7. Respiration Flashcards
How do living organisms respire?
It releases the energy stored in organic molecules such as glucose.
The energy is used to synthesise molecules of ATP.
ATP can by hydrolysed to release energy needed to drive biological processes.
What biological processes need respiration to occur?
active transport, endocytosis, exocytosis, synthesis of large molecules, DNA replication, cell division and movement
What are anabolic reactions?
Metabolic reactions where large molecules are synthesised from smaller ones.
What are catabolic reactions?
Metabolic reactions involving the hydrolysis of large molecules into smaller ones.
What is the structure of ATP?
It is a phosphorylated nucleotide.
Consists of one ribose molecule attached to three phosphate groups and an adenine.
The three phosphates are bonded by phosphoanhydride bonds
It is relatively stable when in solution in cells but readily hydrolysed by enzyme catalysis.
What is the role of ATP?
ATP is hydrolysed to ADP and P.
A small quantity of energy is released for use in the cells.
Some energy is released as heat to help keep organisms warm and allow enzyme-catalysed reactions to proceed at their optimum rate.
Why is ATP referred as the universal energy currency?
Because it occurs in all living cells and is a source of energy that can be used in small amounts.
What are the 4 stages of aerobic respiration?
Glycolysis (in the cytoplasm)
The link reaction (in the mitochondrial matrix)
The kreb’s cycle (in the mitochondrial matrix)
Oxidative phosphorylation (in the cristae of mitochondria)
What is glycolysis?
A biochemical pathway that occurs in the cytoplasm of all living organisms that respire.
It is not an aerobic process.
4 ATP molecules are produced for each glucose molecule during glycolysis.
What are the three main stages of Glycolysis?
1) Phosphorylation of glucose.
2) Splitting hexose bisphosphate molecule into two triose phosphate molecules.
3) Oxidation of triose phosphate to pyruvate.
Each step is enzyme catalysed
How is glucose phosphorylated?
Two ATP molecules are hydrolysed to form two ADP + P. The phosphate (P) molecules are added to the glucose to form hexose bisphosphate which is more reactive.
How many carbons does each molecule in glycolysis contain?
Glucose and hexose bisphosphate= 6
Triose phosphate and pyruvate= 3
How is triose phosphate oxidised into pyruvate?
2 NAD molecules take the hydrogen from each triose phosphate to form 2 pyruvate.
The 2 reduced NAD produced are needed later on in oxidative phosphorylation.
Enough energy is released in these reactions to produce 2 ATP molecules for each pyruvate formed (so 4 ATP molecules are produced overall).
What is NAD?
It is a coenzyme that assists enzymes in redox reactions.
They accept the hydrogen atoms removed during oxidation.
After it has carried out its function where it is reduced, it can be re-oxidised by giving up the hydrogen that it has accepted and be reused.
Why is NAD described as a nucleotide derivative?
Because it has the same sub-units as nucleotides.
It contains 2 five-carbon sugars, 2 phosphate groups and an adenine nitrogenous base.
However, it also contains a nicotinamide unit.
What are the products of glycolysis?
2 molecules of ATP per glucose,
4 molecules of ATP are made overall, two were used up, so the net gain is 2.
2 molecules of reduced NAD- these are actively transported into the mitochondria.
Two molecules of pyruvate- these are actively transported into the mitochondrial matrix as they are used in the link reaction.
What is the structure of mitochondria?
They have an inner and outer phospholipid membrane making up the envelope.
Between the membranes is the intermembrane space.
The inner membrane is folded into cristae.
It is embedded with proteins and protein channels.
The mitochondrial matrix contains ribosomes, looped DNA and enzymes.
The matrix is where the link reaction and Krebs cycle occurs, what structures does it contain to carry out these functions?
Molecules of the coenzyme NAD and FAD.
Oxaloacetate which accept the acetyl group from the link reaction.
Mitochondrial DNA codes for enzymes involved in the reactions.
Mitochondrial ribosomes are the sites for assembling proteins.
How is the outer membrane adapted to its function?
It contains carrier and channel proteins that allow the passage of molecules into the mitochondrion.
How is the inner membrane adapted to its function?
The folds give it a large surface area for the electron carriers and ATP synthase enzymes embedded in them.
