Respiration
General biology
Dr. Abboud ElKichaoui
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
• If you replace the energy with light
and reverse the equation, it will
describe photosynthesis.
General biology
Dr. Abboud ElKichaoui
General biology
Dr. Abboud ElKichaoui
Glycolysis
• Glycolysis
is
the
decomposition (lysis) of
glucose (glyco) to:
pyruvate (or pyruvic acid).
General biology
Dr. Abboud ElKichaoui
5
Nine intermediate products
are formed, and, of course,
each one is catalyzed by
an enzyme.
6
1
7
In six of the steps,
magnesium ions (Mg2+)
are cofactors that promote
enzyme activity.
2
8
3
9
4
General biology
Dr. Abboud ElKichaoui
5
• The steps are summarized as follows.
A. 2 ATP are added. The first several steps require the input of energy.
This changes glucose in preparation for subsequent steps.
B. 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 energyrich 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.)
C. 4 ATP are produced.
D. 2 pyruvate are formed.
General biology
Dr. Abboud ElKichaoui
• 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).
General biology
Dr. Abboud ElKichaoui
The Krebs Cycle
• The Krebs cycle details
what happens to the
pyruvate end product of
glycolysis.
General biology
Dr. Abboud ElKichaoui
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.
General biology
Dr. Abboud ElKichaoui
•
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.
The Krebs Cycle
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.
•
The CO2 produced by the Krebs cycle is the
CO2 animals exhale when they breathe.
General biology
Dr. Abboud ElKichaoui
There are 7 intermediate
products
General biology
Dr. Abboud ElKichaoui
Oxidative
Phosphorylation
Oxidative phosphorylation is
the process of extracting ATP
from NADH and FADH2.
General biology
Dr. Abboud ElKichaoui
Oxidative Phosphorylation
• 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.
General biology
Dr. Abboud ElKichaoui
Oxidative Phosphorylation cont…
• 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.
General biology
Dr. Abboud ElKichaoui
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).
General biology
Dr. Abboud ElKichaoui
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).
General biology- Dr. Abboud ElKichaoui
• 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
General biology
Dr. Abboud ElKichaoui
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
embedded in the cristae (singular, crista).
are
• 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.
General biology
Dr. Abboud ElKichaoui
• 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.
General biology
Dr. Abboud ElKichaoui
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).
General biology
Dr. Abboud ElKichaoui
Chemiosmotic Theory cont..
• 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).
General biology
Dr. Abboud ElKichaoui
Chemiosmotic Theory cont..
• 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.
General biology
Dr. Abboud ElKichaoui
Chemiosmotic Theory cont..
• 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.
General biology
Dr. Abboud ElKichaoui
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.
•
•
•
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.
General biology
Dr. Abboud ElKichaoui
• 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.
General biology
Dr. Abboud ElKichaoui
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.
General biology
Dr. Abboud ElKichaoui
•
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.
General biology
Dr. Abboud ElKichaoui
Lactate Fermentation
•
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.
General biology
Dr. Abboud ElKichaoui
Oxygen Debt
“‫“الدين األوكسجيني‬
• 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.
General biology
Dr. Abboud ElKichaoui
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 .
General biology
Dr. Abboud ElKichaoui
• 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 .
General biology
Dr. Abboud ElKichaoui
• 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 .
General biology
Dr. Abboud ElKichaoui
• 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 .
General biology
Dr. Abboud ElKichaoui