3.3 Respiration Flashcards
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
Define oxidative phosphorylation
- inner membranes of mitochondria in aerobic respiration
- energy for making ATP comes from oxidation-reduction reactions and is released in the transfer of electrons along a chain of electron carrier molecules
Define photophosphorylation
- thylakoid membranes of the chloroplast
- energy from light and is released in transfer of electrons along electron carrier molecules
Define substrate-level phosphorylation
- phosphate groups transferred from donor molecules
- ie ADP to ATP
Describe briefly the key stages of respiration
- glycolysis - occur in cytoplasm and generates pyruvate, ATP and reduced NAD
- link reaction - occur n matrix of mitochondria. Pyruvate converted to acetyl coenzyme A, reduced NAD and CO2
- Krebs cycle - mitochondrial matrix generates CO2 and reduced NAD and FAD
- electron transport chain - cristae of inner mitochondrial membrane, ADP to ATP
Where does glycolysis happen?
- occurs in cytoplasm because glucose cannot pass through the mitochondria as enzymes not present
Define anabolic and catabolic
Anabolic: build
Catabolic: break
What happens when H+ is lost and gained?
- gain = reduce
- lose = oxidise
Properties of phosphorylated glucose
- more reactive due to lower Ea
- more polar so less likely to diffuse
Outline glycolysis
- glucose molecule phosphorylated by addition of 2Pi groups using 2 molecules of ATP to make hexose diphosphate
- hexose diphosphate converted to 2x triose phosphate, 3C sugar and glyceraldehyde-3-phosphate
- 2 triose phosphate are dehydrogenated, oxidising to pyruvate
- hydrogen atoms transferred to NAD, a hydrogen carrier molecule, making reduced NAD which releases energy for 4 molecules of ATP
- net gain of 2 ATPs from each molecule of glucose
Draw glycolysis
Outline link reaction
- pyruvate diffuses from cytoplasm into mitochondrial matrix
- pyruvate is dehydrogenated and hydrogen released is accepted by NAD to form reduced NAD
- pyruvate is decarboxylated which leaves 2 carbon acetate group which combines with coenzyme A to make acetyl coenzyme A which enters krebs
Overall link reaction equation
Pyruvate + NAD + CoA ——> AcCoA + NADred + CO2
Draw link reaction
Outline Krebs cycle
- acetyl CoA enters Krebs cycle by combining with 4C acid to make citric acid
- 6C acid is dehydrogenated making reduced NAD and decarboxylated to make CO2 and 5C acid
- 5C acid is dehydrogenated to make reduced NAD and FAD and decarboxylated to make 4C acid
- 4C combine with AcCoA to repeat
How many times does dehydrogenation occur
2
How many times does decarboxylation occur
4
What does each turn of the Krebs cycle produce?
- one ATP
- 3x redNAD
- 1x redFAD
- 2x CO2
What enzyme reduces NAD
Dehydrogenase
Draw krebs
Products of krebs per glucose
- 2x ATP
- 6x NADred
- 2x FADred
- 4x CO2
What is the acceptor molecule in krebs?
Oxaloacetate
What is the final electron acceptor in krebs?
Oxygen
Why does the ETC only work while O2 is present?
- oxygen is the final electron acceptor and removes H from NADred to make water
Explain why if no oxygen is available, the Krebs cycle and link reaction stop
- NAD needs to be oxidised to get reduced to NADH
Outline the anaerobic and aerobic pathways (whiteboard)
anaerobic
Glycolysis —> fermentation —> 2ATP per glucose
aerobic
Glycolysis —> Krebs cycle —> ETC —> 38ATP per glucosw
Where does glycolysis take place?
Cytoplasm
Where does ETC and krebs take place?
Mitochondria
Aerobic respiration products
38 ATP
CO2 and H2O
Anaerobic respiration products
2 ATP
Lactic acid
Why is the max yield of ATP never quite achieved
- cost of moving pyruvate and ADP into the mitochondrial matrix
- proton gradient compromised by proton leakage across inner mitochondrial membrane
- molecules leak through membrane
Efficiency of ATP production equation
Energy made available
——————————————— x100
Energy released in combustion
Difference between aerobic and anaerobic respiration
- only glycolysis can take place in anaerobic
How can lipids be used as a respiratory substrate?
- fat can be hydrolysed to glycerol and fatty acids
- glycerol is phosphorylated with ATP, dehydrogenated with NAD and converted to triose phosphate which enters glycolysis
Why might lipids be good as an alternative respiration pathway?
- produce large number of ATP molecules
- depending in chain length
—> more C so meow CO2 produced than can be removed
—> more H so more reduced NAD and FAD therefore more ATP
—> more H so more H2O produced - metabolism
Outline the use of protein as a respiratory substrate
- in prolonged starvation, tissue protein is mobilised to supply energy
- protein is hydrolysed to amino acids which are delaminated in the liver
- amino converted to urea and excreted
- residue converted to AcCoA, pyruvate and other Krebs intermediates before being oxidised
Where is the ETC located?
Cristae of the inner mitochondrial membranes
How do hydrogen atoms enter the ETC?
