Biochemistry Grab Bag of Discrete Questions for the MCAT

Session 95

Bryan from Blueprint MCAT (formerly Next Step Test Prep) and I cover biochemistry, a huge pain point for many premed students. Take a listen and learn some biochem with us.

The Premed Playbook: Guide to the MCAT is finally available in Paperback ($9.99) and in Kindle ($4.99) formats. Also, stay tuned for The Premed Playbook: Guide to the Medical School Personal Statement, coming out soon!

[02:00] Insulin Function

Question 28: All of the following are functions of insulin except:

(A) Increasing glycogen synthesis
(B) Increasing glucogenesis
(C) Increasing glucose uptake by liver and muscles
(D) Decreasing proteolysis

My thought process:

I have a father who’s a Type 1 Diabetic who’s always taking his insulin. So we know that insulin is secreted from the pancreas after meals and some sugar spikes in the blood to help store glucose. My best guess here is that A is true. (B) sounds like a big red flag – a false fact, therefore, the correct answer.

Bryan’s Insights:

Insulin is the most powerful anabolic hormone in the body. It’s for building up big molecules. Glycogen is a big molecule and it does that by taking up glucose. So A and C go right out. Anabolic is about building up big molecules so proteolysis, breaking down proteins would be a catabolic process. Gluconeogenesis is the exact opposite of what insulin would do. Insulin is to lower your blood sugar, not fabricate and then dump more sugar into your blood.

[04:20] Informed Consent: Who Gives Them?

Question 29: In order to ensure approval by their institutional review board ethics committee, which of the following with cancer cell researchers need to obtain prior to testing human cell samples taken from cervical cancer patients?

(A) Informed consent of the surgeons to remove the tumors
(B) Informed consent of the medical oncologists that were treating the women
(C) Informed consent of the women who had their cervical cancer removed
(D) Informed consent is not required because the samples were obtained during a voluntary procedure

My thought process:

Informed consent is everything in medicine these days. As physicians, we always go to the patient for consent. So would need informed consent from the patient who had their cervical cancer removed. Every premed student should hopefully know Henrietta Lacks and what her cancer cells have done for research (her cells now called HeLa). It was a big ethical thing because she didn’t give an informed consent.

Bryan’s Insights:

Bryan actually admits he was able to work with HeLa cells as an undergrad in the 90s. He had no idea what HeLa stood for and the professor he was working for didn’t know what it stood for. That being said, it was just a part of the landscape. It wasn’t until the mid2000’s when it really became a big news story about this woman who had made such important contribution but have never been asked.

More broadly, you get informed consent from the subject of any study. So the woman who had the cervical removed is the right answer obviously.

[06:50] Nociception and Baroception Pathways

Question 44: A medical student stubbed her toe and observed that there was a momentary gap between when she realized she had stubbed her toe and when she felt the onset of pain. To wonder if this might relate to a structural difference in the neurons involved in baroception versus those involved in nociception. Which of the following is the best hypothesis for explaining this observation?

(A) The neurons in the nociception pathway are not myelinated whereas those involved in the baroception pathway are myelinated.
(B) The neurons in the nociception pathway have more dendrites than those in the baroception pathway.
(C) The neurons in the baroception pathway are not myelinated whereas those involved in the nociception pathway are myelinated.
(D) The neurons in the baroception pathway have more dendrites than those in the nociception pathway.

Bryan’s Insights:

The toe hit the chair at a certain point in time. So all the nerves fired at that moment. So you’re not going to explain the differences in when the nerve signal fired, rather the differences in conduction speed.

Conduction speed comes down to myelination. Nerves are myelinated to increase the speed of conduction where that action potential jumps from the Node of Ranvier in between the myelin. Being myelinated increases the speed of transmission. And with the baroception moving faster, we would assume that baroreception is myelinated where as the nociception is not.

The correct answer here, therefore, is (A). When you stub your toe, that signal has to go from your toe all the way up to your leg and to your spinal cord. Once it hits your spinal cord, it’s myelinated so it goes right up to your brain. So that little quarter second difference is the fact that the touch or the baropressure gets transmitted right up to your spine right away. Then the pain takes a quarter second because it’s not myelinated.

[10:30] People with MS as an Interesting Example

I have three spinal cord lesions from my MS and I have one particular finger that if I hit it with a safety pin during the testing, where a neurologist will do when they poke your finger with something sharp, I experience a weird sensation from where my lesion is. Then the pain takes longer to go through the lesion. So it’s very cool physiologically to have that happen.

Although I don’t have brainstem or brain lesions, I also have facial symptoms. It doesn’t make sense because the facial nerve is coming out of the brain stem so obviously it needs to be something there. The trigeminal nerve has a spinal trigeminal nucleus. So the trigeminal nerve goes down into the spinal cord where I happen to have a lesion and goes back up into the face. It serves some facial sensory issues. Anatomically, it’s cool to have a spinal cord lesion affect facial sensations.

[14:00] About Blueprint MCAT (formerly Next Step Test Prep)

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