Download Cellular Respiration Scenarios – Teacher Answers

Arrive at solutions for the following by always taking an energy focus and looking at how your
metabolic pathways would be affected.
1) A person has just experienced a stroke cutting off oxygen to certain parts of the brain.
Describe the events that would occur leading to the death of brain cells.
B/c oxygen is not available there would be a back up of electrons in the ETC (similar to
a traffic jam waiting for the ferry). All events stop. This would include the release of
energy via electron transfer that would drive proton pumps. No electrochemical
gradient would be made in the IMS, and thus no chemiosmosis through the ATP
synthase channel. Thus, no ATP formed to drive any cellular processes. The cell
would die. If this were a muscle cell, they could revert to anaerobic respiration for a
short time to recycle their NAD+ and make ATP via glycolysis. Gradually, the muscle
will stiffen and it will succumb too.
2) You are the designer of what you believe is the “wonder” weight loss drug. The drug
makes the inner membrane leaky to protons. Why would this drug make you lose
weight? What serious concerns might people have over the use of this drug?
Oxygen is still available to siphon off the electrons. Electron transfer can still occur but
the drug will uncouple the formation of a steeper gradient. Therefore, less ATP will be
formed. In response to its need, the cell will continue to oxidize (burn) fuels to make
NADH, FADH2 to feed into the ETC. This would include accessing fat stores, breaking
them down and oxidizing them. B/c the rate of reactions will increase (exergonic
release heat) and b/c energy from the gradient will be dissipated as heat (rather than
captured up in ATP), the person’s temperature will rise.
3) Your friend is a drug user of barbituates. You learn these drugs act by stopping
electron transfer in the ETC. What symptoms would you expect? Why would the use of
these drugs be dangerous?
High doses will create difficulties in the ETC as oxygen won’t be able to continue its job
to move electrons along. The roadblock created from the drug will uncouple the proton
pumps from making the gradient and affect ATP production. The person will be fatigued
b/c of no ATP. No energy to drive cellular processes could will lead to cell death.
4) You just had your last meal.(let’s say you had pasta). Describe how your bodily
metabolic processes would change as you go longer and longer without food. What
other metabolic pathways would occur?
Generally, carbs are oxidized first as energy, followed by fats, and then proteins as a
last resort.
After glycogen stores (carb) have been depleted, fats would become the primary source
of energy for cellular respiration. Triglycerides would be moved to the liver/muscle
where they would be hydrolyzed into glycerol and fatty acids. The glycerol would then
be converted into G-3-P of glycolysis to either go through gluconeogenesis to make new
glucose or continue down through glycolysis. The fatty acids would undergo betaoxidation. This involves oxidizing the fatty acids in consecutive oxidations that lead to
the formation of 2 carbon units of acetyl Co A. In the process, LOTS and LOTS of
NADH and FADH2 are formed for oxidative phosphorylation. The acetyl CoA’s
produced will be shuttled through the Kreb’s cycle where even more NADH, FADH2 and
a bit of substrate-level ATP will be produced.
When needed, proteins will be broken into amino acids in the liver/muscle. Each amino
acid will be deaminated to remove the amino group. Left will be various carbon
skeletons depending upon the R-side chain of the amino acid worked on. These
skeletons resemble intermediates of glycolysis, pyruvate oxidation, and Kreb’s cycle
and can be fed into these processes accordingly to make ATP in the end.
5) You are an athlete looking to increase your aerobic fitness. What steps would you take
in your training regime? Connect these steps to the changes you would see at the
cellular/metabolic level?
Aerobic fitness is connected to your ability to undergo aerobic respiration to make lots of
ATP to drive cellular processes. This can increase with a better ability to deliver oxygen
to your muscle cells (VO2 max is a variable used in exercise physiology to measure this)
and having your cells make more mitochondria. Any exercise that improves blood
circulation and oxygen delivery will help. Interval training will help trigger your body to
improve its ability to remove lactate. Cardio training will help strength your heart and
circulation. Stretching will help to improve muscular flexibility. Weight training will help
to encourage the building of muscle. Having a good mental attitude will help motivate
one to do the above exercises.
6) A) Yeast thrive under anaerobic conditions making them perfect tools for making
alcoholic beverages and for making bread. Explain how these cells are still able to
function under these conditions.
They undergo alcohol fermentation as a form of anaerobic respiration. By converting
pyruvate to acetylaldehyde and then to ethanol, they are able to recycle the NADH to
NAD+ to keep glycolysis going (Recall: in eukaryotic cells, this recycling is
accomplished at the beginning of the ETC but in prokaryotes they don’t have
mitochondria). Keeping glycolysis going allows them to make 2 NET ATP/glucose.
B) With some strains of yeast, fermentation stops before sugar is exhausted, usually at
an alcohol concentration in excess of 12%. What is a plausible explanation?
As a by-product of fermentation is the making of alcohol. Just like in us, the build up of
alcohol is a toxin. If the yeast are trapped cannot get rid of the alcohol from their
environment they will die. Hence, alcohol concentration won’t get greater.
C) Draw a diagram that illustrates the process of respiration taking place in yeast cells.
Why is the yeast necessary to make the bread rise?
See diagram in your text/notes
In making acetylaldehyde, carbon dioxide is released which expands the dough during
baking (gets trapped within)
7) A) Compare the process in #6 to how muscle cells/bacteria anaerobically respire using
lactic fermentation.
Instead of making acetylaldehyde/ethanol in recycling their NADH to NAD+ to drive
glycolysis, these cells convert pyruvate to lactate. This step recycles NAD+ for
glycolysis allowing 2 NET ATP/glucose.
B) Following anaerobic activity, one often goes into oxygen debt. Discuss what this
terminology means, and elaborate on how the body compensates in order to return
oxygen levels to normal.
Build up of the outcomes of anaerobic respiration leads to the cessation of exercise.
The build up of lactic acid needs to be addressed. One begins panting after exercise to
bring in oxygen. This will be used to help oxidize the lactate back to pyruvate to
continue on in aerobic respiration. The oxygen debt refers to how much oxygen is
needed to get rid of all the lactate.
C) Discuss how the body rids itself of lactic acid following anaerobic respiration. How
does it use the lactic acid for a good purpose?
As mentioned in B, lactate is converted back to pyruvate when oxygen becomes
available again. Thus, the energy potential from lactate is not wasted. By converting it
back to pyruvate, the substrate can be still used in oxidative phosphorylation to make
lots of ATP. Also, b/c glycogen stores are depleted during exercise the lactate when
converted back into pyruvate can go through gluconeogenesis to make new glucose
molecules that can be joined to restore glycogen stores.