Cellular Respiration:

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Chapter 8

• Cellular Respiration
• Harvesting Chemical Energy

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Aerobic Anaerobic Metabolism

• Aerobic metabolism - When enough oxygen reaches
  cells to support energy needs
• - Maximum energy production
• Anaerobic metabolism
• When the demand for oxygen outstrips the bodys
  ability to deliver it
• Low energy production

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AEROBIC HARVEST OF FOOD ENERGY

• Cellular respiration is the main way that
  chemical energy is harvested from food and
  converted to ATP for cellular work
• Cellular respiration is an aerobic process
  requiring oxygen

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The Versatility of Cellular Respiration

• Cellular respiration can burn other kinds of
  molecules besides glucose
• Diverse types of carbohydrates
• Fats
• Proteins

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The Overall Equation for Cellular Respiration

• A common fuel molecule for cellular respiration
  is glucose
• This is the overall equation for what happens to
  glucose during cellular respiration

Glucose
Oxygen
Carbon dioxide
Water
Energy
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But Remember

• Cellular Respiration is a metabolic pathway, not
  a single reaction
• Many chemical reactions, both aerobic and
  anaerobic, are involved in the process of
  cellular respiration
• Lots of enzymes are required for the process to
  occur

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The Relationship Between Cellular Respiration and
Breathing

• Cellular respiration and breathing are closely
  related
• Cellular respiration requires a cell to exchange
  gases with its surroundings
• Breathing exchanges these gases between the blood
  and outside air

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The Role of Oxygen in Cellular Respiration

• During cellular respiration, hydrogen and its
  bonding electrons change partners
• Hydrogen and its electrons go from sugar to
  oxygen, forming water

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Comparison
Respiration Photosynthesis
Occurs in all organisms Occurs in only chlorophyll containing organisms
Breaks down glucose Stores light energy as chemical energy in the bonds of glucose
Releases carbon dioxide, water, ATP Produces glucose and oxygen
Exergonic Reaction Endergonic reaction
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The Metabolic Pathway of Cellular Respiration

• All of the reactions involved in cellular
  respiration can be grouped into three main stages
• Glycolysis occurs in cytoplasm
• The Krebs cycle occurs in matrix of
  mitochondria
• Electron transport occurs across the
  mitochondrial membrane

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A Road Map for Cellular Respiration
Mitochondrion
Cytosol
High-energy electrons carried mainly by NADH
High-energy electrons carried by NADH
Glycolysis
Krebs Cycle
2 Pyruvic acid
Electron Transport
Glucose
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Glycolysis

• Stage One

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Stage 1 Glycolysis

• Glycolysis takes place in the cytoplasm
• Oxygen NOT required
• Process breaks a six-carbon glucose into two,
  three-carbon molecules
• A molecule of glucose is split into two molecules
  of pyruvic acid
• These molecules then donate high energy electrons
  to NAD, forming NADH

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Glycolysis
METABOLIC PATHWAY
2 Pyruvic acid
Glucose
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Glycolysis
CoA
Acetic acid
Pyruvic acid
Acetyl-CoA (acetyl-coenzyme A)
CO2
Coenzyme A
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Krebs Cycle

• Stage Two

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Stage 2 The Krebs Cycle

• The Krebs cycle completes the breakdown of sugar
• It occurs inside the mitochondria
• In the Krebs cycle, pyruvic acid from glycolysis
  is first prepped into a usable form by
  combining it with enzyme Co-A to make Acetyl-CoA

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ACETYL Co-A
Input
Output
2
Acetic acid
1
2 CO2
3
ADP
Krebs Cycle
3 NAD?
4
FAD
5
6
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Electron Transport

• Stage 3

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Stage 3 Electron Transport

• Electron transport releases the energy your cells
  need to make the most of their ATP
• The molecules of electron transport chains are
  built into the inner membranes of mitochondria

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Stage 3 Electron Transport

• The chain functions as a chemical machine that
  uses energy released by the fall of electrons
  to pump hydrogen ions across the inner
  mitochondrial membrane
• These ions store potential energy

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Electron transport chain

• Cytochromes carry electron carrier molecules
  (NADH FADH2) down to oxygen
• Chemiosmosis energy
  coupling mechanism
• ATP synthase produces ATP by using the H
  gradient (proton-motive force) pumped into the
  inner membrane space from the electron transport
  chain this enzyme harnesses the flow of H back
  into the matrix to phosphorylate ADP to ATP
  (oxidative phosphorylation)

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Protein complex
Electron carrier
Inner mitochondrial membrane
Electron flow
ATP synthase
Electron transport chain
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Food
Polysaccharides
Fats
Proteins
Sugars
Glycerol
Fatty acids
Amino acids
Amino groups
Acetyl- CoA
Krebs Cycle
Glycolysis
Electron Transport
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Adding Up the ATP
Cytosol
Mitochondrion
Glycolysis
2 Acetyl- CoA
Krebs Cycle
2 Pyruvic acid
Electron Transport
Glucose
Maximum per glucose
by ATP synthase
by direct synthesis
by direct synthesis
Figure 6.14
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FERMENTATION ANAEROBIC HARVEST OF FOOD ENERGY

• Some of your cells can actually work for short
  periods without oxygen (anaerobic respiration)
• For example, muscle cells can produce ATP under
  anaerobic conditions
• Called Fermentation
• Involves The anaerobic harvest of food energy

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Fermentation in Human Muscle Cells

• Human muscle cells can make ATP with and without
  oxygen
• They have enough ATP to support activities such
  as quick sprinting for about 5 seconds
• A secondary supply of energy (creatine phosphate)
  can keep muscle cells going for another 10
  seconds
• To keep running, your muscles must generate ATP
  by the anaerobic process of fermentation

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• Glycolysis is the metabolic pathway that provides
  ATP during fermentation
• Pyruvic acid is reduced by NADH, producing NAD,
  which keeps glycolysis going
• In human muscle cells, lactic acid is a
  by-product

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2 ADP 2
Glycolysis
2 NAD?
2 NAD?
Glucose
2 Pyruvic acid
2 H?
2 Lactic acid
Lactic acid fermentation
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Fermentation in Microorganisms

• Various types of microorganisms perform
  fermentation
• Yeast cells carry out a slightly different type
  of fermentation pathway
• This pathway produces CO2 and ethyl alcohol

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2 ADP 2
2 CO2 released
2 ATP
Glycolysis
2 NAD?
2 NAD?
2 Ethyl alcohol
Glucose
2 Pyruvic acid
2 H?
Alcoholic fermentation
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• The food industry uses yeast to produce various
  food products

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Related metabolic processes

• Fermentation alcohol pyruvate to ethanol
  lactic acid pyruvate to lactate
• Facultative anaerobes (yeast/bacteria)

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Review Cellular Respiration

• Glycolysis
• 2 ATP (substrate-level phosphorylation)
• Krebs Cycle
• 2 ATP (substrate-level phosphorylation)
• Electron transport oxidative phosphorylation
• 2 NADH (glycolysis) 6ATP
• 2 NADH (acetyl CoA) 6ATP
• 6 NADH (Krebs) 18 ATP
• 2 FADH2 (Krebs) 4 ATP
• 38 TOTAL ATP/glucose
  
  

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Sunlight supplies the energy!
Sunlight energy
Bonds of Glucose, made in chloroplasts, contain
the stored energy
Ecosystem
Photosynthesis (in chloroplasts)
Raw materials for cellular respiration
Carbon dioxide
Raw materials for photosynthesis
Glucose
Oxygen
Water
Glucose broken down to release energy for
cellular work
Cellular respiration (in mitochondria)
Cellular energy
Heat energy
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