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Metabolism
Cellular Metabolism
 Consists of all of the chemical reactions
that take place in a cell
Biol 105
Lecture 6
Read Chapter 3 (pages 63 – 69)
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Cellular Metabolism
Summary of Cellular Respiration
 Aerobic cellular respiration – requires
oxygen, produces carbon dioxide
Electrons
transferred
by NADH
Blood
vessel
Glucose
 Anaerobic Fermentation – does not require
oxygen
Cytoplasm
Electrons
transferred
by NADH
Electrons
transferred
by NADH
and FADH2
Plasma
membrane
Carrier
protein
Citric
Acid
Cycle
Transition
Reaction
Glycolysis
glucose
pyruvate
Electron
Transport
Chain
Oxygen
Mitochondrion
Extracellular fluid
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Aerobic Cellular respiration
 In aerobic cellular respiration cells take in
sugar (glucose) and breaks it down to into
carbon dioxide and water, this requires
oxygen.
 This process produces energy in the form
of ATP
+2 ATP
+2 ATP
+32 ATP

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36 ATP
Figure 3.27
Aerobic Cellular respiration

There are four steps of aerobic cellular
respiration:
1.
2.
3.
4.
Glycolysis
Transition Reaction
Citric Acid Cycle (Krebs Cycle)
Electron Transport Chain
 C6H12O6 + 6O2 → 6CO2 +6H2O + Energy
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Cellular Respiration - Glycolysis
 Phase 1: Glycolysis
 Occurs in the cytoplasm
 Splits one glucose into two pyruvate molecules
 Generates a net gain of 2 ATP and 2 NADH
molecules
 Does not require oxygen
NADH and FADH2 are important carriers of electrons
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Cellular Respiration - Glycolysis
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Glycolysis
Glycolysis (in cytoplasm)
 Starts with glucose
Cytoplasm
During the first steps,
two molecules of ATP are
consumed in preparing
glucose for splitting.
 Ends with 2 ATP, 2 NADH, 2 pyruvate
Glucose
2 ATP
Energyinvestment
phase
During the remaining
steps, four molecules
of ATP are produced.
2 ADP
4 ADP
4 ATP
The two molecules of
pyruvate then diffuse
from the cytoplasm into
the inner compartment
of the mitochondrion,
where they pass through
a few preparatory steps
(the transition reaction)
before entering the citric
acid cycle.
2 NAD +
2 Pyruvate
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Energyyielding
phase
2 NADH
Two molecules of nicotine
adenine dinucleotide
(NADH), a carrier of
high-energy electrons,
also are produced.
Figure 3.23
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Cellular Respiration – Transition Reaction
 Phase 2: Transition reaction
 Occurs within the mitochondria
In Cytosol
 Coenzyme A combines with pyruvate and
CO2 is removed from each pyruvate
 Forms 2 acetyl CoA molecules
 Produces 2 NADH
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Transition Reaction
Transition Reaction
Transition Reaction (in mitochondrion)
 Start with:
Pyruvate (from glycolysis)
 2 pyruvate (3 carbon molecules)
 2 Coenzyme A
One carbon (in the form
of CO2) is removed
from pyruvate.
A molecule of NADH is
formed when NAD+
gains two electrons
and one proton.
CO2
NAD+
 End with:
Coenzyme A
NADH
 2 CO2
 2 NADH
 2 Acetyl CoA (2 carbon molecule)
(electron passes
to electron
transport chain)
CoA
Acetyl CoA
The two-carbon
molecule, called
an acetyl group,
binds to
coenzyme A
(CoA), forming
acetyl CoA,
which enters the
citric acid cycle.
Citric Acid Cycle
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Cellular Respiration – Citric acid cycle
 Phase 3: Citric acid cycle
 Occurs in the mitochondria
 Acetyl CoA enters the citric acid cycle
 Releases 2 ATP, 2 FADH2 and 6 NADH, 4
CO2 molecules
 Requires oxygen
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Figure 3.24
Citric Acid Cycle
 Also called the Krebs Cycle
 Start with 2 Acetyl CoA
 End with:
 4 CO2
 2 ATP
 6 NADH and 2 FADH2
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Citric Acid Cycle
Cellular Respiration
Citric Acid Cycle (in mitochondrion)
 Phase 4: Electron transport chain
Acetyl CoA, the
tw o-carbon compound
form ed during the
transition reaction,
enters the citric acid
cycle.
The citric acid cycle also
yields several m olecules of
FADH2 and NADH, carriers of
high-energy electrons that
enter the electron transport
chain.
