Transcript ATP synthase

How Cells Harvest Chemical Energy
• Cellular respiration is the process by which
energy is harvested by cells from sugar
– Requires Oxygen (O2)
– Releases Carbon Dioxide (CO2) , water (H2O)
and a large amount of ATP
• All of our cells harvest chemical energy (from
food)
Cellular Respiration stores energy in ATP
molecules
• A cell uses energy to build and maintain its
structure, transport materials, manufacture
products, move, grow and reproduce
• Cellular respiration involves mainly sugars, but
other organic compounds can be broken down
(nearly all the equations you’ll see use glucose
as the representative food molecule)
• Our bodies require a continuous supply of
energy just to stay alive
Organisms use energy from ATP for all its
activities
• Breathing
• Heart
pumping
• Maintaining
body
temperature
• Thinking,
dreaming
Organisms use energy from ATP for all its
activities
• Above and beyond the energy we need for body
maintenance, cellular respiration provides
energy for voluntary activities
• The amount of energy it takes to perform these
activities are expressed as kilocalories (a
“calorie” on a nutritional label actually equals 1
kilocalorie)
• A kilocalorie is the quantity of heat required to
raise the temperature of 1L water by 1 ̊C
Energy consumed by various activities
(kilocalorie consumed per hour)
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Running
Dancing
Bicycling
Swimming
Walking
Sitting
979
510
490
408
245
28
Cellular Respiration
• C6H12O6 + 6O2 + 38ADP +38P→ 6H2O + 6CO2 + 38ATP
• Cellular respiration occurs in 3 stages
– Glycolysis
– Citric Acid Cycle
– The Electron Transport Chain (Oxidative
Phosphorylation)
• All of these steps occur in and around the
mitochondria in eukaryotic cells
NADH
High-energy electrons
carried by NADH
NADH
FADH2
and
GLYCOLYSIS
Glucose
Pyruvate
OXIDATIVE
PHOSPHORYLATION
(Electron Transport
and Chemiosmosis)
CITRIC ACID
CYCLE
Pyruvate
Cytoplasm
Inner
mitochondrial
membrane
CO2
CO2
2 ATP
2 ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
34 ATP
Oxidative
phosphorylation
Cellular Respiration – Glycolysis
• What two words do you see immediately in the
word “glycolysis”?
• Glycolysis literally means the “splitting of sugar”
• Glycolysis begins with a molecule of glucose (6Carbon sugar) and ends with 2 molecules of
pyruvate (a 3-Carbon compound)
• Requires the initial input of 2 ATP molecules
Glycolysis
• Glucose (C6H12O6)+ 2ATP  2 Pyruvate
• Glycolysis is a multi-step pathway, which utilizes
at least 6 different enzymes in a metabolic
pathway that is anaerobic (without oxygen)
• In the later stages of glycolysis, 4 ATP molecules
are synthesized using the energy given off
during the chemical reactions; net gain of 2 ATP
• Additionally, 2 hydrogen atoms are removed
from the molecules that are formed as glucose is
converted into pyruvate.
– These hydrogen atoms are picked up by the
coenzyme NAD to form NADH (2 total) which
are used during the Electron Transport Chain
Glycolysis
http://highered.mcgrawhill.com/sites/0072507470/student_vie
w0/chapter25/animation__how_glycoly
sis_works.html
The Citric Acid Cycle (aka “The Krebs
Cycle”)
• As pyruvate is formed at the end of glycolysis, it
is transported from the cytoplasm into a
mitochondrion
• The pyruvate is converted into 2 molecules of
acetate which also produces 2 molecules of
CO2 and 2 molecules of NADH
• The Citric Acid Cycle breaks down acetate in the
mitochondrial matrix
• The Citric Acid Cycle produces 2 ATP molecules
plus 6 NADH and 2 FADH (another coenzyme)
The Electron Transport Chain
• The Electron Transport Chain is oxygen-driven
and produces the largest amount of ATPs in the
entire cellular respiration process
• For every glucose molecule that enters
glycolysis, there is a total net production of 38
ATPs by the end of the Electron Transport Chain
• The many folds of the mitochondrial inner
membrane enlarge its surface area, providing
space for thousands of copies of the Electron
Transport Chain occurring at once, producing
many ATP molecules
Electron Transport Chain
• A group of 3 integral proteins and 2 membrane
coenzymes associated with the inner mitochondrial
membrane called the electron transport chain (ETC)
creates a H+ gradient between the intermembrane
space and the matrix of the mitochondria using the H
of from NADH and FADH2 that accumulate in the
mitochondrial matrix as products of glycolysis and the
Krebs cycle
• 3 (integral) enzyme complexes of the ETC remove the
