Transcript RESPIRATION

Metabolic Pathways
A metabolic pathway is a series of chemical reactions occurring within a
cell. Each step is catalyzed by a specific enzyme and involves small
changes in the energy and form of the substrate. The product of one
enzyme will become the substrate for the next in the chain.
Enzyme
1
A
Substrate
Enzyme
Enzyme
Enzyme
B
C
D
2
Substrate
Product
3
Product
Substrate
4
5
Product
Substrate
Product
Metabolism
building up
breaking down
Anabolic pathway
Catabolic pathway
e.g. Photosynthesis
e.g. Respiration
Respiration
Respiration: The process by which organisms
oxidise organic matter to release energy.
There are two types:
i. Anaerobic respiration: which does not require
oxygen, is less efficient and which usually produces
ethanol and carbon dioxide or lactic acid as end
products.
ii. Aerobic respiration which requires oxygen, is
much more efficient than anaerobic and produces
carbon dioxide and water as end products
ATP
ATP Structure
ATP is a nucleotide
made from:
1. The nitrogenous base
Adenine
2. A pentose sugar
Ribose
3. Phosphate groups
ATP: Function
1. It is a coenzyme involved in many
enzyme reactions in cells.
2. It is the major energy currency of cells
entrapping or releasing energy in most
metabolic pathways.
3. The energy is released from ATP in a
single step and in a small manageable
amount.
4. It is a small molecule so will diffuse rapidly around the cell to where it is
needed.
5. It is one of the monomers used in the synthesis of RNA and, after conversion
to deoxyATP (dATP), DNA.
ATP: and energy
When the third phosphate group of ATP is removed by hydrolysis, a substantial
amount of free energy is released, the exact amount depends on the conditions. For
this reason, this bond is known as a "high-energy" bond. The bond between the first
and second phosphates is also "high-energy". But note that the term is not being
used in the same sense as the term "bond energy". In fact, these bonds are actually
weak bonds with low bond energies.
ATP + H2O -> ADP + Pi
ADP is adenosine diphosphate. Pi is inorganic phosphate.
* Hydrolysis: Decomposition of a substance by the insertion of water molecules between
certain of its bonds. Food is digested by hydrolysis)
*Free energy: The energy that can be harnessed to do work.
ADP to ATP
Although ATP is always formed in a cell from ADP and P, the energy
needed for the conversion may be supplied in 3 possible ways:
1. Substrate level phosphorylation
Here energy comes from an exergonic reaction such as the conversion of triose
phosphate to pyruvate in glycolysis, or the conversion of α Ketoglutarate to
Succinate in Krebs cycle.
ADP + P
Triose
Phosphate
ATP
Pyruvate
Exergonic reaction
Substrate level phosphorylation does not need oxygen - it is always anaerobic.
*Exergonic
ADP to ATP
2. Oxidative phosphorylation
Here ATP is formed from ADP and P in oxidative phosphorylation on the
mitochondrial cristae. Energy is supplied by the oxidation of hydrogen and so
this process is aerobic.
3. Photophosphorylation
Here ATP is formed from ADP and P on the granal lamellae within the
chloroplast. Energy is supplied by sunlight. This process is anaerobic.
NAD
NAD Function
Nicotinamide adenine dinucleotide (NAD+) and
nicotinamide adenine dinucleotide phosphate
(NADP) are two important cofactors found in cells.
NADH is the reduced form of NAD+, and NAD+ is the
oxidized form of NADH. It forms NADP with the
addition of a phosphate group to the 2' position of the
adenosyl nucleotide through an ester linkage. NAD is
used extensively in glycolysis and the citric acid cycle
of cellular respiration. The reducing potential stored in
NADH can be converted to ATP through the electron
transport chain or used for anabolic metabolism. ATP
"energy" is necessary for an organism to live. Green
plants obtain ATP through photosynthesis, while other
organisms obtain it by cellular respiration.
Respiration
Cell respiration has 4 main stages
1. Glycolysis
2. The Link Reaction
3. Krebs cycle
4. Oxidative Phosphorylation
Glycolysis
1. Glycolysis = carbohydrate-splitting
2. It occurs in the cytoplasm
3. It converts 6c, hexose sugar glucose into 3c pyruvate
4. It is an anaerobic process
IB
GLYCOLYSIS
Glucose
1. Glycolysis starts in the
cytoplasm with the 6 carbon
(hexose) sugar Glucose.
2. The glucose is given
activation energy by being
phosphorylated twice by ATP.
3. The phosphorylated hexose
sugar now has enough energy
to split into two triose sugars.
C
C
C
C
C
C
P
P
C
C
C
C
C
C
P
P
C
Triose
phosphate
C
C
C
C
C
Triose
phosphate
GLYCOLYSIS
4. One triose sugar
(Dihydroxyacetone phosphate) is
converted into the other triose
sugar GP, (Glycerate phosphate).
5. Each of the two triose sugars
are then phosphorylated again
by inorganic phosphates.
At the same time the triose
sugar is oxidised, losing
hydrogen; the hydrogen
reducing the coenzyme NAD.
6. The triose sugars are then
converted to Pyruvate in the
process two ADPs for each
triose are phosphorylated to
ATP. This is called substrate
level phosphorylation
Gross ATP = 4, Net = 2
P
P
C
x2
C
C
C
C
C
NAD
Oxidoreductase
Reduced
NAD
x2
P
P
C
C
C
ATP
ATP
x2
C
C
C
GLYCOLYSIS
Hexose x2P
ATP
Hexose P
ATP
x2 TRIOSE-P
Energy Level
Hexose
Energy used to
split molecule
4 ADP + 2Pi
4 ATP
2 PYRUVATE
Glycolysis
Anaerobic Respiration
Glucose
Glycolysis is the first step in
x 2 ATP
aerobic respiration. However on
x 2 ADP
its own it is also the first part of
Anaerobic respiration.
