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Respiration
Learning Outcomes
• Discuss the role and production of ATP
with particular reference to the transfer
of chemical energy, the role of ATP in
cellular processes and the regeneration of
ATP from ADP and inorganic phosphate
(Pi).
Respiration
• Respiration is the process by which
chemical energy is released from
food (by oxidation).
• It occurs in every living cell and
involves the regeneration of ATP by a
series of chemical reactions.
Adenosine Triphosphate
• Adenosine Triphosphate (ATP) is an important
substance found in all living cells. It is created
from the energy released during respiration and
acts as an energy storage and transfer molecule.
• A molecule of ATP is made up of Adenosine and 3
inorganic phosphate groups.
Adenosine
Pi
Pi
Pi
Adenosine Triphosphate
• Energy stored in an ATP molecule is released
when the bond attached to the terminal
phosphate is broken down by enzyme action.
When this bond is
broken, energy is
released
Adenosine
Pi
Pi
Pi
• This results in the formation of Adenosine
Diposphate and Pi.
Synthesis of ATP
• The breakdown of ATP to ADP + Pi releases
energy for the cell to use for a number of
processes.
• To build up ATP from ADP + Pi, this process uses
energy.
• The process of regenerating ATP from ADP + Pi is
called phosphorylation.
ATP
(high energy
state)
Breakdown releasing
energy
Build up requiring energy
ADP + Pi
(Low energy
state)
Formation of ATP
• ATP is created by joining together an Adenosine
Diphospate molecule to a free Inorganic
Phosphate molecule (Pi).
• In order to join these two molecules together,
the energy released from the breakdown of
glucose is used. None of the energy released from
the breakdown of glucose is used for cell
processes, it is all used to make ATP molecules.
Breakdown of ATP
• ATP stores the energy released during respiration
in the bond attaching its third Pi molecule. When
energy is required for cellular processes, the
bond can be broken - releasing the energy.
Adenosine
Pi
Pi
Pi
Enzyme controlled
reaction
Adenosine
Pi
Pi
+ PiPi
Role of ATP
• Since ATP can easily revert to ADP +
Pi, it is able to make energy available
for energy requiring processes such
as:
–
–
–
–
Muscular contraction
Synthesis of proteins and nucleic acids
Active transport of molecules
Transmission of nerve impulses
Learning Outcome
• Describe Glycolysis in terms of the
breakdown of glucose (6C) to pyruvic
acid (3C) with a net production of ATP.
Oxidation and Reduction
• Oxidation occurs when hydrogen is removed
from a substrate and energy is added.
• Oxidation occurs in a cell during respiration.
• Reduction involves the addition of hydrogen
to a substrate and the loss of energy. It
happens during photosynthesis.
Remember: OILRIG
Respiration
• Respiration is a series of reactions in which
6-carbon glucose is oxidised to form carbon
dioxide. The energy released due to the
oxidation of glucose is used to synthesize
ATP from ADP + Pi.
• Respiration is a series of reactions involving
oxidation and reduction.
Respiration
• There are 3 stages of respiration:
– Stage 1 = Glycolysis
– Stage 2 = the Krebs cycle
– Stage 3 = the cytochrome system
Glycolysis
• The first stage of respiration is called glycolysis
and it happens in the cytoplasm.
• In glycolysis, a molecule of 6-carbon glucose is
broken down to form 2 molecules of 3-carbon
pyruvic acid.
• 2 ATP molecules are needed to start this process
but 4 molecules are produced. So there is a net
gain of 2 ATP during glycolysis.
Glycolysis
• This first stage of respiration does not
require oxygen, so it occurs during aerobic
and anaerobic respiration.
Glycolysis
• During glycolysis, the hydrogen that is
oxidised from glucose becomes
temporarily bound to a coenzyme molecule
which acts as a hydrogen carrier.
• The coenzyme involved is NAD, when it is
reduced (gains hydrogen), it becomes
NADH2.
Learning Outcome
• Describe how Co-enzyme A, in combining
with (2C) acetyl group to form acetyl CoA,
converts a (4C) compound into (6C) citric
acid.
• Give an account of the detailed structure
and function of a mitochondrion with
particular reference to the membrane, the
matrix and the cristae.
Fate of Pyruvic acid
• Each molecule of 3 carbon pyruvic acid
that is made during glycolysis diffuses into
the central matrix of a mitochondria.
• Once there it is broken down to carbon
dioxide and a 2-Carbon fragment called an
acetyl group.
Fate of pyruvic acid
• Each 2C acetyl group becomes
attached to coenzyme A (CoA) to
form a molecule of acetyl CoA.
• This coenzyme ‘helps’ the 2C acetyl
group into the second stage of
aerobic respiration: the krebs cycle.
Learning Objective
• Describe the Krebs cycle in cells,
identifying the main substrates and
products involved.
The Krebs’ Cycle
• The Krebs’ cycle is an aerobic stage of respiration
that occurs in the matrix of the mitochondria.
• The Krebs’ cycle starts with a 2C acetyl CoA
molecule.
• This reacts with a 4-Carbon compound that is
present in the matrix, to form 6-Carbon citric
acid.
Krebs’ Cycle
• The 6C citric acid is gradually converted
back to the 4-Carbon compound by a series
of enzyme controlled reactions which
release carbon dioxide and hydrogen
(which combines with NAD).
2Pyruvic Acid
- 3 carbon molecule
2NADH to
cytochrome system
2CO2
2 Acetyl
- 2 carbon molecule
Co-enzyme A (co-A)
binds to Acetyl
Acetyl co-A
Citric Acid
6 carbon molecule
2NADH to
cytochrome system
Intermediate
4 carbon molecule
KREBS’
CYCLE
2CO2
5 carbon molecule
2NADH to
cytochrome system
2NADH to
cytochrome system
Intermediate
4 carbon molecules
Intermediate
4 carbon molecules
2NADH to
cytochrome system
2CO2
Learning Outcome
• Describe How the cytochrome
system in a cell is used to generate
most of the ATP used by the cell.
The cytochrome System
• The third stage of aerobic respiration is
the cytochrome system.
• The hydrogen from previous stages is
carried to the cytochrome system as
NADH2.
• The NADH2 transfers hydrogen to a chain
of hydrogen carriers called the
cytochrome system.
The cytochrome system
• Each mitochodrion has many of these
cytochrome systems attached to each of
its cristae.
• Oxygen is the final hydrogen acceptor.
Hydrogen and oxygen combine to form
water.
• This stage is aerobic.
The cytochrome system
• Oxygen is essential for hydrogen to pass
along the cytochrome system.
• In the absence of oxygen, the oxidation
process can’t go beyond glycolysis.
• This system of hydrogen carriers is the
most important means of releasing energy
during respiration.
The cytochrome system
• Energy can be released from a few steps
in the process of aerobic respiration, but
most of the energy is made available by
the cytochrome system.
• A total of 38 ATP are produced during
aerobic respiration- 2 during glycolysis and
36 during the aerobic stages.
video
Alternative respiratory
substrates
• Glucose is the most common substrate used
for respiration, however fats and proteins can
also be used.