Top Score Biology Question

[Ibraiz]

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How do we work this problem out?

If a eukaryotic cell has a diameter that is 10 times that of a bacterial cell, proportionally how much more surface area would the eukaryotic cell have?

Answer: 100 times the surface area

Another question:

Which of the following best describes gene regulation and expression in a repressible system?

A) The repressor binds to the operator, forming a barrier that prevents genes from being transcribed
B) Not significant
C) The repressor-corepressor binds to the operator and represses enzyme systhesis
D) In a constant state of transcription without a corepressor
E) C & D --> Correct Answer

Even in the explanation it is stated that repressor stops the transcription of the structural gene. Why is answer choice C is correct as it states "represses enzyme synthesis." Why is answer choice A not correct? My understanding is repressor stop the transcription of the genes not the enzyme synthesis. right. A & D looks like a valid choice.

 

[rippinitez]

The question is specifically asking you about the induced fit hypothesis, and answer A fits that hypothesis the best.

 

[gigawatt]

The question is specifically asking you about the induced fit hypothesis, and answer A fits that hypothesis the best.

😕

Don't know where you're getting that from. Induced fit has to do with enzymes being changed upon binding a substrate...this isn't a question about that.

Choice A is incorrect because the repressor alone won't bind the operator. It needs to be bound to the corepressor first. That's why choice D is true.

Choice C isn't the best-worded, but without transcription, you can't have translation...so really it does repress the overall enzyme synthesis as an end result. There might be more to it, but that's what I'm thinking.

On the first question:

Volume is proportional to the cube of diameter/radius
Surface area is proportional to the square of diameter/radius

Increasing the diameter 10x, increases the surface area 100x and the volume 1000x.

 

[whatDATmean]

1st Question

Since area is in units squared.
Whatever increased gets squared

If diameter increased 10 times this means (10)^2 which is 100.


2nd Question

A repressible system means that it can be repressed or turned off which means it is always "on". "On" in the sense of it is always transcribing thus translating thus making protein because enzymes are proteins.

In order to repress the system, a repressor + corepressor binds to the operator (site of transcription) and blocks transcription factors from binding to the DNA to start transcription. If no transcription happens, no enzymes are made. Confirming choice C.

Being that it is always on confirms choice D

What I can recall from Cell Bio + Genetics lol

 

[gigawatt]

Surface Area is the square of the Area.

If area increased 10 times this means (10)^2 which is 100.

No.

Surface area is absolutely NOT the square of the area? What does that even mean?

Surface area is proportional to the square (second power) of the diameter or radius (or any other linear dimension).

 

[whatDATmean]

No.

Surface area is absolutely NOT the square of the area? What does that even mean?

Surface area is proportional to the square (second power) of the diameter or radius (or any other linear dimension).

yeah wrong wording
you got me before i edited it lol

 

[gigawatt]

yeah wrong wording
you got me before i edited it lol

Haha...it's all good. 👍 I just didn't want someone seeing that and going with it.

 

[Baylor2011]

Look up the trp operon...it's the prime example of the 2nd question you had.

Bacteria are constantly making tryptophan until they injest tryptophan, then they no longer have a need to be synthesizing it.

Once tryptophan is injested by E. coli, the tryptophan acts as a corepressor which binds to the repressor and changes it's shape to be able to bind to the operator region, blocking enzyme synthesis

Once trytophan runs low again, the corepressor leaves the repressor protein, and it no longer "fits" into the operator, and synthesis begins again

This contrasts the lac operon however!

The lac operon represses the system until lactose is injested! Therefore the repressor binds to the operator region until lactose is injested, then an isomer called allolactose acts as the inducer of the system, binds to the repressor and changes its shape so it no longer "fits" into the operator..allowing RNA polymerase to attach and synthesize the enzymes

The lac operon is an example of an inducible system (has to be turned on), whereas the trp operon is an example of a repressing system (has to be turned off)

 

[Ibraiz]

rippinitez answered the question I originally had and he answered it on point. I edited the question after that.