Energy Flow: Photosynthesis

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Energy FlowPhotosynthesis Cellular Respiration
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Functions of ATP

• Chemical work synthesizing compounds
• Transport work moving substances across the
  plasma membrane
• Mechanical work moving cell structures and
  cells

• Energy coupling use of an exergonic process to
  drive and endergonic process
• ATP mediates most energy coupling in cells

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ATP

• Consist of
• a sugar called ribose
• N containing Adenine
• Three phosphate groups

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• Unstable w/3 PO4-
• All negative charge-repel each other
• ADP is more stable
• A change from a less stable molecule to a more
  stable molecule releases energy.

Covalent Bonds
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• The energy can then be used to drive other
  reactions (energy coupling)
• ATP carries Energy

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The structure and hydrolysis of ATP
All are negatively charged crowded and repel,
creating instability
When bonds are broken from ATP to ADP
(hydrolysis).
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The ATP cycle
ATP is a renewable resource that can be
regenerated
FAST working muscle cell recycles its entire
ATP pool once each minute -Turnover represents
10 million molecules of ATP generated per second
in a cell.
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Photosynthesis
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• Process by which plants and other organisms use
  sunlight, CO2 H20 to produce high energy
  carbohydrates such as sugars and starches.
• Prokaryotes- photosynthetic capability is present
  within five major groups of bacteria.

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Where Photosynthesis Occurs
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The Internal Structure of a Leaf
Section 23-4
CO2 enters through the stomata
Epidermis
Chloroplasts
Stomata
Guardcells
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• Chloroplasts are only found in photosynthetic,
  eukaryotic cells.
• Chloroplasts are capable of harnessing energy
  from the sun's rays of light.

• Using this energy from the sunlight, chloroplasts
  are able to form ATP as well as synthesizing
  sugars from water and carbon dioxide.

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Things to know about Chloroplasts

1. have a double membrane
2. have their own DNA (carries the info
   to make enzymes)
3. have their own ribosomes (more like the ribosomes
   of prokaryotes) -used to synthesize proteins
4. make their own enzymes required for
   photosynthesis
5. require CO2 and H2O produce C6H12O6
6. contain chlorophyll (green chemical "traps"
   sunlight energy)

Now lets look at structure
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• The chloroplast is made up of 3 types of
  membranes
• A smooth outer membrane which is freely permeable
  to molecules.
• A smooth inner membrane which contains many
  transporters
• A system of thylakoid membranes

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Light and Pigments

• In addition to water and carbon dioxide,
  photosynthesis requires light. Light energy is
  absorbed by the pigment CHLOROPHYLL and other
  accessory pigments.

Pigments are molecules that absorb light energy
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Accessory Pigments

• Other pigments that trap other wavelengths --
  found in chromoplasts
• Capture light and pass the energy along to
  chlorophyll A.
• Ex. Carotenoids
• xanthophyll yellows
• beta carotene oranges
• These are masked by presence of chlorophylls,
  except in autumn (when leaf cells stop
  synthesizing chlorophyll) fall colors
• Also is very obvious in ripe fruits, veggies
• Ex. Apple, tomato

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Sunlight is a mixture of many different
wavelengths
ROYGBIV (vibgyor)
(light energy is measured in units called photons)
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Pigments

• Substances in organisms that can absorb light.
• The color that you see is the one being REFLECTED
• CHLOROPHYLL is the major photosynthetic pigment
  in plants
• 2 types chlorophyll a directly involved in
  transformation of photons to
  chemical energy
• chlorophyll b helps trap other
  wavelengths and transfers it to
  chlorophyll a

Accessory Pigments

• Chlorophylls (green) and carotenoids (yellow,
  orange and red.)

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Chlorophyll A and B Absorption Spectrum
b
a
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action spectrum and the absorption spectra
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Location and structure of chlorophyll molecule
Photosystem
Double bonds are the source of the e- that flow
through the ETC
The pigment molecules have a large head section
that is exposed to light in the surface of the
membrane the hydrocarbon tail anchors the
pigment molecules into the lipid bilayer.
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Photosystems
Where is the chlorophyll located?

