IB Biology
3 Chemistry of Life
3.4 DNA Replication
All syllabus statements ©IBO 2007
All images CC or public domain or link to original material.
http://www.flickr.com/photos/sblackley/3572873378/
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
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
Meet polymerase. This is
DNA polymerase from a
human.
Its 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
Which means…..
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
http://commons.wikimedia.org/wiki/File:DNA_replication_split_horizontal.svg
3.4.2 Explain the significance of complementary base pairing in the conservation of the base
sequence of DNA
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)
http://commons.wikimedia.org/wiki/File:Base_pair_AT.svg
http://commons.wikimedia.org/wiki/File:Base_pair_GC.svg
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?
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