Chapter 9
Cellular
Respiration
How Cells Harvest
Chemical Energy
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
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
Breathing supplies oxygen to cells
1. Breathing brings
oxygen into the
body
6. Blood carries CO2 back
to lungs - exhaled
5. CO2 diffuses out of
cells into blood
4. Oxygen diffuses into
body cells, is used in
cell respiration.
2. Oxygen in lungs
diffuses into blood
3. Blood delivers
oxygen to all
body cells
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
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
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
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
Stages of Cell Respiration
1. Glycolysis
• Splits glucose in half
• In cytoplasm
2. Kreb’s Cycle
• In mitochondria
• Finishes glucose
breakdown
3. Electron Transport Chain
• In mitochondria
• Generates the most ATP
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
glycolysis
Kreb’s cycle
Electron transport Chain
2 stages of breakdown
glycolysis
fermentation
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
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)
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
Pyruvic Acid Breakdown
NOT a separate stage
PREPARES pyruvic acid for Kreb’s cycle
2) Hydrogens removed
 NADH
1) Carbon removed
 CO2
3) 2-carbon acetyl
attaches to
Coenzyme A
4) Acetyl-Co A
begins Kreb’s cycle
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”
Kreb’s citric acid cycle
Stage 2 in aerobic respiration
Completes breakdown of glucose to CO2
- generates many molecules of NADH and FADH2
1) Pyruvic acid: broken
down  acetyl (2-C)
- joins to coenzyme A
2) starting molecule –
acetyl CoA
3) 4-C compound in
matrix + acetyl
 6 C citric acid
7) 4-C
compound
recycled
6). Hydrogens removed
to carriers NAD, FAD
5) one ATP
forms
4) two carbons
removed as CO2
Final Products of Kreb’s Cycle
1. 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
Electron Transport Chain
Stage 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
1
Starting molecules
NADH, FADH2
release H+ and electrons
6. Final electron
acceptor is oxygen
O + H+ + e-  H2O
ADP + P  ATP
2
Electrons pass
from one protein in
transport chain to
next
5
4
3
Electron energy pumps H+
across membrane
- make H+ gradient
H+ ions diffuse through
ATP synthase
(chemiosmosis)
Energy Yield In Aerobic Resp.
Total Energy yield/ glucose:
Glycolysis – 2 ATP
Krebs – 2 ATP
ETC -- 30-32 ATP
Total/glucose = 34-36 ATP
Summary of Aerobic Respiration
PATHWAYS
GLYCOLYSIS
KREBS
CYCLE
ELECTRON
TRANSPORT
# ATP
REACTANTS
PRODUCTS
Glucose + O2
2 pyruvic acid
2 NADH
2
acetyl CoA
2 CO2
8 NADH,FADH2
2
NADH, FADH2
H2O
30 - 32
Total ATP
LOCATION
cytoplasm
matrix
cristae
34-36
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
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  Kreb’s  finish aerobic
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
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