Energy and
Respiration
Why living organism need energy?
From where it come?
How we take this energy?
The need for energy in living organisms

continuous supply of energy for:




Synthesis of complex substances from
simpler ones (anabolic reactions)
Active transport (movement of
molecule)
Mechanical work – movement
Maintenance of internal body
temperature
What is ATP



Adenosine triphosphate
Energy released is not then directly
used, it is passed on to ATP.
ATP is made of:



Adenine
Ribose
3 phosphate molecules
ATP is energy currency




When a phosphate group is removed
from ATP, ADP is formed and energy
is released.
ATP + H2O = ADP + H3PO4 ± 30.5kJ
AMP
± 14.2kJ
ATP is the universal intermediary
molecule. It is known as the energy
currency.
ATP is energy currency
Energy currency & storing



Energy currency- act as a immediate
donor of energy to the cell energy
requiring reaction.
Energy storage- a short term
(glucose/sucrose)
long tem (glycogen, starch, triglycerides)
Synthesis of ATP
1. Energy released by reorganizing
chemical bonds (glycolysis and Krebs
cycle) .
2. Using electrical potential energy when
electrons are transferred by electron
carriers. This is called chemiosmosis.
Hydrogen carrier molecules
(NAD & FAD)
.
Respiration
Organic molecules are broken down to release
energy to make ATP.
 Two types:
A) Aerobic respiration – in the presence of oxygen.
B) Anaerobic respiration – in the absence of
oxygen.


Both start with glycolysis.
Respiration
4 main stages...
1. Glycolysis
2. The Link Reaction
3. The Krebs Cycle
4. The Electron Transport Chain
Respiration
Glycolysis




Phosphorylation (adding phosphate) to glucose
using ATP
Occurs in the cytoplasm.
Splitting hexose phosphate (6C) into two triose
phosphate molecules (3C)
These are then oxidised, releasing ATP and
reducing NAD
Glucose (hexose) (6C)
Hexose phosphate (6C) produced by phosphorylation using ATP
Hexose bisphosphate (6C) adding another phosphate using ATP
This splits into two
2 molecules of triose phosphate (3C)
A sequence of Intermediate molecules are formed, by reducing
NAD and losing phosphates to produce 4 molecules of ATP
2 x Pyruvate (3C)
Glucose
1st Phosphorylation
Glucose-6Phosphate
Isomerisation
1. Glycolysis
H+ taken to
reduce NAD
2 x ATP
PYRUVI
C ACID
Triose
Phosphate
Fructose-6Phosphate
H+ taken to
reduce NAD
2 x ATP
PYRUVI
C ACID
Triose
Phosphate
Fructose-1-6
Bisphosphate
They
are
then
converted into pyruvic
acid.splits
This
involves
removal
ofcalled
hydrogen
and
it’s
transfer
to a
This
The
isThe
fructose-1-6-bisphosphate
then
phosphorylated
forobtained
a then
second
time,
into
splitting
twothe
molecules
aproduct
molecule
ofvia
ATP,
TRIOSE
forming
PHOSPHATE.
fructose-1The
glucose
The
glucose
glucose-6-phosphate
is
phosphorylated
molecule
is
into
changes
glucose-6-phosphate
as
the
to
fructose-6-phosphate
digested
by
taking
of
eating
a
phosphate
isomerisation
carbohydrates
from
ATP
hydrogen carrier molecule (NAD) to form reduced NAD. Each pyruvic acid yields 2 molecules of ATP in the
They each have
6-bisphosphate
3 carbons and 1 phosphate
process of it’s creation
Glycolysis- Summary
•
•
•
•
•
•
Breaking down a glucose molecule into two
molecules of pyruvate (pyruvic acid)
It uses 2 ATP molecules for substrate level
phosphorylation
It creates 4 ATP molecules
There is a NET TOTAL of 2 ATP molecules made.
The 2 reduced NAD made goes to the electron
transport chain
The 2 molecules of pyruvate go into the link
reaction
Glycolysis- Summary
Process
Glycolysis
Number of ATP
used
(per glucose)
2
Number of ATP
produced (pg)
4
Net Total ATP (pg)
2
Number of reduced
NAD produced (pg)
2
Number of reduced
FAD produced (pg)
0
Other products
made (pg)
2 molecules of
pyruvic acid
The Link
Reaction
The Krebs Cycle
Link reaction