In yeast in the absence of
oxygen the pyruvate is
converted into ethanol and CO2. x 4 ADP
This step regenerates the NAD
from the reduced NAD. Without
this there would be no NAD to
allow the conversion of the GP
to Pyruvate.
Animals generally produce
lactic acid instead of ethanol and
CO2.
GP x2
x 4 ATP
NAD x2
Reduced
NAD x2
Pyruvate x2
Gross ATP = 4, Net = 2
Ethanol
Lactic
acid
+ CO2
Mitochondria
Outer Membrane
Inner Membrane
Matrix
Cristae
Cytoplasm
The Link Reaction
7. The Pyruvate leaves the
cytoplasm and enters the matrix
of the mitochodria
8. The three carbon pyruvate
losses a carbon as carbon
dioxide. (It is decarboxylated)
At the same time the coenzyme
NAD removes hydrogen from
the pyruvate, the pyruvate is
oxidised and the NAD reduced.
The reaction is catalysed by an
Oxidoreductase enzyme.
9. The two carbons from the
pyruvate join with Coenzyme A
to form Acetyl Coenzyme A.
Pyruvate
C
C
C
Mitochondria
Oxidoreductase
CO
C2
C
Reduced
NAD
NAD
C
Coenzyme A
Cytoplasm
The Link Reaction
Mitochondria
10. The link reaction is a major
crossroads in metabolism and
Acetyl CoA can be formed from
fatty acids as well as
carbohydrates.
Carbohydrates
Coenzyme A
Fatty acids
C
C
The Krebs Cycle
1. The Krebs Cycle occurs in the matrix of the mitochondria
2. Two carbon dioxide molecules are produced
3. One ADP is phosphorylated to ATP
4. Four coenzymes are reduced
Cytoplasm
The Krebs Cycle
1. Two carbons from Acetyl
Mitochondrial
Coenzyme A pass to a 4 carbon
matrix
Coenzyme A C C
(oxaloacetate) compound
making a 6 carbon compound
(citrate).
2. In a series of reactions the 6C
compound is converted back to
the 4C. In the process 3 NADs
are reduced.
Krebs Cycle
4C
6C
In addition the coenzyme FAD
compound
compound
is also reduced, both reductions
are catalysed by oxidoreductase
enzymes
ADP
CO2 ATP
NAD
3. One ADP is phosphorylated
x2
to ATP
4. Two carbons are released as
carbon dioxide
Reduced
FAD
FAD
Reduced
NAD
x3
Glucose
Respiration Summary
x 2 ATP
Glycolysis produces a nett gain
of x2 ATPs and two reduced
NADs per glucose molecule.
The Link reaction produces 2
reduced NADs per glucose.
The Krebs cycle produces 6
reduced NADs 2 reduced FADs
and 2 ATPs per glucose.
Six molecules of carbon
dioxide are produced from the
Link reaction and the Krebs
cycle combined
x 2 ADP
GP
x2 NAD
x 4 ADP
x 4 ATP
x2
NAD
x2 Reduced
NAD
x2
Reduced NAD
Pyruvate
CO2
Acetyl Coenzyme A
4C
compound
ATP
24
Reduced NAD
10
24
CO2
Reduced FAD
2
x2
The
Krebs
Cycle
x2
ATP
Reduced FAD
6C
compound
x2
ADP
x6
x2 FAD
x6
NAD
Reduced NAD
Oxidative Phosphorylation
Matrix
H+
H+
H+
H+
H+
H+
H+
Cytochrome chain
The reduced NAD’s and reduced
FAD in the mitochondria pass
their hydrogen's and electrons to
a chain of cytochrome carriers
found in the cristae of the
mitochondria. The cytochromes
are alternately reduced and
oxidised as they gain and lose
electrons. This process separates
the H+ from the electrons
creating a proton gradient across
the cristae.
electrons
NAD
Reduced NAD
Oxidative Phosphorylation
Hydrogens + Oxygen = Water
ADP
ATP
Matrix
H+
H+
H+
H+
H+
H+
H+
Cytochrome chain
The H+ pass back through the
membrane to the matrix through the
stalked particles which are ATPase
enzymes. So ultimately the energy
contained in the reduced coenzymes
is used to phosphorylate ADP to
ATP. The final acceptor for the
Hydrogen is Oxygen combining to
producing water. The whole process
is called oxidative phosphorylation.
Oxidative phosphorylation in
combination with the Krebs cycle
and glycolysis form the pathways of
aerobic respiration. This is much
more efficient than anaerobic
producing about 38 ATP as opposed
to the net gain of 2 produced by
anaerobic respiration.
NAD
Reduced NAD
electrons
End
IB
Glycolysis
Glucose 6C
Glycolysis is the first step in
aerobic respiration. In the first
steps two ATP coenzymes
donate energy to the glucose
This provides the activation
energy to allow the glucose to
split into two 3 carbon
molecules which are then
converted to pyruvate. In the
process four molecules of ATP
are produced, a net gain of two.
x 2 ATP
x 2 ADP
GP 3C (x2)
x 4 ADP
NAD
x 4 ATP
Reduced
NAD
Pyruvate 3C (x2)
Gross ATP = 4, Net = 2