2. The mitochondrion
Do you remember the structure of the
mitochondrion? Lets’s recap.
The shape varies from spherical to elongated.
They are approximately 5 µm in length and 0.2 µm
in width.
They have a double membrane.
The outer is selectively permeable.
The inner is folded to form cristae.
3. The mitochondrion con’t
The cristae increase the surface area for respiration.
The cristae have on their surfaces, stalked granules.
The cristae elongate in a transparent material called
the matrix.
The matrix may contain protein, lipids and traces of
DNA.
4. Role of respiration
Living systems require a constant supply of energy.
The universal currency of energy is ATP (Adenosine
TriPhosphate).
ATP is a temporary store for energy.
There is never enough stored ATP within a cell to
maintain it for much longer than a second.
Consequently, there must be a process to ensure that
ATP is constantly produced.
Respiration ensures that ATP is constantly
produced.
5. Adenosine TriPhosphate
As stated before, it is the universal currency for
energy.
It is a nucleotide consisting of the base adenine, the
sugar ribose and three phosphate groups.
When the terminal phosphate group is removed
approximately 30.6kJ mol-1
of energy is released.
ATP is formed when ADP is combined with a
phosphate group.
In humans, the phosphate is stored in a compound
called creatine phosphate.
6. Stages of respiration
Respiration can be divided into 4 stages;
1. Glycolysis – this occurs in the cytoplasm
2.Link reaction – this occurs in the mitochondrion
(matrix)
3.Kreb’s cycle – this occurs in the mitochondrion
(matrix)
4.Electron transport chain – this occurs in the
membranes of the cristae.
7. Glycolysis
Can you break this word into its prefix and suffix and
derive its meaning? I’m sure you can.
Yes! ‘glyco’ refers to sugar, and ‘lysis’ refers to
splitting.
So during this process, among other things, sugar is
split.
8. Glycolysis con’t
1. Glucose(6C) is phosphorylated to form glucose
phosphate(6C).
The energy and phosphate group for this process
comes from 1 molecule of ATP.
Phosphorylating the glucose does several things:
- It makes it more reactive.
- It prevents its movement out of the cell thus
preventing it from disturbing the osmotic balance.
- It helps to create a concentration gradient so more
glucose can move into the cell.
9. Glycolysis con’t
2. Glucose phosphate is then reorganised into
fructose phosphate(6C).
3. ATP is used to phosphorylate fructose phosphate
forming Fructose bisphosphate(6C).
This makes it even more reactive.
4. Fructose bisphosphate is split into two three
carbon sugars called glyceraldehyde-3-phosphate
(3C).
Sounds familiar? A hah!, it’s the same molecule
from the Calvin Cycle also known as triose
phosphate.
10. Glycolysis con’t
5. Inorganic phosphate is used to phosphorylate
Glyceraldehyde-3-phosphate.
6. Glyceraldehyde – 3-phosphate is also
dehydrogenated (2 H atoms removed from each
molecule) to form Glycerate 1, 3 bisphosphate (3C).
7. Each molecule of Glycerate 1, 3 bisphosphate loses
a phosphate molecule to form glycerate -3-
phosphate(3C).
These two phosphate molecules are used to form 2
molecules of ATP.
11. Glycolysis con’t
8. Each molecule of glycerate -3- phosphate loses a
phosphate molecule to form pyruvate (3C).
Another 2 molecules of ATP are made.
9. For the formation of pyruvate, a molecule of water
is also lost from each glycerate-3-phosphate
molecule.
OK, how many molecules of ATP can be obtained
from one molecule of glucose during glycolysis?
12. Glycolysis con’t
Each pair of hydrogen atom can yield 3 ATP
molecules later on in the electron transport chain
(=6).
2 molecules are formed as Glycerate 1,3-
bisphosphate is dephosphorylated to form glycerate
-3- phosphate.
2 molecules are also formed when glycerate -3-
phosphate is dephosphorylated to form pyruvate.
2 molecules of ATP are used in the early stages so the
net gain is 8.
13. The link reaction
This is a very short process. Yes it is.
1. Pyruvate is decarboxylated by losing a molecule of
Carbon dioxide.
2.Pyruvate is also dehydrogenated (loses 2H).
3.The remaining molecule is combined with coenzyme
A to form Acetyl coenzyme A.
4.3 molecules of ATP are produced from the 2 atoms of
H.
This is counted in the energy gained from the Kreb’s
cycle.
14. The Kreb’s cycle
The steps involved in the Kreb’s cycle are;
1. Acetyl Coenzyme A(2C) combines with Oxaloacetate
(4C) to form Citrate (6C).
2.The Citrate is dehydrogenated and decarboxylated
(loses CO2) to form α- ketoglutarate (5C)
3. α- ketoglutarate is dehydrogenated and
decarboxylated to form Succinate (4C).
15. The Kreb’s cycle con’t
During the conversion from α- ketoglutarate to
Succinate, one molecule of ATP is formed. This is
the only stage in the Kreb’s cycle where ATP is
formed directly.
4.Succinate is dehydrogenated to form Malate (4C).
5.Malate is dehydrogenated to reform Oxaloacetate
(4C).
When this is reformed, the cycle is repeated.
