Biology Grab Bag of Questions for the MCAT

Session 94

In today’s MCAT Podcast, we cover biology, including pregnancy, connective tissue disease, and skeletal myocytes. Follow along in the blog post for the questions.

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[02:57] Conception and Menstruation

Question 47: A couple trying to conceive without using IVF methods would most likely have their highest chance of pregnancy:

  • (A) Early in the follicular phase of the menstrual cycle.
  • (B) After the onset of menses.
  • (C) During the luteal phase of the menstrual cycle.
  • (D) Midway through the follicular phase of the menstrual cycle.

Byran’s Insights:

To maximize your chance of conception, you want sex to happen right before ovulation, not on the day of ovulation itself because the sperm would need time to make the trip up the fallopian tube.

Remember the basic order of the follicular phase, then ovulation, the luteal phase. So if you’re waiting until the luteal phase, you’re late to the game.

The highest chance of pregnancy is around 1-4 days before ovulation. So this makes (D) the right answer. The only concern here is that midway is a little bit of a squishy word so it doesn’t tell your precisely when the sperm was starting their journey.

If you try to figure it, the follicular phase is something like 13 days long and the ideal time increase your chances of conception would be 1-5 days before then.

The other way to get around the answer is by doing the process of elimination. Early in the follicular phase would be right after menstruation is over. This is way to early. After the onset of menses, you missed it. And the luteal phase, ovulation has already happened so you’re a bit too late. By the process of elimination, D has got to be the winner here.

[06:10] Ehlers-Danlos Syndrome

Question: Patients with Ehlers-Danlos syndrome commonly suffer from hypermobile, unstable joints, and fragile, easily bruised skin. Which of these loss of function mutations is most likely to cause Ehlers-Danlos syndrome?

  • (A) Mutation in actin
  • (B) Mutation in keratin
  • (C) Mutation in elastin
  • (D) Mutation in collagen

Bryan’s Insights:

The right answer here is (D). Collagen is the primary supportive and structural connective tissue protein. So when in doubt, go for collagen.

Actin is not viable with life. If the actin fibers wouldn’t be working properly, your muscle tissue wouldn’t be working properly. If your muscles didn’t work, then your heart wouldn’t work either and you’d never make it out of the womb.

A problem with keratin would be related to hairs and nails. Whereas elastin, depending on the nature of the function, you’d either end up with tissues that were super stretchy or not stretchy enough. Neither of those gets to the joint problem.

[07:45] Actin and Myosin

Question 58: In skeletal myocytes, calcium is normally released from the sarcoplasmic reticulum after:

  • (A) The muscle begins to relax.
  • (B) Myocin releases actin.
  • (C) The membrane depolarizes.
  • (D) Physical damage to the muscle occurs.

Bryan’s Insights:

Remember that the MCAT may have tricky passages, but it doesn’t have trick questions. When in doubt, they’re just testing the normal, straightforward, base level understanding taught in every freshman college bio 101 class.

In this case, they want you to remember that the nerve signal comes down the axon to the skeletal muscle. And that action potential that comes down the nerve fiber is a whole depolarization-repolarization cycle. And when you get to the motor end plate and the neurotransmitter goes across to the muscle, the first thing that happens in the muscle is you depolarize the muscle cell. That causes the sarcoplasmic reticulum to dump its calcium out into the main body of the muscle itself. That kicks off the whole cycle. In this case, the answer is (C) because that’s the response to the nerve.


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