADH and FADH2,
these molecules become
oxidized.
• The electrons from
hydrogen travel down a
chain of electron carrier
molecules like “HOT
POTATO”.
• Oxygen has diffused
into the matrix and
accepts the electrons
The ETC
takes place
on the cristae
(inner
membrane)
Role of Oxygen in the ETC?
•
•
Oxygen is the final acceptor of
electron on the ETC
Oxygen is needed to bind with
the free protons in the
mitochondrial matrix to
maintain the hydrogen
gradient, resulting in the
formation of water.

Thousands of copies of the electron
transport chain are found in the
extensive surface of the cristae, the
inner membrane of the
mitochondrion.


Most components of the chain are
proteins that can alternate between
reduced and oxidized states as they
accept and donate electrons.
Electrons drop in free energy as they
pass down the electron transport
chain.
animation
animation


Electrons carried by NADH are
transferred to the first molecule in the
electron transport chain, flavoprotein.
 The electrons continue along the
chain which includes several
cytochrome proteins and one lipid
carrier.
The electrons carried by FADH2 have
lower free energy and are added to a
later point in the chain.


Electrons from NADH or FADH2
ultimately pass to oxygen.
 For every two electron carriers (four
electrons), one O2 molecule is
reduced to two molecules of water.
The electron transport chain
generates no ATP directly but aids in
the chemiosmotic synthesis of ATP.

A protein complex,
ATP synthase, in the
cristae actually
makes ATP from ADP
and Pi.


H+ ions are pumped
into the
intermembrane space
of the mitochondria as
the electron transport
chain occurs. These
come from NADH and
FADH2 hydrogens.
This creates a proton
gradient on either side
of the cristae.
animation

The proton gradient is produced by
the movement of electrons along the
electron transport chain.
+ in the
 This high concentration of H
intermembranal space sets up
facilitated diffusion along the F1
complex (ATP synthase)
 The energy from this diffusion
process allows ADP to gain a
phosphate to form ATP.




The ATP synthase molecules are
the only place that will allow H+
to diffuse back to the matrix.
This exergonic flow of H+ is used
by the enzyme to generate ATP.
32 more ATP molecules are
formed from this phase of
respiration.
This coupling of the redox
reactions of the electron
transport chain to ATP synthesis
is called chemiosmosis.

The mechanism of
ATP generation by
ATP synthase is still
an area of active
investigation.
movie

Chemiosmosis is an energy-coupling
mechanism that uses energy stored in
the form of an H+ gradient across a
membrane to drive cellular work.



In the mitochondrion, chemiosmosis
generates ATP.
Chemiosmosis in chloroplasts also
generates ATP, but it’s used to power the
production of food.
Prokaryotes generate H+ gradients across
their plasma membrane since they don’t
have mitochondria.
A Closer Look at Mitochondria Structure


Sketch a mitochondria labeling all
structures seen in an electron
micrograph.
Annotate your drawing by
describing which reactions of the
aerobic pathway occur in each
section of your drawing.
Structure vs. Function?



Highly infolded cristae allows for more
surface area for reactions (ETC) to occur
to generate maximum ATP
Compartmentalization of organelle
(matrix vs. intermembranal space)
allows for proton gradient to be
established which is key to making ATP
Matrix is fluid filled area for reactions to
occur (e.g. Krebs) and where many
enzymes are stored.
P. Cellular respiration generates many
ATP molecules for each sugar molecule
it oxidizes: a review



During respiration, most energy flows from
glucose -> NADH & FADH2-> electron
transport chain and proton-gradient -> ATP.
Considering the fate of carbon, one sixcarbon glucose molecule is oxidized to six
CO2 molecules.
Some ATP is produced by substrate-level
phosphorylation during glycolysis and the
Krebs cycle, but most comes from oxidative
phosphorylation.
Click here for a cool rap on
respiration
animation



Each NADH from the Krebs cycle and
the conversion of pyruvate
contributes enough energy to
generate a maximum of 3 ATP
(rounding up).
Each FADH2 from the Krebs cycle can
be used to generate about 2ATP.
In some eukaryotic cells, NADH
produced in the cytosol by glycolysis
may be worth only 2 ATP.

