5.2.2 - Respiration Flashcards
Why is cellular respiration needed?
Respiration transfers energy stored in complex organic molecules to ATP which is required for:
- Active transport for the conduction of nerve impulses and uptake of nitrates by root hair cells
- Muscle contraction
- Anabolic processes such as the synthesis of proteins and amino acids for growth and repair of tissues
What is the structure of mitochondria?
- Smooth outer mitochondrial membrane
- Inner mitochondrial membrane which is folded into many cristae
- Matrix
- Mitochondrial DNA
What is the first stage of aerobic and anaerobic respiration?
Glycolysis
Where does glycolysis take place?
In the cytoplasm
What happens during glycolysis?
- 2 ATP molecules break down into 2 ADP molecules
- An enzyme adds the 2 phosphate groups to glucose in a process called phosphorylation
- This produces a molecule of hexose bisphosphate
- Hexose bisphosphate breaks down into 2 molecules of triose phosphate
- Triose phosphate is oxidised and the hydrogen lost is transferred to NAD forming NADH (oxidation-reduction reaction and dehydrogenation)
- Another phosphate group is added resulting in 2 ATP molecules per triose phosphate molecule
- This converts triose phosphate to pyruvate
What is the overall yield of glycolysis?
2 ATP molecules
What happens after glycolysis?
Link reaction
Where does the link reaction take place?
Mitochondrial matrix
What happens in the link reaction?
- Pyruvate is actively transported into the mitochondrial matrix
- A molecule of carbon dioxide is removed (decarboxylation)
- Pyruvate is oxidised and the hydrogen lost is transferred to NAD forming NADH (oxidation-reduction reaction)
- Pyruvate is converted to a molecule of acetate
- A molecule of CoA is added to acetate producing Acetyl-CoA
What happens after the link reaction?
Krebs cycle
Where does the Krebs cycle take place?
Mitochondrial matrix
What happens in the Krebs cycle?
- Acetyl-CoA reacts with a 4 carbon molecule called oxaloacetate
- This forms a new 6 carbon molecule called citrate and loses CoA
- Citrate then undergoes a series of oxidation-reduction reactions to reform oxaloacetate
- During these reactions citrate loses 2 carbon atoms in the form of carbon dioxide
- These reactions produce 3NADH, FADH2 and ATP which is produced in a reaction called substrate-level phosphorylation
What happens after the Krebs cycle?
Oxidative phosphorylation
Where does oxidative phosphorylation take place?
Inner mitochondrial membrane
What happens during oxidative phosphorylation?
- NADH and FADH2 travel to the inner mitochondrial membrane
- They donate electrons to proteins in the membrane producing NAD, FAD and protons
- These electrons move along the proteins known as the electron transfer chain through a series of oxidation-reduction reactions
- As the electrons travel they transfer energy to the proteins which is used to actively transport protons from the matrix into the intermembrane space
- This maintains a proton gradient between the 2 areas
- The electrons at the end of the chain react with oxygen (final electron acceptor) and protons forming water
- As a result of the proton gradient protons in the intermembrane space diffuse by chemiosmosis back into the matrix via ATP synthase
- Chemiosmosis supplies ATP synthase with energy which it uses to catalyse the production of ATP
How are mitochondria able to make a large amount of ATP?
Their cristae provide a large surface area for oxidative phosphorylation
Where does anaerobic respiration take place?
In the cytoplasm
What happens during anaerobic respiration in mammals?
- Glycolysis takes place
- Pyruvate is converted to lactate through gaining hydrogen from NADH
What happens during anaerobic respiration in plants and microorganisms?
- Glycolysis takes place
- Pyruvate is converted to ethanol and carbon dioxide through gaining hydrogen from NADH
Why does anaerobic respiration produce a much lower yield of ATP than aerobic respiration?
- In anaerobic respiration glucose is only partially oxidised meaning only some of its chemical potential energy is released and transferred to ATP
- As there is no oxygen to act as the final electron acceptor none of the reactions within the mitochondria can take place meaning only the ATP from glycolysis is produced
How do the respiratory substrates differ in relative energy values?
Lipids > Proteins > Carbohydrates
Why do the respiratory substrates differ in relative energy values?
Lipids release the most energy because more hydrogen atoms are released as lipids break down compared to proteins and carbohydrates
What is the formula for the respiratory quotient?
CO2 produced/ O2 consumed
What are the respiratory quotients for the different respiratory substrates?
Carbohydrate - 1
Protein - 0.9
Lipid - 0.7
What does the respiratory quotient depend on?
The number of C-H bonds in the substrate
