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Honors Biology
Chapter 6
Cellular
Respiration
How Cells Harvest
Chemical Energy
Honors Bio Ch. 6:Cell Respiration
All life activities need energy
a. Maintain homeostasis; do life functions
breathe, circulate blood
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
1 gram carb = 4 cal
1 gram fat
= 9 cal
1 gram protein = 4 cal
6.1 Photosynthesis and cellular respiration
provide energy for life
Photosynthesis – makes food
Light energy  chemical energy in food
– Plants, algae, cyanobacteria
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 and anaerobic
Energy flow is one-way
Chemicals recycle
Oxygen and Energy
Aerobic respiration harvests the most ATP from glucose
Aerobic
Anaerobic
Breaks down glucose completely
Glucose partly broken down
Yields max amount of ATP
Yields 2 ATP/glucose
Most organisms
Only a few microorganisms
3 stages of breakdown
1. Glycolysis
2. Kreb’s cycle
3. Electron Transport Chain
Products: CO2 and H2O
2 stages of breakdown
1. Glycolysis
2. Fermentation
Products: depends on organism
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
Gas exchange is by diffusion
In the lungs:
Air inhaled, fills alveoli
- O2 diffuses into blood
CO2 diffuses from blood
- into alveoli
- is exhaled
In cells: O2 goes IN - CO2 goes OUT
Cells use oxygen for respiration
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
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
Redox reactions in cellular respiration
Overview:
Glucose loses energy – oxidized
Oxygen gains energy – reduced
Glucose breakdown is a series of redox reactions
-electron energy is used to make ATP
Electron/H+ 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
Oxidation
dehydrogenase
Reduction
NAD
2H 
2H

2eNADH
H
2 e
Enzymes and coenzymes in cellular respiration
Dehydrogenase enzyme - removes H
Hydrogen/Electron Acceptors (coenzymes)
NAD+ + 2 H  NADH + H+ (reduced)
FAD + 2 H  FADH2 (reduced)
NAD = nicotinamide adenine dinucleotide
FAD = flavin adenine dinucleotide
LE 6-6
Cellular respiration occurs in three main stages
NADH
High-energy electrons
carried by NADH
FADH2
NADH
and
GLYCOLYSIS
Glucose
CITRIC ACID
CYCLE
Pyruvate
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
Cytoplasm
Mitochondrion
CO2
CO2
ATP
Substrate-level
phosphorylation
Begins glucose
breakdown
ATP
ATP
Substrate-level
phosphorylation
Removes CO2
Harvests H+ and e-
Oxidative
phosphorylation
Chemiosmosis
makes ATP
1st stage – Glycolysis (in cytoplasm)
Glycolysis - “sugar splits” - forms two smaller molecules
Energy invested
a. 2 ATP phosphorylate glucose
b. glucose splits in two
c. 3-carbon intermediate forms (PGAL, G3P)
2 ATP invested
Energized glucose splits
Hydrogen ions and
electrons removed
4 ATP made
Net yield 2
Final carbon compound
Glycolysis breakdown
1) Each G3P (PGAL) loses hydrogen to NAD+
a) makes NADH
b) G3P 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 (3 carbons)
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
6.8 IF oxygen is present, pyruvate is
prepared for citric acid cycle
One carbon is
removed  CO2
More
hydrogens to
NAD  NADH
Coenzyme A bonds
to 2-carbon acetyl
 acetyl CoA
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”
Krebs 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)
Krebs Cycle
1) START – acetyl CoA
2) 4-C oxaloacetate
in matrix
7) END:oxaloacetate
recycled
3) acetyl + oxalo 
6 C citric acid
4) 2 carbons
removed 
CO2
6) hydrogens removed,
NADH, FADH2 form
5) one ATP forms
LE 6-9b
CoA
Acetyl CoA
CoA
2 carbons enter cycle
Oxaloacetate
Citrate
NADH
 H
leaves
cycle
CO2
NAD
NAD
CITRIC ACID CYCLE
Malate
NADH
ADP
FADH2

P
ATP
Alpha-ketoglutarate
FAD
CO2
Succinate
NADH
 H
NAD
leaves
cycle
 H
Products of Krebs 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
Review: Krebs Cycle
1. START – acetyl CoA (2C)
2. Joins 4C compound in matrix (oxaloacetate)
3. Forms 6C citric acid  2 CO2
4. Carriers NAD+, FAD reduced
5. Each cycle makes 1 ATP (2 ATP/glucose)
6. 4C compound returned
7. END: CO2, NADH, FADH2, ATP
Most ATP is made in Stage 3
Electron Transport Chain (in cristae)
– H ions power ATP synthesis
Electron transport chain
NADH and FADH2 give up
their electrons and H+
Electrons pass from one
acceptor molecule to the next
The energy released is used to make ATP
