C1- Respiration Flashcards
Define metabolism.
All the reactions of the organism.
What is a metabolic pathway?
A sequence of reactions controlled by enzymes.
Respiration is a catabolic reaction, what does this mean?
It breaks down energy rich macromolecules, such as glucose and fatty acids.
When ATP is hydrolysed what occurs?
Energy is released and available to use by the cell or lost as heat.
What are the three types of phosphorylation?
- Oxidative phosphorylation
- Photophosphorylation
- Substrate-level phosphorylation
What is oxidative phosphorylation and where does it occur?
- occurs in the inner membranes of the mitochondria in aerobic respiration
- the energy for making ATP comes from the oxidation-reduction reactions and is released in the transfer of electrons along a chain of electron carrier molecules
What is Photophosphorylation and where does it occur?
- occurs in the thylakoid membranes of the chloroplasts during the light dependent stage of photosynthesis
- the energy for making the ATP comes from light and is released in the transfer of electrons along a chain of electron carrier molecules.
What is substrate level phosphorylation?
Occurs when phosphate groups are transferred from donor molecules e.g.
- glycerate-3-phosphate to make ADP to ATP in glycolysis
OR
When energy released for a reaction to bind inorganic phosphate to ADP e.g.
- the Krebs cycle
What are obligate anaerobes?
Respire without oxygen and cannot grow in its presence
What are obligate aerobes?
Break down substrates using oxygen, with the release of relatively large amounts of energy.
What are facultative anaerobes?
Respire aerobically, but can also respire without oxygen.
Define aerobic respiration.
The release of large amounts of energy made available as ATP, from the breakdown of molecules, with oxygen as the terminal electron acceptor.
Define anaerobic respiration.
The breakdown of molecules in the absence of oxygen, releasing relatively little energy, making a small amount of ATP by substrate level phosphorylation.
What four stages can aerobic respiration be divided into?
- Glycolysis
- The link reaction
- The Krebs cycle
- The electron transport chain
What does glycolysis generate?
- pyruvate
- ATP
- reduced NAD
Where does glycolysis occur?
in solution in the cytoplasm
Where does the link reaction occur?
in solution in the matrix of the mitochondria
Extremely briefly explain what occurs during the link reaction.
Pyruvate is converted into acetyl coenzyme A
Where does the Krebs cycle occur?
in solution in the matrix of the mitochondria
What does the Krebs cycle generate?
- carbon dioxide
- reduced NAD
- reduced FAD
Where is the electron transport chain located?
on the cristae of the inner mitochondrial membrane.
What is generated by the electrons and protons in the electron transport chain?
ATP is generated from ADP and inorganic phosphate Pi.
Why does glycolysis occur in the cytoplasm?
- Glucose cannot pass through the mitochondria membranes.
- There are no enzymes present in the mitochondria, so it could not be metabolised there.
What is the initial stage of both anaerobic and aerobic respiration.
Glycolysis
Define dehydrogenation
The removal of one or more hydrogen atoms from a molecule
Describe the stages of glycolysis.
- A glucose molecule (6C) is phosphorylated with two molecules of ATP to produce glucose diphosphate.
- Glucose diphosphate splits into two molecules of triose phosphate- glyceraldehyde-3-phosphate
- The triose phosphate molecules are dehydrogenated, oxidising them to pyruvate- the hydrogen then bonds with NAD (a hydrogen carrier molecule) to make two molecules of reduced NAD.
What is NAD?
a hydrogen carrier molecule
Describe two features of glucose diphosphate.
- more reactive so less activation energy is required for the enzyme controlled reactions
- polar and therefore less likely to diffuse out of the cell
What type of phosphorylation occurs during glycolysis and how many ATP molecules does it produce overall?
- Four ATP molecules are formed by substrate level phosphorylation- the phosphate from the triose phosphate converts ADP to ATP without the electron transport chain producing pyruvate.
- Of four ATP molecules produced, two were used to phosphorylate the glucose molecule so there is a net gain of two ATP per molecule of glucose.
Two molecules of NAD are synthesised during glycolysis, if oxygen is available how many more molecules of ATP might be produced?
Each has the potential to synthesise an additional three molecules of ATP, making six all together from the electron transport chain.
During aerobic respiration which two stages is the link reaction between?
It links glycolysis with the Krebs cycle.
Describe the stages of the link reaction.
- Pyruvate diffuses from the cytoplasm into the mitochondria matrix.
- The pyruvate is dehydrogenated- the hydrogen released binds to NAD forming reduced NAD
- The pyruvate is decarboxylated- a molecule of CO2 is removed from it.
