Download Respiration Review Glycolysis

Review
• Photosynthesis is the process
of incorporating energy from
light into energy-rich molecules
like glucose.
• Respiration is the opposite
process extracting that stored
energy from glucose to form
ATP (from ADP and Pi).
• The chemical equation
describing this process is
Respiration
• If you replace the energy with
light and reverse the equation,
it will describe photosynthesis.
Glycolysis
• Glycolysis is the
decomposition (lysis) of
glucose (glyco) to pyruvate
(or pyruvic acid).
• The steps are summarized as follows.
1. 2 ATP are added. The first several steps require the
input of energy. This changes glucose in preparation for
subsequent steps.
2. 2 NADH are produced. NADH (Nicotinamide adenine
dinucleotide) is a coenzyme, accepting 2 electrons from
the substrate molecule. Like NADPH in photosynthesis,
it is an energy-rich molecule. (You can keep the two
coenzymes NADH and NADPH associated with the
correct processes by using the P in NADPH as a
reminder of the P in photosynthesis. The P in NADPH,
however, actually represents phosphorus.)
3. 4 ATP are produced.
4. 2 pyruvate are formed.
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• Nine intermediate
products are
formed, and, of
course, each one
is catalyzed by an
enzyme.
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• In six of the steps,
magnesium ions
(Mg2+) are
cofactors that
promote enzyme
activity.
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The Krebs Cycle
• The Krebs
cycle details
what happens
to the pyruvate
end product of
glycolysis.
The Krebs Cycle
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1. Pyruvate to acetyl CoA. In a step leading
up to the actual Krebs cycle, pyruvate
combines with coenzyme A (CoA) to
produce acetyl CoA. In that reaction 1
NADH and 1 CO2 are also produced.
2. Krebs Cycle: 3 NADH, 1 FADH2, 1 ATP,
CO2. The Krebs cycle begins when acetyl
CoA combines with OAA (oxaloacetic acid)
to form citric acid.
There are 7 intermediate products.
Along the way, 3 NADH and 1 FADH2 (Flavin
adenine dinucleotide) are made and CO2 is
released.
FADH2, like NADH, is a coenzyme,
accepting electrons during a reaction.
Because the first product made from acetyl
CoA is the 3-carbon citric acid, the Krebs
cycle is also known as the citric acid cycle
or the tricarboxylic acid (TCA) cycle.
• In summary, glycolysis takes 1 glucose
and turns it into 2 pyruvate, 2 NADH, and
a net of 2 ATP (made 4 ATP, but used 2
ATP).
The Krebs Cycle
• Although the Krebs cycle
is described for 1
pyruvate, remember that
glycolysis produces 2
pyruvate.
• In Figure 4-1, the “× 2”
next to the pyruvate and
the Krebs cycle is a
reminder to multiply the
products of this cycle by
2 to account for the
products of a single
glucose.
The CO2 produced by the Krebs cycle is the
CO2 animals exhale when they breathe.
Oxidative
Phosphorylation
• Oxidative
phosphorylation is
the process of
extracting ATP
from NADH and
FADH2.
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There are 7
intermediate
products.
Oxidative Phosphorylation
Oxidative Phosphorylation
•
• The last electron acceptor at the end of the chain is oxygen.
• The 1⁄2O2 accepts the two electrons and, together with 2 H+, forms
water.
• NADH provides electrons that have enough energy to phosphorylate
3 ADP to 3 ATP.
• FADH2 produces 2 ATP.
How Many ATP?
How many ATP are made from the energy released from the breakdown of 1 glucose?
• Glycolysis produces 2 ATP and 2 NADH.
• When 2 pyruvate (from 1 glucose) are converted to 2 acetyl CoA, 2 more NADH are
produced.
• From 2 acetyl CoA, the Krebs cycle produces 6 NADH, 2 FADH2, and 2 ATP.
• If each NADH produces 3 ATP during oxidative phosphorylation, and FADH2
produces 2 ATP, the total ATP count from 1 original glucose appears to be 38 (Table
4-1).
Mitochondria
• The Krebs cycle and the conversion of pyruvate to acetyl CoA occur in
the mitochondrial matrix (the fluid part) (Figure 4-2).
• The electron transport chain proteins
are embedded in the cristae (singular, crista).
