biology questions from AAMC 5

[2010premed]

In comparison with the wall of the right ventricle of the heart, the left ventricular wall is:
A: thicker, and generates a higher pressure when it contracts.
I get that the left side of the heart generate higher pressure, but how do you know that the left ventricular wall is thicker? Is it just something to memorize?
2. If an artery that supplied blood to a lung lobe was blocked but ventilation to the love was unaffected, how would alveolar gas partial pressure change?
A: PO2 would increase, and PCO2 would decrease
What do they mean by ventilation to the love was unaffected?
I see how if the artery stopped supplying deoxygenated blood, then PCO2 would decrease in the lungs, but how would you know what happens to Oxygen?
3. An autosomal recessive, nonlethal mutation (deletion) of the Ach receptor gene occurs in some rats. Which of the following organelles will most likely be abnormal in the rats having this stimulation?
A: Plasma membrane.
Are all receptors always found on the plasma membrane?
4. Which of the following media would most likely be used to grow virions in the laboratory?
A. suspension of human DNA
B. a tissue culture
Answer: B
Why not A? Don’t viruses use humans just to reproduce?
5. DNA polymerase catalyzes the replication of chromosomal DNA in bacteria. A double-stranded DNA molecule contains bases with a ratio of (A+T)/(G+C) = 3:1. This molecule is replicated with DNA polymerase in the presence of the four deoxynucleside triphosphates with a molar ratior of (A+T)/(G+C)=1:2. What is the expected ratio of (A+T)/(C+G) in the double-stranded daughter DNA molecule?
A: 3:1
What is this kind of replication? What is the role of the four dexynucloeside triphosphates?
6. Assuming that the breathing rate is 10 breaths/min, the tidal volume is 800mL/breath, and the nonalveolar respiratory system volume (dead space) is 150 mL, what is the net volume of fresh air that enters the alveoli each minute?
A: 6,500mL
Can someone please give me some formulas for these kinds of calculations?

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[GRod18]

1. If you ever taken anatomy and dissected a heart you would see that ventricles are thicker than atrium and left ventricle in particular are the thickist. This is because that the left ventricle pumps blood to entire systemic circulation therefore it requires more pressure.

2. Ventilation is unaffected meaning you are stilll breathing normal (no problem with inspiration or expiration), but since the artery is blocked you will not able to effectively exchange O2 and CO2, therefore because you have more O2 coming into the lungs, but not effectively going into the blood stream, you will get greater partial pressure of O2 in lungs than you normally would, and artery cannot effectively supply the CO2 that was produced to get expired, therefore CO2 partial pressure would decrease.

3. No, steroid hormone receptors can be found are found on the plasma membrane, in the cytosol and also in the nucleus of target cells, because they can freely bypass the lipid bilayer, they don't have to attach to receptor and create the cascade.

4. Yes, virus use Human machinery to reproduce, DNA only codes for those machinery, it is better to use a cultured tissue because it already has various organelles that bacteria use to reproduce with.


5. DNA always replicates semi conservatively, the role of the DNTP are that they are building blocks to the new strand of DNA. (I don't even think the molar ratio of them are very significant in this question) The Ratio should stay the same because daughter strand should have identical ratio as parent strand.

6. No magic formula here,

tidal volume is how much you are inspiring - dead space volume which does not get into the alveoli = net volume x breath per min = volume per minute.

 

[2010premed]

Thanks a lot!

For number 2, this is why I'm confused: the pathway foes from deoxygenated artery to lungs to veins to right atrium, etc...therefore the artery, which normally contributes mainly CO2, will not be able to contribute CO2 anymore, therefore the PCO2 in the lungs would decrease. But usually blood gets oxygenated in the lungs, and since ventillation is normal, why does the oxygen partial pressure change at all?

 

[enoknight]

Thanks a lot!

For number 2, this is why I'm confused: the pathway foes from deoxygenated artery to lungs to veins to right atrium, etc...therefore the artery, which normally contributes mainly CO2, will not be able to contribute CO2 anymore, therefore the PCO2 in the lungs would decrease. But usually blood gets oxygenated in the lungs, and since ventillation is normal, why does the oxygen partial pressure change at all?

If the artery is blocked, the blood will not get oxygenated in the lungs nor will it exchange CO2. I think of it as that parts of the lung (the part where the pulmonary capillaries are blocked off) will have more oxygen and lower CO2 than the rest of the capillaries. Since the lungs cannot displace all the gas in one smooth inspiration/expiration gesture, those parts where the capillaries are blocked off will have higher PO2 and lower PCO2 since the O2 and the CO2 cannot equilibrate with the same percentage as the atmosphere.

A nice extension of this problem would be talking about short-term effects (respiratory acidosis and an increase in respiratory rate) to compensate for this blockage.