Occurs when oxygen available
It is decarboxylated (carbon removed)
Dehydrogenated (hydrogen removed)
As a result of this, CO2 is formed and NAD
is reduced
2. The Link Reaction
From Glycolysis
To Krebs Cycle
PYRUVIC
ACID
(3C)
ACETATE
Acetyl
coA
2C
H+ to
reduce
NAD
The
link
reaction
connects
Glycolysis
tocycle
the
cyclethe Krebs via
This forms
which
is
taken
by coenzyme
Amitochondrial
(coA)
recycled
from
cycle to
This isacetate,
decarboxylated
The
pyruvic
via
acid
decarboxylase
diffuses
into
tothe
the
produce
CO
and dehydrogenated
matrix
This
isup
taken
into
krebs
2 Krebs
coA
dehydrogenase to produceform
H+ , acetyl
used to
reduced a molecule of NAD
The Link Reaction- Summary
Process
Glycolysis
The Link
Reaction
Number of ATP
used
(per glucose)
2
0
Number of ATP
produced (pg)
4
0
Net Total ATP (pg)
2
0
Number of reduced
NAD produced (pg)
2
2
Number of reduced
FAD produced (pg)
0
0
Other products
made (pg)
2 molecules of
pyruvic acid
2 x Carbon Dioxide
2 x Acetyl coA
The Krebs Cycle
Krebs cycle

Closed pathway of enzyme-controlled reactions

Occurs in matrix of mitochondria



Acetyl CoA (2C) enters the cycle and joins with a
4 carbon compound to make a 6 carbon
compound.
A series of steps now transfer the 6C (citrate)
back to the 4C (oxaloacetate)
These steps include more decarboxylation and
dehydrogenation
Pg 203
LINK REACTION. Pyruvate molecules (3-carbon)
from glycolysis are converted into another type
of molecule called Acetyl-CoA in a process
known as pyruvic oxidation. This conversion
occurs when the pyruvate is broken down by a
complex of 3 enzymes called pyruvate
dehydrogenase, releasing a carbon atom which
goes on to form carbon dioxide (CO2). The 2
remaining carbon molecules bond with
coenzyme A forming Acetyl-CoA. During this
process, electrons and a hydrogen ion are
passed to NAD+, thus oxidizing the pyruvate,
hence the name of the process.
Step 1. The Acetyl-CoA then enters the
Krebs cycle. It initially combines with a
4-carbon molecule called oxoaloacetic
acid, forming a 6-carbon molecule of
citric acid (citrate). This reaction is
catalyzed by the enzyme citrate
synthase. Upon this formation, the
coenzyme A is released, returning to the
link reaction.
Step 2. The citrate molecule is then
dehydrated (H20 molecule is removed)
and then rehydrated by the enzyme
aconitase. The resulting molecule is just
a rearranged form of citrate known as
isocitrate.
Step 3. Next, isocitrate undergoes what is
known as a oxidative carboxylation, which
simply means that a carbon and hydrogen
are given off. The result of this is a 5-carbon
molecule called alpha-ketoglutarate. This
process is catalyzed by the enzyme
isocitrate dehydrogenase. Additionally, the
carbon that broke off forms CO2, while the
hydrogen reduces NAD+ to form NADH.
Step 4. In the next reaction, alphaketoglutarate has yet another carbon
molecule removed and is then
transferred to a CoA molecule by the
enzyme alpha-ketoglutarate
dehydrogenase. The resulting product is
a 4-carbon molecule of Succinyl-CoA.
Additionally, CO2 and NADH is formed.
Step 5. After succinyl-CoA is formed, the
molecule then undergoes the removal of the
CoA carrier, resulting in the production of
succinate. Additionally, the enzyme succinylCoA synthetase that removes the CoA also
produces GTP (Guanosine Triphosphate)
through substrate level phosphorylation
(phosphate molecule directly added to another
molecule). (GTP is a high energy molecule
similar to ATP, and later an ADP molecule
takes the phosphate from GTP and makes
ATP)
Step 6. Next, succinate is dehydrated by the
enzyme succinate dehydrogenase. The
resulting product is furmate.
Step 7. Furmate is then hydrated (water
added) by enzyme furmase to form malate
Step 8. Lastly, the malate is dehydrogenated
by the enzyme malate dehydrogenase,
forming the original molecule oxaloacetate.
From this reaction, NADH and H+ are also
produced.
SUMMARY
Every pyruvate molecule that enters the Krebs cycle generates 3
molecules of CO2, one molecule of ATP, one molecule of FADH and 4
molecules of NADH
ADP+P
ATP
Pyruvate
3CO2
4NAD+
4NADH
FAD+
FADH
The reduced NAD and FAD molecules enter the electron transfer
chain, and result in a large number of ATP molecules being
produced.
Acetyl
coA
2C
Oxaloacetic
Acid
4C
3. The Krebs Cycle
Citric Acid
6C
Keto-Glutaric
Acid
5C
1x
ATP
Malic Acid
4C
Succinic
Acid
4C
The
function
of
the Krebs
cycle
is a means
of liberating
from
carbon
bonds
toreduce
The
This
Acetyl
6C
4C
Compound
coA
compound
enters
(citric
the
isisthen
Krebs
acid)
dehydrogenated
Cycle
undergoes
combining
decarboxylation
again.
This
aenergy
4C
H+
and
acid
ion
dehydrogenation
emitted
to again,
form
is
aproducing
6C
used
compound.
produce
This
5C
compound
then
decarboxylated
and with
dehydrogenated
aprovide
4C
The
Oxaloacetic
acid
is by
regenerated
from
malic
acid
by
atofinal
ATP,
r.NAD
and
r.FAD
,
with
the
release
of
carbon
dioxide
CO
and H+ ion,
Thethis
Acetyl
is used
is regenerated
to reduce
an
andNAD.
recycle
These
back
processes
into
link
produced
reaction
Compound.
This
produced
enough
energy
to
synthesise
the the
production
of a1 5C
ATPcompound
Molecule
2
FAD reducing NAD
dehydrogenation,
The Krebs Cycle- summary






