Chapter 9: Cellular Respiration
9-1 Chemical Pathways
Chemical Energy and Food
• Cellular respiration happens slowly and in many
steps.
• If all the energy was release in one step . . . Most
would be lost as light and heat!
– Cellular respiration breaks down glucose
molecules and banks their energy in ATP
Chemical Energy and Food
PHOTOSYNTHESIS
6 CO
6H O
2 + _________
2
___________
+ ___________
C6H12O6 + __________
6O2
→_______________
CELLULAR RESPIRATION
C6H12O6 + _________
6 CO2 + __________
6 H2O + __________
6O2 →________
_____________
The two equations are exact opposites!
Chemical Energy and Food
• Amount of heat it takes to raise 1 gram of
water 1o Celsius = calorie
• Unit for measuring energy in food = Calorie
• 1 Calorie = 1,000 calories
Overview of Cellular Respiration
Occurs in three main stages
Stage 1: Glycolysis
• Occurs in the cytoplasm
• Breaks down glucose into
pyruvate, producing a small Stage 1
amount of ATP
Stage 2: The citric acid cycle
Stage 2
(Krebs cycle)
• Takes place in the
Stage 3
mitochondria
• Completes breakdown of
glucose, produces a small
amount of ATP
• Provides third stage of cell
respiration with electrons
Overview of Cellular Respiration
•
Cellular respiration
– Stage 3: Oxidative
phosphorylation (ETC)
• Occurs in the mitochondria
• Uses the energy released
by “falling” electrons to
pump H+ across a
membrane
• Harnesses the energy of the
H+ gradient through
chemiosmosis, producing
ATP
Stage 3
Understanding Oxidation and Reduction
•Oxidation is the loss of electrons; electrons are
removed from hydrogen atoms contained in glucose.
•Reduction is the gain of electrons; oxygen atoms
accept hydrogen and electrons forming water H2O.
•Remember OIL RIG (oxidation is loss, reduction is
gain)
Electron Carriers (enzymes) Involved
•NAD+ (Nicotinamide adenine dinucleotide)
Accepts H+ to become NADH
•FAD (Flavin adenine dinucleotide)
Accepts 2H+ to become FADH2
Overview of Cellular Respiration
NADH
High-energy electrons
carried by NADH
NADH
FADH2
and
Stage 1
Stage 3
Stage 2
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
GLYCOLYSIS
Glucose
CITRIC ACID
CYCLE
Pyruvate
Krebs
Mitochondrion
Cytoplasm
ATP
Substrate-level
phosphorylation
CO2
CO2
ATP
ATP
Substrate-level
phosphorylation
Oxidative
phosphorylation
9.2 Glycolysis
•
•
•
•
(Glykos = sweet, Lysis = split apart)
The first step in cellular respiration = Glycolysis
Happens in the CYTOPLASM outside the
mitochondria
Does not require oxygen, BUT it needs some
energy to get it started.
What molecule is going to supply the energy?
ATP
Glycolysis
________
↓
GLUCOSE
___________
ATP
→
PYRUVIC ACID
→ 2 _____________
↓
ATP
ATP
ATP
NADH
NADH
____________________ + _______________
PUT IN 2 ATP and GET BACK 4 ATP
Net gain of 2 ATP and 2 NADH
Glycolysis
• Produces pyruvic acid
(pyruvate – a 3 carbon
compound)
• Cell needs to invest
some energy to get a
higher return (2 ATP
gained)
• Occurs quickly, in
miliseconds to
respond to increased
energy demand
9-2 The Krebs Cycle and
Electron Transport
Mitochondria Structure
• Has a double membrane, with an intermembrane space
between the two layers.
• Cristae are folds of the inner membrane
• The matrix is the innermost compartment, which is
filled with a gel-like fluid.
• Krebs Cycle occurs in the matrix of the mitochondria.
The Krebs Cycle
• Pyruvic acid enters the
mitochondria matrix
• Pyruvic acid is converted
into an intermediate 2
carbon molecule called
Acetyl-CoA before
entering the Krebs Cycle.
