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
