Chapter 12 Flashcards
Describe the events of glycolysis?
- Glucose is phosphorylated to gluocse phospahte by the addition of two phophate molecules from the hydrolysis of two ATP molecules. This lowers the activation energy for the following.
- Each phosphorylated glucose is split into two 3-carbon triose phopshate molecules.
- Triose phosphate is oxidised by the removal of hydrogen which is then transferred to NAD to from reduced NAD.
- Each triose phosphate molecule is converted to a pyruvate molecule by enzyme conrolled reaction. Two molecules of ATP are regenarated from ADP
What is the overall yield of glycolysis from one glucose molecule?
- Two molecule of ATP (four are produced but two is used to phosphorylate glucose)
- Two molecules of reduced NAD
- Two molecules of pyruvate
Describe the link reaction?
- The pyruvate molecules are actively transported into the matrix of the mitochondria.
- In the matrix pyruvate is oxidised to acetate by losing a CO2 molecule and two hydrogens. These hydrogens are accepted by NAD forming reduced NAD.
- The two carbon acetate combines with coenzyme A froming acetylcoenzyme A
How is the krebs cycle named?
Named after the british biochemist Hans Krebs who worked out it’s sentence
Describe the events of the krebs cycle?
- The 2-carbon acetylcoenzyme A combines with a 4-carbon compound to produce a 6 carbon compound
- The 6-carbon compound loses CO2 and hydrogen to give a 4-carbon compound and a single molecule of ATP by substrate level phosphorylation.
- The 4-carbonm compound can now combine with acetylcoenzyme A to recommence the cycle.
For each molecule of pyruvate, what is produced from the link reaction and the krebs cycle?
- Two molecules of reduced NAD
- Three molecules of CO2
- One ATP molecule
Why is the krebs cycle so important?
- Breaks down macromolecules into smaller ones, eg pyruvate into CO2
- Produces hydrogen atoms that are carried by NAD to the ETC, providing energy for oxidative phosphorylation.
- Regenerates the 4- carbon compound which acetyl coenzyme A.
- Source of intermediate compounds used by cells in the manufacture of other substances e.g. fatty acids, amino acids and chlorophyll
Where do mitochondria occur in greater numbers?
Liver, muscles and epithilial cells which occur in greater numbers. The mitochondria in these cells also have more densely packed cristae providing a greater surface area of membrane incorporating enzymes and proteins involved in oxidative phosphorylation
What is the site of oxidative phosphorylation?
Mitochondria
Describe the synthesis of ATP by oxidative phosphorylation?
- The hydrogen atoms produced during glycolysis and the krebs cycle combine with the coenzymes NAD and FAD.
- The reduced NAD and FAD donate the electrons of the hyrogen atoms they are carrying to the first molecule in the electron transport chain.
- The elecrons pass through a chain of electron transfer carrying molecules in a series of oxidation- reduction reactions.
- The energy the electrons release as they flow through the chain causes the active transport of protons across the inner mitchondrial membrane and into the inter-membranal space.
- The protons accumulate in the inter membranal space before they diffuse back into the mitochondrial matrix through ATP synthase channels embedded in the inner mitochondrial membrane.
- Electrons combine with the protons and oxygen to form water. Thus oxygen is the final acceptor of electrons in the electron transport chain.
Describe the respiration of lipids?
- Lipids are hyrolysed to glycerol and fatty acids
- Glycerol is phosphorylated and converted to triose phosphate to enter glycolysis.
- The fatty acid is broken down and converted to the 2-carbon compound acetyl coenzyme A to enter the krebs cycle.
Describe the respiration of proteins?
- Protein is hydrolysed to it’s constituent amino acids.
- Their amino group is removed (deamination).
- 3 carbon compounds are converted to pyruvate, whilst 4 and 5 carbon compounds are converted to intermediates in the krebs cycle.
Why would ethanol be produced in plants?
- Anaerobic respiration leads to the production of ethanol in bacteria and fungi as well as in the roots of water logged plants
- The pyruvate molecule loses a CO2 molecule and accepts a H molecule from reduced NAD to prouduce NAD.
Pyruvate + reduced NAD = ethanol + CO2 + NAD
Why would lactate be produced in animals?
- Occurs to overcome a temporary shortage of O2 and in muscles as a result of strenuous exercise
- In these conditions NAD from glycolysis can accumulatemust be removed.
- Each pyruvate molecule will take up two hydrogen atoms from reduced NAD froming lactate.
Pyruvate + reduced NAD = lactate + NAD
What is substrate level phosphorylation?
The direct transfer of phosphate from a respiratory substrate to ADP, producing ATP.