• The Krebs cycle breaks
down carbon compounds
into carbon dioxide
(waste), ATP, NADH,
and FADH2
The Krebs Cycle
The Krebs Cycle Produces
(in one turn)
3
____
1
____
1
____
4
____
The Krebs Cycle
Carbon dioxide is lost to the
atmosphere as waste
ATP can be used directly to
supply energy for the cell
High energy electron carriers
move into the ELECTRON
TRANSPORT CHAIN
Electron Transport Chain
•Electrons from NADH and FADH2
travel down the electron transport
chain, between protein complexes to
oxygen (final electron acceptor),
which picks up H+ to form water
•Energy released by the redox
reactions is used to pump H+ into
the space between the mitochondrial
membranes
•Virtual Cell ETC Animation
NADH
NAD
+
H
+
ATP

2e
+
Controlled
release of
energy for
synthesis of
ATP

2e
2
H
1
+
2
H2O
O2
Chemiosmosis
• In chemiosmosis, the H+ diffuses back through the
inner membrane through ATP synthase complexes.
Driving the synthesis of ATP
H+
H+
H+
H+
+
Intermembrane
space
Inner
mitochondrial
membrane
.
H
H+
Protein
complex
H+
Electron
carrier
FADH2
Electron
flow
NADH
H+
H+
FAD
NAD+
H+
1O
+ 2 H+
2 2
+
Mitochondrial
matrix
ATP
synthase
H
H+
H2O
ADP
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
+
P
ATP
H+
Chemiosmosis
Fermentation
• Pyruvic acid moves to the next step
– If there is no oxygen = anaerobic
– If there is oxygen = aerobic
Fermentation
• Fermentation – process by which cells
release energy in the absence of oxygen
• Two types of fermentation:
– Alcoholic Fermentation
– Lactic Acid Fermentation
Alcoholic Fermentation
PYRUVIC
ACID +_____
_______
+
ALCOHOL
CO
NAD
2
→__________ + ______ + _____
• Happens when yeast makes bread dough rise,
CO2 bubbles make air spaces in bread.
(Alcohol evaporates during cooking)
• Happens when:
– Yeast make beer and wine
Lactic Acid Fermentation
PYRUVIC
ACID +_____
_______
+
LACTIC
ACID
NAD
→______________ + ________
• Happens in muscles during exercise when
body can’t get oxygen to tissues fast enough.
• Lactic acid builds up in muscles causing
soreness.
• Bacteria use lactic acid fermentation to make:
yogurt, cheese, sour cream, pickles, sauerkraut,
kimchi
The Totals
• Cellular Respiration (aerobic: with oxygen)
1 glucose → 36 ATP
• Fermentation (anaerobic: without oxygen)
1 glucose → 2 ATP
Respiration Questions
1. List the reactants and products of
respiration
2. List the three steps (stages) involved in
respiration
3. Name two electron carriers involved
4. What step produces the most ATP
Respiration Questions
In your group:
5. See if you can write the chemical equation for
respiration (inputs and outputs)
6. What is the organelle in cells that is “releasing”
energy during respiration?
7. What primary molecule is energy being “released”
from?
8. How is the sun indirectly involved in respiration?
Fermentation Questions
1. List two types of fermentation
2. List the reactants for both types of
fermentation
3. List the products for fermentation used to
brew beer
4. List the products for fermentation used to
make yogurt
5. What important molecule cycles back from
fermentation to keep glycolysis going?
6. What process starts fermentation?
Krebs Cycle
1.___________
2.___________
7.________
3.________
4.________
6.________
5.________
Electron Transport Chain (ETC)
H+
H+
H+
H+
+
Intermembrane
space
H
H+
Protein
complex
H+
Electron
carrier
.
H+
H+
ATP
synthase
Inner
mitochondrial
membrane
Electron
flow
FADH2
NAD+
NADH
Mitochondrial
matrix
FAD
H+
1
O2 + 2 H+
2
H+
H+
H2O
Electron Transport Chain
OXIDATIVE PHOSPHORYLATION
ADP
+
ATP
P
H+
Chemiosmosis