 Electrons of FADH2 and NADH are
transferred from one protein to another, until
they reach oxygen
 Releases energy that results in 32 ATP
 Requires oxygen
Acetyl CoA
CoA
CoA
Oxaloacetate
Citrate
NADH
CO2
leaves
cycle
NAD+
NAD+
Citric Acid Cycle
Malate
NADH
FADH2
ADP + Pi
ATP
FAD
 -Ketoglutarate
Succinate
CO2 leaves cycle
+
NAD
The citric acid cycle yields
One ATP from each acetyl
CoA that enters the cycle,
for a net gain of tw o ATP.
NADH
Figure 3.25
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The Big Pay Off – Electron Transport Chain
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The Big Pay Off – Electron Transport Chain
 NADH and FADH2 are important carriers of
electrons
 Electron Transport Chain produces ATP using the
ATP synthase protein molecule
 They donate electrons to the electron transport
chain
 The Electron Transport Chain produces 32 ATP
 At the end of the chain oxygen accepts the
electrons.
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Electron Transport Chain
Electron Transport Chain (inner membrane of mitochondrion)
The molecules of NADH and
FADH2 produced by earlier phases
of cellular respiration pass their
electrons to a series of protein
molecules embedded in the inner
membrane of the mitochondrion.
High
NAD+
NADH
As the electrons are transferred
from one protein to the next,
energy is released and used to
make ATP.
Potential energy
2e –
FADH2
Membrane
proteins
2e –
FAD
2e –
2e –
Eventually, the
electrons are
passed to oxygen,
which combines
with two hydrogens
to form water.
2e –
Low
Energy released is used
for synthesis of ATP
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H2O
1
2 H+ + 2 O2
Figure 3.26
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How is ATP made using the ETC
1. In the mitochondria, the NADH and FADH
donate electrons to the electron transport chain
(ETC)
2. Oxygen is the final electron acceptor from the
ETC
3. The ETC uses the energy from the electrons to
transport H+ against the concentration
gradient, transporting them from the lumen of
the mitochondria to the intermembrane space.
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How is ATP made using the ETC
Summary of Cellular Respiration
4. The ATPsynthase transports the H+ back to the
lumen of the mitochondria.
5. The H+ falling through the ATPsynthase
provides the energy for the ATPsynthase to
catalyze the reaction of ADP + P →ATP
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Summary of Cellular Respiration
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Summary of Cellular Respiration
 One molecule of glucose is broken down
and 36 ATP are generated.
 Glycolysis: Starts the process by taking in
glucose. Produces 2 ATP
 Oxygen is used by the electron transport
chain – it accepts electrons from the ETC
 The Transition Reaction produces CO2 and
NADH
 Carbon dioxide is produced by the
Transition Reaction and the Citric acid
cycle
 The Citric acid cycle: Produces 2 ATP but
also produces lots of NADH and FADH2.
Produces CO2.
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Table 3.5
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Summary of Cellular Respiration
Complex Carbohydrates
must first be broken
down into glucose before
entering glycolysis
 Electron transport chain
 Takes electrons from NADH and FADH2
and uses them to produce ATP using
the ATP synthase molecule.
 Requires oxygen. Oxygen is the final
electron acceptor on the electron
transport chain
Fats and proteins enter
the process at different
steps
 One glucose can produce a total of 36 ATP
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Oxygen
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Anaerobic Fermentation
 Cellular respiration requires oxygen – this is
aerobic cellular respiration
 Breakdown of glucose without oxygen
 Sometimes organisms, including humans,
need to produce energy without using oxygen
 Takes place entirely in the cytoplasm
 When you need energy quick, or if there is
not enough O2 then the cell will use only
glycolysis
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Anaerobic Fermentation
 Anaerobic Fermentation: Anaerobic pathway
to produce ATP from glycolysis without the
Krebs and ETC
 It is very inefficient - results in only two ATP
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Fermentation in Animals
 When cells need energy quick they will use this
pathway for a short time
 2 pyruvic acid + 2 NADH → 2 lactate and 2
NAD+
 End result = lactate and 2 ATP produced (from
glycolysis) and NAD+ is regenerated
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Important Concepts
 Read Ch 4
 What is Cellular respiration and Anaerobic
Fermentation and what are the differences
between them.
 What are the four steps of aerobic cellular
respiration, what happens in each step, what
are the starting molecules, what comes out of
each step, where in the cell does each step
occur, how many ATP and NADH/FADH2 are
produced in each step.
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Important Concepts
Important Concepts
 Describe in detail how is ATP made using the
electron transport chain
 What is the role of oxygen in cellular respiration,
what steps produce carbon dioxide
 What is the role of ATPsynthase, H+, O2, NADH
and FADH2 and the electron transport chain in
ATP production?
 What is anaerobic fermentation, what steps are
involved in fermentation, what end products are
produced in humans, is oxygen required? when is
it used.
 Know the overall picture of cellular respiration
(summary slides)
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Definitions
 Aerobic cellular respiration, anaerobic
fermentation , ATP synthase, metabolism
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