Key area 2 – Cellular respiration
The Role of ATP
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You should already know that:
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the chemical energy stored in glucose must be released by all cells
through a series of enzyme-controlled reactions called respiration;
the energy released from the breakdown of glucose is used to generate
ATP from ADP and phosphate;
the chemical energy stored in ATP can be released by breaking it down to
ADP and phosphate;
ATP can be regenerated during respiration;
each glucose molecule is broken down via pyruvate to carbon dioxide and
water in the presence of oxygen, and yields 38 molecules of ATP;
the breakdown of each glucose molecule via the fermentation pathway
yields two molecules of ATP when oxygen is not present;
in the absence of oxygen in animal cells, glucose is broken down into
lactate via pyruvate;
in the absence of oxygen in plant and yeast cells, glucose is broken down
into alcohol/ethanol and carbon dioxide via pyruvate;
fermentation occurs in the cytoplasm;
aerobic respiration starts in the cytoplasm and is completed in the
mitochondria.
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Learning Objectives
By the end of this topic you should be able to:
• Describe how glucose is broken down to
ultimately deliver ATP
• Explain that ATP is used to transfer energy
to carry out cell processes.
• Explain the reversible nature of ATP
production
• Describe how ATP is synthesised
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ATP (Adenosine triphosphate)
• ATP is essential to
biological systems as
it is the link between
reactions that
release energy
(catabolic) and those
that use energy
(anabolic).
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Think back to the beginning of
the unit
Write down an example of anabolic
reaction and a catabolic reaction
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ATP = Energy Currency
• ATP is ‘spent’ during
cellular work such as
muscular contraction
or the formation of
proteins, and is
'banked' or stored
when glucose is
broken down during
cellular respiration.
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ATP – crash course video
• http://www.youtube.com/watch?v=00jb
G_cfGuQ
Watch the first 4 minutes
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How is ATP made?
• ATP comes from the breakdown of food –
usually glucose
Remember the equation
Glucose + Oxygen ---- > ATP + carbon dioxide + water
In the presence of oxygen glucose is broken
down in to energy (ATP), carbon dioxide and
water.
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ATP
When glucose is broken down
in a cell, it releases energy
which is used to produce ATP.
ATP is made from joining a
phosphate to ADP
The end phosphate bond
contains a lot of energy which
is released when broken off.
This is used by cells to do
work and carry out anabolic
reactions
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ATP’s other role
• ATP also has the role of carrying out
phosphorylation reactions in cells (adding
phosphates to things).
• This is an enzyme controlled process.
• E.g during glycolysis ATP is broken down to
ADP + Pi and the phosphate group is used to
phosphorylate the substrate of glycolysis.
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ATP cycling
• ATP breakdown and
production is
reversible.
• Think back to the
reaction coupling
diagram!
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How much do you know?
• Define the terms anabolic and catabolic.
• Label this diagram
• How is ATP produced?
• What other role does ATP have?
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The chemistry of respiration
By the end of this topic you should be
able to:
• Describe glycolysis
• Describe the progression of respiration
pathways, in the presence and absence
of oxygen
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The chemistry of respiration
There are 3 sets of reactions in
cellular respiration that release the
energy contained in food, by oxidation.
1. Glycolysis
2. The citric acid cycle
3. The electron transport chain
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Respiration
• During respiration, glucose is gradually
broken down and hydrogen released at
various stages along the pathway. Each
of these stages is controlled by an
enzyme called a dehydrogenase.
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Glycolysis (revision from N5)
• It is a series of reactions (enzymecontrolled) that break down the sugar
glucose in to pyruvate.
• Glycolysis takes place in the
_________ of the cell and _____
require oxygen.
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• To start the process off,
energy from two ATP
molecules is needed.
GLYCOLYSIS
• This can be thought of as
an energy investment
phase where ATP is used
to phosphorylate
intermediates in
glycolysis.
• The series of reactions
eventually produces four
ATP molecules, so there is
a net gain of two ATP
from glycolysis (energy
pay-off stage).
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Dehydrogenase
enzymes remove
hydrogen ions and
high energy electrons
that are passed to a
co-enzyme called
NAD which is
reduced to form
NADH..
GLYCOLYSIS
Later on the NADH
will be used to
produce ATP
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How much do you know?
• Where does glycolysis take place in the
cell?
• What is the net gain in ATP from one
glucose molecule during glycolysis?
• Is glycolysis anabolic or catabolic?
Why?
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Respiration continues…
• If Oxygen is present pyruvate gets
passed on to the CITRIC ACID CYCLE..
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Learning objectives
By the end of this topic you should be
able to:
• Describe the citric acid cycle.
• Understand that respiration is a series
of enzyme mediated reactions
• Explain the importance of the products
of the citric acid cycle
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Citric acid cycle
• From N5 you should
know that in the
presence of oxygen,
pyruvate can
continue to be
broken down in the
MITOCHONDRIA of
the cell
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Mitochondria
• Has a double membrane
• The inner membrane is
folded in to many
cristae which provide a
large surface area.
• On the inner membrane
the reactions of the
ETC occur (electron
transport chain)
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Citric acid cycle
• The fluid filled
matrix contains the
enzymes involved in
the CAC reactions.
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Citric acid cycle
Pyruvate preparation!
Pyruvate diffuses from the
cytoplasm to the
mitochondria.
