Cellular Respiration

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Cellular Respiration
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Pulling some things together

• What did the previous slide represent?
• Notice that during each energy transformation,
  heat is lost!
• What is this called?

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Combustion Reactions

• A chemical reaction that involves a hydrocarbon
  and oxygen. It produces energy (heat) so rapidly
  that a flame results.
• The products of this reaction include carbon
  dioxide and water.
• C(x)H(x)O2?H2O(g)CO2(g)
• Combustion is commonly called burning.
• It is an exothermic reaction.

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Cells and Energy
Glycolysis and respiration as source of energy
for the cell
How do cells make ATP? Phosphorylation!
Chapter 6
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Cells need to generate ATP!

• Substrate level phosphorylation
• Uses enzymes
• Transfers phosphate group from an organic
  substrate to ADP.
• X-P ADP enzyme ?X ATP

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Chemiosmotic Phosphorylationa.k.a. Chemiosmosis

• Needs a membrane.
• Uses the potential energy to create a
  concentration gradient of H (hydrogen ions)
  across a membrane.
• Uses special enzymes, ATP synthases.

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Things to keep in mind... (we are going to go
over this)
Respiration C6H12O6 6O2 ? 6CO2 6H2O

• Exergonic or endergonic?
• What is oxidized?
• What is reduced?
• In what form is energy released?
• What is the importance of CO2 in the atmosphere?
• What is the source of oxygen in the atmosphere?

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Reminder

• While cellular respiration, in total, is an
  exergonic reaction, it is made up of a series of
  reactions which involve both types!
• C6H12O6 6O2 ? 6CO2 6H2O ENERGY RELEASED
  (ATP)

• Endergonic reactions have a net absorption of E
• Exergonic reactions have a net release of E.
• These reactions are coupled, one does not occur
  without the other!

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Redox Reactions

• The movement of electrons from one molecule to
  another is an oxidation-reduction reaction.
• Loss of electrons is oxidation
• Gain of electrons is reduction
• LEO the lion goes GER
• ex. C4H6O5 NAD ? C4H4O5 NADH H

oxidized
reduced
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The master formula
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There are 2 types of cellular respiration

• With oxygen aerobic cellular respiration (What
  are aerobic exercises?)
• Without oxygen anaerobic cellular respiration
  a.k.a. fermentation

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Eukaryote vs Prokaryote Glycolytic pathways
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Overview of Cellular Respiration
A. Glycolysis (anaerobic)
Without oxygen With oxygen
B. Fermentation B. Aerobic
Respiration 1. Citric Acid Cycle 2.
Electron Transport Chain
(anaerobic respiration)
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Would you like that with or without oxygen?

• Aerobic - environments with oxygen
• Anaerobic - environments without oxygen
• Most organisms need O2 but there are some that
  can live in either environment and a few that
  must live in the absence of O2!

Saccharomyces cerevisiae (yeast) images provided
by Peter Hollenhorst and Catherine Fox
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Obligate Anaerobes

• Clostridium botulinum - Gram-positive,
  endospore-forming, rod prokaryote. Vegetative and
  spore stages. Note the flagella.
• Causes botulism.Magnification x2,000Type
  SEM

• Clostridium tetani - Gram-positive, rod
  prokaryote vegetative and spore stages. Note the
  flagella.
• Causes tetanus. SEM Magnification x1,750Type
  SEM

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Review of Mitochondria

• Eukaryotic organisms carry out cellular
  respiration in the mitochondria (power house of
  the cell) http//www.sci.sdsu.edu/TFrey/MitoMovies
  /CrisMitoMovie.htm

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Reminder Possible evolution of
mitochondria-endosymbiont
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The Mitochondria

• Double membrane
• Has its own DNA!!
• Can reproduce in cell!
• Endosymbiont??
• Possible evolution?

http//hybridmedicalanimation.com/anim_mitosis_wmV
ideo.html
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Introduction to Cellular Respiration

• The process by which food molecules (glucose) are
  broken down to release energy (ATP)
• C6H12O6 6O2 ? 6CO2 6H2O Energy
• In eukaryotic organisms, this process takes place
  in the mitochondria. In prokaryotic organisms,
  this process takes place in the cell membrane.

