# As biology unit 1 21/5/2014 panic threadWatch

4 years ago
#101
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4 years ago
#102
please could someone explain to me how dna replication occurs?
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#103
please could someone explain to me how dna replication occurs?
Semiconservative replication:
-involved in making more DNA
-when DNA replicates, the two strands unwind and hydrogen bonds between bases using an enzyme called DNA helicase.
-the strands act as a template for the new DNA strands.
-exposed bases attract free DNA nucleotides and new hydrogen bonds form
-The strands join to form DNA using enzymes DNA ligase and DNA polymerase
-Each new DNA molecules contains one new strand and one original strand
-New DNA is identical to the original DNA
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4 years ago
#104
if 30% of the DNA in a cell consists of guanine, why does it contain 20% adenine?
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4 years ago
#105
(Original post by trialbyc0mbat)
if 30% of the DNA in a cell consists of guanine, why does it contain 20% adenine?
Since guanine and cytosine pair up together as bases, we know that the percentage of cytosine is equal to that of guanine. Therefore that makes it 30+30=60. We know that adenine pairs with thymine, therefore they must contain same amount. So subtract 60 from 100 and you get 40 then divide by 2 and you will get 20%.

Hope you understood

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4 years ago
#106
(Original post by trialbyc0mbat)
if 30% of the DNA in a cell consists of guanine, why does it contain 20% adenine?

Because there will be 30% cytosine. This means there will be 40% left so you do 40%/2 = 20%
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4 years ago
#107
(Original post by trialbyc0mbat)
if 30% of the DNA in a cell consists of guanine, why does it contain 20% adenine?
this is because of chargaff's rule.
chargaff's rule states that A=T and C=G

so if guanine is 30%, then cytosine is 30%

adenine and guanine r from the same family,, so they make up 50% (as there r 4 bases in total, so 2/4 =50%)

hope that makes sense
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4 years ago
#108
wow 3 fast replies. got it now. thanks!
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4 years ago
#109

If anyone wants the Jan 2014 IAL paper (not sure if posted)
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4 years ago
#110
http://www.scribd.com/doc/54621588/E...Revision-Notes here's a pretty good summary for Unit 1. Goodluck everyone ^_^
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4 years ago
#111
Has anyone finished studying and solving papers, I've only begun solving now

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4 years ago
#112
(Original post by mr osaka)
this is because of chargaff's rule.
chargaff's rule states that A=T and C=G

so if guanine is 30%, then cytosine is 30%

adenine and guanine r from the same family,, so they make up 50% (as there r 4 bases in total, so 2/4 =50%)

hope that makes sense
actually what do you mean by adenine and guanine are from the same family? A=T and C=G are base pairs right?
so what is the relationship between AG and CT?
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#113
(Original post by trialbyc0mbat)
actually what do you mean by adenine and guanine are from the same family? A=T and C=G are base pairs right?
so what is the relationship between AG and CT?
there isn't a direct relationship between A and G as far as i know ._. dont worry man its not in our specification.All we need to know is that A=T and C=G and U replaces T in RNA ....as far as percentages are concerned ,its all simply reasoning like the others mentioned above

Edit:corrected my silly mistake after a few aggressive members of TSR tore my noble-good hearted post apart
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4 years ago
#114
(Original post by trialbyc0mbat)
actually what do you mean by adenine and guanine are from the same family? A=T and C=G are base pairs right?
so what is the relationship between AG and CT?
there are 2 types of nitrgenous bases,,
1. Purine - 2 ring molecule

Adenine and Guanine are purine bases
Cytosine, thymine and uracil are pyramidine bases
1
4 years ago
#115
guys for anyone who sat for C12 paper on 19th may ial n would want to discuss follow this link:http://www.thestudentroom.co.uk/show....php?t=2686829
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4 years ago
#116
Hey guys, what is DNA polymerase used for? Is it the same as DNA helicase?
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4 years ago
#117
(Original post by Alnassenigzig)
there isn't a direct relationship between A and G as far as i know ._. dont worry man its not in our specification.All we need to know is that A=T and C=G and U replaces G in RNA ....as far as percentages are concerned ,its all simply reasoning like the others mentioned above
Uracil replaces Thymine mate, not Guanine
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4 years ago
#118
(Original post by trialbyc0mbat)
actually what do you mean by adenine and guanine are from the same family? A=T and C=G are base pairs right?
so what is the relationship between AG and CT?
dont worry about that , its just my teacher told us that Cytosin and Thymine r from a group called "Pyrimidine" (as both have 'Y' in their names) and guanine and adenine is from a group called "purine".
but dont worry this wont come , i didnt c it in any past paper , i dont know y my teacher said it in the first place
anyways just understand how to do those percentages and ull be fine
sorry if i confused u , i shouldnt mentioned "same family"
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4 years ago
#119
(Original post by Alnassenigzig)
there isn't a direct relationship between A and G as far as i know ._. dont worry man its not in our specification.All we need to know is that A=T and C=G and U replaces G in RNA ....as far as percentages are concerned ,its all simply reasoning like the others mentioned above
dont you mean U replaces T?
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4 years ago
#120
(Original post by mr osaka)
dont worry about that , its just my teacher told us that Cytosin and Thymine r from a group called "Pyrimidine" (as both have 'Y' in their names) and guanine and adenine is from a group called "purine".
but dont worry this wont come , i didnt c it in any past paper , i dont know y my teacher said it in the first place
anyways just understand how to do those percentages and ull be fine
sorry if i confused u , i shouldnt mentioned "same family"
yeah got it now, thanks!
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