A2 Revision
Respiration
Mrs Kavanagh
Revision lesson: objectives and outcomes
To understand why we need respiration to take place
Why we need respiration to release energy for cell metabolism
Revision lesson: objectives and outcomes
To understand why we need anaerobic respiration to take place
To understand that there are other respiratory substrates available
Respiration produces energy, in the form of ATP
The site of aerobic respiration, is the mitochondria
Aerobic respiration takes place with oxygen
ATP is the unit of energy currency
Anaerobic respiration takes place without oxygen
Success!
Why do we need to carry out respiration?
We need energy for processes in our body such as muscle contraction and cell division
We need to carry out respiration to release energy in our cells
Glucose is a very energy-rich substrate which is broken down and used to produce energy
In respiration a series of enzyme catalysed reactions take place in cells - these reactions are catabolic, this means that larger, complex molecules are broken down into smaller,
simpler molecules
A brief summary…
During the process, some energy is transferred to make ATP (adenosine triphosphate) from ADP (adenosine diphosphate) and some energy is released as thermal energy
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Adenosine triphosphate consists of a ribose sugar, a base (adenine) and 3 phosphate groups.
This phosphate can phosphorylate other compounds making them more reactive
ATP hydrolase is an enzyme. It is used to hydrolyse ATP into ADP and a (inorganic) phosphate
Enzymes associated with ATP
ATP synthase catalyzes the condensation reaction between ADP and the inorganic phosphate, making ATP
Where does respiration take place?
Four stages of aerobic respiration
Electron Transport Chain
Krebs Cycle
Link Reaction
Glycolysis
ATP x 2
ATP x 4
ADP x 2
ADP x 4
Glucose
Triose Phosphate x 2
Pyruvate x 2
NAD
Reduced NAD
Glucose is phosphorylated
Cytosol
ETC: electron transport chain
ATP is hydrolysed into ADP and inorganic phosphate
Electron carrier
Glycolysis takes place in cytosol
Net gain of 2 ATP
2 ATP used for phosphorylation
Conversion of TP to pyruvate = 4 ATP
Pyruvate moves to mitochondria
Stage 2: The Link Reaction
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Takes place in the mitochondrial matrix
The link reaction joins glycolysis and the Krebs cycle
In the link reaction pyruvate in converted into acetyl coenzyme A, otherwise known as acetyl CoA
In this stage, no energy is produced (in the form of ATP), but reduced NAD and acetyl CoA are produced
The acetyl CoA will be used in stage 3, in the Krebs Cycle and the reduced NAD will be used in oxidative phosphorylation
A carbon atom is removed from the pyruvate - this forms carbon dioxide
Stage 2: The Link Reaction Continued
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The pyruvate now becomes a 2C molecule called acetate
Hydrogen is also removed during this conversion process - this is picked up by the coenzyme NAD to form reduced NAD
Acetate combines with coenzyme A (CoA) forming acetyl CoA
The link reaction takes place twice for each glucose molecule, therefore each molecule of glucose produces 2 molecules of pyruvate
Coenzyme A
CO2
NAD
Reduced NAD
Acetate
Acetyl
CoA
Pyruvate
Matrix of mitochondria
Cytosol
or
Where does the link reaction take place?
2
or
How many carbon atoms
are found in pyruvate?
3
2
or
How many carbon atoms are found in the acetyl group CoA?
3
CO2, ATP, reduced NAD and reduced FAD are produced
Acetyl CoA enters the Krebs cycle. Here glucose is oxidized
Reduced NAD and FAD are later used in oxidative phosphorylation
Stage 3: The Krebs Cycle - Summary
Stage 3: The Krebs Cycle Continued
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A 6-carbon molecule called citrate is produced
Carbon and hydrogen are removed; CO2 and reduced NAD are formed
Citrate is now
a 5C compound
Decarboxylation and dehydrogenation occur, converting 5C compounds into 4C oxaloacetate, the molecule we started with
ATP, 3 molecules of reduced NAD, 1 molecule of reduced FAD and CO2 are also formed
This takes place twice for each glucose molecule
Acetyl CoA
Oxaloacetate
CoA
Courtesy of the BBC
Stage 4: Oxidative Phosphorylation
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Reduced NAD and reduced FAD release
their Hydrogen atoms
The electrons move to electron carriers, which are embedded within the inner mitochondrial membrane
As the electrons move between the electron carriers, they lose energy
Hydrogen ions accumulate in the intermembrane space
Hydrogen ions then flow back into the matrix through the enzyme ATP synthase
At the end of the ETC, the electrons are passed onto oxygen. This is the final electron acceptor
This is the final stage
of aerobic respiration
It is the part where most
of the ATP is made
The electrons carried by reduced NAD and reduced FAD that have been made
in the first 3 stages
are now used
This process takes
place across the inner mitochondrial membrane
and there are two parts
to the process:
1 chemiosmosis and the
2 electron transport chain
Exam Questions
ATP is regarded as a universal energy currency, as it is used in all organisms for cellular processes. Draw a simple, fully labelled diagram of ATP.
Q
Explain the importance of ATP in cells (Max 3)
Q
(i) The detailed diagram opposite, shows the link reaction and Krebs Cycle. Most of the intermediates involved are named.
Using the diagram, and your own knowledge, determine how many carbons there are in the following Krebs Cycle intermediates:
Citrate…………….