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Overview Respiration occurs in 4 (5) main
stages

• Glycolysis
• Exergonic
• Occurs in the cytoplasm
• Splits glucose into 2 molecules of pyruvic acid
• Pyruvic acid is modified into Acetyl CoA as it
  diffuses into the mitochondria.
• Each pyruvic acid loses a carbon to CO2
• This is a high energy fuel molecule for the next
  stage

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• Krebs Cycle
• Exergonic
• Occurs in the matrix of the mitochondria
• Produces CO2 as a waste product
• Main function of first 2 stages supply 3rd
  stage with electrons!
• Electron Transport Chain and Chemiosmotic
  Phosphorylation
• Occurs on the cristae of the mitochondria
• Uses oxygen
• Produces the most ATP

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Overview of Aerobic Cellular Respiration
Define the four stages of respiration and their
location in the cell
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Stage 1 Glycolysis

• glyco- sugar (glucose)
• -lysis to split

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A. Glycolysis (Overview)

• A molecule of glucose (6 carbon compound) is
  broken apart making 2 pyruvic acid compounds (3
  carbons each)
• 2 ATP and 2 NADH molecules produced

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Glycolysis

• STEP 1 - 2 phosphates are attached to glucose,
  forming a new 6-C compound. The phosphate groups
  come from 2 ATP, which are converted to ADP.
  (Glucose is phosphorylated!)
• STEP 2 - The 6-C compound formed in Step 1 is
  split into 2 3-C molecules of PGAL.
• STEP 3 - The 2 PGAL molecules are oxidized (LEO),
  and each receives a phosphate group forming 2 new
  3-C compounds. The phosphate groups are provided
  by 2 molecules of NAD forming NADH.

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• STEP 4 - The phosphate groups added in Step 1 and
  Step 3 are removed from the 3-C compounds.
• This reaction produces 2 molecules of Pyruvic
  Acid.
• Each phosphate group combines with a molecule of
  ADP to make a molecule of ATP.
• Because a total of 4 phosphate groups were added,
  FOUR MOLECULES OF ATP ARE PRODUCED.

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Substrate-level phosphorylation

• Enzymes in the cytoplasm pass a high energy
  phosphate to ADP to make ATP.
• Not very efficient
• FYI The high energy phosphates came from the
  oxidation of BPG, in the presence of an enzyme,
  forming PGAL (a.k.a. G3P) and ATP.

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Keep up with totals
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Summary of glycolysis
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Dont panic you do not need to memorize this,
but it will give you a greater appreciation for
what really is happening to get from glucose to
pyruvate! How many different enzymes are involved?
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Question 1
How much ATP is needed to activate glycolysis?
Glucose
Energy investment phase and splitting of glucose
2 ATP
3 steps
2 ADP
Fructose-1,6-bisphosphate
P
P
2 X Glyceraldehyde phosphate (G3P)
P
P
(see next slide)
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Question 2
How much ATP/net ATP is produced in glycolysis?
2 X Glyceraldehyde phosphate (G3P)
Energy capture phase
P
P
(G3P)
(G3P)
NAD
NAD
NADH
NADH
5 steps
2 ADP
2 ADP
2 ATP
2 ATP
Net yield per glucose? ATPs and ? NADH
Pyruvate
Pyruvate
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Question 3
Identify the exergonic and endergonic reactions
in the following exergonic coupled enzyme steps
in glycolysis

• Energy investment phase
• Glucose ATP ? Glucose-6-phosphate ADP
• Energy capture phase
• Phosphoenolpyruvate ADP ? Pyruvate ATP

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In summary.

