Chapter 9 Cellular Respiration

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Chapter 9Cellular Respiration

• How Cells Harvest Chemical Energy

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All life activities need energy
a. Maintain homeostasis do life functions
breathing, blood circulation active transport,
biosynthesis regulate temperature, etc. b.
Physical and mental activity c. Cells use energy
in ATP molecules
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Food energy is measured in calories
Food labels Calorie (Kcal) 1000
calories calorie energy needed to raise the
temperature of one mL water 1 degree Celsius
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Breathing supplies oxygen to cells

• 1. Breathing brings oxygen into the body

2. Oxygen in lungs diffuses into blood
6. Blood carries CO2 back to lungs - exhaled
3. Blood delivers oxygen to all body cells
5. CO2 diffuses out of cells into blood
4. Oxygen diffuses into body cells, is used in
cell respiration.
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Gas exchange is by diffusion
In the lungs Oxygen from air in air sacs -
into blood in capillaries - carried to all body
cells Carbon dioxide from blood - into air in
air sacs (alveoli) - removed from body In body
cells oxygen diffuses in CO2 diffuses out
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Overview of Cellular Respiration

• Breaks down glucose in many small steps
• a biochemical pathway
• Energy released is stored in molecules of ATP
• Each ATP has enough energy for one cell task
• One glucose molecule yields 34-36 ATP

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Mitochondria power house

• Compartments
• - for different stages
• Matrix
• Space enclosed by inner membrane
• Inner membrane
• Deeply folded for more surface area
• Many reactions at the same time
• Cristae - folds in membrane
• Intermembrane space
• Between inner and outer membrane

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Electron Acceptors

• NAD and FAD
• Accept hydrogen ions and electrons
• from glucose as it breaks down
• Transfer them to another molecule
• in Electron Transport Chain
• makes ATP

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Stages of Cell Respiration

• Glycolysis
• Splits glucose in half
• In cytoplasm
• Krebs Cycle
• In mitochondria
• Finishes glucose breakdown
• 3. Electron Transport Chain
• In mitochondria
• Generates the most ATP

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Oxygen and Energy
Aerobic respiration harvests the most ATP
from glucose Aerobic
Anaerobic Breaks down glucose
completely Glucose only partly broken
down Yields maximum amount of ATP Yields
only 2 ATP/ glucose molecule Most organisms
Only a few microorganisms 3 stages of
breakdown 2 stages of breakdown
glycolysis glycolysis Krebs
cycle fermentation Electron transport Chain
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Glycolysis 1st stage in cell respiration

• Glycolysis sugar splits
• Glucose ? two smaller molecules
• - small amount of energy released
• USE 2 ATP to start
• a. Two ATP are added to glucose
• b. Glucose splits ? PGAL (3-C)
• c. Some hydrogens go to NAD
• d. Several more reactions

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Final Products of Glycolysis

• Glucose splits
• a. forms 2 molecules of pyruvic acid (3-C)
• (further breakdown in aerobic)
• b. 2 NADH (these will make ATP later)
• c. net 2 ATP (made 4 but used 2 to start)

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Advantages of glycolysis

• All life forms do glycolysis
• Need no oxygen or special organelles
• Probably evolved very early in history of life
• Can meet energy needs of some simple organisms

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Pyruvic Acid Breakdown
NOT a separate stage PREPARES pyruvic acid for
Krebs cycle
3) 2-carbon acetyl attaches to Coenzyme A

• Hydrogens removed
• ? NADH

• Carbon removed
• ? CO2

4) Acetyl-Co A begins Krebs cycle
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Sir Hans Krebs 1900-1981

• German chemist
• Described the cycle of reactions that make energy
  in cells
• 1930s
• Received Nobel in 1953
• Krebs Cycle or Citric Acid Cycle

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Krebs citric acid cycle Stage 2 in aerobic
respiration
Completes breakdown of glucose to CO2 -
generates many molecules of NADH and FADH2
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2) starting molecule acetyl CoA
1) Pyruvic acid broken down ? acetyl (2-C) -
joins to coenzyme A
3) 4-C compound in matrix acetyl ? 6 C
citric acid
7) 4-C compound recycled
6). Hydrogens removed to carriers NAD, FAD
4) two carbons removed as CO2
5) one ATP forms
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Final Products of Krebs Cycle

• 2 ATP/glucose molecule
• 2. Many molecules of NADH and FADH2
• These will yield energy in stage 3
• 3. Last carbons in glucose form CO2
• - diffuse out of cell

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Electron Transport ChainStage 3 in aerobic
respiration

• What is it?
• Chemiosmosis same as in photosynthesis
• Series of proteins in inner membrane (cristae)
• Pass electrons along chain
• Electron energy makes ATP

Only proceeds if oxygen is available to
take electrons at end of chain O 2
H 2 e- ? H2O
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6. Final electron acceptor is oxygen O H
e- ? H2O
1 Starting molecules NADH, FADH2 release H
and electrons
5 ADP P ? ATP
2 Electrons pass from one protein in transport
chain to next
4 H ions diffuse through ATP synthase (chemiosmo
sis)
3 Electron energy pumps H across membrane - make
H gradient
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Energy Yield In Aerobic Resp.
Total Energy yield/ glucose Glycolysis 2
ATP Krebs 2 ATP ETC -- 30-32 ATP
Total/glucose 34-36 ATP
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Summary of Aerobic Respiration
PATHWAYS REACTANTS   PRODUCTS ATP LOCATION
GLYCOLYSIS   Glucose O2 2 pyruvic acid 2 NADH   2   cytoplasm
KREBS CYCLE acetyl CoA 2 CO2 8 NADH,FADH2 2  matrix 
ELECTRON TRANSPORT NADH, FADH2  H2O 30 - 32  cristae
Total ATP   Total ATP   Total ATP   Total ATP   34-36
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• Fermentation is anaerobic respiration
• Needs no oxygen
• Makes no additional ATP after glycolysis
• Hydrogens on NADH return to pyruvic acid
• NAD can be reused
• Pyruvate is rearranged into a final product

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Lactic Acid Fermentation

• Pyruvic acid (3-C) ? lactic acid (3-C)
• Anaerobic bacteria -make lactic (and other)
  acids
• Commercial uses cheese, yogurt, soy products,
  sauerkraut, vinegars
• Muscle cells can do fermentation temporarily
• lactic acids builds up ? Muscles fatigue, cramp
• oxygen debt
• With fresh oxygen Lactic acid ? converted back
  to pyruvate ? Krebs ? finish aerobic

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Alcohol Fermentation

• Some yeasts
• pyruvic acid (3-C) ? ethyl alcohol (2-C) CO2
• Baking, brewing beer and wine
• CO2 gas makes bread dough rise, bubbles in beer
  and champagne

NAD returned for reuse No additional ATP made
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Comparing Photosynthesis and Respiration

• Photosynthesis makes food
• Light energy ? chemical energy
• 6 H2O 6 CO2 ? C6 H12 O6 6 O2
• Respiration breaks down food for cell energy
• C6 H12 O6 6 O2 ? 6 H2O 6 CO2
• Energy in food ? energy in ATP
• All living things
• Aerobic or anaerobic
• Energy flow is one-way
• Nutrient chemicals recycle