• Chlorophyll molecules are located in
  photosystems.
• light-harvesting complexes in the thylakoid
  membranes.
• Photosystem Structure
• 1-Protein
• 2-Reaction Center contains chlorophyll A and
  several antenna pigments.
• Two PS
• PS I and PS II
• PS II acts BEFORE PS I ..go figure...

antenna pigments are predominantly chlorophyll b,
xanthophylls, carotenoids
PSI 700nm range Also referred to as P700
PS II 680nm range Also referred to as P680.
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• Now that you know all of thatlets actually
  look at the process of photosynthesis

Mr. Andersons Photosynthesis
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Photosynthesis Quick Overview
STAGE 1 LIGHT DEPENDENT REACTIONS
STAGE 1
STEP 1 PS I (P700) and PS II (P680) capture
energy from sunlight. 
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Photosynthesis Quick Overview
STAGE 1
-Water is Split (photolysis) into H, Electrons,
O2 -O2 diffuses out of the Chloroplasts
(Byproduct). -Light Energy is Converted to
Chemical Energy, which is temp. stored in ATP and
NADPH.
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Photosynthesis Quick Overview
Step 2 -ATP and NADPH from Step 1, along with
CO2, is converted to glucose in the Calvin Cycle
STAGE 1
STAGE 2
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Light Dependent Reaction ?
Light Independent Reaction ?
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Steps of Light Dependent Reaction(Noncyclic
Photophosphorylation)

• PSII absorbs energy.
• e- from double bonds in the head of ChloroA
  become energized and move to a higher energy
  level. They are captured by a primary electron
  acceptor.
• Photolysis H2O gets split apart into 2 e- , 2
  H, and one oxygen atom.. The e- replace those
  lost by ChloroA.
• 2 oxygen molecules combine and is released into
  the air.
• H are released into the inner thylakoid space,
  which creates a higher H inside the
  thylokoid.
• e- from ChloroA are passes along a ETC consisting
  of plastoquinone (PQ)---complex of 2 cytochromes
  and several other proteins.
• This flow is exergonic and provided energy to
  produce ATP by chemiosmosis. (photophosphorylation
  )
• The ATP is used to power the Light Independent
  Reaction (Calvin Cycle).this is a coupled
  reaction!
• The e- end up at PS I.
• PS I absorbs energy.
• e- from double bonds in the head of ChloroA
  become energized and move to a higher energy
  level. They are captured by a primary electron
  acceptor.
• E- that are lost are replaced by the e- from PSII
  (step7).
• e- from ChloroA are passes along a ETC
  consisting of ferrodoxin.
• NADPH is produced.
• NADP in the stroma pick up 2 H and form NADPH
  and enter the calvin cycle.

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Photosynthesis Light Dependent Reaction Overview

• Clip

Overview clip
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The light reactions and chemiosmosis
organization of the thylakoid membrane
The production of ATP using the energy of
sunlight is called photophosphorylation.
NADPNicotinamide adenine dinucleotide phosphate
P700
P680
Photolysis
H
H
H
H
H
H
H
H
H
H
H
Chemiosmosis
Animation
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• Chemiosmosis
• Chemiosmotic Theory
• -Peter Mitchell -1961
• Energy coupling mechanism.
• Uses potential energy stored in the form of a
  proton gradient to phosphorylate ADP to produce
  ATP.

ATP synthase-The Movie
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Chemiosmosis

• Protons can not diffuse through the membrane.
• SO they must flow through the ATP synthase
  protein channel.
• 90 of all ATP is produced this way.
• Proton Motive Force generates ATP

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Cyclic Photophosphorylation

• Periodically the chloroplasts runs low on ATP.
• Does this to replenish ATP levels.
• e- travel from the P680 ETC to P700 then to

• a primary e- acceptor, then back to the
  cytochrome complex in the P680 ETC.
• No NADPH is produced.
• No O2 is released.

