Drawing DNA

[andy456]

Will we ever be asked to draw a section of DNA on the exam??
I think its a waste of time to be copying something out from the data booklet??
Should we bother remebering it??

Also does it matter which directiono the Double bonded oxygen on the phosphate group is facing??

[chansthename]

yes the direction matters, if they do ask  you to draw it they will say either 5'->3' or 3'->5'

I think on the end the double bonded oxygen is facing up and in between it is facing inwards (pointing to the nitrogenous bases)

[samiira]

wat are these prime numbers..??  5'?? 3'?? does it mean its on carbon number 5 and carbon number 3

[scocliffe09]

Yeah that's all 3' and 5' mean - the phosphate group is connected to Carbon 5, and the phosphate group of the next nucleotide is connected to Carbon 3. Therefore, at the 3' end of a nucleic acid, you'll find an -OH group and at the 5' end you'll find a phosphate group.

[andy456]

I have another question..... When do we have to multiply by a dilution factor? I keep getting confused...
Eg In this question:
A 10.0 mL sample of the sports drink was diluted to 100 mL with deionised water. Then
10.0 mL of this diluted solution was further diluted to 100 mL with deionised water.
When a sample of the final dilute solution was aspirated into the atomic absorption
spectrometer, an absorbance of 0.510 was recorded.

[Studyinghard]

Im not 100% but that is a double dilution. So the absorbance reading times 10 and times 10 again.

[andy456]

So i dont have to do anything when it says
'Then 10.0 mL of this diluted solution' (so theyve removed 10ml from the first lot of diluting)

[Studyinghard]

Yep because when they are taking that 10ml they are taking an AMOUNT not changing the concentration. Remember at this stage the solution is meant to be homogeneous (equal concentration all around).

Its like if you have a bowl of soup of 100ml and the concentration is X. If i take 50ml its not like the concentration is going to change.

[andy456]

even if your dealing with number of moles??

[Studyinghard]

Not for mole. When it says Person A took an aliquot of 25ml from 250ml then you times it by 10.

[appianway]

Just clarifying, what do they mean when they say 3-5? I know it's a reference to the carbon atoms, but what exactly does it indicate? Is it only to give the order of bases if you draw several?

[stonecold]

yes the direction matters, if they do ask  you to draw it they will say either 5'->3' or 3'->5'

I think on the end the double bonded oxygen is facing up and in between it is facing inwards (pointing to the nitrogenous bases)

please explain!

[stonecold]

Just clarifying, what do they mean when they say 3-5? I know it's a reference to the carbon atoms, but what exactly does it indicate? Is it only to give the order of bases if you draw several?

I thought all it had to do with was the anti parallel arrangement of the two strands. Where one strand runs 3-5, and the opposite strand runs 5-3...

[stonecold]

http://www.vcbio.science.ru.nl/images/cellcycle/mdnasinglechain_zoom.gif

Is this correct people, because it's what I've learnt haha...

[kenhung123]

I doubt they would tell you to draw more than 1 nucleotide.....