Transcript Aerobic Respiration

Cellular Respiration
The importance of ATP
 Glycolysis
The link reaction
The Kreb’s cycle
The electron transport chain
What is respiration?
 The gradual release of energy in a number of
small steps from the breakdown of glucose
 Enzymes are required for the breakdown of
glucose forming a metabolic pathway
 Small quantities of energy are released at
each stage which are carried by ATP, ‘the
universal energy currency in living
organisms’
All cells need energy
 Cells need energy to undertake a
variety of metabolic functions:
 Active
transport
 Secretion
 Synthesis of large molecules from
smaller ones e.g. making proteins from
amino acids
 Replication e.g. DNA, organelles
 Muscle contraction
The structure of ATP
ATP is the energy currency of cells. It is a nucleotide with
high energy bonds between the terminal phosphate
groups.
Phosphates
How does ATP function?
 Energy is stored in the bond between
the second and third phosphate group.
 When the bond is broken, energy is
released and ADP is formed.
ATP
Adenine
Ribose
ADP + iP + 30.666kJmol-1
How ATP is made and used
 Energy is released when ATP is broken down
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(exergonic reaction).
The hydrolysis is catalysed by an enzyme called ATP
ase. The hydrolysis liberates 30.66kJmol-1 of free
energy.
Energy is needed to combine ADP and iP to form
ATP (endergonic reaction).
The addition of phosphate to ADP is called
phosphorylation (making ATP)
There are two kinds of phosphorylation:
Oxidative phosphorylation (respiration)
Photophosphorylation. (photosynthesis)
Energy released is used in
anabolic reactions
Exergonic
reaction
Endergonic
reaction
Energy made
from catabolic
reactions. e.g
respiration
Occurs in the cells
and uses an
enzyme ATPase and
water
Occurs in the
mitochondria and
uses an enzyme
ATP synthetase,
water is made
ATP is a means of transferring free energy from respiration to
cells. It is known as the energy currency of the cell
Advantages of ATP as an
intermediate energy carrier
 Only one enzyme is required to release
energy whilst many are required for the
release of energy from glucose.
 It releases energy in small amounts unlike
glucose – so it can be released only when
required.
 A common source of energy that increases
efficiency and control by the cell.
ATP is not stored but
synthesised as required.
The rate of synthesis
keeps pace with demand.
A metabolically active cell
6
may require 2.0 X 10
molecules of ATP per
second!
There are four main stages in aerobic
respiration
 Glycolysis (cytoplasm)
 Link reaction (mitochondrial matrix)
 Krebs cycle (mitochondrial matrix)
 Electron transport chain (stalked particles on
the cristae of mitochondria)
Where does cellular respiration occur?
Mitochondrion
Rough ER
Vacuole
Centrioles
Smooth ER
Golgi apparatus
Cytoplasm
Nucleolus
Nuclear envelope
Chromatin
Cytoskeleton
Lysosome
Cell Membrane
The organelle of aerobic respiration
A site separate
from the rest of
the cytoplasm
where enzymecatalysed
reactions take
place to convert
ADP and iP into
ATP.
How are mitochondria adapted for
respiration?
 Double membrane with inner membrane
highly folded to form cristae
 This arrangement provides a large surface
area for chemical reactions to take place
 The cristae are lined with stalked particles
with contain the enzyme ATP synthetase
Glycolysis
 Literally means “sugar breakdown”.
 Occurs in the cytoplasm of ALL cells.
 Hexose sugars (such as glucose) are the usual
substrates.
 Net production of 2 X ATP molecules.
 The end product is pyruvic acid (pyruvate) and two
molecules of reduced NAD
Two molecules of
triose phosphate
Dehydrogenation
 Glucose (6C hexose) is phosphorylated to make it
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bigger and more reactive. The phosphate is
obtained from ATP. glucose biphosphate (6C
hexose biphosphate) is formed.
The 6C glucose biphosphate is cleaved to form two
triose phosphates (3C). Each has one phosphate
group from the glucose biphosphate.
Each triose phosphate is converted to pyruvic acid
(3C) (pyruvate)
In the final stage enough energy is made to yield four
molecules of ATP. This is called substrate level
phosphorylation.
The breakdown of one molecule of glucose yields
two molecules of ATP, two molecules of reduced
NAD and two molecules of pyruvate
The link reaction
 This is the link between Glycolysis (in the cytoplasm) and
Kreb’s Cycle (in the matrix of the mitochondrion).
