Download Electron Transport System – oxidative phosphorylation

Basal Metabolic Rate
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•
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Minimum energy required to stay alive
Kj / g / hr
Measured at rest
In thermostatically controlled room
No food in previous 12 hours
• What factors would affect your BMR?
Breathing and cell respiration are not the same
but are related
O2
BREATHING
CO2
Lungs
CO2
Bloodstream
O2
Muscle cells carrying out
CELLULAR RESPIRATION
Sugar + O2  ATP + CO2 + H2O
Cellular respiration uses oxygen and glucose
to produce carbon dioxide, water, and ATP.
Glucose
Oxygen
Carbon
dioxide
Water
Energy
How efficient is cell respiration?
Energy released
from glucose
(as heat and light)
Energy released
from glucose
banked in ATP
Gasoline energy
converted to
movement
About
40%
25%
100%
Burning glucose
in an experiment
“Burning” glucose
in cellular respiration
Burning gasoline
in an auto engine
ATP = the universal energy currency
Role of ATP in the human body
The molecule ATP can be thought of as cash carrying a “piece of chemical energy” to
wherever it’s needed. The mechanism responsible for cellular work is the transfer of a
phosphate group (Pi). Enzymes shift a phosphate group from ATP to some other molecule.
This molecule becomes phosphorylated, also known as activated, and can perform work.
ATP itself is deactivated to ADP as its phosphate group is removed. For example, ATP
activates transport proteins in cell membranes for active transport, motor proteins for
muscular contractions or chemical substances for chemical reactions.
Reduction and Oxidation
OILRIG
Oxidation is losing electrons (or gain of O, or loss of H)
Reduction is gaining electrons (or loss of O, or gain of H)
Loss of hydrogen atoms
Energy
Glucose
Gain of hydrogen atoms
Glucose gives off energy as it is oxidised
The coenzymes NAD+ and FAD act as an
electron shuttle
FAD
+ 2H

FADH2
The mitochondrion
Glycolysis
https://www.youtube.com/watch?v=EfGlznwfu9U
Occurs in the cytoplasm
Breaks down glucose (6 C) into 2 pyruvate (3 C)
Produces 2 ATP molecules + 2 NADH
Glycolysis
Glycolysis
Steps 1 – 3 A fuel
molecule is energized,
using ATP.
Glucose
Step
1
Glucose-6-phosphate
2
Fructose-6-phosphate
Energy In: 2 ATP
3
Fructose-1,6-diphosphate
Step 4 A six-carbon
intermediate splits into
two three-carbon
intermediates.
4
Glyceraldehyde-3-phosphate
(G3P)
5
Step 5 A redox
reaction generates
NADH.
6
Energy Out: 4 ATP
Steps 6 – 9 ATP
and pyruvic acid
are produced.
1,3-Diphosphoglyceric acid
(2 molecules)
7
3-Phosphoglyceric acid
(2 molecules)
8
2-Phosphoglyceric acid
(2 molecules)
2-Phosphoglyceric acid
(2 molecules)
NET 2 ATP
9
Pyruvic acid
(2 molecules
per glucose molecule)
Link reaction
Pyruvate is decarboxylated and dehydrogenated in the
mitochondria if oxygen is available
The products are CO2 and acetyl CoA (2 C) and NADH
Pyruvic Acid
Acetyl CoA
The Krebs cycle (TCA cycle /citric acid cycle)
In the mitochondial matrix https://www.youtube.com/watch?v=JPCs5pn7UNI
Electron Transport System – oxidative phosphorylation
https://www.youtube.com/watch?v=VER6xW_r1vc
Protein
complex
Intermembrane
Electron
space
carrier
Inner
mitochondrial
membrane
Electron
flow
Mitochondrial
matrix
ELECTRON TRANSPORT CHAIN
ATP
SYNTHASE
ATP Synthase, a molecular mill
Generation of ATP
Chemiosmosis
Cells use the energy released
by “falling” electrons in the
ETS to pump H+ ions across a
membrane.
The H+ ions can only move
back through the inner
membrane via a special
channel in ATP synthase.
This drives the reaction
between ADP and Pi, making
ATP.
Review of cellular respiration
How each molecule of glucose yields many ATP
Fermentation versus respiration
Pyruvate, the end product of glycolysis, represents the fork in the
catabolic pathways of glucose.
Fermentation
Respiration involves glycolysis, the Krebs cycle, and electron transport: an overview
Respiration is a cumulative function of three metabolic stages, diagrammed in Figure 9.6:
1) Glycolysis
2) The Krebs cycle
3) The electron transport chain and oxidative phosphorylation
The first two stages, glycolysis and the Krebs cycle, are the ___________ pathways that decompose
glucose and other organic fuels. Glycolysis, which occurs in the ____________, begins the degradation by
breaking glucose into two molecules of a compound called _____________.