The electrons must be shuttled to the
mitochondrion.



34 ATP are produced by oxidative
phosphorylation
This plus the 4 ATP (total) from
substrate-level phosphorylation gives
a bottom line of 38 ATP
Considering 2 ATP are put in for
activation energy during glycolysis,
the total ATP made aerobically is
36 ATP
Animation on the mitochondria in
action- by Biovisions

How efficient is respiration in
generating ATP?

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
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
Complete oxidation of glucose releases
686 kcal per mole.
Formation of each ATP requires at least
7.3 kcal/mole.
Efficiency of respiration is 7.3 kcal/mole
x 38 ATP/glucose/686 kcal/mole glucose
= 40%.
The other approximately 60% is lost as
heat.
Cellular respiration is remarkably
efficient in energy conversion.
Q.Body temperature and
Metabolic Rate



Most of the energy from glucose is
released as heat. What do animals do
with this heat?
Cold-blooded (aka ectothermic or
poikilothermic) animals cannot retain
this heat. Their body temperature
fluctuates with the environmental
temperature.
Warm-blooded (aka endothermic or
homeothermic) animals retain part of
this heat to regulate their internal body
temperatures.
•
•
What does this
graph show
about
homeotherms
& ectotherms?
How would the
metabolic rate
compare in
each at
different
temperatures?
How do poikilotherms regulate
their body temperatures?




These organisms must adapt to changes
in temperature by changing their
position, body orientation, location or
time of day that they are active.
For example, butterflies vibrate their
wings to increase muscle temperature
needed for flying.
Turtles bask in the sun to warm up on a
hot day.
Desert animals may be nocturnal to
avoid extreme daily temperatures.
How do Homeotherms regulate
their body temperature?


Mammals and birds are the only two
groups of homeotherms.
To maintain a constant body
temperature, these animals have
adaptations like having effective
insulation (ie. fat, fur, feathers), having
the ability to shunt blood towards or
away from blood vessels, shivering,
sweating or panting.
Metabolic rate is inversely
proportional to body size



In homeotherms, smaller animals have
greater surface-to-volume ratios and
therefore larger heat loss.
These animals must oxidize food at a
high rate and have a greater
metabolism to survive.
Shrews must eat constantly to stay alive
while an elephant may eat a meal
periodically throughout the day.
R. Glycolysis and the Krebs cycle connect
to many other metabolic pathways

Glycolysis can accept a wide range of
carbohydrates.



Polysaccharides, like starch or glycogen,
can be hydrolyzed to glucose monomers
that enter glycolysis.
Other hexose sugars, like galactose and
fructose, can also be modified to undergo
glycolysis.
The other two major fuels, proteins and
fats, can also enter the respiratory
pathways, including glycolysis and the
Krebs cycle, used by carbohydrates.


Proteins must first be digested to
individual amino acids.
Amino acids that will be catabolized
must have their amino groups
removed via deamination.


The nitrogenous waste is excreted as
ammonia, urea, or another waste
product.
The carbon skeletons are modified by
enzymes and enter as intermediaries
into glycolysis or the Krebs cycle
depending on their structure.