Animation
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• STAGE 2 Dark Reaction /Light Independent
  reaction/Calvin-Benson Cycle).
• The ATP and NADPH created in the light reaction
  are used to power the formation of Organic
  Compounds (Sugars), using CO2.
• This is a light Independent reaction. It can
  happen during the daylight, it just does NOT need
  light be completed.
• Occurs in the stroma.
• Cyclical pathway where carbon enters as CO2 and
  exits as PGAL (phosphoglyceraldehyde.)
• Called carbon fixation.
• Carbon is fixed into PGAL. (2 PGAL1 Glucose)
• This is a reduction reaction (carbon is GAINING
  hydrogen)
• Must repeat 6 times.

Review step 1 / Intro to step 2 Clip
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Review of Light Dependent and Intro to Light
Independent
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The Calvin cycle
C3 plants
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CO2 attaches to a 5-C sugar-RuBP. Ribulose
biphosphate. This is called Fixation This forms
a 6-C molecule (PGA) Catalyzes by the enzyme
Rubisco.
Fixation
RuBP
PGA
1)RuBP CO2 ? PGA
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The Calvin cycle
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PGA is broken down into 2 3-C molecules called
PGAL (phosphoglycerate)
RuBP
PGA
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12
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PGAL
2
1)RuBP CO2 ? PGA 2) PGA ATP NADPH ? PGAL
1
PGAL
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The Calvin cycle
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PGAL converted to RuBP
RuBP
PGA
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12
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PGAL
1) RuBP CO2 ? PGA 2) PGA ATP NADPH ? PGAL 3)
PGAL? Glucose RuBP regenerated
Summary 6CO2 18 ATP 12 NADPH H ?
18ADP 18 Pi 12NADP 1 Glucose
PGAL
2
1
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Ted Ed Calvin Cycle
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Photorespiration
Problem RUBISCO catalyzes two different
reactions.

• Occurs when the CO2 levels inside a leaf become
  low.
• Happens on hot dry days when a plant is forced to
  close its stomata to prevent excess water loss.
• If the plant continues to attempt to fix CO2 when
  its stomata are closed, the CO2 will get used up
  and the O2 ratio in the leaf will increase
  relative to CO2 concentrations.

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• When the CO2 levels inside the leaf drop to
  around 50 ppm, Rubisco starts to combine O2 with
  RuBP instead of CO2.
• The net result of this is that instead of
  producing 2 3C PGA molecules, only one molecule
  of PGA is produced and a toxic 2C molecule called
  phosphoglycolate is produced.

Photorespiration

• The plant must get rid of the phosphoglycolate
• Converts it to glycolic acid, which is then
  transported to the peroxisome and converted to
  glycine.
• The glycine is then transported into a
  mitochondria where it is converted into serine.
• The serine is then used to make other organic
  molecules. All these conversions cost the plant
  energy and results in the net lost of CO2 from
  the plant.

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C3, C4 CAM Plants

• C-3
• Calvin cycle occurs in all photosynthetic cells.
• Risk of photorespiration...
• C-4
• C4 plants separate the site of oxygen production
  (PSII) from rubisco (Calvin cycle).
• Called C-4 because the CO2 is first incorporated
  into a 4-carbon compound.
• Keeps O2 Away from RuBP (NO Photorespiration)
• Light reaction occurs ONLY in the mesophyll cells
  Calvin cycle occurs in bundle-sheath cells.
• SPATIAL SEPARTATION

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C4 leaf anatomy and the C4 pathway
Different anatomy from a C-3 plant
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PhotosynthesisA dry climate adaptation

• CAM Plants (Crassulacean Acid Metabolism) -plants
  live in very dry condition and, unlike other
  plants, open their stomata to fix CO2 only at
  night.
• -Fix CO2 at night and store it.
• C4 plants that also have a TEMPORAL SEPARTAION
• .