Once inside the
mitochondria, a carbon and
two oxygen atoms are
removed, forming carbon
dioxide as a waste.
The molecule that remains
is a 2-carbon acetate
molecule.
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Citric acid cycle
Pyruvate preparation
When carbon dioxide is
removed from pyruvate
to make acetate, extra
high energy electrons
are produced. NAD+
captures these
electrons and attracts
H+ to balance the
charge, forming a
molecule of NADH.
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Citric acid cycle
Pyruvate preparation
Because the acetate
molecule produced from
pyruvate is so small and
can easily diffuse away,
co-enzyme A is attached
to it forming Acetyl
CoA. This is now ready
for the Citric acid cycle.
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Citric acid cycle
Each acetyl CoA (2C)
combines with
oxaloacetate (4C) to form
a molecule called citrate
(6C).
Citrate then goes through
a series of enzymecatalysed reactions back
to oxaloacetate. As each
carbon is lost from the
citrate molecule a carbon
dioxide molecule and
hydrogen ions are released
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Citric acid cycle
• Hydrogen ions and high
energy electrons
become bound to to
NAD to form NADH.
• Hydrogen and e- can
also be bound to a
different co-enzyme
FAD which is reduced to
form FADH2.
• NADH and FADH2 will
be used in the next
stage for ATP
production
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Citric acid cycle
intermediate
NAD+
CO2
NADH
intermediate
CO2
intermediate
Oxaloacetate
NAD+
ATP
NADH
ADP + Pi
Acetyl CoA
Pyruvate
Draw this in your jotter
then fill in the boxes with
the labels on the left
CO2
NADH
NAD+
NAD+
NADH
Citrate
FADH2
FAD
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How much do you know?
• What happens to the carbon dioxide that is
produced in the citric acid cycle?
• What is the molecule produced when
oxaloacetate combines with acetylCoA?
• Does the citric acid cycle require oxygen?
• Where does the CAC take place?
• What are NAD and FAD?
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Watch this!
• From 4 minutes
• http://www.youtube.com/watch?v=00jb
G_cfGuQ
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Cool links to help learn!
• http://freevideolectures.com/Course/3
160/Biology-I/36#
• http://www.wiley.com/college/boyer/04
70003790/animations/tca/tca.htm
• https://www.youtube.com/watch?v=juM
2ROSLWfw
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The Electron Transport Chain (ETC)
By the end of this topic you should be able to:
• Describe the electron transport chain as a
membrane bound system.
• Explain the role of the dehydrogenase
enzymes.
• Understand the key role of NAD and FAD and
their reduced forms.
• Explain the role of oxygen in the ETC and the
consequences of it’s absence.
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The Electron Transport Chain
• The ETC is a series
of proteins in the
inner mitochondrial
membrane
• All the Hydrogen
ions and electrons
that have been
transferred to NAD
or FAD are passed
to the ETC.
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The Electron Transport Chain
• Within the ETC the
H ions and electrons
now separate with
the high energy
electrons cascading
down the ETC and
releasing their
energy
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The Electron Transport Chain
• The electrons are used
to pump Hydrogen ions
across the mitochondrial
membrane. The return
flow of these H ions
rotates part of the
membrane protein ATP
synthase.
• ATP synthase is an
enzyme which catalyses
the synthesis of ATP
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The Electron Transport Chain
Oxygen is the final
electron acceptor,
which combines with H
ions and electrons
forming water.
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Why is oxygen needed?
• Without oxygen the CAC and
ETC cannot function!
• Oxygen is needed to oxidise
pyruvate to yield 36ATP
• With 2 ATP from glycolysis
(doesn’t require O2) the
yield from one glucose
molecule oxidised is 38ATP
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How much do you know?
• What enzyme is required to produce
ATP?
• What is the final acceptor of hydrogen?
• What do the high energy electrons in
the ETC do?
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Anaerobic Respiration
• You should know from N5 that with no oxygen
only glycolysis can take place and pyruvate
follows a fermentation pathway.
• For both plants and animals complete the flow
chart using the words; pyruvate, lactate,
glucose and ethanol + CO2.
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Anaerobic respiration – Animal cells
oxygen debt
builds up
Glucose
Pyruvate
Lactate
oxygen debt
repaid
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This should be revision….
• In animal cells
pyruvate is broken
down in to lactate.
This happens when
doing vigorous
exercise when O2 is
used up. This is
reversible!
• In plant and yeast
cells pyruvate gets
converted to ethanol
and CO2. This is
irreversible because
CO2 is lost from the
cell!
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Which is more efficient?
• How many ATP are produced during
aerobic respiration?
• How many ATP are produced during
anaerobic respiration?
• Which is more efficient?
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Measuring the rate of respiration
• You can measure
respiration rate
using a respirometer.
If you’re lucky your
teacher will show
you how this works.
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Measuring the rate of respiration
• As the creatures
produce carbon
dioxide through
respiration this is
absorbed by the
sodium hydroxide
beads
• As the creatures use
up the oxygen in the
tube, the level of
liquid will rise. This
can then be
measured to see the
volume of oxygen
used.
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Alternative Respiratory
Substrates
• Other sugar molecules can be converted into
glucose or intermediates of glycolysis;
• Proteins can be broken down to amino acids and
converted into intermediates of glycolysis or the
citric acid cycle;
• Fats can also be broken down to intermediates of
glycolysis and the citric acid cycle.
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