Transcript Cellular Respiration

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
Food energy is
measured in calories
calorie = energy needed to
raise the temperature of one
mL water 1 degree Celsius
Food labels:
Calorie (Kcal) = 1000 calories
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
Phosphorylate - add a phosphate group to a molecule
- transfers energy to new molecule
When cell needs energy for work, 3rd phosphate
comes off ATP and attaches to molecule doing work
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ATP – ADP Cycle
• ATP breakdown products (ADP + P) stay in cell
• used again to make more ATP when needed
ATP made in
cell respiration
ATP used for
cellular work
Very fast!! 10 million ATP/second in a cell
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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
Kreb’s cycle
Electron Transport Chain
2 stages of breakdown
Glycolysis
Fermentation
Mitochondria – “power house”
Compartments
- for different stages
• Matrix
– Space enclosed by inner
membrane
• Inner membrane
– Deeply folded, more surface
– Many reactions at the same time
• Cristae - folds in membrane
• Intermembrane space
– Between inner and outer
membrane
Gas exchange is by diffusion
In the lungs:
Oxygen from air
- diffuses into blood
- carried to body cells
Carbon dioxide from blood
- diffuses into air sacs
- removed from body
Cells need oxygen for respiration
In cells:
- oxygen diffuses IN
- CO2 goes OUT
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
Stages of Cell Respiration
1. Glycolysis
• In cytoplasm
• Splits glucose in half
2. Kreb’s Cycle
• In mitochondria
• Finishes glucose
breakdown
3. Electron Transport Chain
• In mitochondria
• Generates the most ATP
Glycolysis 1st stage in cell respiration
Glycolysis = “sugar splits”
Glucose  two smaller molecules
small amount of energy released
Need 2 ATP to start
a. Two ATP attach to glucose
b. glucose splits in two
c. 3-carbon PGAL forms
d. PGAL goes through several
more reactions
e. PGAL becomes pyruvic acid
Glycolysis breakdown
1) Each PGAL loses hydrogen to NAD+
a) makes NADH
b) PGAL changes to pyruvic acid
2) 4 ATP are produced, but net yield is 2
Products of glycolysis:
1) 2 ATP
2) 2 NADH
3) 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”
Pyruvic Acid Breakdown
PREPARES pyruvic acid for Kreb’s cycle
NOT a separate stage
1) Hydrogen removed  NADH 3) Acetyl-CoA forms
2) Carbon removed  CO2
4) Ready for Kreb’s cycle
Kreb’s Citric Acid Cycle
Stage 2 in aerobic respiration
In MATRIX
Completes breakdown
of glucose to carbon
dioxide
Makes many
molecules of NADH
and FADH2
(make energy later)
Products of Kreb’s Cycle
1. 2 ATP/glucose molecule (one each “turn”)
2. Several molecules of NADH and FADH2
–
These will yield energy in stage 3
3. Last carbons in glucose form CO2 and
diffuse out of cell
Electron Transport Chain
Stage 3 in aerobic respiration
• 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
Chemiosmosis and ATP
• ATP Synthase – enzymes in cristae
• Electron energy creates H+ concentration
• H+ ions diffuse through ATP synthase
• activate synthase enzyme
• make (synthesize) ATP
ADP + P  ATP
2)Electron energy
pumps H+ across
membrane
- Forms H+ gradient
1)Starting molecules
NADH, FADH2
release H+ and
electrons
3) H+ ions diffuse
through ATP
synthase
(chemiosmosis)
5) Final electron
acceptor is oxygen
4) ADP + P  ATP
O + H+ + e-  H2O
Electrons power ATP synthase
enzyme makes ATP
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
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
Breathing supplies oxygen to cells
1) Breathing
brings oxygen
into the body
6) Blood carries CO2 back
to lungs - exhaled
2) Oxygen in lungs
diffuses into blood
5) CO2 diffuses out
of cells into blood
4) Oxygen is used in
cell respiration.
3) Blood delivers
oxygen to all
body cells
1) Pyruvic acid is
broken down to CO2
and acetyl (2-C)
-- joins to coenzyme A
2) starting molecule – acetyl CoA
4. Carbon “fixed”  6 C citric acid
3) 4-C compound in matrix
8) 4-C compound
recycled
5) two carbons  CO2
7) hydrogens removed
- NAD, FADH reduced
6) one ATP forms