ib biology core 3.4: dna replication
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A slideshow for students and teachers of IB BiologyTRANSCRIPT
IB Biology3 Chemistry of Life
3.4 DNA Replication
Jason de Nys
All syllabus statements ©IBO 2007All images CC or public domain or link to original material.
http://www.flickr.com/photos/sblackley/3572873378/
This is a helicase molecule from E. coli
The ‘-ase’ suffix should clue you in that this is an enzyme.
It’s job is to break the hydrogen bonds between the strands of DNA and unwind them
http://en.wikipedia.org/wiki/File:Helicase.png
3.4.1 Explain DNA replication in terms of unwinding the double helix and separating the strands by helicase, followed by the formation of the new complementary strands by DNA polymerase
Meet polymerase. This is DNA polymerase from a human.
It’s job is to help the right bases attach to the separated
strands of DNA and join the bases together to make the DNA double-stranded again
What sort of reaction is the polymerisation reaction?
The polymerisation reaction is a
condensation reaction
http://commons.wikimedia.org/wiki/File:DNA_replication_split_horizontal.svg
DNA Polymerase adds bases from the surrounding “soup” to the separated strands
Helicase
DNA Polymerase
http://commons.wikimedia.org/wiki/File:DNA_replication_split_horizontal.svg
You’ll notice that there is more than one DNA polymerase at work
Helicase
DNA Polymerase
http://commons.wikimedia.org/wiki/File:DNA_replication_split_horizontal.svg
You’ll notice that there is more than one DNA polymerase at work.This is explained in 7.2 and is not required at SL
Helicase
DNA Polymerase
3.4.2 Explain the significance of complementary base pairing in the conservation of the base sequence of DNA
http://commons.wikimedia.org/wiki/File:Base_pair_AT.svghttp://commons.wikimedia.org/wiki/File:Base_pair_GC.svg
A fits T and C fits G, they are complementary
The way the molecules fit together makes it very unlikely that they will bond with the wrong partner.So the genetic code is faithfully copied during replication
When things do go wrong, we have a point mutation. (See 4.1.3 and 4.1.4)
2 H bonds
3 H bonds
3.4.3 State that DNA replication is semi-conservative.
Semi-conservative?
http://commons.wikimedia.org/wiki/File:Mitt_Romney_2012_CPAC.jpg
Semi-conservative?Means: half
In this case, means: conserved or saved
There are three ways that DNA could be copied:
http://en.wikipedia.org/wiki/File:DNAreplicationModes.png
Each time DNA is copied, the new double stranded molecule consists of one old template strand plus a new complementary strand made
from previously free bases
http://www.flickr.com/photos/pagedooley/5283257753/
Further information:
Three of the best sites for IB-specific Biology information. The top link takes you to the PPT by Stephen Taylor