α-ketoglutarate ………….
Succinate…………….
(ii) Explain precisely how you have arrived at these figures.
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and
Q
Name the two enzyme types involved in the conversion of pyruvate to acetyl CoA
dehydrogenase;
decarboxylase;
Q
Acetyl CoA: 2-carbon molecule formed in the link reaction, when acetate reacts with Coenzyme A
Anaerobic respiration: form of cellular respiration that takes place in the absence of oxygen
Aerobic respiration: form of cellular respiration that takes place in the presence of oxygen and produces carbon dioxide, water and ATP
Deamination: the removal of an amino group from a molecule - in the liver, amino acids are deaminated to form keto acids and ammonia
FAD: coenzyme that becomes reduced when it takes up hydrogen atoms during the Krebs cycle forming reduced FAD - flavin adenine dinucleotide
Respiration: set of metabolic reactions that take place in organisms and break down respiratory substances such as glucose, into smaller inorganic molecules, like water and carbon dioxide - this is linked to the synthesis of ATP
NAD: coenzyme that becomes reduced when it takes up hydrogen atoms during the Krebs cycle forming reduced NAD - Nicotinamide adenine dinucleotide
Triose phosphate: a 3-Carbon compound formed
in glycolysis
What have
you learnt?
Name the 4 main stages of aerobic respiration and state where they occur:
Q
Oxygen acts at the final electron acceptor
State the role of oxygen in the ETC
Q
What is anaerobic respiration?
The product of anaerobic respiration is Lactic Acid
Less ATP is formed than in aerobic respiration
Anaerobic respiration is a form of respiration in cells, that takes place without oxygen
A summary of anaerobic respiration
A small amount of energy is released, in the form of ATP
After glycolysis, the reduced NAD, which is a product of glycolysis transfers the H to pyruvate, forming lactic acid, in animals
In mammals, respiration can occur without oxygen, the process of anaerobic respiration is the same as aerobic only until glycolysis
ATP x 2
ATP x 4
ADP x 2
ADP x 4
Glucose
Triose Phosphate x 2
Pyruvate x 2
NAD
Reduced NAD
Lactate x 2
NAD
Reduced NAD
Glycolysis
Step 1
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This first step is the same as anaerobic respiration - glycolysis
Glucose is converted to pyruvate with the net release of 2 ATP molecules
2 molecules of reduced NAD are also formed
Step 2
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Reduced NAD donates hydrogen (and electrons) to pyruvate, producing lactate and NAD
This process regenerates more oxidized NAD for glycolysis
This means that anaerobic respiration can continue and ensures that small amounts of energy can still be made in the absence of oxygen
Anaerobic respiration means that biological processes can continue, in the absence of oxygen
Lactate can build up as anaerobic respiration continues
Cells convert lactate back to pyruvate - the pyruvate can enter aerobic respiration at the Krebs cycle
The lactate needs to be broken down
Liver cells can convert lactate into glucose, which can then be respired aerobically if oxygen is available - or it can be stored to be accessed later
In animals and some bacteria, reduced NAD transfers hydrogen to pyruvate to form lactic acid - pyruvate is reduced to lactate
This process is termed lactic acid fermentation
The lactic acid that has been produced is part of a reversible process, if oxygen is available - the amount of oxygen to remove the lactic acid is called the oxygen debt
The reduced NAD transfers hydrogen to pyruvate to form ethanol and carbon dioxide - the pyruvate is reduced to ethanol
Alcohol fermentation is not reversible, ethanol is toxic and will eventually kill the cells
Comparing the yield of aerobic and anaerobic respiration
Anaerobic = 2 ATP
Aerobic = 30 - 32 ATP
Glycerol and fatty acids from lipids
Amino acids from proteins
Other respiratory substrates
Glycogen, starch, sucrose and fructose
Glycerol is converted to a 3-carbon sugar, triose phosphate and this enters glycolysis
Lipids are hydrolysed to glycerol and fatty acids
Fatty acids are broken down into 2-carbon acetate parts, this enters the Krebs cycle as acetyl CoA
Lipids used in respiration
Proteins are hydrolysed to amino acids
Amino acids are deaminated in the liver
They form keto acids and ammonia, one of the keto acids, pyruvate, is used in the link reaction
Other Keto acids enter glycolysis and the Krebs cycle
Proteins used in respiration
Fructose is a structural isomer of glucose and is used in processed foods as it is much sweeter than glucose
Glycogen and starch are polymers of alpha glucose - they release glucose when hydrolysed, this then enters glycolysis
Sucrose is a disaccharide that contains fructose - it is also used in processed foods. It can be converted into hexose phosphate and enter glycolysis
Glycogen, starch, sucrose and fructose used in respiration
Review…
A form of cellular respiration that takes place in the presence of oxygen.
Less ATP is produced than in aerobic respiration
or
Define anaerobic respiration
A form of cellular respiration that takes place in the absence of oxygen.
Less ATP is produced than in aerobic respiration
Acetic acid
or
State the product of anaerobic respiration
Lactic Acid
ethanol
carbon dioxide
or
State the products of anaerobic respiration in plants and microorganisms
ethanol
carbon monoxide
Exam Questions
NAD, ethanol + carbon dioxide in correct places (not: alcohol)
Accept hydrogen / reduced by;
NADH2 / reduced NAD / NADH H+;
lactate / lactic acid;