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Cellular Metabolism
Biol 105
Lecture 6
Read Chapter 3 (pages 63 – 69)
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Metabolism
Consists of all of the chemical reactions
that take place in a cell
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Metabolism
Animation—Breaking Down Glucose For Energy
http://wps.aw.com/bc_goodenough_boh_4/177/45509/11650544.cw/index.html
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Cellular Metabolism
Aerobic cellular respiration – requires
oxygen, produces carbon dioxide
Anaerobic Fermentation – does not require
oxygen
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Summary of Cellular Respiration
Figure 3.27
Blood
vessel
Carrier
protein
Glucose
Oxygen
Extracellular fluid
Plasma
membrane
Glycolysis
glucose pyruvate
Mitochondrion
Citric
Acid
Cycle
Electron
Transport
Chain
Transition
Reaction
Electrons
transferred
by NADHCytoplasm
Electrons
transferred
by NADH
and FADH2
Electrons
transferred
by NADH
+32 ATP 36 ATP+2 ATP +2 ATP
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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
C6H12O6 + 6O2 → 6CO2 +6H2O + Energy
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Aerobic Cellular respiration
There are four steps of aerobic cellular
respiration:
1. Glycolysis
2. Transition Reaction
3. Citric Acid Cycle (Krebs Cycle)
4. Electron Transport Chain
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NADH and FADH2 are important carriers of electrons
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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
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Cellular Respiration - Glycolysis
Starts with glucose
Ends with 2 ATP, 2 NADH, 2 pyruvate
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Glycolysis
Figure 3.23
Cytoplasm
2 ADP
Glucose
Energy-
investment
phase
Glycolysis (in cytoplasm)
2 NADH
2 NAD+
4 ATP
4 ADP
Energy-
yielding
phase
2 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.
During the remaining
steps, four molecules
of ATP are produced.
During the first steps,
two molecules of ATP are
consumed in preparing
glucose for splitting.
2 Pyruvate
Two molecules of nicotine
adenine dinucleotide
(NADH), a carrier of
high-energy electrons,
also are produced.
In Cytosol
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Cellular Respiration – Transition Reaction
Phase 2: Transition reaction
Occurs within the mitochondria
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
Start with:
2 pyruvate (3 carbon molecules)
2 Coenzyme A
End with:
2 CO2
2 NADH
2 Acetyl CoA (2 carbon molecule)
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Transition Reaction
Figure 3.24
NADH
(electron passes
to electron
transport chain)
NAD+
Pyruvate (from glycolysis)
Acetyl CoA
CoA
Coenzyme A
CO2
Transition Reaction (in mitochondrion)
Citric Acid Cycle
A molecule of NADH is
formed when NAD+
gains two electrons
and one proton.
One carbon (in the form
of CO2) is removed
from pyruvate.
The two-carbon
molecule, called
an acetyl group,
binds to
coenzyme A
(CoA), forming
acetyl CoA,
which enters the
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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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
Figure 3.25
Acetyl CoA
CoA
Citrate
CO2leaves
cycle
NAD+
NADH
-Ketoglutarate
CO2 leaves cycle
NADH
FAD
Succinate
FADH2
Malate
NAD+
ATP ADP
Citric Acid Cycle
NADH
Oxaloacetate
NAD+
Pi+
Acetyl CoA, the
two-carbon compound
formed during the
transition reaction,
enters the citric acid
cycle.The citric acid cycle also
yields several molecules of
FADH2 and NADH, carriers of
high-energy electrons that
enter the electron transport
chain.
The citric acid cycle yields
One ATP from each acetyl
CoA that enters the cycle,
for a net gain of two ATP.
Citric Acid Cycle (in mitochondrion)
CoA
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Cellular Respiration
Phase 4: 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
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The Big Pay Off – Electron Transport Chain
NADH and FADH2 are important carriers of
electrons
They donate electrons to the electron transport
chain
At the end of the chain oxygen accepts the
electrons.
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The Big Pay Off – Electron Transport Chain
Electron Transport Chain produces ATP using the
ATP synthase protein molecule
The Electron Transport Chain produces 32 ATP
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Electron Transport Chain
Figure 3.26
The molecules of NADH andFADH2 produced by earlier phasesof cellular respiration pass their electrons to a series of protein molecules embedded in the inner membrane of the mitochondrion.
As the electrons are transferred from one protein to the next, energy is released and used to make ATP.2e
–
2e–
2e–
2e–
2e–
NAD+
High
Low
Membrane
proteins
H2O
2 H+ + O2Energy released is used
for synthesis of ATP
FADH2
NADH
Electron Transport Chain (inner membrane of mitochondrion)
FAD
12
Po
ten
tial en
erg
y
Eventually, the electrons are passed to oxygen, which combines with two hydrogens to form water.
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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
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
Table 3.5
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Summary of Cellular Respiration
One molecule of glucose is broken down
and 36 ATP are generated.
Oxygen is used by the electron transport
chain – it accepts electrons from the ETC
Carbon dioxide is produced by the
Transition Reaction and the Citric acid
cycle
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Glycolysis: Starts the process by taking in
glucose. Produces 2 ATP
The Transition Reaction produces CO2 and
NADH
The Citric acid cycle: Produces 2 ATP but
also produces lots of NADH and FADH2.
Produces CO2.
Summary of Cellular Respiration
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Electron transport chain
Takes electrons from NADH and FADH2and uses them to produce ATP using the
ATP synthase molecule.
Requires oxygen. Oxygen is the final
electron acceptor on the electron
transport chain
One glucose can produce a total of 36 ATP
Summary of Cellular Respiration
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Complex Carbohydrates
must first be broken
down into glucose before
entering glycolysis
Fats and proteins enter
the process at different
steps
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Oxygen
Cellular respiration requires oxygen – this is
aerobic cellular respiration
Sometimes organisms, including humans,
need to produce energy without using oxygen
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
Breakdown of glucose without oxygen
Takes place entirely in the cytoplasm
It is very inefficient - results in only two ATP
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Anaerobic Fermentation
Anaerobic Fermentation: Anaerobic pathway
to produce ATP from glycolysis without the
Krebs and ETC
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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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What is the starting molecule of glycolysis?
1. Acetyl CoA
2. Protein
3. Glucose
4. Pyruvate (pyruvic
acid)
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Which stage produces CO2
1. Glycolysis
2. Electron
Transport Chain
3. Transition
4. Citric acid Cycle
5. Both 3 and 4
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Which stage uses O2
1. Glycolysis
2. Krebs Cycle
3. Electron
Transport Chain
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Which stage produces the most NADHs
1. Glycolysis
2. Krebs Cycle
3. Electron
Transport Chain
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Which stage produces the most ATP
1. Glycolysis
2. Krebs Cycle
3. Electron
Transport Chain
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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
Describe in detail how is ATP made using the electron transport chain
What is the role of ATPsynthase, H+, O2, NADH and FADH2 and the electron transport chain in ATP production?
Know the overall picture of cellular respiration (summary slides)
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Important Concepts
What is the role of oxygen in cellular respiration, what steps produce carbon dioxide
What is anaerobic fermentation, what steps are involved in fermentation, what end products are produced in humans, is oxygen required? when is it used.
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Definitions
Aerobic cellular respiration, anaerobic
fermentation , ATP synthase, metabolism