Respiration 3.5.2 Flashcards
What is respiration
Respiration is the conversion of chemical energy in substrates (eg, glucose) into chemical energy in ATP.
Aerobic
Aerobic respiration requires oxygen and forms the waste products CO2 and H2O.
Anaerobic
Anaerobic respiration is in the absence of oxygen forms the waste produces ethanol and CO2 in bacteria and lactic acid in animals.
Mitochondria structure
- Site of aerobic respiration within eukaryotic cells.
- Bound by a double membrane structure. Outer membrane is permeable to small molecules and ions. Inner membrane is impermeable to most materials.
- A semi-rigid matrix is enclosed by the inner membrane. The matrix contains many enzymes, DNA and ribosomes.
- Inner membrane is folded into a number of cristae. These increase the surface area to provide lots of space for enzymes and electron carriers.
- The inter membrane space between the 2 membranes is important in maintain proton gradients.
Mitochondria labelled
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Glycolysis
- Activation - make glucose reactive by phosphorylations using 2ATP - ADP + Pi.
- Splitting - splits into 2x triose phosphate.
- Oxidation - e- and p+ are picked up by NAD (coenzyme) (NAD-NADH) (ADP + PI - ATP).
- Substrate level phosphorylation - phosphate donated to ADP triose phosphate oxidised into pyruvate.
Overall - 2x pyruvate, 2x NADH, 2x ATP
Takes place in the cytoplasm.
Link reaction
- Pyruvate is decarboxylated - removal of CO2.
- Pyruvate is oxidised, donating electrons to coenzyme NAD.
- These result in acetyl group that combines with CoA to form acetyl coenzyme A which enters the kerbs cycle.
Overall - 2x CO2, 2x NADH, 2x acetyl-coenzyme
Takes place in the mitochondrial matrix.
Link reaction diagram
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Krebs cycle
- Acetyl coenzyme A combines with 4C compound = 6C compound.
- The 6C compound is decarboxylated releasing CO2. 6C compound also oxidised releasing H2 which are picked up by NAD. This makes 5C compound.
- 5C decarboxylated releasing CO2 and oxidised, released 3H2 - 2 pairs picked up by NAD and other pair by FAD.
- 2NAD to 2NADH and FAD to FADH2.
- ATP made by substrate level phosphorylation.
- This cycle regenerates 4C compound.
Overall - 4CO2, 6NADH, 2FADH2, 2ATP
The Krebs cycle can also be called the citric acid cycle.
The Krebs cycle takes place in the mitochondrial matrix.
Krebs cycle diagram
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When is decarboxylated and dehydrogenase enzyme used in respiration? (Glycolysis, Link, Krebs)
Glycolysis - dehydrogenase
Link - dehydrogenase and decarboxylase
Krebs - dehydrogenase and decarboxylase
Electron transfer chain
- Coenzymes NAD and reduced FAD released H+ and e-.
- The electrons move down ETC in a series of redox reactions that release energy.
- This energy pumps protons across the inner mitochondrial membrane by AT to the inter membrane space.
- Proton gradient present in IMM
- Protons diffuse back into matrix through ATP synthase (ADP + Pi = ATP - oxidative phosphorylation).
- Oxygen is the final e- acceptor (1/2O2 + 2H+ + 2e-).
Electron transfer chain alternative name and explanation of what is is
The electron transport chain is also referred to as oxidative phosphorylation.
A chain of protein complexes embedded in the cristae in which the energy released in the passage of electrons from one molecule to the next is used to produce ATP.
Electron transfer chain graph
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Importance of NAD and FAD
These co-enzymes help enzymes to function by carrying hydrogen atoms from one molecule to another. These hydrogen atoms are donated to the ETChain, allowing for ATP to be made.
- 1 reduced NAD makes 3 ATP
- 1 reduced FAD makes 2 ATP
ATP breakdown (how many ATP’s are made in each step)
Glycolysis (8ATP)
Link reaction (6ATP)
Krebs cycle (24ATP)
Overall = 38ATP.
NAD and FAD activity investigation
The activity of coenzymes (NAD and FAD) can be investigated using methylene blue. This dye can accept hydrogen atoms so becomes reduced. Reduced methylene blue becomes colourless.
- Add the methylene blue to a suspension containing yeast cells and glucose. The yeast will respire and hydrogen will be produced. The methylene blue picks up the hydrogen and becomes reduced (blue to colourless). Record the time taken for solution to become colourless – determines rate of respiration.
Importance of oxygen in respiration
Oxygen is the final electron acceptor. It combines with protons and electrons to form water. Without its role at the end of the chain, the protons and electrons would ‘back up’ and respiration would stop.
Cyanide in respiration
Cyanide is a respiration poison and is lethal because it’s a non-competitive inhibitor of the final enzyme in the ETC. This causes protons and electrons to accumulate on the carriers, stopping respiration and killing the organism.
Alternative respiratory substrates
Sugars aren’t the only substance that can be used as a respiratory substrate (oxidised to release energy. Both lipids and proteins can, under certain circumstances, be used without first being converted into carbohydrates.
Respiration of proteins
Proteins hydrolysed into AA.
Deaminatoon = the removal of amino group to form keto acids.
Can enter in Krebs cycle or as acetyl coA.
Respiration Lipids
Hydrolysis of fats to glycerol and fatty acids.
Glycerol converted into TP by phosphorylation and enters glycolysis.
Fatty acids converted into acetyl coA by beta oxidation.
Respiratory quotient - anaerobic glucose
Less than 1
Respiratory quotient - aerobic carbohydrate
1
Respiratory quotient - aerobic protein
Approx 0.9
Respiratory quotient - aerobic lipid
Approx 0.7
Anaerobic respiration (bacteria)
In bacteria, fungi (yeast), some cells of higher plans such as root cells in waterlogged soils.
- Pyruvate + NADH —> ethanol + CO2 + NAD
Anaerobic respiration (animals)
- Pyruvate + NADH —> lactate + NAD
This is most common in muscles during strenuous exercise where O2 is used up quicker than it can be supplied so oxygen debt occurs. At some point the lactate has to be removed from muscle cells by the blood and oxidised back into pyruvate to prevent fatigue.
Pyruvate can then enter the Krebs cycle and be fully oxidised to CO2 and H2O, releasing many more ATP molecules or is converted into glycogen in the liver. This occurs when O2 is available again.
