OCR 2010 A2 Biology Unit 2 - Control, Genome and Environment Watch

Beating Around The Bush
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#2581
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#2581
(Original post by AnniG)
Just been doing this past question - could someone please explain why in both transcription and DNA replication "both DNA polynucleotide chains act as templates"? I'd have thought that in transcription only one strand (the template strand) acted as a template?
I think you may have the wrong end of the stick with the question. Doesn't it refer to "both DNA polynucleotide chains" in the sense for one for transcription and one in replication...?
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Archen
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#2582
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#2582
(Original post by AnniG)
Just been doing this past question - could someone please explain why in both transcription and DNA replication "both DNA polynucleotide chains act as templates"? I'd have thought that in transcription only one strand (the template strand) acted as a template?
i think it is because only one strand is used at one time
but BOTH strands are used as templates at some time otherwise there would be no point in having double stranded DNA.. :\
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AnniG
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#2583
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#2583
(Original post by Beating Around The Bush)
I think you may have the wrong end of the stick with the question. Doesn't it refer to "both DNA polynucleotide chains" in the sense for one for transcription and one in replication...?
No the question is laid out with a list of statements and 2 columns and you tick which statements are correct for either transcription, replication, both or neither...

(Original post by Archen)
i think it is because only one strand is used at one time
but BOTH strands are used as templates at some time otherwise there would be no point in having double stranded DNA.. :\
That's a bit confusing coz we've always learnt that there is a template strand which always acts as a template (the mRNA is complementary to this) and a coding strand (the mRNA is always a copy of this)... But I'm sure you're right - if it comes up again I'll know what they want at least, even if I don't really understand it!
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-F-
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#2584
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#2584
(Original post by Sakujo)
What is the null hypothesis? That there is not difference between expected and observed values ie our model is correct?
yeah, it means expected are correct any difference shown is less than 5% and due to chance.
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_lynx_
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#2585
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This goes someway to explain the above.... if you can stand the generic science video music :p:

http://www.youtube.com/watch?v=teV62zrm2P0
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Beating Around The Bush
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#2586
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#2586
(Original post by AnniG)
No the question is laid out with a list of statements and 2 columns and you tick which statements are correct for either transcription, replication, both or neither...



That's a bit confusing coz we've always learnt that there is a template strand which always acts as a template (the mRNA is complementary to this) and a coding strand (the mRNA is always a copy of this)... But I'm sure you're right - if it comes up again I'll know what they want at least, even if I don't really understand it!
Ahhh ritey oh, yeah I'm wrong then, Archen is probably right. :o:
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AnniG
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#2587
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(Original post by Sakujo)
What is the null hypothesis? That there is not difference between expected and observed values ie our model is correct?
When using chi squared you have come up with a hypothesis. The null hypothesis is effectively saying "the hypothesis is not true". Eg. if the hypothesis is "all bananas are blue", the null hypothesis is "all bananas are not blue". You accept the null hypothesis if the value of chi squared is greater than the critical value (that at p=0.05) and you reject the null hypothesis if the value of chi squared is less than the critical value. Therefore, rejecting the null hypothesis is actually confirming your hypothesis and vice versa!
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Sakujo
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#2588
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#2588
(Original post by AnniG)
When using chi squared you have come up with a hypothesis. The null hypothesis is effectively saying "the hypothesis is not true". Eg. if the hypothesis is "all bananas are blue", the null hypothesis is "all bananas are not blue". You accept the null hypothesis if the value of chi squared is greater than the critical value (that at p=0.05) and you reject the null hypothesis if the value of chi squared is less than the critical value. Therefore, rejecting the null hypothesis is actually confirming your hypothesis and vice versa!
Double negatives :facepalm2:

I think I get it, the null is opposite of what you think so when chi is less than critical value, you reject the null and accept what you think.
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Falcon91
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#2589
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(Original post by Sakujo)
Double negatives :facepalm2:

I think I get it, the null is opposite of what you think so when chi is less than critical value, you reject the null and accept what you think.
That is correct Sakujo.

