Hi Lydia,

1) q 10, if ADH increases water retention in kidneys, then why does more ions leave in the ascending loop of henle in response to this? does more water in the medulla cause ions to want to leave more? im just confused since usually collecting ducts gets more concentrated after ADH works.

Yes, you are right that more water in the medulla causes ions to want to leave the ascending loop of Henle more. The ascending loop of Henle is impermeable to water, and so to equilibrate properly to respond to the increased water reabsorption into the medulla, the only possible thing to do in the ascending loop of Henle to compensate for this reabosrption is to transport ions to the medulla, decreasing the osmolarity inside the ascending loop of Henle.

2) q 15, i was just not understanding how the side chain is supposed to coonect to the molecule for example A vs D, the explanation says that D is connected to the N terminus but im not understanding what that means and why it shouldn't be connected like that

For D, it is less important that D is connected to the N terminus and it is more important that the passage specifically talks about mannose linked sugars - this question really wants you to convert the D-Mannose fischer provided in the text to a Haworth projection, and find the correct sugar out of the given options (as only one of those Haworths is mannose).

As for why N terminal glycosylation is a problem, it is just that most glycosylations observed in the body are to peptide side chains, and I don't believe that N-terminal glycosylation is that common in real cases. I think it would be unlikely to be expected to know this without prompting, and it was not information needed to answer this question.

3)q 41, im not getting how glycolysis produces lactic acid... i thought it was due to fermentation?

I don't love the way that it's worded, but the implication when they say that:

muscles relying exclusively on glycolysis fatigue more quickly than muscles that utilize aerobic respiration

This question stem implies that by glycolysis, they mean anerobic glycolysis, which would recycle electron carriers by reducing pyruvate to lactate, and not going through the kreb's cycle/ETC.

4) q46, i thought that all of our genome is half maternal and half paternal

Yes, for our nuclear chromosomes. However, the mitochondria are special. If you think about human eggs vs sperm, the eggs actually contribute all of the cell like material that becomes the zygote (while sperms only contribute the genetic information encased in a little torpedo package). As a result, a fun fact I would know for the MCAT, as it has become pretty in vogue in science/bio, is that the mitochondria that you inherit actually all came from your mother.

I hope this helps!

Katt