Key area 2 – Cellular respiration
The Role of ATP
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.
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
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).
Think back to the beginning of
the unit
Write down an example of anabolic
reaction and a catabolic reaction
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.
Coupling of reactions
ATP – crash course video
• http://www.youtube.com/watch?v=00jb
G_cfGuQ
Watch the first 4 minutes
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.
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
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.
ATP cycling
• ATP breakdown and
production is
reversible.
• Think back to the
reaction coupling
diagram!
How much do you know?
• Define the terms anabolic and catabolic.
• Label this diagram
• How is ATP produced?
• What other role does ATP have?
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
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
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.
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.
• To start the process off,
energy from two ATP
molecules is needed.
• 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).
GLYCOLYSIS
Dehydrogenase
enzymes remove
hydrogen ions and
high energy electrons
that are passed to a
co-enzyme called
NAD which is
reduced to form
NADH..
Later on the NADH
will be used to
produce ATP
GLYCOLYSIS
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?
Respiration continues…
• If Oxygen is present pyruvate gets
passed on to the CITRIC ACID CYCLE..
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
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
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)
Citric acid cycle
• The fluid filled
matrix contains the
enzymes involved in
the CAC reactions.
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.
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.
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.
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
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
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
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?
Watch this!
• From 4 minutes
• http://www.youtube.com/watch?v=00jb
G_cfGuQ
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
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.
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.
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
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
The Electron Transport Chain
Oxygen is the final
electron acceptor,
which combines with H
ions and electrons
forming water.
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
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?
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.
Anaerobic respiration – Animal cells
oxygen debt
builds up
Glucose
Pyruvate
Lactate
oxygen debt
repaid
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!
Which is more efficient?
• How many ATP are produced during
aerobic respiration?
• How many ATP are produced during
anaerobic respiration?
• Which is more efficient?
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.
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.
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.