Molecular Bio Questions

[pnoybballin]

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Hey guys I need some help with some questions that stumped me. Thanks a lot!

-In several types of secretory cells found in fly larvae, all of the homologous chromosome copies remain side by side, creating a giant polytene chromosome. In the salivary glands of Drosophila larvae, each of the four chromosomes has been replicated through ten cycles without separation of the daughter chromosomes. How may identical strands of chromatin are lined up side by side?

A. 128
B. 256
C. 512
D. 1024

The answer is D. Could someone please explain to me how this is the answer?

There is another question based on a passage. In the passage it says "Translation is not an error-proof process. Roughly 1 in every 10^4 amino acids that are incorporated into proteins is inserted incorrectly."

-Given that the average size of a protein molecule is 400 amino acids, one can conclude that there should be a translation error in one out of how many protein molecules?

A. 10
B. 25
C. 50
D. 100

The answer is B.

Thanks again guys!

 

[Phlame217]

#1) it says each chromosome, it tries to confuse you by talking about homologous chromosomes earlier, but now they are separate.
So, 1 -> 2 -> 4 -> 8 -> 16 -> 32 -> 64 -> 128 -> 256 -> 512 -> 1024
ten cycles

#2 change 400 to 4 X 10^2 then divide (1 X 10^4)/(4 X 10^2)
~ (1 X 10^2)/(4)
~ 100/4
=25

 

[pnoybballin]

#1) it says each chromosome, it tries to confuse you by talking about homologous chromosomes earlier, but now they are separate.
So, 1 -> 2 -> 4 -> 8 -> 16 -> 32 -> 64 -> 128 -> 256 -> 512 -> 1024
ten cycles

How come you started with only one? Since the question says there are 4 chromosomes, wouldn't you start with 4 -> 8 and go through the rest of the 10 cycles?

#2 change 400 to 4 X 10^2 then divide (1 X 10^4)/(4 X 10^2)
~ (1 X 10^2)/(4)
~ 100/4
=25

How come you divided 10^4 / 4 X10^2

Thanks for the help! Sorry if I sound pretty ******ed. I'm just pretty confused ..

 

[Bacchus]

For your first question, 2^n works, but I can't explain why in terms that will make sense, perhaps someone else can.

For the second problem you know that the chance is 1 in 10,000 for a misplaced amino acid. That said, if each protein is 400 amino acids, you need to find a multiplier that will get you to your ultimate goal, a 1 in 10000 chance. 400 X 25 = 10000, so the answer is 25 proteins.

 

[Phlame217]

Pay attention to the passages!
each of the four chromosomes has been replicated through ten cycles

And part 2, I converted everything to exponents because its easier to deal with large numbers that way.

 

[csau]

1) It states that there are 4 chromosomes. The key is to see that they are asking for the number of identical chromosomes. This means that you should only count one of the four. Thus, you use 2^10.

2) Every 10 000 amino acids gives you an error. How many proteins can you generate with 10 000 amino acids? You can find out by dividing.

10 000 amino acids / 400 amino acids per protein

You can even do dimensional analysis to confirm your number. Amino acids cancel out and you're left with protein units.