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Factors affecting Photosynthesis

• Amount of water available too little, stop
  photosynthesis
• Temperature best between OC 35C (too high,
  damage enzymes too low, stop photosynthesis)
• Intensity of light up to a point, increasing
  light intensity increases rate of photosynthesis

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Spinach Chromatography

• A plant physiology manual (Reiss 1994) identifies
  six pigments from spinach leaves extracted with
  hexane and chromatographed with petroleum
  ether-acetone-chloroform (311) on silica-gl
  chromatography. The pigments and their Rf's were
  
• carotene - 0.98
• chlorophyll a - 0.59
• chlorophyll b - 0.42
• pheophytin - 0.81
• xanthophyll 1 - 0.28
• xanthophyll 2 - 0.15
• The color of the bands can be a general guide to
  identify the pigments. Carotene is orange.
  Chorophylls are green. Chlorophyll a is a
  blue-green. Chlorophyll b is a yellow-green.
  Xanthophylls are yellow. Phaeophytin is
  chlorophyll lacking the central magnesium ion.
  Pheophytin is an olive-green."

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• Cellular Respiration

-The process that occurs in cells in which cells
break down sugar for ENERGY!
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Cellular Respiration Overview

• We get our energy from the food we eat.
• The unit for energy is the calorie.
• Plants are producers and make glucose by the
  process of photosynthesis.
• Heterotrophs (consumers) breakdown glucose for
  energy.
• There are two important ways a cell can harvest
  energy from food fermentation and cellular
  respiration.

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Basic overview
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3
1
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• Step 1 gylcolysis
• Splitting of glucose into 2 pyruvate molcules

9 steps
cellular respiration
fermentation
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GlycolysisOverall Important Points
Clip McGraw Hill

• Occurs in Cytoplasm
• Does not require oxygen
• Glycolysis occurs in both aerobic (With oxygen)
  and anaerobic (without oxygen) respiration.
• Evolved early in Earths history (evolutionary
  relationships)
• First 3 steps are endothermic
• Energy of activation 2 ATP
• Last 6 steps are exothermic
• producing 4 ATPs.
• 4-2 2 ATP (net yield)
• Releases less then 25 of energy from glucose.

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TYPES of Phosphorlation

• Substrate Level
• When an enzyme transfers a PO4- from a substrate
  DIRECTLY to ADP.
• Oxidatative
• During Chemiosmosis.
• 90 of all ATP is produced this way in the ETC
• NAD FAD lose protons (become oxidized) to the
  ETCpumps protons to innermembrane space creating
  a gradient. This powers the phosphorlation of ADP
• This is what occurs in the light reaction in
  Photosynthesis

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A closer look at glycolysis The 9 Steps
Important regulatory step PFK is inhibited by ATP
Step 1
Step 2
Step 4
Step 3
PFK
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A closer look at glycolysis The 9 Steps
"high energy" e- carrying molecule
Step 5
Step 6
Substrate-level phosphorylation
Step 7
Nicotinamide adenine dinucleotide
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A closer look at glycolysis The 9 Steps
Step 5
Step 8
Step 6
Substrate-level phosphorylation
Step 9
Step 7
3- Carbon Cpd
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• Net Yield
• 2 NADH
• 2 ATP

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Glycolysis Review
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In the presence of OXYGENStep 2 Krebs
CycleStep 3 Electron Transport
What happens next???

• Happens in the Mitochondria
• Starts with Pyruvate.
• Pyruvate moves into the mitochondria and is
  broken completely down into CO2 , O2 ATP.