Per cycle we obtain…
1 ATP
3 r.NAD
1 r.FAD
2 Carbon Dioxide Molecules
Remember that the Krebs Cycle turns
twice per glucose molecule.
The Krebs Cycle -Summary
Process
Glycolysis
The Link
Reaction
The Krebs Cycle
Number of ATP
used
(per glucose)
2
0
0
Number of ATP
produced (pg)
4
0
2
Net Total ATP (pg)
2
0
2
Number of reduced
NAD produced (pg)
2
2
6
Number of reduced
FAD produced (pg)
0
0
2
Other products
made (pg)
2 molecules of
pyruvic acid
2 x Carbon
Dioxide
4 x Carbon
Dioxide
4. The Electron Transport Chain
•
A series of carriers and pumps, releasing
energy in the form of ATP
Electron Transport Chain

1.
2.
3.

NADH and FADH2 oxidised - electron and proton
released
electron picked up by an electron carrier on the
inner membrane
It is passed from one acceptor to another along
a chain.
electron has a high potential energy at
beginning of chain but as it is passed along the
electron falls to a lower energy state.
energy released actively pumps the hydrogen
ion (proton) into the intermembrane space.


electron reaches the end of the chain it
rejoins to the hydrogen ion to make a
hydrogen atom.
These hydrogen atoms then join to
oxygen to form water.
4. The Electron Transport Chain
4. The Electron Transport Chain
Inter
membrane
space
High Concentration of H+ ions
- The pump is pumping them from the
matrix, they are taking them from
reduced NAD and FAD
ATP
PUMP
PUMP
PUMP
Low Concentration of H+ ions is maintained
-When they pass through ATP
synthetase they combing with oxygen
and electrons to form water.
Matrix
ATP
SYNTHETASE
Chemiosmosis


hydrogen ions actively transported into the
intermembrane space.
Chemiosmosis is the movement of ions across
a selectively-permeable membrane, down their
electrochemical gradient.
Energy Budget
Process
Glycolysis
The Link
Reaction
The Krebs Cycle
Number of ATP
used
(per glucose)
2
0
0
Number of ATP
produced (pg)
4
0
2
Net Total ATP (pg)
2
0
2
Number of reduced
NAD produced (pg)
2
2
6
Number of reduced
FAD produced (pg)
0
0
2
Other products
made (pg)
2 molecules of
pyruvic acid
2 x Carbon
Dioxide
4 x Carbon
Dioxide
Energy Budget
Altogether, per molecule of glucose, we
obtain
Each reduce FAD is
capable of making 2 ATP
4 ATP
in the electron transport
chain
10 r.NAD x 3 = 30 ATP
2 r.FAD x 2 = 4 ATP
•
Altogether, per
glucose molecule,
38 ATP are made
Each reduce NAD is
capable of making 3 ATP
in the electron transport
chain
Anaerobic Respiration