 The two pyruvate molecules produced from glycolysis diffuse
from the cytoplasm to the mitochondrial matrix
 Here the two molecules of pyruvate are converted to two
molecules of 2-carbon acetate with the formation of two
molecules of reduced NAD and the loss of two molecules of
carbon dioxide
 The acetate combines with coenzyme A to from acetyl
coenzyme A
The link reaction
Pyruvate (3C)
Decarboxylation
2H
CO2
NAD+
Acetyl Co.A (2C)
NADH.H+
Dehydrogenation
Kreb’s Cycle
The function of the Kreb’s cycle is to
oxidise the acetyl group of the acetyl CoA to
two molecules of carbon dioxide.
Produce one molecule of ATP
NAD and FAD remove hydrogen atoms and
deliver hydrogen to the electron transport
system (next stage)
Stage of the kreb’s cycle
 The stages involve decarboxylation-removal of
carbon as carbon dioxide.
 The stages involve dehydrogenation-removal of
hydrogen atoms which are collected by carriers NAD
and FAD which are reduced to NADH/H+ and FADH2
 For each turn of the cycle the overall production is:
 One ATP
 Three reduced NAD
 One reduced FAD
 Two molecules of carbon dioxide
The electron transport chain
 At the end of the kreb’s cycle we are left with
reduced NAD and reduced FAD which are
carrying hydrogen atoms
 These enter the electron transport chain
which is on cristae of the mitochondria
 The Hydrogen will be used to make lots of
ATP
Intermembrane space
Matrix
The electron transport system
 The electron transport chain is a series of proton pumps and electron
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carriers
Reduced NAD and reduced FAD donate hydrogen atoms. The carriers
become re oxidised in the process (due to loss of hydrogen) and return
to glycolysis, link reaction or the krebs cycle to collect more hydrogen
The hydrogen atoms split into protons (H+) and electrons. (occurs in the
matrix)
The electrons are transported along a series of carriers embedded in
the inner mitochondrial membrane
Each electron carrier is at a lower energy level that the one before
As electrons flow along the electron transport chain, energy is released
and used to pump the protons from the matrix into the intermembrane
space using special protein pumps.
This creates an electrochemical gradient with a build up of protons in
the intermembrane space. Can also be called proton gradient and a pH
gradient
The electron carriers become reduced then oxidised as the electron is
past along the chain, which are a series of redox reactions.
Animation to watch
The chemiosmotic theory
The chemiosmotic theory
 The protons cannot flow back through the phospholipid
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membrane but can diffuse through special protein channels
which are an ATP synthetase complex (facilitated diffusion)
It is the flow of protons back into the matrix via the ATP synthase
(stalked particles) which drives the synthesis of ATP
The flow provides the energy to attach P to ADP
These protons then recombine in the matrix with the electrons to
from hydrogen atoms
The hydrogen atoms combine with oxygen to form water
This reaction is catalysed by the enzyme oxidase.
Oxygen is therefore the final electron acceptor
How is ATP generated here?
How many ATP’s are formed?
 If NADH is initial acceptor, each pair of
hydrogen atoms releases three molecules of
ATP
 If FADH replaces NADH as the initial acceptor
then only two molecules of ATP are produced
Glycolysis
Link reaction
Krebs
2NADH
2ATP
2NADH
6NADH
2FADH
2ATP
In total, respiration produces:
10 molecules of NADH in total produces 30 ATP’s
2 molecules of FAD in total produces 4 ATP’s
4 molecules of ATP are made by substrate level phosphorylation
In total 38 molecules of ATP from one molecule of glucose
Respiration of proteins and lipids
Glycerol
as Triose Sugars
in Glycolysis
Proteins
3C
Lipids
2C
Amino acids
4C
Fatty acids
4C
4C
5C
Acetyl CoA-can
be produced by
respiration of
carbohydrates,
proteins and
fats
Respiration of fats and proteins
 Fats and proteins can be used as respiratory substrates
 Fats are hydrolysed into fatty acids and glycercol
Glycerol converted into 3C sugar (triose phosphate) which
enters respiration
 Fatty acids are split into 2C’s and enter the Kreb’s cycle as
acetyl coA (the length of the carbon chain determines the
number of ATP produced because the hydrogen ions
released are fed into the electron transport chain) fats carry a
lot of energy
 Protein is only used during starvation
 Protein is hydrolysed to amino acids which are deaminated in
the liver
 The amino group is converted to urea and excreted
 The other component is converted to a Kreb’s cycle
intermediate
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Deamination of amino acids
The remaining keto group can be used in respiration
either converted to acetyl CoA, pyruvic acid or a krebs
intermediate
Deamination of amino acids
•The liver removes the amino group (deamination) and produces
ammonia which is toxic and needs to excreted as urea
• Carbon dioxide reacts with ammonia as part of the ornithine cycle to
produce urea
ammonia +carbon dioxide=urea and water
2NH3+CO2=CO(NH2)2+H20