The energy of fats can also be accessed via
catabolic pathways.
Fats must be digested to glycerol and fatty
acids.
 Glycerol can be converted to
glyceraldehyde phosphate, an
intermediate of glycolysis.
 The rich energy of fatty acids is accessed
as fatty acids are split into two-carbon
fragments.
 These molecules enter the Krebs cycle as
acetyl CoA.
In fact, a gram of fat will generate twice as
much ATP as a gram of carbohydrate via
aerobic respiration.
Reactions of fats entering the
aerobic pathway are
REVERSIBLE!
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If you eat too many cookies or
potato chips which are mostly
carbohydrates, your cells cannot
process all of the glucose for
energy.
Therefore, some of these
carbohydrates can follow
reversible reactions within the
mitochondria and end up forming
FAT!
Check this out
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Carbohydrates,
fats, and
proteins can all
be catabolized
through the
same
pathways.
S. Negative feedback
mechanisms control cellular
respiration
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Basic principles of supply and demand
regulate the metabolic economy.
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If a cell has an excess of a certain amino
acid, it typically uses feedback inhibition to
prevent synthesis pathway of that amino
acid.
The rate of catabolism is also regulated,
typically by the level of ATP in the cell.
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If ATP levels drop, catabolism speeds up to
produce more ATP.
Be able to answer the
following review questions
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
Compare reduction and oxidation.
How many ATP’s are needed to begin glycolysis?
What happens in Phosphorylation?
What are the products of lysis in glycolysis
Relate the structures of the mitochondrion to their functions.
What are the three major stages of cellular respiration?
What is the net gain of ATP from glycolysis per glucose molecule?
When does the link reaction occur?
What is the exact location where the Krebs cycle occurs?
During one rotation of the Krebs cycle, how many molecules of carbon dioxide are
produced?
How many molecules of ATP are produced with each turn of the Krebs cycle?
What happens to the pH of the inter-membrane space as electrons move along the
ETC?
Of what value is the folding of the inner-mitochondrial membrane?
What is the enzyme called through which protons pass when going from the intermembrane space to the matrix?
More questions to answer
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Explain what, in general, happens in cell respiration.
What are the products of glucose breakdown when it occurs in the
cytoplasm?
What are the products of glucose breakdown when it occurs in the
mitochondria?
What are the products of anaerobic respiration in plants and yeast
(fungi)?
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What are the products of anaerobic respiration in animals?
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What organelle must be present for aerobic respiration?
More review questions to consider:
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What is the form of energy used by cells to carry out
life processes?
Write out the balanced equation for cellular
respiration
Explain the difference between anaerobic and
aerobic respiration.
Compare ATP production in aerobic and anaerobic
respiration.
Where does glycolysis occur?
What stage is common to all types of respiration?
What gas is a waste to both aerobic respiration and
alcoholic fermentation.
Finally….
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What are the products of glycolysis?
Which type of respiration do prokaryotes carry out?
Where in the cell do lactic acid and alcoholic
fermentation occur?
How many carbons does each pyruvate molecule
produced by glycolysis have?
When does decarboxylation occur in aerobic
respiration and what usually forms as a result?
What is the link reaction?
Give at least 3 examples of when oxidation
reactions occur in aerobic respiration. What gets
reduced?
Review…facts you need to know!
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1. Cellular respiration includes
glycolysis, anaerobic respiration, and
aerobic respiration. The link reaction,
the Krebs cycle, and oxidative
phosphorylation occur in aerobic
respiration with the mitochondrion.
Glycolysis and anaerobic respiration
occur in the cytosol.
Review…facts you need to know!
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2. The ETC and chemiosmosis is the process
by which most ATPs are produced. These
processes occur on the inner mitochondrial
membrane and on the membranes of the
cristae. FADH2 and NADH bring the energy
rich electrons to the ETC. oxygen is the final
acceptor of the chain’s energy rich electrons
to form “water of metabolism”.
Review…facts you need to know!
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3. The final ATP net gain of aerobic
cellular respiration is 36. the cell is most
efficient at breaking down the
carbohydrate glucose; however, other