In the absence of oxygen only glycolysis
can take place
The rNAD/rFAD cannot be reoxidised and
therefore able to pick up more hydrogen
so the link reaction and krebs can’t occur
The yield of ATP is only 2
- If there is no oxygen there is no where for
the hydrogen to go
- which then blocks the electron transport
chain
- which stops the NAD from being
regenerated
- so the krebs cycle is blocked
- so the link reaction is blocked
- and only glycolysis can occur – anaerobic
respiration.
Anaerobic Respiration




To regenerate NAD to be able to continue
glycolysis, pyruvate becomes the hydrogen
acceptor.
This either forms lactic acid or ethanol.
In animals end product is lactic acid
C6H12O6 → 2CH3CH(OH)COOH + 2 ATP
In plants and yeast end product is ethanol and
carbon dioxide
C6H12O6 → 2CH3CH2OH + CO2 + 2ATP


Lactic acid is produced just by adding 2
hydrogen molecules to pyruvate.
Ethanol is produced by first removing a
carbon molecule (releasing carbon
dioxide) and then adding the 2 hydrogen
molecules. That is why alcoholic
fermentation is accompanied by evolution
of carbon dioxide.
Anaerobic Respiration
Fermentation
Takes place in yeast where the pyruvate is
converted into alcohol and carbon dioxide
1. The pyruvate is first decarboxylated to
produce ethanal
2. The hydrogen released during glycolysis
is passed to NAD
3. Reduced NAD passes its hydrogen to
ethanal, reducing it to ethanol
•




Plants cannot use the ethanol.
It cannot be converted back into pyruvate
and it cannot be oxidised
The ethanol is toxic and if anaerobic
respiration continues for too long the plant
will be poisoned and die.
Seeds and plants growing in waterlogged
conditions can respire anaerobically for a
short time.





Adaptation of rice to anaerobic condition
1. Plant grow taller so leaves have access to oxygen in
atmosphere.
2. Stem and root have loosely packed cell, parenchyma,
with large air space. That allow diffusion of oxygen from
air part.
3. contain high level of enzyme alcohol dehydrogenase,
when oxygen available it convert ethanol back to
ethanal.
4.Rice tissue are tolerant to ethanol.
Anaerobic Respiration
•
•
•
During vigorous exercise the human body
has to respire anaerobically
This involves glycolysis , but the reduced
NAD produced passes it’s protons straight to
pyruvic acid, reducing it to lactic acid
A build up of lactate can cause muscle
cramp. When oxygen becomes available it is
broken down by the liver. Most is converted
to glycogen and stored.
Anaerobic Respiration
Respiratory Quotient


It is a unitless number used in calculations
of basal metabolic rate (BMR)
It is the ratio of the volume of carbon
dioxide released to the volume of oxygen
consumed by a body tissue or an
organism in a given period.

The respiratory quotient (RQ) is
calculated from the ratio:


RQ = CO2 eliminated / O2 consumed
The range of respiratory coefficients for
organisms in metabolic balance usually
ranges from 1.0 (representing the value
expected for pure carbohydrate oxidation)
to ~0.7 (the value expected for pure fat
oxidation).








Carbohydrates
The value of RQ is equal to 1 if carbohydrates are the respiratory
substrates in aerobic respiration.
Fats
When the respiratory substrate is fat, the RQ is about 0.7.
Example: Tripalmitin
Fats contain less oxygen than carbohydrates and so they require
more oxygen for oxidation.
Anaerobic respiration
The value of RQ is infinity during anaerobic respiration because
CO2 is produced but O2 is not utilised.
Measuring RQ

This is done by measuring the change in the volume of
gas surrounding the material as it respires –



first as carbon dioxide is absorbed (to measure the rate of
oxygen consumption)
and then without absorbing the carbon dioxide (from which you
can calculate the rate of production of carbon dioxide by
comparison with the first measurment).
The apparatus consists of two vessels. One vessel
contains the organisms and the other acts as
a thermobarometer – small changes in temperature or
pressure cause air in this vessel to expand or contract,
compensating for similar changes in the first vessel.
Changes in the manometer level are thus due only to the
activities of the respiring material.