Reject the null hypothesis if chi squared is less than the critical value
Uber edit: tiredness, i remember. IF CHI SQUARED IS LARGER than critical value - you reject it, if its less than critical value, you accept the null hypothesis and there is no SIGNIFICANT difference between observed and expected.
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Sakujo
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#2590
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(Original post by Falcon91)
That is correct Sakujo.

Reject the null hypothesis if chi squared is less than the critical value
Thank you
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_lynx_
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#2591
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(Original post by Sakujo)
Double negatives :facepalm2:

I think I get it, the null is opposite of what you think so when chi is less than critical value, you reject the null and accept what you think.
I thought that the book explained it quite clearly:
(Original post by OCR Heinemann)
...It is based on the assumption that 'there is no (statistically) significant difference between the observed and expected numbers. If there is no significant difference between the observed and expected then we accept the null hypothesis
Pg 134

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I wouldn't want to disagree with you Sakujo :p:
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Archen
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#2592
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(Original post by AnniG)

That's a bit confusing coz we've always learnt that there is a template strand which always acts as a template (the mRNA is complementary to this) and a coding strand (the mRNA is always a copy of this)... But I'm sure you're right - if it comes up again I'll know what they want at least, even if I don't really understand it!
is that the last question in the cellular control question pack?
i've just done that too

i was confused as to why is said:
"the original DNA molecule is unchanged after the process"
NO for replication and YES for transcription..

explanation pleeeeease :love:
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Sakujo
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#2593
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(Original post by _lynx_)
I thought that the book explained it quite clearly:

Pg 134

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I wouldn't want to disagree with you Sakujo :p:
Why not? :laugh:

I think you just the opposite what everyone else was saying, the null says that what you think is correct anything else is chance. If chi is less than critical we accept null and therfore the results are consistent with the theory.

I think I get it
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Sakujo
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#2594
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(Original post by Archen)
is that the last question in the cellular control question pack?
i've just done that too

i was confused as to why is said:
"the original DNA molecule is unchanged after the process"
NO for replication and YES for transcription..

explanation pleeeeease :love:
I think you got that the wrong way round, it should be Yes for replication and No for transcription.
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Nixani
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#2595
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#2595
i agree wiv sakujo

null hypothesis states that the observed results are close to expected ones due to pure chance so there is no significance...i think
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Archen
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#2596
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(Original post by Sakujo)
I think you got that the wrong way round, it should be Yes for replication and No for transcription.
well the mark scheme says otherwise :ninja:

so VERY confused
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Falcon91
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#2597
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(Original post by Sakujo)
Thank you
I failed.
tiredness, i remember. IF CHI SQUARED IS LARGER than critical value - you reject it, if its less than critical value, you accept the null hypothesis and there is no SIGNIFICANT difference between observed and expected.
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Remarqable M
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#2598
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#2598
can someone please quickly go through the methods used to inject modified plasma into E.coli?
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_lynx_
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#2599
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#2599
(Original post by Sakujo)
Why not? :laugh:

I think you just the opposite what everyone else was saying, the null says that what you think is correct anything else is chance. If chi is less than critical we accept null and therfore the results are consistent with the theory.

I think I get it
No, that's what the book is saying

Spoiler:
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SIBERIAN BLIZZARD looks painful!!
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Sakujo
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#2600
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#2600
(Original post by _lynx_)
No, that's what the book is saying

Spoiler:
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SIBERIAN BLIZZARD looks painful!!
(Original post by Falcon91)
I failed.
tiredness, i remember. IF CHI SQUARED IS LARGER than critical value - you reject it, if its less than critical value, you accept the null hypothesis and there is no SIGNIFICANT difference between observed and expected.

Took me a while to pick up on it:rofl:

Thank you I get it.
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