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Krebs and ETC take place in a mitochondrion
Double membrane
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Mitochondria Anatomy
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Step 2 Krebs Cycle (aka Citric Acid
Cycle) -Mitochondrial Matrix Step 3 Electron
Transport -Cristae
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Krebs Cycle Overview (Citric Acid Cycle)
Clip McGraw Hill

• Occurs in the mitochondrial matrix
• Cyclical series of enzyme-catalyzed reactions.
• Pyruvate (product of glycolysis) enters the mito.
  and combines with coenzyme A (vitamin A) to form
  acetyl coenzyme A.
• ? Yields 1 NADH
• Krebs starts with acetyl coA.
• Each turn (cycle) uses 1 pyruvate and yields
• 3 NADH, 1 ATP, 1 FADH
• Byproduct CO2

NAD FADCoenzymes that carry protons (H) and
electrons from glycolysis Krebs to the ETC
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How the Krebs Cycle Works
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A summary of the Krebs cycle

• Occurs in the mitochondrial matrix
• Pyruvate (product of glycolysis) enters the mito.
  and combines with coenzyme A (vitamin A) to form
  acetyl coenzyme A.
• ? Yields 1 NADH
• Krebs starts with acetyl coA.
• Cyclical series of enzyme-catalyzed reactions.

NAD FAD-Coenzymes that carry protons (H) and
electrons from glycolysis Krebs to the ETC
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• Each turn (cycle) uses 1 pyruvate
• Net yield
• 3 NADH,
• 1 ATP,
• 1 FADH
• Byproduct
• CO2

Krebs Cycle
Substrate-level phosphorylation
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The Story So Far
ETC Clip McGraw Hill

• 2 NADH
• 2 ATP

• 3 NADH
• 1 ATP
• 1 FADH2
• Byproduct CO2

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ETC Overview
Whats a proton motive force? How is it produced?
Why is it produced how does it help the cell?
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Electron Transport
Step 3 Electron Transport
What happens next???

• The ETC a series of protiens that serve to pump
  protons to the inner mito membrane.
• Its uses the energy released from the exergonic
  flow of electrons.
• This sets up a proton gradient across the
  membrane
• chemiosmosis
• oxidatative phosphorylation

The production of ATP using the energy of
electrons is called oxidatative phosphorylation.
(where have we seen this before)
Extra Overview Clip
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Oxidative Phosphorylation and Chemiosmosis Energy
from falling e- (exergonic) is used to pump H
across the membrane (endergonic).
What happens next???
Clip 2 Formation of ATP
Oxygen is the final e- acceptor!!
oxidatative phosphorylation
H cant get through the membrane, so they MUST
pass through the channel. Ex Hydroelectric plant
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Figure 9.15 Chemiosmosis couples the electron
transport chain to ATP synthesis
Oxidative Phosphorylation The Phosphorlation of
ADP into ATP by the oxidation of carrier
molecules (NADH FADH2)
36-38 Total ATP
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ETC Review
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With With out Oxygen
With oxygen
Glucose
Krebs cycle
Electrontransport
Glycolysis
Alcohol or lactic acid
Fermentation (without oxygen)
With out oxygen
Go to Section
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Fermentation
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• Without oxygen Pyruvate is converted into Lactic
  Acid or Alcohol during Fermentation.
• Lactic Acid- Muscle cells
• Alcohol- Yeast

Anaerobic Respiration
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Fermentation
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Lactic Acid Fermentation
Section 9-1
Lactic acid
Glucose
Pyruvic acid
Without a means to convert NADH to NAD,
Glycolysis would shut down
Go to Section
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Alternative Energy Sources

• From Fats
• Enzymes cleave the bonds between the glycerol and
  the fatty acids, which enter the blood stream.
  Enzymes in the liver convert the glycerol into
  PGAL.
• Enzymes in cells break apart the fatty acids?
  acetyl-CoA.
• More C-H bonds, so yields more ATP.

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Alternative Energy Sources

• From Proteins
• Cells dont store protein.
• Enzymes breakdown proteinsinto AA units, then
  strip of the NH3 group.
• Carbon backbone either gets converted into fats
  or carbohydrates.
• Or, enter krebs cycle.

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Calvin Cycle (extra video)