organic compounds are commonly
broken down by respiration.
Review…facts you need to know!
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4. Oil/rig = oxidation is loss/reduction is
gain. In oxidation, there is loss of
electrons and hydrogen. In reduction,
there is gain of electrons and hydrogen.
Oxidation results in C-O bonds. Reduction
results in C-H bonds. Photosynthesis is, in
general, a reduction process. Cellular
respiration, in general, is an oxidation
process.
Review…facts you need to know!
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5. Summary of glycolysis:
2 ATPs are used to start
A total of 4 ATPs are produced- a net gain of 2 ATPs
2 molecules of NADH are produced
Involves substrate level phosphorylation, lysis, and
oxidation and ATP formation
Occurs in the cell cytoplasm
Whenever ATP levels in the cell are high, feedback
inhibition will block the first enzyme of the pathway. Thus,
slowing or stopping the production of more ATPs
Review…facts you need to know!
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Summary of glycolysis continued:
2 pyruvate molecules are present at the end of the
pathway
Glycolysis produces ATPs by substrate level
phosphorylation since the phosphate groups are
transferred directly to ADP from the original phosphatebearing molecule
Review…facts you need to know!
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6. Once pyruvate is produced in
glycolysis, the next pathway is
determined by the presence or absence
of oxygen. If oxygen is present,
pyruvate will go through the link
reaction and enter the mitochondrion. If
oxygen is not present, pyruvate will
remain in the cytoplasm and go through
the process of anaerobic respiration.
Review…facts you need to know!
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7. In the link reaction, pyruvate is
converted into acetyl CoA, which is the
compound that enters the Krebs cycle.
During this link reaction, each pyruvate
also results in the formation of 1 NADH
and 1 carbon dioxide. This acetyl CoA
can also be produced from other
carbohydrates and lipids, not just a
hexose, usually glucose.
Review…facts you need to know!
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8. The Krebs cycle begins and ends with
the 4C compound called oxaloacetate. This
cycle results in the formation of the
following from 1 molecule of glucose:
2 ATP molecules
6 molecules of energy-rich NADH and 2 molecules of energyrich FADH2 move to the ETC
4 molecules of carbon dioxide which are released from the cell
as waste
Review…facts you need to know!
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9. Most of the ATP produced from glucose
catabolism occurs in the ETC, the last phase
of cellular respiration. This reaction involves
inner mitochondrial membrane of the cristae
and the space between the inner and outer
membranes of the mitochondrion.
The inner membrane includes proteins called electron carriers
These electron carriers pick up the energy-rich electrons from
NADH and FADH2 and pass them from one another in a series
of oxidations and reductions
Review…facts you need to know!
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At each exchange at these proteins, small amounts of energy
are released. This energy is used to transport hydrogen ions
into the inter-membrane space.
These hydrogen ions, protons, then passively move from the
inner-membrane space back into the matrix through a large
protein that includes ATP synthase
The ATP synthase is an enzyme which allows the attachment of
a phosphate group to ADP to make ATP
This overall process is also called chemiosmosis. The chemiportion means that electrons, not water, are passively moving
through a selectively permeable membrane
Review…facts you need to know!
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10. Chemiosmosis is called oxidative
phosphorylation because it uses the
energy released by oxidation to add
phosphate to ADP to produce ATP.
Remember, substrate-level
phosphorylation did not involve electron
flow.
Review…facts you need to know!
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11. Theoretically, 36 ATPs are produced
by cellular respiration involving 1
molecule of glucose.
4 ATPs are produced in glycolysis (net gain of 2)
2 ATPs are produced in the Krebs cycle
32 ATPs are produced in the ETC by chemiosmosis
Review…facts you need to know!
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12. Overall, respiration equation:
C6H12O6  6CO2 + 6H20 + energy
(heat or ATP)
Review…facts you need to know!
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13. Mitochondrial parts versus
functions:
Outer membrane: separates the mitochondrion from the
remainder of the cell
Matrix: inner cytosol like area which contains the enzymes for
the link reaction and the Krebs cycle
Cristae: shelf-like membranes with inner space allowing for
oxidative phosphorylation
Inner mitochondrial membrane: contains the carriers for the
ETC and ATP synthase for chemiosmosis
Space between inner and outer membranes: space for the
accumulation of protons (hydrogen ions) so that chemiosmosis
can occur