NAD+ and FAD can now be reused
Chemiosmosis
Only proceeds if oxygen is available to take
electrons at end of chain  makes water
O + 2H+ + 2 e-  H2O
2) Electrons pass from
one protein in
transport chain to next
3) Electron energy
used to pump H+ into
intermembrane space
1) Starting
molecules
NADH, FADH2
release their
electrons and H+
6) Final electron
acceptor is oxygen
5) ADP + P  ATP
4) H+ diffuse through
ATP synthase
(chemiosmosis)
Electrons power ATP synthase
enzyme makes ATP
Total ATP yield per glucose:
Glycolysis – 2 ATP
Krebs
– 2 ATP
ETC
- 32 ATP
Total
= 36 ATP
OXIDATIVE PHOSPHORYLATION
- Inorganic PO4 added to ADP
- ADP + P  ATP
Summary of Aerobic Respiration
Pathway
Glycolysis
Reactants
Products
Glucose +
O2
Pyruvic Acid
Krebs
Cycle
Acetyl CoA
Electron
Transport
Chain
NADH
FADH
O2
# ATP Location
2
cytoplasm
CO2 NADH
FADH2
2
Mitochondrial
H2O
32
NADH
matrix
Mitochondrial
cristae
Total ATP
36
CYTOCHROMES in transport chain
- used to find evolutionary relationships
LE 6-12
Review Aerobic Respiration – 3 stages
Electron shuttle
across membrane
Cytoplasm
2 NADH
Mitochondrion
2
NADH
(or 2 FADH2)
2 NADH
6
GLYCOLYSIS
2
Pyruvate
Glucose
2 Acetyl
CoA
 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
CITRIC ACID
CYCLE
NADH
2 FADH2
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
 2 ATP
 about 34 ATP
by substrate-level
phosphorylation
by oxidative
phosphorylation
About
38 ATP
Fermentation
anaerobic respiration
Needs no oxygen
•Makes no additional ATP after glycolysis
•Hydrogen on NADH returns to pyruvic acid
– Pyruvate is the “final electron acceptor”
•NAD+ can be reused
•Pyruvate is rearranged into a final product
Lactic acid Fermentation
Pyruvic Acid (3 carbons)  Lactic acid (3 carbons)
•No more ATP made
•No further glucose breakdown
•NAD+ returned for reuse
Lactic Acid Fermentation
• Many anaerobic bacteria
• make lactic (and other) acids
• Commercial uses: cheese, yogurt, soy products,
sauerkraut
• Muscle cells – can do fermentation temporarily
•
lactic acids builds up  “oxygen debt”
• Muscles fatigue, cramp
• With fresh oxygen: Lactic acid converted back to
pyruvate Kreb’s
Alcohol Fermentation
• Some yeasts
• Pyruvic acid (3C)  CO2 + ethyl alcohol (2C)
• Baking, brewing beer and wine
• CO2 gas makes bread dough rise, bubbles in
beer and champagne
NAD+ returned for reuse
No more ATP made
Cells use many kinds of organic molecules as fuel
for cellular respiration
• Complex Carbohydrates
• Digested to glucose  glycolysis
• Lipids
• Digested to glycerol (3-C)  intermediates
in glycolysis
• fatty acids  2-C acetyls  Krebs cycle
• Proteins
• Digested to amino acids  most used by
organism in synthesis of new proteins
• Excess  Intermediates in glycolysis or
Krebs cycle (2-3 carbons)
• Nitrogen waste is toxic  urine or other
compounds
LE 6-14
Food, such as
peanuts
Fats
Carbohydrates
Sugars
Glycerol
Proteins
Fatty acids
Amino acids
Amino groups
Glucose
G3P
Pyruvate
Acetyl
CoA
GLYCOLYSIS
ATP
CITRIC
ACID
CYCLE
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
Cells make all the molecules they need
using raw materials in food - biosynthesis
1. Not all food is used for energy
2. Cells can use monomers in food to make new molecules
• Also use intermediate compounds in glycolysis and Kreb’s
3. can make molecules not found in food
• Ex. Human protein from plant or animal protein
4. Biosynthesis uses ATP
LE 6-15
ATP needed to drive biosynthesis
ATP
CITRIC
ACID
CYCLE
GLUCOSE SYNTHESIS
Acetyl
CoA
Pyruvate
Fatty acids
Glycerol
G3P
Glucose
Amino
groups
Amino acids
Proteins
Fats
Cells, tissues, organisms
Sugars
Carbohydrates
Some Poisons Block ETC and
Stop Chemiosmosis
How Poisons Kill
a) Some block proteins in ETC
- no electron transfer, no H+ gradient
 no ATP
b) Some block H+ flow through ATP synthase
 no ATP
c) Some let H+ ions cross membrane freely
- no gradient  no ATP
Glycolysis
1.
2.
3.
4.
5.
6.
2 ATP used
Glucose split into 2 PGAL (3C each)
PGAL (G3P) undergo a series of reactions
2 NAD+ are reduced (will yield energy later) NADH
4 ATP are produced (net yield 2 ATP)
End products – 2 pyruvate (3C each)
Substrate-level phosphorylation
– Phosphate from one molecule is transferred to another
– In glycolysis, phosphate goes from 1) ATP to glucose;
2) from energized PGAL to ADP, forming ATP