- All that remains of the original glucose molecule is a acetate group (2C) which combines with coenzyme A (CoA), making acetyl coenzyme A (AcCoA).
- AcCoA enters the Krebs cycle.
Describe an equation to summaries the link reaction.
pyruvate + NAD + CoA → AcCoA + reduced NAD + CO2
Define decarboxylation.
the removal of a carboxyl group from a molecule releasing carbon dioxide.
what is the purpose of the Krebs cycle?
- To liberate energy from C-C, C-H or C-OH bonds and produce ATP that contains the energy once held in those bonds.
- It also produces reduced NAD and FAD which delivers hydrogen atoms to the electron transport chain.
How many molecules of water are used in reactions in the Krebs cycle?
three molecules of water
Describe the stages of the Krebs cycle.
- AcCoA eneters he Krebs cycle by combining with a 4C acid to form a 6C compound- this regenerates CoA
- The 6C acid is dehydrogenated to make reduced NAD and decarboxylated to make 5C acid and carbon dioxide
- The 5C acid is dehydrogenated making reduced NAD and FAD, and decarboxylated to make (regenerate) 4C acid and carbon dioxide
- Th 4C acid combines with more AcCoA and the cycle repeats.
What two types of reaction occur during the Krebs cycle?
- carboxylation
- hydrogenation
How many times does decarboxylation occur during the Krebs cycle?
Twice- removes carbon dioxide from the COOH groups of Krebs cycle intermediates as…
6C acid → 5C acid → 4C acid
How many times does hydrogenation occur during the Krebs cycle?
Four times- four hydrogen atoms are removed from Krebs cycle intermediates, which are then collected by hydrogen carriers creating three molecules of reduced NAD and one of reduced FAD.
By the end of the Krebs cycle what is the acetate group broken down into?
carbon dioxide and water
In summary what is produced for every turn of the Krebs cycle?
- one ATP by substrate level phosphorylation
- three molecules of reduced NAD
- one molecule of reduced FAD
- two molecules of carbon dioxide
Define coenzyme
a molecule required by an enzyme in order to function
What is the electron transport chain made up of?
A series of protein molecules that are carriers and pumps, which are sometimes called respiratory enzymes.
name a type of carrier molecule in the electron transport chain.
cytochromes- proteins conjugated to iron or copper and the metal ions are oxidised and reduced by electron transport.
What coenzymes carry hydrogen into the electron transport chain?
NAD and FAD
Summaries reduced NAD and reduced FADs role in producing ATP.
- NAD feeds electrons and protons into the electron transport chain at an earlier point than FAD does.
- each pair of hydrogen atoms carried by reduced NAD provides enough energy for the synthesis of three molecules of ATP, using three proton pumps.
- reduced FAD passes hydrogen atoms directly to the second proton pump, hence two molecules of ATP are produced for each pair of hydrogen atoms.
Describe the passage of electron in the electron transport chain.
- reduced NAD donates the electrons of the hydrogen atoms to the first of a series of electron carriers in the electron transport chain.
- electrons from these atoms provide energy for the first proton pump and protons from the hydrogen atoms are pumped into the inter-membrane space
- the electrons pass along the chain of carrier molecules providing energy for each of the three proton pumps in turn
- at the end of the chain the electrons combine with protons and oxygen to form water
What is the equation to represent the formation of water at the end of the electron transport chain?
2H^ + 2e^- + 1/2O2 → H2O
Describe the passage of protons in the electron transport chain.
- the inner membrane is impermeable to protons so protons accumulate in the inter membrane space
- the concentration in the inter membrane space become higher than in the matrix- this creates a gradient in charge and concentration maintained by the proton pumps
- Protons flow back into the mitochondrial matrix through protein complexes in the membrane.
- The enzyme ATP synthetase is associated with each channel the protons flow back through- as they flow through their electrical potential energy produces ATP
- at the end of the chain, the protons combine with electrons and oxygen to form water.
relevant equation:
ADP + Pi → ATP + H2O
Why is oxygen referred to as the ‘final electron/ hydrogen acceptor’?
It removes the hydrogen and electrons once they’ve passed through the electron transport chain- it is reduced by their addition to make water.
Explain how cyanide causes a cell to die.
- it is a non-competitive inhibitor of the final carrier in the electron transport chain
- it prevents electrons and protons being transferred to water
- the accumulate destroying the proton gradient
- ATP synthetase cannot operate and the cell dies quickly
For each molecule of glucose entering the Krebs cycle the electron transport system receives…? That produces how many molecules of ATP?
10 reduced NAD- 30 ATP
2 reduced FAD- 4 ATP
If no oxygen is present what cannot occur that would normally during respiration?