• 2 ATP molecules were used in Step 1, but 4 are
  produced in Step 4. Therefore, glycolysis has a
  NET YIELD of 2 ATP molecules for every molecule
  of glucose that is converted into Pyruvic Acid

http//biology.clc.uc.edu/courses/bio104/atp.htm
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2 pyruvic acid molecules
Glucose
4 H energy stored in 2 ATP molecules
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Glycolysis Facts

• Glycolysis is the universal E-harvesting process
  of life.
• Because glycolysis occurs universally, it is
  thought to be an ancient metabolic system.
• The net gain of two ATP molecules represents only
  5 of the E that a cell can harvest from a
  glucose molecule.

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Pyruvic Acids 2 Possible Pathways

• If O2 is not available
• Fermentation
• alcoholic
• lactic acid
• many types of fermentation!

• If O2 is available
• Kreb cycle

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2 Possible Paths if no O2 present
Why must pyruvate be converted to either ethyl
alcohol or lactate in the absence of oxygen?
Glycolysis
Glucose
2 NAD
2 NADH
2 ATP
2 Pyruvate
2 Lactate (C3)
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Stage 2 The Preparatory Reaction

• Acetyl CoA Production

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B.O.P. (Breakdown of Pyruvate)

• 1. The 2 pyruvic acid compounds (3C) are changed
  into 2 2-carbon compounds and 2 molecules of CO2
• 2. Occurs in the space between the membranes of
  the mitochondria

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Takes place as pyruvate moves into the matrix of
the mitochondria
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Production of Acetyl CoA

• When pyruvic acid enters the mitochondrial
  matrix, it reacts with a molecule called coenzyme
  A to form Acetyl Coenzyme A, abbreviated acetyl
  CoA. CO2, NADH, and H are produced in this
  reaction.
• Remember There are 2 pyruvic acids formed from
  1 glucose!

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Question 1
How many of the six carbons of glucose are lost
in this way?
Pyruvate (C3) CoA NAD ? Acetyl(C2)Co
A CO2 NADH
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Question 2
Considering the transition reaction and the first
reaction of the Krebs cycle below, how would you
describe the role of Coenzyme A?
Transition reaction Pyruvate (C3) CoA ?
Acetyl(C2)CoA CO2 Krebs cycle first
reaction Oxaloacetate (C4) AcetylCoA ? Citrate
(C6) CoA
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Stage 3

• Krebs Cycle a.k.a. Critic Acid Cycle

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Krebs Cycle

• Named for German-British researcher Hans Krebs
  (1900-1980).
• Also called the Citric Acid Cycle
• The Krebs cycle is a biochemical pathway that
  breaks down Acetyl CoA, producing CO2, H, NADH,
  FADH2, and ATP.

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Step 1

• A 2-Carbon molecule of Acetyl CoA combines with a
  4-Carbon compound, OXALOACETIC ACID, to produce a
  6-Carbon Compound CITRIC ACID.

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Step 2

• Citric Acid releases a CO2 molecule and a H atom
  to form a 5-Carbon compound. By losing a H atom
  with its electron , Citric Acid is OXIDIZED. The
  H atom is transferred to NAD, REDUCING it to
  NADH.

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Step 3

• The 5-Carbon compound releases a CO2 molecule and
  a H atom, forming a 4-Carbon compound. NAD is
  reduced to NADH. A Molecule of ATP is also
  synthesized from ADP.

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Step 4

• The 4-Carbon compound releases a H atom to form
  another 4-Carbon compound. The H atom is used to
  reduce FAD (Flavin Adenine Dinucleotide) to
  FADH2, a molecule similar to NAD that accepts
  electrons during Redox Reactions.

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Step 5

• The 4-Carbon compound releases a H atom to
  regenerate oxaloacetic acid, which keeps the
  Krebs cycle operating. The H atom reduces NAD to
  NADH.