H from NADH and FADH2 (oxidized back to NAD+ and
FAD+) in the matrix
ETC and Oxidative Phosphorylation
FADH
FAD+
NADH and the Electron Transport Chain
• NADH is oxidized by Enzyme complex 1 of the ETC
• The H that is removed by Enzyme complex 1 is split
into an electron (e-) and a proton (H+)
• The e- is passed from the beginning to the end of the
ETC and energizes the 1st, 2nd and 3rd Enzyme
complexes along the way
– Once energized, each enzyme complex pumps a
free proton from the mitochondrial matrix into the
intermembrane space (3 total)
FADH and the Electron Transport Chain
• FADH is oxidized by Enzyme complex 2 of the ETC
• The H that is removed by Enzyme complex 2 is split
into an electron (e-) and a proton (H+)
• The e- is passed to the end of the ETC and energizes
the 2nd and 3rd Enzyme complexes along the way
– Once energized, each enzyme complex pumps a
free proton from the mitochondrial matrix into the
intermembrane space (2 total)
ATP Synthase
• ATP synthase is an integral membrane protein in the
inner mitochondrial membrane that has 2 functions:
– it acts as a H+ channel
• allows H+ to diffuse down its gradient from the
intermembrane space into the matrix
– it acts as an enzyme
• uses the energy that is released by the diffusion
of H+ to synthesize ATP from ADP and P
• This type of ATP synthesis is called oxidative
phosphorylation because, this process requires the
oxidation of NADH and FADH
ATP Synthesis During Oxidative Phosphorylation
• For each NADH that is oxidized, 3H+ are pumped into
the intermebrane space and the allowed to diffuse
back into the matrix through ATP synthase. Each H+
that diffuses through ATP synthase provides enough
energy to synthesize 1 molecule of ATP
– Therefore each NADH oxidized provides enough
energy to synthesize 3 molecules of ATP
– Since 10 molecules of NADH are made between
glycolysis and the Citric Acid cycle, 30 molecules of
ATP are made once all 10 NADH are oxidized
• 10 NADH x 3 ATP = 30 ATP
ATP Synthesis During Oxidative Phosphorylation
• For each FADH that is oxidized, 2H+ are pumped into
the intermebrane space and the allowed to diffuse
back into the matrix through ATP synthase. Each H+
that diffuses through ATP synthase provides enough
energy to synthesize 1 molecule of ATP
– Therefore each FADH oxidized provides enough
energy to synthesize 2 molecules of ATP
– Since 2 molecules of FADH are made between
glycolysis and the Citric Acid cycle, 4 molecules of
ATP are made once all 2 FADH are oxidized
• 2 FADH2 x 2 ATP = 4 ATP
Formation of Water
• After the electrons arrive to the last enzyme complex
of the ETC they are transferred to atoms of oxygen in
the mitochondrial matrix
– this makes oxygen especially negative
• In the matrix, these oxygen atom are combined with
the H+ that have diffused back into the matrix from the
intermembrane space to form water (H2O)
– the protons become “reunited” with their electron
Fermentation enables cells to produce ATP
without oxygen
• In the absence of oxygen, ATP may still be
produced via a process called fermentation
• Fermentation is the process of deriving energy
from organic compounds such as carbohydrates
in the absence of oxygen
• Cellular respiration always begins with
glycolysis; the presence or absence of oxygen
will then determine whether cellular respiration
or fermentation will follow
Fermentation
• Remember, glycolysis results in the formation of
2 3-carbon pyruvate molecules from 1 6-carbon
glucose molecule, and 2 ATP molecules are
released
• When oxygen is lacking, certain organisms
(such as yeasts) can convert pyruvate into ethyl
alcohol and CO2 which removes electrons and
allows continuous ATP production
• Yeasts are able to perform this process because
they have the necessary enzyme to convert
pyruvate into ethyl alcohol
Fermentation continued…
• In muscle cells, another type of fermentation
takes place
• When muscle cells contract too quickly (e.g.,
strenuous exercise), they rapidly use up their
oxygen supply, which slows ATP production
• Muscle cells, however, have the ability to
produce a small amount of ATP through
glycolysis in the absence of oxygen = lactic
acid fermentation
• The muscle cells convert
glucose to pyruvate, and
then an enzyme in the
muscle cells converts
pyruvate into lactic acid,
releasing 2 ATP molecules
• Lactic acid is toxic and
must be removed by the
liver (& converted back to
pyruvate); heavy breathing
after exercise helps restore
oxygen back to the muscle
cells