Week 8 Application Questions Flashcards
Question 1:
Cyanides are commonly occurring toxins and are used both as defense compounds in plants and as a poison by
humans. They act by reversibly binding to- and so blocking- cytochrome oxidase three within complex IV, preventing complex IV from interacting with oxygen.
How would the ETC be affected?
Would H2O still be produced?
What would happen to the NADH?
Would oxidative phosphorylation still occur?
How would the ETC be affected?
• Complexes gain electrons
• Electrons can’t leave the ETC
• All the complexes fill up with electrons, and electrons stop moving.
Would H20 still be produced?
• No
• Cyanide blocks transfer of electrons from Complex IV to O2
• O2 is not reduced to form H2O
• O2 is the terminal electron acceptor
– Disposal site for low energy electrons once they are no longer needed
What would happen to the NADH?
• NADH would not be able to donate its electrons to the ETC.
• Because electrons can’t leave the ETC, they will fill up all the complexes
• Once the complexes are full, there is nowhere for NADH (andFADH2) to donate electrons
• NADHand FADH2 will accumulate in the matrix
Would oxidative phosphorylation still occur?
• ATP would not be synthesized
• No electron movement means no proton pumping
• No proton gradient means that ATP synthase has no energy source, so can’t make ATP
Question 2:
Brown adipose tissue (BAT), also called brown fat, has a thermogenic function. This means that it uses chemical
energy (derived from food) to produce heat, so it can help regulate body temperature.
In these cells, a protein called thermogenin is produced in the inner mitochondrial membrane. Thermogenin is a channel protein that allows protons to freely diffuse from the intermembrane space to the mitochondrial matrix (i.e. it makes the membrane leaky to protons).
a) How would the ability of the mitochondria in brown fat cells to produce ATP be affected by the presence of thermogenin?
Question 2:
Brown adipose tissue (BAT), also called brown fat, has a thermogenic function. This means that it uses chemical
energy (derived from food) to produce heat, so it can help regulate body temperature.
In these cells, a protein called thermogenin is produced in the inner mitochondrial membrane. Thermogenin is a
channel protein that allows protons to freely diffuse from the intermembrane space to the mitochondrial matrix
(i.e. it makes the membrane leaky to protons).
b) Explain why the presence of thermogenin in brown fat results in the generation of heat.
• A proton gradient stores potential energy
• As protons diffuse down their concentration gradient, that energy is
released
• If energy is not trapped and used, it will be released as heat.
Question 2:
Brown adipose tissue (BAT), also called brown fat, has a thermogenic function. This means that it uses chemical
energy (derived from food) to produce heat, so it can help regulate body temperature.
In these cells, a protein called thermogenin is produced in the inner mitochondrial membrane. Thermogenin is a
channel protein that allows protons to freely diffuse from the intermembrane space to the mitochondrial matrix
(i.e. it makes the membrane leaky to protons).
c) It was once thought that brown fat was only present and functional in infants, but research over the past decade has shown that brown fat is also present and functional in adults. BAT activity may reduce the risk of excessive fat accumulation, and people with reduced BAT function may be prone to obesity.
Explain why having a lot of brown fat would reduce the risk of obesity.
• In brown fat, chemical energy from food is used to produce heat
• If there is less excess energy from food stored in white fat cells = reduced weight
Question 3
Fats can be used as a starting material for cellular respiration. To do this, the fatty acids in the fats are converted to acetyl-CoA.
a) Which process(es) would occur in the cell to convert this acetyl-CoA to CO2, and to produce energy for use by the cell
Question 3
Fats can be used as a starting material for cellular respiration. To do this, the fatty acids in the fats are converted to acetyl-CoA.
b) Imagine that a cell uses a fat containing three 18-carbon fatty acids in its metabolism. This would allow the cell to make 27 acetyl-CoA. What method(s) would be used to produce ATP?
• Both substrate-level and oxidative phosphorylation
• Each acetyl-CoA produces:
– 1 ATP by substrate-level phosphorylation (citric acid cycle)
– 3 NADH x 2.5 ATP/NADH by oxidative phosphorylation = 7.5 ATP – 1 FADH2 x 1.5 ATP/FADH by oxidative phosphorylation = 1.5 ATP – Total=10ATP
• 27 acetyl-CoA = 270 ATP
Question 3
Fats can be used as a starting material for cellular respiration. To do this, the fatty acids in the fats are converted to acetyl-CoA.
c) If you consumed a fatty meal and the fat was metabolized by this mechanism, how would you expect the activity of the phosphofructokinase enzyme to be affected?
PFK activity would decrease.
• ATP and citric acid are inhibitors of PFK activity (feedback inhibition by allosteric regulation)
• ADP is an activator (allosteric regulation)
Question 4
“Photosynthesis is a prerequisite for cellular respiration and therefore complex life”.
Explain this statement based on what you know about cellular respiration.
Without photophosphorylation there would be no oxidative phosphorylation.
• O2 is the final e-acceptor in cellular respiration,
• H2O always was abundant, O2 built up over time until oxygen revolution/crisis/great oxidation event.
——————-
• Great oxidation event
• O2 first accumulates in the oceans, is toxic to many species “oxygen crisis”
• Some organism adapt, can become more complex, eukaryotes appear
• When oceans are saturated with O2 it starts to diffuse into the atmosphere, prerequisite for life on land
