Download DO NOW

Monday March 5,12
• AIM: How can we create a
semiconservative model?
• DO NOW: Explain in two complete
sentences what the DNA semi
conservative model is.
• HOMEWORK: Text page 314 questions
16 and 17
http://www.mcb.harvard.edu/losic
k/images/trombonefinald.swf
Figure 11.16 The Two New Strands Form in Different Ways
Why does the leading strand form
continuously while the lagging
strand is formed in fragments?
The Final product
• When the replication process is complete, two
DNA molecules — identical to each other and
identical to the original — have been produced.
• Each strand of the original molecule has
remained intact as it served as the template for
the synthesis of a complementary strand.
• This mode of replication is described as semiconservative: one-half of each new molecule of
DNA is old; one-half new.
Each DNA chromosome of the
entire genome is replicated before
division can occur
• Replicated
chromosomes are
now called sister
chromatids
With all this drama, do you think
errors occur during DNA
replication?
Nothing is perfect in this world so yes
errors do occur.
An error occurs only about once in
each 10-100 billion bases.
Proofreading: DNA polymerase
recognizes and repairs its own
mistakes
Nonsense mutation
• Since there are 64 codons that specify 20
amino acids, sometimes a mutation still
codes for the same amino acid