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A level Biology: Post your doubts here!

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After dividing once, all DNA will be 14+15 so all will be at L and after 2 divisions, there will be half 14+14 and half 15+14
im still a bit confused in this i dont understand the 2nd division part sorry for my dumbness
 
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im still a bit confused in this i dont understand the 2nd division part sorry for my dumbness
I hope this is understandable...the red ones are those from the original strand and the green ones are the newly synthesised strands....because it is cultured in a medium containing N-14 only, so all the new strands will be N-14
 

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I hope this is understandable...the red ones are those from the original strand and the green ones are the newly synthesised strands....because it is cultured in a medium containing N-14 only, so all the new strands will be N-14
This is just perfect thanks(y)
 
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One thing more pls hisham this time control ur angry birds don't let them to escape it's my humble request
 
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The hydrogen bonds between A-T is double, and between G-C, it's triple.
The maximum number would be if the entire length of DNA would contain G-C. This means 700 pairs of G-C.
Therefore:
700 (total nucleotides) * 3 (total hydrogen bonds) = 2100. [MAXIMUM]
2100 Hydrogen bonds is the maximum number.

Now, the minimum one is a little complicated. Traditionally, since A-T have double bonds, and if we assume that the entire length of DNA would contain A-T, this would give 700*2 = 1400 bonds. But the two hydrogen bonds between A-T and the three bonds between G-C form to achieve stability. Therefore, if we assume that the DNA molecule is unstable, and if we assume that the entire length of DNA would contain A-T, then we'd have to also assume that this is due to single bonds between A-T, which does not achieve stability. Therefore, 700 nucleotides with one bond per nucleotide:
700*1 = 700. [MINIMUM]
2100 is not the maximum number of hydrogen bonds. since there are two strands of DNA, we divide 700 by 2, which is equal to 350 base pairs.
G-C pairs have three hydrogen bonds as opposed to two hydrogen bonds between A-T pairs. we assume that all the nucleotides are G-C to maximize the number of hydrogen bonds (as the question states).
therefore, if 1 base pair equals three hydrogen bonds, how many hydrogen bonds exist between 350 base pairs? cross multiply and youll get the answer as 1050, which is the option C :)
 
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the answer for question 13 is B (i guess) because look;
A - is partially true, the cell surface membrane and the membranes of the organelles allow intracellular transport but they also allow extracellular transport. because the term "extracellular transport" is not stated, im guessing that A is only partially true.
B - seems the correct option because the carbohydrate chains that are present on glycoproteins form hydrogen bonds with water molecules and help to stabilise the membrane structure.
C - not really sure but why would enzymes attach to the membranes of organelles?
D - lyzomes themselves have a membrane to prevent their contents from coming into contact with other organelles so why would the membranes protect the organelles?
 
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the answer for question 13 is B (i guess) because look;
A - is partially true, the cell surface membrane and the membranes of the organelles allow intracellular transport but they also allow extracellular transport. because the term "extracellular transport" is not stated, im guessing that A is only partially true.
B - seems the correct option because the carbohydrate chains that are present on glycoproteins form hydrogen bonds with water molecules and help to stabilise the membrane structure.
C - not really sure but why would enzymes attach to the membranes of organelles?
D - lyzomes themselves have a membrane to prevent their contents from coming into contact with other organelles so why would the membranes protect the organelles?
No u were right it was C
 
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