- there is no oxygen to remove hydrogen atoms from reduced NAD and make water so the electron transport chain cannot function- subsequently there is no oxidative phosphorylation so no ATP is formed.
- without oxygen NAD cannot be regenerated to pick up more hydrogen- subsequently the Krebs cycle and link reaction cannot take place, only glycolysis.
How does glycolysis continue to occur despite a lack of oxygen?
The pyruvate and hydrogen is constantly removed and reduced NAD is regenerated by the pyruvate accepting the hydrogen from the reduced NAD.
How is ATP produced during glycolysis when no oxygen is present?
by substrate level phosphorylation
How many different anaerobic pathways are there to remove hydrogen from reduced NAD and where do these pathways occur?
There are two different pathways, both o which take place in the cytoplasm.
Describe anaerobic respiration within animals and the conditions which must be met for this to occur.
- muscle cells do not get sufficient oxygen during vigorous exercise
- pyruvate becomes the hydrogen acceptor and is converted to lactate
- if oxygen becomes available the lactate can be respired to carbon dioxide and water- releasing the energy it contained
Describe anaerobic respiration within microorganisms such as yeast and plant cells in waterlogged conditions and the conditions which must be met for this to occur..
- pyruvate is converted into carbon dioxide and to ethanal- a hydrogen acceptor by carboxylase
- ethanal is reduced to ethanol and NAD is regenerated in alcoholic fermentation
- the pathway is not reversible in the presence of oxygen- it can accumulate within the cells and rise to toxic levels
Explain why cells are not a efficient in respiration as the theoretical total of ATP molecules would suggest?
- ATP is used to move pyruvate
- ADP is used to move reduced NAD and reduced FAD across the mitochondrial membrane
- The proton gradient may be compromised by proton leakage across the inner mitochondrial membrane- rather than passing through ATP synthetase
- molecules may also leak though the membrane
Describe the theoretical yield of ATP.
Glycolysis:
- 2 ATP- SLP
- 6 ATP from 2x reduced NAD- OP
The link reaction:
- 6 ATP from 2x reduced NAD- OP
The Krebs cycle:
- 2 ATP- SLP
- 18 ATP from 6x reduced NAD
- 4 ATP from 2x reduced FAD
SLP- substrate level phosphorylation
OP- oxidative phosphorylation
On average how many ATP molecules are actually produced per molecule of glucose?
30- 32 molecules of ATP
How do you calculate the efficiency of ATP production?
(energy made available through ATP/ energy released in combustion) x 100
Why is the Krebs cycle referred to as the ‘metabolic hub’?
- The metabolic pathways of carbohydrates, lipids and proteins can feed into it.
- In some situations fats and proteins can be used as respiratory substrates.
What links the metabolism of the three types of macromolecules?
Acetyl coenzyme A
When is fat used as a respiratory substrate?
When carbohydrate in the body such as glycogen and blood glucose are low.
Describe how lipids can be used to produce ATP.
Fat is hydrolysed into its constituent molecules- glycerol and fatty acids.
Glycerol:
- glycerol is phosphorylated with ATP to produce glycerol-3-phosphate
- glycerol-3-phosphate is dehydrogenated with reduced NAD and converted into a triose phosphate
- triose phosphate then enters the glycolysis pathway
Fatty acids:
- fatty acids split into two carbon fragments
- they enter the Krebs cycle as AcCoA
- hydrogen is released and picked up by NAD to be fed into the electron transport chain
- this produces a large number of ATP molecules- the exact amount depends on the length of the hydrocarbon chain of the fatty acid
What is the problem with respiring longer fatty acid chains?
- more carbon atoms so more carbon dioxide is produced
- muscles have a limited blood supply so if they respire fat rather than glucose they will produce more carbon dioxide than could be removed quickly enough
Why do tissues with a large blood supply, such as the liver, respire fat?
- fat has more hydrogen atoms so more reduced NAD is produced
- this means a large amount of ATP can be produced and readily transported around the body
Why do desert animals respire fat?
- fat contains more hydrogen atoms so more water is produced
- metabolic water is very important for desert animals and explains why they respire fat
When is protein used as a respiratory substrate?
- When carbohydrates and fats are lacking in a diet protein is diverted from food supply energy
- During prolonged starvation tissue protein is metabolised to supply energy
During prolonged starvation which tissue protein is metabolised to supply energy first?
- heart muscle
- kidney tissue
Describe how protein enters the Krebs cycle.
- it is hydrolysed into its constituent amino acids
- they are then deaminated in the liver
- the amino group is converted into urea and excreted
- the residue is converted into acetyl CoA or pyruvate or another Krebs cycle intermediate
- it is the oxidised