• The cristae are internal convoluted membranes
that separate the mitochondrion into an inner
compartment that contains the matrix and an
outer compartment between the cristae and the
outer mitochondrial membrane.
• Note how the spatial arrangement of the
respiratory processes in the mitochondrion
is similar to the spatial arrangement of
photosynthetic processes in the chloroplasts.
In chloroplasts, the carrier proteins of electron
transport chains are embedded in the inner
membranes, the thylakoids, while the enzymes
for the Calvin-Benson cycle are in the stroma.
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Electrons from NADH and FADH2 pass along an electron transport chain
analogous to electron transport chains in photophosphorylation.
These electrons pass from one carrier protein to another along the chain,
losing energy at each step.
Cytochromes and various other modified proteins participate as carrier
proteins in this chain.
One of these cytochromes, cytochrome c, is often compared among
species to assess genetic relatedness.
How Many ATP?
• How many ATP are made
from the energy released from
the breakdown of 1 glucose?
• Glycolysis produces 2 ATP
and 2 NADH.
• When 2 pyruvate (from 1
glucose) are converted to 2
acetyl CoA, 2 more NADH are
produced.
• From 2 acetyl CoA, the Krebs
cycle produces 6 NADH, 2
FADH2, and 2 ATP.
• If each NADH produces 3
ATP during oxidative
phosphorylation, and FADH2
produces 2 ATP, the total ATP
count from 1 original glucose
appears to be 38 (Table 4-1).
• The actual number, however, is 36. This is because
glycolysis occurs in the cytoplasm and each NADH
produced there must be transported into the
mitochondria for oxidative phosphorylation. The transport
of NADH across the mitochondrial membrane reduces
the yield of these NADH to only 2 ATP.
Not 6 ATP
Chemiosmotic Theory
• Electrons from NADH and FADH2 lose energy as they pass along
the electron transport chain in oxidative phosphorylation.
• That energy is used to phosphorylate ADP to ATP.
• Chemiosmotic theory describes how that phosphorylation occurs.
• The process is analogous to ATP generation in chloroplasts (Figure
4-3).
• In the cytoplasm, glycolysis
produces 2 pyruvate, 2
NADH, and 2 ATP.
• In order for ATP to be
extracted from the pyruvate
and NADH, these molecules
must be shipped across the
mitochondrial membrane
and into the matrix.
• Within the mitochondria,
pyruvate (after conversion
to acetyl CoA) enters the
Krebs cycle.
• The 2 NADH begin oxidative
phosphorylation with the
electron transport chain in
the cristae.
• These NADH, however, to
produce a net of only 2 ATP
each because 1 ATP is
required to move each of
them into the mitochondria.
Chemiosmotic Theory
• 2. A pH and electrical gradient across the crista membrane is
created. The accumulation of H+ in the outer compartment creates
a proton gradient (equivalent to a pH gradient) and an electric
charge (or voltage) gradient. These gradients are potential energy
reserves in the same manner as water behind a dam is stored
energy.
• 1. H+ accumulate in the outer compartment. The Krebs cycle
produces NADH and FADH2 in the matrix. As these two molecules
move through the electron transport chain, H+ (which is only a
proton) are pumped from the matrix across the cristae and into the
outer compartment (between the cristae and the mitochondrial outer
membrane).
Anaerobic Respiration
What if oxygen is not present?
• If oxygen is not present, there is no
electron acceptor to accept the
electrons at the end of the electron
transport chain.
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If this occurs, then NADH accumulates.
Once all the NAD+ has been converted
to NADH, the Krebs cycle and
glycolysis both stop (both need NAD+
to accept electrons).
Once this happens, no new ATP is
produced, and the cell soon dies.
• 3. ATP synthases generate ATP. Channel proteins (ATP
synthases) in the cristae allow the protons in the outer compartment
to flow back into the matrix. The protons moving through the channel
generate the energy for these channel proteins to produce ATP. It is
similar to how turbines in a dam generate electricity when water
flows through them.
• Anaerobic respiration is a
method cells use to escape
this fate.
• The pathways in plants and
animals, alcoholic and
lactate fermentation,
respectively, are slightly
different, but the objective
of both processes is to
replenish NAD+ so that
glycolysis can proceed
once again.
• Anaerobic respiration
occurs in the cytoplasm
alongside glycolysis.
