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CP BIO
Chapter 9
Cellular Respiration
How Cells
Harvest
Chemical Energy
CP BIO: Ch. 9 Cell Respiration
All life activities need energy
a. Maintain homeostasis; do life functions
breathe, circulate blood
active transport, synthesize molecules
regulate temperature, etc.
b. Physical and mental activity
c. Cells use energy in ATP molecules
Basics 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 36 ATP
Cells use ATP for energy
ATP - adenosine triphosphate
High-energy bond between phosphate groups
- breaks easily, bond energy is released
Energy is used by cell to do work
All organisms do respiration
• Need oxygen - aerobic
• No oxygen - anaerobic
Energy flow is one-way
- sun plants  ATP
Chemicals recycle
Oxygen and Energy
Aerobic respiration harvests the most ATP from glucose
Aerobic
Breaks down glucose completely
Anaerobic
Glucose partly broken down
Yields max amount of ATP
Yields only 2 ATP/glucose
Most organisms
Only a few microorganisms
Products: CO2 , H2O
Products: depends
3 stages of breakdown
Glycolysis
Krebs cycle
Electron Transport Chain
2 stages of breakdown
Glycolysis
Fermentation
Mitochondria – “power house”
Compartments
- for different stages
• Inner membrane
– Deep folds for more surface
– Many reactions at the same time
• Cristae - folds in membrane
• Matrix
– Space enclosed by inner
membrane
• Intermembrane space
– Between inner and outer
membrane
Cells need
oxygen for cell
respiration
In lungs: O2 goes into blood; CO2 out
In cells: O2 goes into cells; CO2 out
Cells use O2 for respiration, make CO2
Electron Acceptors
• Help in reaction pathway, re-used
• 2 in respiration: NAD and FAD
• Accept hydrogen ions and electrons
from glucose as it breaks down
• Transfer them to another molecule
later in pathway
–makes ATP
3 Stages in Respiration
1.Glycolysis
• In cytoplasm
• Splits glucose in half
2.Krebs Cycle
• In mitochondria
• Finishes glucose breakdown
• 3. Electron Transport Chain
• In mitochondria
• Generates the most ATP
3 Stages
of Cell
Respiration
Glycolysis 1st stage
Glycolysis = “sugar splits”
Glucose 2 smaller molecules
- makes 2 ATP
Need ATP to start
a. Two ATP attach to glucose
b. glucose splits in two
c. forms 3-carbon PGAL
d PGAL becomes pyruvic acid
2 ATP invested
Energized glucose splits
Hydrogen ions and
electrons removed
4 ATP made
Net yield 2
Final carbon compound
Glycolysis – splits glucose
1) NAD takes H from glucose – makes NADH
2) PGAL changes to pyruvic acid
3) 4 ATP are produced, but net yield is 2
Products of glycolysis:
2 ATP
2 NADH
2 pyruvic acid
All organisms do glycolysis
• Need no oxygen or special organelles
• Probably evolved very early in history
of life
• Can meet energy needs of some
simple organisms
Sir Hans Krebs
1900-1981
• German chemist, 1930s
• Described the cycle of reactions that
make energy in cells
• Received Nobel in 1953
• “Krebs Cycle” or “Citric Acid Cycle”
IF OXYGEN IS PRESENT,
pyruvic acid moves into mitochondrion
More H go to NAD
CO2 comes off
Forms Acetyl-CoA
Ready for Krebs Cycle
PREPARES pyruvic acid for Kreb’s cycle
NOT a separate stage
Krebs Citric Acid Cycle
Stage 2 in aerobic respiration
In MATRIX
Completes breakdown
of glucose to CO2
Makes many
molecules of NADH
and FADH2
(make ATP in Stage 3)
Why is it a “Cycle”?
Carbon
compound in
matrix is used
and returned
-”recycled”
Each cycle
makes 1 ATP
Acetyl CoA starts
the “cycle”
Citric Acid is first
carbon compound to
form in cycle
Products of Krebs Cycle
• 2 ATP/glucose molecule (one each “turn”)
• Several molecules of NADH and FADH2
– These will yield energy in stage 3
• Last carbons in glucose form CO2 and
diffuse out of cell
Stage 3 - Electron Transport Chain
• SAME AS ETC IN PHOTOSYNTHESIS
• Chain of proteins in inner membrane
• Take electrons from NADH, FADH
• Electron energy makes ATP
MOST ATP made in this stage
ETC in Respiration
Only happens if oxygen is
available to take electrons at end of
chain and form WATER
O + 2 H+ + 2 e-  H2O
Electrons power ATP synthesis
Total ATP yield per glucose:
Glycolysis – 2 ATP
Krebs
– 2 ATP
ETC
- 32 ATP
Total
= 36 ATP
Summary of Aerobic Respiration
Pathway
Glycolysis
Reactants
Glucose +
Products
# ATP Location
2
cytoplasm
CO2 NADH
FADH2
2
Mitochondrial
H2O
32
Pyruvic Acid
NADH
Krebs
Cycle
Acetyl CoA
Electron
Transport
Chain
NADH,
FADH2
O2
matrix
Mitochondrial
cristae
Total ATP
36-38
Anaerobic Respiration
FERMENTATION follows glycolysis
– Needs NO oxygen
– Makes NO additional ATP after glycolysis
– NAD is reused
– Pyruvic acid is changed into a final product
Fermentation: two kinds
Alcohol
lactic acid
Alcohol Fermentation
Some yeasts
• pyruvic acid  ethyl alcohol + CO2
•Baking, brewing beer and wine
• CO2 gas makes bread dough rise,
bubbles in beer and champagne
No more ATP made
Lactic Acid Fermentation
• Pyruvic acid  lactic acid
• Anaerobic bacteria -make lactic (and other) acids
• Commercial uses: cheese, yogurt, soy products,
sauerkraut, vinegars
• Muscle cells – can do fermentation only temporarily
•
lactic acids builds up  “oxygen debt”
• Muscles fatigue, cramp
• With fresh oxygen: Lactic acid  blood  liver,
changed back to pyruvic acid  Kreb’s cycle
Other foods in respiration
Carbs are #1 choice for cell energy: 4 cal/g
Fats: twice the calorie store: 9cal/g
Proteins: LAST choice:
– needed for many important roles
4 cal/g
-Fats and proteins are also broken down in
many small steps
-Amount of ATP depends on molecule