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Campbell and Reece 8th edition

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Re: Campbell and Reece 8th edition

Postby Stephen1993 » Wed May 11, 2011 12:32 pm

thank you for that

Pg 314
“The unwound sections of parental DNA strands are now available to serve as templates for the synthesis of a polynucleotide; they can only add nucleotides to the end of an already existing chain that is produced during DNA synthesis is actually a short stretch of RNA, not DNA”
What does the second part of the paragraph mean?

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Postby canalon » Wed May 11, 2011 1:50 pm

They describe the primers known as Okazaki fragments. The DNA polymerase can only extend a Nucleic acid chain, it cannot start it from scratch. Those bits of RNA serves as the starting block that are then extended by the polymerase.
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Re: Campbell and Reece 8th edition

Postby Stephen1993 » Thu May 12, 2011 8:48 am

thank you for that

Pg 314
Why is DNA polymerase called DNA polymerase (III) which adds nucleotides to the RNA primer?? What is special about the number 3?

and also

pg 316
"After reaching the next RNA primer to the right, DNA pol (III) detaches."
how does the DNA pol (III) know when to detach?

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Postby JackBean » Thu May 12, 2011 8:55 am

1) there are several DNA Pols, just by accident the major one is called Pol III, due to historical reasoning.

2) when it's stuck
http://www.biolib.cz/en/main/

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Re: Campbell and Reece 8th edition

Postby Stephen1993 » Thu May 12, 2011 8:59 am

wow thank you for the quick reply

Pg 316
Proofreading and repairing DNA
“We cannot attribute the accuracy of DNA replication solely to the specificity of base pairing.”
Just exactly what it means particular the word “attribute” used in this context?
Also following that:
“Although errors in the completed DNA molecule amount to only one in 10 billion nucleotides, initial pairing errors between incoming nucleotides and those in the template strand are 100,000 times more common- an error rate of one in 100,000 nucleotides.”
What does this mean????

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Postby JackBean » Thu May 12, 2011 9:44 am

attribute means something like assign or credit

That means, that the base-pairing during DNA synthesis has mistake rate 1 in 100 000 nucleotides. But the final error rate is only 1 in 10 billions. Thus there must be some additional correcting mechanism
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Postby Stephen1993 » Thu May 12, 2011 10:22 am

thank you for that

Pg 317
In the table 16.1
“DNA pol 1- Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides.”
What does this mean?

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Postby JackBean » Thu May 12, 2011 10:45 am

you don't speak English? I'm sorry, but these are quite stupid questions about solitary senteces.

As canalon already told you and you have maybe read, the DNA replication starts from primers, which are RNA. But the DNA cannot contain pieces of RNA, because it's unstable. Thus the primers must be replaced and they are replaced by DNA Pol I.
http://www.biolib.cz/en/main/

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Re: Campbell and Reece 8th edition

Postby Stephen1993 » Fri May 13, 2011 7:58 am

thank you for that
well i find it pretty hard to learn this by myself because of the bad teacher i have so could you please bear with me?

pg 309
figure 16.7
The double helix .... ... .. . "The helix is right-handed, curving up to the right"
what on earth does this mean- all i see is a spiral of DNA

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Postby canalon » Sat May 14, 2011 3:01 am

this refer to the sense of the rotation of the helix.
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Re: Campbell and Reece 8th edition

Postby Stephen1993 » Sat May 14, 2011 4:05 am

thank you for that

pg 233
The two liberated daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore shorten. Because these microtubules are attached at the centromere region, the chromosomes move centromere first (at about 1um/min).

what does this mean?


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Re: Campbell and Reece 8th edition

Postby JackBean » Sun May 15, 2011 6:35 pm

the chromosomes consist of several parts, the chromatids and centromere. And the centromere is the place, where the microtubules attach and are pulled away, thus the chromosomes look like this
Image

the centromere goes first and the chromatids are pulled behind ;)
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