siRNA vs. miRNA

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shaun.deveshwar
Posts: 31
Joined: Tue Sep 25, 2018 5:38 pm

siRNA vs. miRNA

Post by shaun.deveshwar » Wed Feb 13, 2019 12:46 pm

I was having some trouble distinguishing these two different types of RNA by function.

Is there a better way to think about these two?

Thank you
- Shaun
NS_Tutor_Will
Posts: 271
Joined: Fri May 25, 2018 9:15 am

Re: siRNA vs. miRNA

Post by NS_Tutor_Will » Thu Feb 14, 2019 8:21 am

Hi Shaun,

Frankly, for the purposes of the MCAT miRNA and siRNA have essentially the same function which is to regulate translation by preventing the transcription of mRNA!

They do have differences, but getting into them is pretty specialized and obscure. The best ways to tell them apart are by their structure and by their targets. miRNA is a single-stranded RNA molecule that folds back on itself with a loop at one end. These typically bind less specifically than siRNA (meaning it regulates multiple mRNA pathways). siRNA is made of double-stranded RNA and typically has a single mRNA target to regulate.

Essentially, though, they are both ways that translation can be regulated. I'd say this piece is more important than knowing how to tell them apart from one another.

Thanks for the question!
shaun.deveshwar
Posts: 31
Joined: Tue Sep 25, 2018 5:38 pm

Re: siRNA vs. miRNA

Post by shaun.deveshwar » Thu Feb 14, 2019 9:09 am

Ok Thank you.

I have another question regarding the apparent weight and accelerations of an elevator going up, down, and remaining at rest.
If we had an example of a person standing on a scale in an elevator accelerating upward, I know that the normal force and gravitational forces will remain the same, but the forces of the scale on the person and the person on the scale will increase and this will give an erroneous higher reading. Are these sorts of gravitational accelerational problems a bit out of scope for the test? And because velocity is a vector when we are talking about accelerating upward and downward would we include the sign changes of acceleration?

1) When accelerating upward, the Fnet=Fn-Fg, where Fn must be greater than mg?
2) When accelerating downward, Fnet = Fg-Fn, where Fg must be greater than mg?

Thank you.

- Shaun
NS_Tutor_Will
Posts: 271
Joined: Fri May 25, 2018 9:15 am

Re: siRNA vs. miRNA

Post by NS_Tutor_Will » Thu Feb 14, 2019 9:29 am

Remember, a scale will always be recording the normal force, so when accelerating in an elevator, the normal force will change. The force of gravity won't change either, since this is a constant. The net force will change though due to the acceleration of the elevator.

If there is no acceleration in the elevator, Fn = mg. So the scale would read your "typical" weight.

If the elevator were accelerating in the up direction, the floor of the elevator would need to exert a greater force on the person in order to accelerate that person along with the elevator. Thus, the normal force is greater and the scale will read a larger than usual weight. In this case, Fn = mg +ma.

If the elevator were accelerating downward, the opposite would be true. You can almost think of this scenario as "part of the force of gravity is covered by the acceleration of the elevator" which means that the normal force would be reduced and the scale would read a smaller than usual weight. In this case, Fn = mg - ma.

Just for kicks, if the elevator's cable were to snap entirely and it entered into free fall, the downward acceleration would equal gravity and the person would be weightless!

I don't think these are necessarily likely to come up, but they could, so it's good to be familiar with the possibilities.
shaun.deveshwar
Posts: 31
Joined: Tue Sep 25, 2018 5:38 pm

Re: siRNA vs. miRNA

Post by shaun.deveshwar » Thu Feb 14, 2019 10:14 am

Ok cool, that makes sense. The free fall scenario makes sense because it's almost like free falling in the sky and hitting terminal velocity where there is no acceleration but there is still a net movement downward. Thank you for your help with these concepts.

- Shaun
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