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Cell Respiration
Topics 3.7 & 8.1
Definition of cell respiration

Cell respiration is the controlled
release of energy from organic
compounds in cells to form ATP.

It takes place in ALL cells –
prokaryotic and eukaryotic.

It can be aerobic (involving oxygen)
or anaerobic (no oxygen).
Anaerobic Respiration
The process of respiration takes places in
several steps (metabolic pathway).
 Anaerobic respiration occurs in the
CYTOPLASM.
 Glucose is broken down into a simpler
substance called PYRUVATE. (pyruvic acid)
 A small amount of ATP is produced in this
reaction.

Anaerobic respiration contd.
If no O2 is available, the pyruvate is
converted into waste products that are
later removed from the cell.
 In humans the waste product is LACTATE
(lactic acid).
 In yeast the waste products are ETHANOL
and CARBON DIOXIDE.
 No further ATP is made.

Anaerobic respiration contd.
Glucose
GLYCOLYSIS
In humans
Pyruvate
Lactate
Small yield of ATP
Glucose
GLYCOLYSIS
In yeast
Pyruvate
Small yield of ATP
Ethanol +
CO2
Aerobic respiration
If O2 is available, the pyruvate enters the
mitochondria where it is broken down into
CO2 and water.
 A large amount of ATP is produced in
these reactions.

Pyruvate
CO2 + H2O
Large yield
of ATP
Oxidation & Reduction
Oxidation
Reduction
Involves loss of
electrons
Involves gain of
electrons
Addition of oxygen
Removal of oxygen
Removal of hydrogen
Addition of hydrogen
Oxidation & Reduction in Cell
Respiration

Cell respiration involves several redox
reactions.

Hydrogen carriers accept hydrogen atoms
removed from substrates.

NAD+ + 2H
NADH + H+
Glycolysis

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1.
First step in both aerobic and anaerobic
respiration.
Occurs in cytoplasm.
Four steps:Phosphorylation – 2 phosphates are
added to glucose to form hexose
biphosphate. 2ATPs provide the
phosphates and the resulting molecule
now has a higher energy level.
Glycolysis contd.
2.
3.
4.
Lysis – hexose biphosphate splits into 2
molecules of triose phosphate.
Oxidation – 2 hydrogen atoms removed
from each triose phosphate and collected
by NAD+.
ATP formation – Pyruvate is formed by
removal of 2 phosphates that are joined
to ADP to make ATP.
Glycolysis diagram
Glucose
2 ATP
PHOSPHORYLATION
2 ADP
Hexose
biphosphate
LYSIS
2 triose
phosphates
2 NAD+
2 NADH +
H+
4 ADP
4 ATP
OXIDATION
ATP FORMATION
2 pyruvates
Summary
 One glucose is
converted into 2
pyruvates
 2 NAD+ are converted
into 2 NADH + H+
 2 ATP molecules used
per glucose but 4 are
produced giving a net
yield of 2 ATP.
Structure of mitochondria
Aerobic respiration – link reaction

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Pyruvate from glycolysis is absorbed by the
mitochondrion.
The pyruvate is both OXIDIZED and
DECARBOXYLATED.
Enzymes in the matrix of the mitochondrion are
responsible for each process.
The hydrogen that is removed is accepted by
NAD+ to form NADH + H+.
The decarboxylated pyruvate is a 2-carbon
compound (acetyl group) that reacts with
coenzyme A.
Summary of the link reaction
OXIDATION
NAD+
NADH + H+
Pyruvate
acetyl CoA
Coenzyme A
DECARBOXYLATION
CO2
Aerobic respiration – Kreb’s Cycle
An acetyl group (CH3CO) is transferred
from acetyl CoA to a 4-carbon compound
(oxaloacetate).
 This results in the production of a 6carbon compound (citrate).
 Citrate is converted back into oxaloacetate
by a series of reactions involving
DECARBOXYLATION, OXIDATION and

PHOSPHORYLATION.
Kreb’s cycle contd.

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CO2 is removed in 2 of the reactions as a waste
product and excreted together with CO2 from
the link reaction.
Hydrogen is removed in 4 of the reactions. The
hydrogens are picked up by carriers (NAD+ and
FAD).
These oxidations release energy which is stored
by the carriers when they accept hydrogen.
This energy is later released by the electron
transport chain and used to make ATP.
ATP is produced directly in one of the reactions.
Summary of the Kreb’s cycle
acetyl CoA
oxaloacetate
(C4)
CoA
citrate (C6)
NADH + H+
NAD+
NADH + H+
NAD+
FADH2
C5
FAD
ATP
C4
ADP
CO2
The electron transport chain
The electron transport chain (ETC) is a
series of electron carriers, located in the
inner membrane of the mitochondrion.
 NADH supplies 2 electrons (e-) to the first
carrier.
 These e- pass along the chain, giving up
energy at each stage.

The electron transport chain contd.
At 3 points along the chain enough energy
is given up for ATP to be made by the
enzyme ATP synthetase.
 This process is called OXIDATIVE
PHOSPHORYLATION.
 FADH2 also feeds e- into the ETC, but at a
later stage than NADH, resulting in 2 ATP
molecules instead of 3.

Summary of ETC
NADH
NAD
ADP
ATP
FADH
FAD
ADP
ATP
Reduced cytochromes
Oxidized cytochromes
ADP
ATP
Reduced cytochrome
oxidase
H2O
Oxidized cytochrome
oxidase
O2
The final recipient of
these e- is oxygen.
 Oxygen is reduced to
form water.
 This is the only stage
of cellular respiration
that uses oxygen.

Chemiosmosis
The energy released as e- pass along the ETC is
used to pump protons (H+ ions) from the matrix
into the intermembrane space.
 Due to the small volume of this space, it quickly
becomes concentrated with protons.
 This creates 2 areas with different proton
concentrations – LOW in matrix, HIGH in
intermembrane space.

Chemiosmosis contd.
Protons move down the concentration
gradient by passing through channels
provided by the enzyme ATP synthase,
found in the inner membrane.
 When the ATP synthase enzyme is
activated, ADP is phosphorylated into ATP.
 The coupling of ATP synthesis to electron
transport is called CHEMIOSMOSIS.

Relationship between structure &
function of mitochondria
Cristae – foldings of the inner membrane that
increase the surface area for the electron
transport chain and oxidative phosphorylation.
 Fluid matrix – contains enzymes for link
reaction and Kreb’s cycle.
 Intermembrane space – the space between
inner and outer membranes is small to allow for
accumulation of protons for chemiosmosis.

The End
 Now
all you have to do is…..
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