Question

A strain of cells undergos a mutation that increases the permeability of the inner mitochondrial membrane
If the mutant cells survive, what can be assumed about their energy requirements as opposed to the requirements of a non-mutant strain and how could this requirement be met?

Answer 1

This is not the best worded question. But it is an interesting one.

It depends on what the inner mitochondrial membrane becomes more permeable to - I assume it means 'permeable to protons' but it could mean permeable to any other molecule or ion which affects the proton gradient as well.

Basically, if the membrane becomes more permeable to protons it will decrease the ability of the barrier to maintain a proton concentration gradient. That means that the mitochondrion will have to put more electrons through the electron transport chain to maintain the same concentration gradient than a non-mutant mitochondrion, which means it will have an increased metabolic rate (higher flux through metabolic pathways) and consume more nutrients....

Answer 2

so does it mean the cell requires more glucose to increase the metabolic rate?

Answer 3

Nutrients in general.

Glucose via the glycolytic pathway would work. But dietary lipids and proteins can also be converted to substrates of the TCA cycle and metabolised to power electron transport.

Answer 4

but the question asks about the energy requirement of the mutant cell, so isnt that mutant require less energy than non mutant in order to survive?

Answer 5

cuz my answer was the mutant cell will require more energy since they make less ATP, but the teacher marked it wrong

Answer 6

The wording is very picky in this question. First of all, the membrane is permeable to what? Water? Protons? Ions? It affects the answer very much.

Secondly, 'energy' is a very obtuse term. Energy as stored in a proton gradient? Energy as stored in chemical bonds in high energy intermediates (i.e., ATP)? The absolute amount of energy needed by both cells to carry out ordinary cellular processes like DNA replication, transport, etc. is the same. It's just that the mutant cell is less able to harness energy from metabolic processes and convert it into ATP than the non-mutant cell.

Specifically, the mutant has a harder time maintaining a proton gradient across the inner mitochondrial membrane. That means it has to transport more electrons to maintain the same gradient as a non-mutant mitochondrion. In turn, that means that it needs to maintain a higher metabolic rate, which means it needs to consume more nutrients - carbohydrates like glucose and fructose, lipids, proteins, anything which can use used to power electron transport - than non-mutant cells.

Here the problem actually gets a little hairy.

Answer 7

I think the question means permeable to protons
and yea, i get it :) tyty

Answer 8

Cool.

It's actually really difficult to say. You get it; now I'm going to confuse you even more. In real life, the mutant cell would probably increase flux through the TCA cycle by transcribing more copies of the enzymes in that metabolic pathway. That additional translation would require more ATP, so it's metabolic demands would probably be a bit higher than a normal cell's.

In practice most mutations affecting mitochondria tend to be lethal anyway, so the problem is probably academic.

Answer 9

didnt learn about TCA, but it's not confusing :) keke

Answer 10

Tricarboxylic Acid Cycle. Krebs cycle. Same thing.

Answer 11

and btw, i watched one of the videos on the site, and yea, i actually answered one more question correctly on the exam haha
about the evolution of chloroplast and mitochondria :D

Answer 12

I was going to ask you about that. I am glad you're finding it helpful. Watch the videos, do the assignments and you will own that test.

I am one of the flagship students in the MITx program. Class starts on March 5th. The problem is, my class is on electrical circuits and my understanding of electricity is "don't stick wet knives in electric sockets." And I have five online classes in Stanford's grad program also starting on March 5th. So I am desperately trying to learn the entire prerequisite for the MIT course in ten days.

http://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-01sc-introduction-to-electrical-engineering-and-computer-science-i-spring-2011/python-tutorial/part-3/

Answer 13

wow...I dont know much about computer engineering

I watched the mitosis and meiosis lecture, but for some reason still kinda confuse lol
i think is cuz the prof goes thru it quickly, and i basically forget everything i've learned before...so i need to first find some vid that talks abt meiosis more

and ..is there lecture about pedigree ? I couldnt find it..

Answer 14

I know what you mean. I did my senior year of high school as a freshman at MIT and that school is intense. They tend to teach the theory and leave the applications of the theory as exercises and 'recitations' by which they mean labs, so it's possible that pedigrees are in there.

If I you, I'd look up lecture 21 or 23 in class 7.014.

Also, they have a couple other versions of the intro biology course posted from different years. You might want to look up 7.012, lectures 6-9.

I think you are right to focus on pedigrees: those do seem to come up each year in the exam...

Answer 15

yeah, i have to study both the school stuff and the preparation of the contest..:(
I just did bad on my first quiz.. answered so many ques wrong that I know the answers...that's the worst u know :(
gonna post up another question soon if i still couldnt figure out the answer..

Answer 16

Keep working on it; you'll get it in the end. ;D