Alcoholic Fermentation
•
Alcoholic fermentation (or
sometimes, just fermentation)
occurs in plants, fungi (such as
yeasts), and bacteria.
• The steps, illustrated in Figure 4-1,
are as follows:
1. Pyruvate to acetaldehyde. For each
pyruvate, 1 CO2 and 1 acetaldehyde
are produced. The CO2 formed is
the source of carbonation in
fermented drinks like beer and
champagne.
2. Acetaldehyde to ethanol. The important part of
this step is that the energy in NADH is used to
drive this reaction, releasing NAD+.
For each acetaldehyde, 1 ethanol is made and 1
NAD+ is produced.
The ethanol (ethyl alcohol) produced here is the
source of alcohol in beer and wine.
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Lactate Fermentation
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There is only one step in
lactate fermentation. A
pyruvate is converted to lactate
(or lactic acid) and in the
process, NADH gives up its
electrons to form NAD+.
As in alcoholic fermentation,
the NAD+ can now be used for
glycolysis.
When O2 again becomes
available, lactate can be
broken down and its store of
energy can be retrieved.
Because O2 is required to do
this, lactate fermentation
creates what is often called an
oxygen debt.
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It is important that you recognize
the objective of this pathway.
At first glance, you should wonder
why the energy in an energy-rich
molecule like NADH is removed
and put into the formation of
ethanol, essentially a waste
product that eventually kills the
yeast (and other organisms) that
produce it.
The goal of this pathway,
however, does not really concern
ethanol, but the task of freeing
NAD+ to allow glycolysis to
continue.
Recall that in the absence of O2 ,
all the NAD+ is bottled up in
NADH. This is because oxidative
phosphorylation cannot accept the
electrons of NADH without
oxygen.
The purpose of the fermentation
pathway, then, is to release some
NAD+ for use by glycolysis. The
reward for this effort is 2 ATP from
glycolysis for each 2 converted
pyruvate. This is not much, but it’s
better than the alternative—0
ATP.
Oxygen Debt
“‫“اﻟﺪﯾﻦ اﻷوﻛﺴﺠﯿﻨﻲ‬
Why does it build up sooner in some
people than in others?
• The condition of your heart is the
determining factor.
• The job of your heart is to pump
oxygenated blood and deliver it to
your skeletal muscles.
• Most of us have plenty of lung
capacity. Unless you suffer from a
respiratory disease, we all have plenty
of lung capacity to inhale and exhale
enough air.
• But our heart is a muscle and some
people have more powerful hearts
than others. If the condition of your
heart is bad, as in a weak heart, then
there is a decreased ability in the
delivery of oxygenated blood .
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• If all of us were to start running around our blocks, some
people after 3 blocks would be slowing down. Some
people would go for 12 blocks. For some people it might
be 3 miles.
• What accounts for the difference? In part it is due to
lactic acid.
• Doctors mimic this through something
known as a cardiac stress test to see
what your heart can do.
• Doctors want to see how hard they
could push you and make you run on a
treadmill as hard as you can before you
have to tell them to stop the treadmill.
• Once they stop the treadmill, you will
continue to pant because your body
needs to repay the oxygen debt that
was created during exercise.
• The doctor will note how quickly your
heart rate returns back to normal
because it’s a direct indication of the
power and strength of your heart .
• When you’re exercising and your skeletal muscles aren’t getting
enough oxygen, the body must tap into its anaerobic
metabolism .This is where the body goes into a mix of aerobic and
anaerobic energy production.
• Fermentation is an anaerobic respiration reaction that occurs when
there is not enough oxygen to convert glucose into ATP so the
glucose is temporarily converted to lactic acid.
• The accumulation of lactic acid in muscles contributes to muscle
fatigue and muscle cramping.
• If you keep pushing yourself, and building up your oxygen deficit ,
your performance will deteriorate.
• Conversely, if your heart is really strong and powerful, then it’s
pumping lots of oxygenated blood, your muscles are getting plenty
of oxygen and aerobic respiration is continuing in your cells and not
forming as much lactic acid .
• The greater the accumulation of lactic
acid, the more additional oxygen will
be required by your body to breathe in
so that all the lactic acid can be
converted to useful energy through
aerobic respiration
• This is known as oxygen debt following
exercise.
• That is the reason why you are still
panting after you’ve already stopped.
• The stronger your heart is, the shorter
that recovery time will be .
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