The electron carriers are arranged in electron transport chains, involved in oxidative phosphorylation.
What happens in the link reaction?
Each pyruvate is converted to a two-carbon acetyl group.
Pyruvate is decarboxylated and dehydrogenated.
No ATP is produced during this reaction.
How is pyruvate decarboxylated in the link reaction?
The enzyme pyruvate dehydrogenase catalyses the removal of carbon in the form of carbon dioxide from the pyruvate.
How is pyruvate dehydrogenated in the link reaction?
The enzyme pyruvate dehydrogenase, assisted by NAD, catalyses the removal of hydrogen from the pyruvate.
What happens to the acetyl group at the end of the link reaction?
It combines with coenzyme A (CoA) to become acetyl coenzyme A
The coenzyme A contains a ribose, three phosphate groups and a B vitamin
What is the Krebs cycle?
A series of enzyme-catalysed reactions that oxidise the acetyl coenzyme A from the link reaction into two molecules of carbon dioxide while reducing coenzyme NAD and FAD.
These carry hydrogen atoms to the electron transport chain on the cristae.
Draw the Krebs cycle…
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How much reduced NAD is produced in the Link reaction and the Krebs cycle?
Link reaction- 2
Krebs cycle- 6
How much reduced FAD is produced in the link reaction and Krebs cycle?
Link reaction- 0
Krebs cycle- 2
How much Carbon dioxide is produced in the link reaction and Krebs cycle?
Link reaction- 2
Krebs cycle- 4
How much ATP is produced in the link reaction and Krebs cycle?
Link reaction- 0
Krebs cycle- 2
What is oxidative phosphorylation?
The final stage of aerobic respiration.
Involves electron carrier proteins and the process of chemiosmosis.
What is the role of the electron transport chain in oxidative phosphorylation?
Electrons pass along the chain, the iron ion in the centre of each electron carrier gain an electron and become reduced, they donate the electron to the next electron carrier protein and reoxidise.
The energy released is used to pump protons across the inner mitochondrial membrane, into the intermembrane space.
What is the purpose of creating a proton gradient across the intermembrane space?
Protons can diffuse through the channel of ATP synthase enzyme, this is chemiosmosis and produces a proton motive force.
This causes the ATP synthase enzyme to turn and combine ADP and P from the matrix and form ATP.
What happens to the electrons that travel along the electron transport chain?
They are accepted by oxygen.
They combine with the protons diffusing down the ATP synthase channel, forming water.
What is the net gain of ATP per molecule of glucose in oxidative phosphorylation?
28
What effect does the absence of oxygen have on respiration?
It cannot act as the final electron acceptor in oxidative phosphorylation.
Oxidative phosphorylation ceases.
Reduced NAD and FAD cannot become reoxidised.
The Krebs cycle and link reaction stops.
What process can occur in the absence of oxygen?
Glycolysis
However, there must be a supply of oxidised NAD to remove the hydrogen ions and produce ATP.
This cannot be done in the normal way without oxygen.
How do eukaryotes reoxidise NAD without oxygen?
Fungi and plants- ethanol fermentation pathway
Mammals- lactate fermentation pathway.
Both take place in the cytoplasm.
Draw the ethanol fermentation pathway…
look at card
Draw the lactate fermentation pathway…
look at card
What happens to lactate after the fermentation pathway?
The lactate produced is carried away from the muscles, in the blood, to the liver.
Here it can be converted to pyruvate which enters the Krebs cycle or recycled to glucose and glycogen.
What is the ATP yield of anaerobic respiration?
The ethanol and lactate fermentation do not produce any ATP.
Because glucose is only partially broken down, many more molecules can undergo glycolysis, so the overall ATP yield is larger than aerobic respiration.
What are the different respiratory substrates?
carbohydrates, lipids and proteins
How do carbohydrates act as respiratory substances in animals?
They store carbohydrates as glycogen, which can be hydrolysed to glucose for respiration.
How do carbohydrates act as respiratory substances in plants?
Plant cells store carbohydrate as starch, and this can be hydrolysed to glucose for respiration.
How are carbohydrates broken down for respiration?
Disaccharides can be digested to monosaccharides.
Monosaccharides can be changed, by isomerase enzymes, to glucose.