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Summary
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Keeping up with totals
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• In Glycolysis 1 glucose molecule produces 2
  Pyruvic Acid molecules, which can then form 2
  molecules of Acetyl CoA.
• 1 Glucose molecule causes 2 turns of the Krebs
  cycle.
• The 2 turns produce 6 NADH, 2 FADH2, 2 ATP, and 4
  CO2 molecules.
• The CO2 is a waste product that diffuses out of
  the cells and is given off by the organism.

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• The bulk of the E released by the oxidation of
  Glucose still has NOT been transferred to ATP.
  Only 4 molecules of ATP have been generated - 2
  from Glycolysis and 2 From the Krebs cycle.
• 10 molecules of NADH and the 2 FADH2 molecules
  from the Krebs cycle DRIVE the next stage of
  Aerobic Respiration - The Electron Transport
  Chain.
• That is where MOST of the E transfer from Glucose
  to ATP actually occurs.

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Stages 4 and 5

• Electron Transport Chain (ETC) and Chemiosmosis

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Electron Transport Chain

• The electron transport chain is a system of
  electron carrying proteins embedded into the
  inner membrane of a mitochondrion, the cristae.
• These proteins transfer e- from one to another,
  down the chain, much in the way a bucket brigade
  passes buckets of water.

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Electron Transport Chain (ETC)

• NADH is oxidized to NAD at the first
  protein/enzyme complex. 2 H are moved across the
  membrane and the high E electron moves through a
  series of membrane proteins.
• As the e- pass through a second protein/enzyme
  complex, its E is used to move another 2 H
  across the membrane.

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ETC cont.

• At protein/enzyme complex 3 another 2 H are
  moved across the membrane.
• Once the e- has spent all of its E, it joins
  oxygen and other Hs and e- s to make a water
  molecule.
• This process creates a gradient by using the high
  energy e- and H from NADH (and FADH2).

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ETC and FADH2

• FADH2 can not enter the ETC at the same point.
  It must enter at the 2nd protein/enzyme complex.
  Here it is oxidized to FAD. Since it only
  passes through 2 protein/enzyme complexes, it can
  only move 4 H across the membrane.
• http//vcell.ndsu.nodak.edu/animations/etc/index.h
  tm
• Oxygen the ultimate electron acceptor!

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Still no ATP!

• The ATP is actually produced by a proton motive
  force. This force is a store of potential energy
  created by the gradient formed when hydrogens
  (protons) are moved across a biological membrane.
  
• Therefore, the electron transport chain merely
  produces a gradient through which ATP can be made
  (this is known as chemiosmosis).

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2H
2H
2H
e-
2H
2H
2H
? NAD
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Chemiosmosis

• A special protein called ATP synthase provides a
  channel for H ions to move across the cristae.
  It also contains the enzyme that catalyzes the
  phosphorylation of ADP to from ATP.
• As H ions move through the port, their flow
  drives the synthesis of ATP.
• http//vcell.ndsu.nodak.edu/animations/atpgradient
  /index.htm

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Summary
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Websites with animations

• http//www.science.smith.edu/departments/Biology/B
  io231/etc.html
• http//www.sp.uconn.edu/terry/images/anim/ETS.htm
  l
• http//www.sci.uidaho.edu/bionet/biol115/t4_energy
  /etc.htm

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Total ATP generated
Glycolysis
Glucose
2 ATP
NADH
2
4  6
ATP
2 Pyruvate
From the scheme, what is the function of the
electron transport stage of respiration?
Substrate-level phosphorylation
Transition reaction
NADH
2
6
ATP
Substrate-level phosphorylation
Citric acid cycle
NADH
6
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ATP
2 ATP
FADH2
2
4
ATP
Electron transport and chemiosmosis
Oxidative phosphorylation
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ATP
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Total Energy Yield
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Are carbs. our only option?
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Other food

• Glucose is not the only material that can be
  metabolized to generate energy. Many
  carbohydrates can be broken down in glycolysis
  and enter the Krebs Cycle. Proteins can be broken
  down into amino acids and those can be deaminated
  and the carbon chains feed into the Krebs Cycle.
  The very long carbon chains of fatty acids can be
  chopped into two carbon pieces by a process known
  as Beta Oxidation. Since the fatty acid chains
  can be up to 20 carbons long there is a very
  great deal of energy stored in fats.