- coenzymes NAD and FAD
Briefly outline the ETC
- Electrons from NADred and FADred pass through electron carriers to make water
- Protons from NADred and FADred are pumped into intermembrane space and flow back through ATP synthetase
- ATP formation
Explain the passage of electrons in the ETC
- NADred donates electrons of H atoms to the first of a series of electron carriers
- electrons provide energy for first proton pump and protons from H are carried into intermembrane spaces
- electrons pass along chain of carrier molecules providing energy for proton pumps
2H+ + 2e- + 1/2O2 —> H2O
Explain the passage of protons in ETC
- inner membrane is impermeable to protons so accumulate in intermembrane space
- proton conc in intermembrane > matrix so gradient of conc & charge is set up
- protein complexes in membrane are associated with ATP synthetase and allow protons to diffuse through channels
ADP + Pi —> ATP + H2O
- protons combine with electrons to form water
How does oxidative phosphorylation result in ATP production?
- inner membrane of mitochondria in aerobic respiration
- energy from redox released from electron transfer along ETC
- flow of protons down electrochemical gradient through ATP synthetase
Draw alcoholic fermentation
2 types of enzymes involved in the conversion of pyruvate to AcCoA
- dehydrogenase
- decarboxylase
What could be deduced if oxygen consumption was low with pyruvate as a substrate?
- pathway to link is not working
- no reduced NAD for ETC
What could be deduced if there was a build up of any one of the Krebs cycle intermediates?
- enzymes catalysing conversion of molecules are not functional
Explain why there is a raised blood lactate level in many patients with mitochondrial disease
- Krebs not working
- pyruvate levels increase
- excess converted to lactate
State where the Krebs cycle takes place
Matrix of mitochondria
Describe briefly what happens to a molecule of carbon dioxide removed
- diffuses out of mitochondria into blood
- carried out at hydrogen carbonate ion
- breathed out
Describe the way in which reduced NAD is produced in the Krebs cycle
- removal of H ions by dehydrogenation
- series of reactions
- NAD to NADH2
Explain what happens to the reduced NAD under anaerobic conditions and why this is essential for glycolysis to continue
- pyruvate used to form lactic acid
- regenerate to NAD
Explain biochemical reasons for anaerobic conversion to lactate
- allows reduced NAD to be converted back to NAD
- allowing ATP production by oxidative phosphorylation
- which enables glycolysis
Explain why the two hydrogen acceptors NAD and FAD lead to the production of different numbers of ATP molecules
Enzymes for alcoholic fermentation
- pyruvate decarboxylase & ethanol dehydrogenase
Enzyme for lactic fermentation
- lactate dehydrogenase
Stages of the biochemical pathway in the cytoplasm that produced reduced NAD
- glycolysis
- dehydrogenation when triose phosphate to pyruvate
Why are fats not the main source of energy in muscles?
- more CO2 than can be removed
- more O2 needed to reduce NAD
Where does the link reaction occur
Mitochondrial matrix
Number of molecules formed in link using NADH
3
Molecules of ATP produced in krebs using NADH
6
Molecules of ATP made in Krebs using FADH
2
Explain why muscles use glycogen as an energy store rather than fat
- glycogen does not need a large O2 supply
- does not need to remove large volumes of CO2 or water
Why does cytochrome c detach from cytochrome oxidase when the electrons are removed?
- changes shape
- no longer complimentary to active site
Why does lactate accumulate in blood if high levels of reduced NAD form?
- lactate is end product of anaerobic respiration
- pyruvate reduced to regenerate NAD
- which enables glycolysis
Why might pyruvate be used as a respiratory substrate instead of glucose?
- glucose used in glycolysis in cytoplasm
- cannot enter mitochondria whereas pyruvate can
- pyruvate used in link reaction in mitochondria
Why is having a high proportion of brown fat beneficial to babies?
- more capillaries
- supply tissue with oxygen and remove CO2
- distribute heat and increase respiration rate
Describe how FADH2 and NADH2 are used to create an electrochemical gradient
- FAD and NAD transport electrons across the electron transfer chain
—> cristae of inner mitochondrial membrane - high energy electrons pump protons into the intermembrane space
- accumulate creating electrochemical gradient
How is NADH2 produced in the Krebs cycle?
- dehydrogenation (removal of H ion)
- series of reactions
- NAD to NADH2
Explain the reasons for NADH2 being required to maintain a proton gradient
- NADH2 supplies protons and brings high energy electrons which supply energy for the proton pumps on the ETC of the cristae of inner mitochondrial membrane
At what point does glycerol enter the respiratory pathway?
During glycolysis
At what point do fatty acids enter the respiratory pathway?
Link reaction
At what point do amino acids enter the respiratory pathway?
End of glycolysis onward
Where does anaerobic respiration occur?
Cytoplasm
Briefly describe how reduced FAD and reduced NAD are used to create an electrochemical gradient
- pass electrons to the ETC
- higher energy electrons power the proton pumps
- protons pumped into intermembrane a space
- accumulate and generate an electrochemical gradient
What could be deduced if the oxygen consumption of mitochondria is low with pyruvate as a substrate, but high which a-ketoglutarate as a substrate?
- link not working
- pathway between keto and rest of cycle is working correctly
What could be deduced if there was build up of any one of the Krebs cycle intermediates?
Enzymes are not functional
Why is there a raised blood lactate level in patients with mitochondrial disease?
- krebs not working
- excess pyruvate gets converted to lactate