The Krebs cycle, which takes place within the _________________________, completes the job by
decomposing a derivative of pyruvate to carbon dioxide. Thus, the carbon dioxide produced by respiration
represents fragments of oxidized organic molecules.
Some of the steps of glycolysis and the Krebs cycle are ___________ reactions in which
________________ enzymes transfer electrons from substrates to NAD+, forming ______________.
In the third stage of respiration, the _________________________ accepts electrons from the breakdown
products of the first two stages (usually via ____________) and passes these electrons from one molecule
to another. At the end of the chain, the electrons are combined with _________________ and
______________ to form water. The energy released at each step of the chain is stored in a form the
mitochondrion can use to make ATP. This mode of ATP synthesis is called _________________________
because it is powered by the redox reactions that transfer electrons from food to oxygen.
The site of electron transport and oxidative phosphorylation is the _____________________ of the
mitochondrion.
Oxidative phosphorylation accounts for almost 90% of the ATP generated by respiration. A smaller amount
of ATP is formed directly in a few reactions of glycolysis and the Krebs cycle by a mechanism called
____________________ phosphorylation. This mode of ATP synthesis occurs when an enzyme transfers a
phosphate group from a substrate molecule to ______________. "Substrate molecule" here refers to an
Respiration involves glycolysis, the Krebs cycle, and electron transport: an overview
Respiration is a cumulative function of three metabolic stages, diagrammed in FIGURE 9.6:
1) Glycolysis
2) The Krebs cycle
3) The electron transport chain and oxidative phosphorylation
The first two stages, glycolysis and the Krebs cycle, are the catabolic pathways that decompose glucose
and other organic fuels. Glycolysis, which occurs in the cytosol, begins the degradation by breaking
glucose into two molecules of a compound called pyruvate. The Krebs cycle, which takes place within the
mitochondrial matrix, completes the job by decomposing a derivative of pyruvate to carbon dioxide. Thus,
the carbon dioxide produced by respiration represents fragments of oxidized organic molecules.
Some of the steps of glycolysis and the Krebs cycle are redox reactions in which dehydrogenase enzymes
transfer electrons from substrates to NAD+, forming NADH.
In the third stage of respiration, the electron transport chain accepts electrons from the breakdown products
of the first two stages (usually via NADH) and passes these electrons from one molecule to another. At the
end of the chain, the electrons are combined with hydrogen ions and molecular oxygen to form water (see
FIGURE 9.5b). The energy released at each step of the chain is stored in a form the mitochondrion can use
to make ATP. This mode of ATP synthesis is called oxidative phosphorylation because it is powered by the
redox
reactions
that
transfer
electrons
from
food
to
oxygen.
The site of electron transport and oxidative phosphorylation is the inner membrane of the mitochondrion
(see FIGURE 7.17).
Oxidative phosphorylation accounts for almost 90% of the ATP generated by respiration. A smaller amount
of ATP is formed directly in a few reactions of glycolysis and the Krebs cycle by a mechanism called
substrate-level phosphorylation (FIGURE 9.7). This mode of ATP synthesis occurs when an enzyme
transfers a phosphate group from a substrate molecule to ADP. "Substrate molecule" here refers to an
organic molecule generated during the catabolism of glucose.
The electron transport chain and oxidative phosphorylation
Fig 9-15. Chemiosmosis couples the electron transport chain to ATP synthesis. NADH shuttles high-energy electrons
extracted from food during glycolysis and the Krebs cycle to an electron transport chain built into the inner mitochondrial
membrane. The gold arrow traces the transport of electrons, which finally pass to oxygen at the "downhill" end of the chain
to form water.
Most of the electron carriers of the chain are grouped into three complexes, each represented here by a purple blob
embedded in the membrane. Two mobile carriers, ubiquinone (Q) and cytochrome c, move rapidly along the membrane,
ferrying electrons between the three large complexes. As each complex of the chain accepts and then donates electrons, it
pumps hydrogen ions (protons) from the mitochondrial matrix into the intermembrane space. Thus, chemical energy
originally harvested from food is transformed into a proton-motive force, a gradient of H+ across the membrane. The
hydrogen ions flow back, down their gradient, through a channel in an ATP synthase, another protein complex built into the
membrane. The ATP synthase harnesses the proton-motive force to phosphorylate ADP, forming ATP. (This phosphorylation
is called oxidative because it is driven by the loss of electrons from food molecules.) The use of an H+ gradient (protonmotive force) to transfer energy from redox reactions to cellular work (ATP synthesis, in this case) is called chemiosmosis.
The catabolism of various food molecules