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Fermentation (a.k.a. anaerobic respiration)

• No oxygen required!

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Anaerobic Respiration

• In some organisms, there are times when cells are
  without O2 for short periods of time. When this
  happens, an anaerobic process called fermentation
  follows glycolysis and provides a means to
  continue producing ATP until O2 is available
  again.

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Anaerobic Respiration

• In the absence of O2, some cells can convert
  Pyruvic Acid into other compounds through
  additional biochemical pathways that also occur
  in the cytosol.
• The combination of Glycolysis PLUS these
  additional pathways are known as FERMENTATION.
• During the processes of fermentation NO
  ADDITIONAL ATP IS SYNTHESIZED.

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2 Types of Fermentation

• Lactic Acid Fermentation
• occurs in some bacteria, in plants, and most
  animals (including humans)

• Alcoholic Fermentation
• occurs in some yeast and bacteria

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Lactic Acid Fermentation

• Pyruvic acid is converted into lactic acid.
• Lactic acid involves the transfer of 2 H atoms
  from NADH and H to Pyruvic Acid. In the process,
  NADH is oxidized to form NAD which is needed to
  keep Glycolysis operating.

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Lactic Acid Fermentation
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Bacteria can do it!

• Lactic acid fermentation by microorganisms plays
  an essential role in the manufacture of food
  products such as yogurt and cheese.

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So can you!

• Certain animal cells, including our muscle cells
  convert pyruvic acid to lactic acid.
• During exercise, breathing cannot provide your
  body with all the oxygen it needs for aerobic
  respiration. When muscles run out of O2, the
  cell switch to lactic acid fermentation.
• This process provides your muscles with the
  energy then need during exercise.

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Lactic Acid Fermentation

• In L.A.F., the 2 molecules of pyruvic acid formed
  from glycolysis are used to make 2 molecules of
  lactic acid and NAD which is necessary for
  glycolysis.
• L.A.F allows glycolysis to happen repeatedly for
  quick energy. Each time glycolysis occurs, 2
  ATP are formed.

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Alcoholic Fermentation

• In alcoholic fermentation, pyruvic acid from
  glycolysis is changed into ethyl alcohol and CO2.
  As a result, NAD is formed which is needed for
  glycolysis. Each time glycolsysis occurs, 2 ATP
  are made.

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Alcoholic Fermentation
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Alcoholic Fermentation cont.

• This process is used in making beer, wine, and
  bread.
• A.F. by the yeast in a bread recipe produces CO2
  bubbles that raise the bread dough.
• Also, many bacteria carry out A.F. under
  anaerobic conditions.

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Fermentation
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Lets Compare Lactic Acid Fermentation and
Alcoholic Fermentation...

• Alcoholic Fermentation
• glucose
• glycolysis (pyruvic acid)
• CO2 ethyl alcohol 2 ATP NAD

• Lactic Acid Fermentation
• glucose
• glycolysis (pyruvic acid)
• lactic acid NAD 2 ATP

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Fermentation Totals
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Comparison of energy from one glucose molecule

• Lactic Acid Fermentation 2ATP
• Alcoholic Fermentation 2 ATP
• Cellular Respiration 36 ATP
• Aerobic Respiration is more energy efficient than
  anaerobic respiration!

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Lets Compare Photosynthesis and Cellular
Respiration...

• Photosynthesis
• food accumulated
• energy from sun stored in glucose
• CO2 taken in
• O2 given off
• needs sunlight
• occurs only in presence of chlorophyll

• Cellular Respiration
• food broken down
• energy in glucose is released
• CO2 given off
• O2 taken in
• does not need sunlight
• occurs in all living cells