16. The Kreb’s cycle con’t
So, how many molecules of ATP are produced from
the Kreb’s cycle from one molecule of glucose?
Remember that each time there is dehydrogenation,
2 H atoms are removed.
For each pair of Hydrogen atoms removed, 3
molecules of ATP will be formed in the electron
transport chain.
Oh, remember to count the ones from the link
reaction.
So, what’s the answer?
17. The Kreb’s cycle con’t
Yes, 32 are produced.
Make sure you remember where dehydrogenation
and decarboxylation take place.
18. The electron transport chain
This is also called the hydrogen carrier system or a
redox chain
This is where the H atoms from the link reaction and
glycolysis and Kreb’s cycle generate ATP.
The H atoms are accepted or taken by a hydrogen
carrier thus reducing them.
The carriers are Nicotamide Adenine Dinucleotide
(NAD), Flavine Adenine Dinucleotide (FAD),
cytochrome and cytochrome oxidase.
19. The electron transport chain con’t
NAD is a derivitive of the vitamin nicotinic acid.
FAD is a derivitive of vitamin B2 – riboflavine.
As the H atoms or electrons are transferred, they are
passed to lower energy levels, thus releasing energy.
The first acceptor is NAD and the steps are outlined
below.
1. NAD accepts 2H and becomes reduced (NADH2 or
NADH + H+
)
2.The H atoms are then passed on to FAD thus
reducing it (FADH2)
20. The electron transfer chain con’t
During the transfer an ATP molecule is produced.
At this point, the H atoms are split into protons and
electrons (2 protons and 2 electrons).
The electrons are passed to the cytochromes forming
ATP in the process.
The same electrons are passed to the cytochrome
oxidase forming another ATP molecule in the
process.
The protons are passed to the cytochrome oxidase
where they recombine with the electrons.
21. The electron transfer chain con’t
The Cytochrome oxidase passes the H atom to be
combined with oxygen to form water.
This is the only place where oxygen is involved in
aerobic respiration.
The purpose of oxygen is to accept the H at the end
of the electron transfer chain.
The Kreb’s cycle and electron transport chain do not
proceed if oxygen is not present.
22. Electron transport chain con’t
Because ATP is formed in the presence of oxygen,
the process is called oxidative phosphorylation.
Please note that the energy generated in the electron
transport chain is by chemiosmosis.
The H atoms from the Kreb’s cycle are split into
protons and electrons.
The protons are pumped into the space within the
cristae as the electrons are transported within the
membrane.
23. Electron transport chain con’t
When a concentration gradient is built up, the
protons move down the gradient through the stalked
particle which is an ATPase molecule.
This molecule makes ATP
24. Importance of the Kreb’s cycle
1. Because the 3-carbon pyruvate is broken down to
carbon dioxide, it facilitates the degradation of
macromolecules.
2. It provides the reducing power for the electron
transport system i.e it provides the H atoms.
3. It provides intermediate compounds for the
manufacture of other substances like amino acids,
fatty acids etc.
25. Question
Explain the inhibition of the Kreb’s cycle and the
electron transfer system which occurs when there is;
1. limited supply of oxygen.
2.limited ADP or inorganic phosphate.
26. Anaerobic respiration
This refers to respiration in the absence of oxygen.
Some organisms can only respire anaerobically and
are called OBLIGATE ANAEROBES.
Some can respire both aerobically and anaerobically.
These are called FACULTATIVE ANAEROBES.
Remember, anaerobic respiration is glycolysis.
In the absence of oxygen, the Kreb’s cycle and
electron transport chain do not occur.
27. Anaerobic respiration con’t
The hydrogen atoms removed during glycolysis
cannot release their free energy without the electron
transport chain.
They have to be removed however, so that glycolysis
can continue.
They are removed in a process called fermentation
to give either ethanol or lactate depending on the
organism involved.
28. Alcoholic fermentation
1. Pyruvate loses a molecule of CO2 (decarboxylation)
to form ethanal.
2. Ethanal combines with the H atoms transported by
NAD (Nicotamide Adenine Dinucleotide) to form
ethanol.
C6H12O6 2 C→ 2H5OH + 2CO2
3. Alcoholic fermentation occurs in yeast and plants.
4. If allowed to accumulate, the ethanol kills the cells.
30. Importance to humans
Alcohol fermentation is used to make wine from
plants.
Alcohol fermentation in yeast is also economically
important.
The alcohol from the yeast is used in making beer.
The Carbon dioxide from the yeast is used in making
bread. It makes the bread light.
31. Lactate fermentation
The H atom from glycolysis is accepted directly by
pyruvate to form lactate.
If oxygen becomes available later, this lactate can be
broken down to release energy.
It can also be used to make carbohydrates or be
excreted.
32. Oxygen debt
Anaerobic respiration also occurs in animals if
necessary.
This has great survival value as it allows us to
withstand short periods of anoxia (without oxygen).
Examples of these periods include: during and
immediately after birth, periods when oxygen levels
fluctuate in water bodies and during strenuous
exercise.
33. Oxygen debt con’t
Only a small amount of energy is released but it
helps.
The lactate causes muscle fatigue which is relieved
when oxygen becomes available.
The accumulation of lactate causes an oxygen debt to
build up.
This is paid as rapid breathing occurs.
