5.7 Flashcards
Why do we need to respire?
- Muscle contraction (breaking cross-bridges)
- Active transport
- Endo/exocytosis
- Protein synthesis (tRNA binding and forming polypeptide bonds)
- Cell division (breaking down spindle fibres)
- DNA replication
Outline the steps of aerobic respiration
- Glycolysis
- Link reaction
- Krebs cycle
- Oxidative phosphorylation
Where does glycolysis occur?
Cell cytoplasm
Outline the steps of Glycolysis
- Glucose is phosphorylated into Hexose Bisphosphate with 2x ATP molecules
- Hexose Bisphosphate is then split into two molecules of Triose Phosphate
- Each Triose phosphate molecule is oxidised to form Pyruvate, forming 2x ATP and Reducing NAD in the process.
Where does the link reaction occur?
Mitochondrial matrix
Outline the process of the link reaction
Each Pyruvate molecule is combined with CoA and reduced to form Acetyl CoA (decarboxylation)
In this process, CO2 is lost and NAD is reduced to form reduced NAD
Where does the Krebs cycle occur?
Mitochondrial matrix
Describe the steps of the Krebs cycle
- Acetyl CoA (2C) is combined with Oxaloacetate (4C) to form Citrate (6C)
- Citrate is decarboxylated and dehydrogenated producing a 5C compound, CO2, and reduced NAD
- The 5C compound is decarboxylated and dehydrogenated again to form another CO2 and reduced NAD
- The 4C compound will combine temporarily with CoA before releasing, forming one molecule of ATP through substrate-level phosphorylation
- This 4C molecule is dehydrogenated forming another 4C compound and reduced FAD
- Atoms in the 4C compound are rearranged and dehydrogenated forming Oxaloacetate so the cycle can repeat.
Define substrate-level phosphorylation
Formation of ATP from ADP and Pi in glycolysis and Krebs cycle.
Describe the importance of dehydrogenation in respiration
It produces reduced NAD and reduced FAD in the link reaction and glycolysis
Why are coenzymes important in respiration?
Reduced coenzymes carry Hydrogen atoms to the electron transport chain
Where does oxidative phosphorylation occur?
Inner mitochondrial membrane
Describe the process of Oxidative Phosphorylation
- Reduced NAD carry Hydrogen atoms to the electron carrier chain
- Hydrogen atoms unbind and break into H+ ions and electrons
- Electrons enter the electron transport chain
- The electrons pass along the electron carrier proteins on the inner mitochondrial membrane
- They reduce this protein so that the carrier protein can then reduce the neighbouring protein
- As the electrons pass across the carrier proteins, some of their energy is provided to the pumps to allow the A.T of H+ ions across IMM into IM Space
- As protons accumulate in the IM space, a chemiosmotic gradient builds, allowing H+ ions to diffuse through ATP synthase on the IMM, changing its shape allowing ADP & Pi to bind -> ATP
- Oxygen is the final electron acceptor, forming water.
Define Chemiosmosis
The diffusion of H+ ions down an electrochemical gradient through ATP synthase which combines ADP + Pi -> ATP
Define Oxidative Phosphorylation
The formation of ATP via chemiosmosis using energy transfer from transported electrons during a series of redox reactions where oxygen is the final electron acceptor.
Define substrate level phosphorylation
when a phosphate group is transferred from a substrate to ADP to form ATP
What are the problems associated with lack of oxygen in respiration?
- No oxygen to act as final electron acceptor and remove electrons from ETC
- H+ can no longer react Oxygen to form water
- Buildup of of H+ ions as no electrons to power transport proteins so electrochemical gradient decreases
- No H+ ions diffuse through ATP synthase
- As no NADH and FADH are oxidised back, earlier steps are stopped
How does anaerobic respiration happen in animals?
- Triose phosphate is oxidised into Pyruvate, reducing NAD
- NADH is then oxidised to reform NAD, in turn reducing Pyruvate into lactic acid using enzyme lactase dehydrogenase
This only forms a small quantity of ATP
What can the liver do to lactate?
Reoxidise it back into Pyruvate
How does anaerobic respiration happen in yeast?
- Triose phosphate is oxidised into pyruvate
- Pyruvate is then decarboxylated to form Ethanal
- Ethanal is then converted to ethanol (ethanol dehydrogenase), during which, NADH oxidised to form NAD
What is respiratory substrate?
A molecule that can be oxidised in respiration, releasing energy to make ATP
How would you measure aerobic respiration in yeast?
Collecting CO2 produced over time using a respirometer by putting yeast cells in glucose and limewater in the other tube that has a gas syringe attached
How would you measure anaerobic respiration in yeast?
Same as aerobic but…
Seal the yeast & glucose tube with liquid paraffin and use an indicator (e.g. Janus Green B) to check for anaerobic conditions
What are some other ways we can measure respiration?
- Capillary tube
- ## Haemocytometer to measure number of cells to estimate cell division
