Download DNA

DNA and the
Language of Life
Chapter 12
How did scientists
learned that DNA is
the genetic material?
Genes are Made of DNA
 Griffin’s experiment (1928)
 Avery’s experiment (1944)
 Hershey and Chase experiment (1952)
Griffith’s experiment 1928
 Griffith showed that although a deadly
strain of bacteria could be made
harmless by heating it, some factor in
that strain is still able to change other
harmless bacteria into deadly ones. He
called this the "transforming factor."
Avery’s experiment - 1944
 Transforming factor - Protein or DNA?
Avery and colleagues treated a mixture of
heat- treated deadly strain and harmless
strain of bacteria with:
 Protein-destroying enzyme
 DNA-destroying enzyme
Hershey and Chase
experiment -1952
 The basic unit of the DNA molecule is
called:
NUCLEOTIDE
A NUCLEOTIDE in DNA has three parts:
 A ring-shaped sugar called deoxyribose
 A phosphate group
 A nitrogenous base (single or double ring of
carbon and nitrogen atoms)
Nucleotide monomers
join together by
covalent bonds
between the sugar of
one nucleotide and the
phosphate of the next,
forming a sugarphosphate backbone.
Nitrogenous Bases
The bases pair up (A-T
& G-C) forming the
DOUBLE HELIX first
described by Watson
and Crick
Watson, Crick and
Franklin
Various ways to model DNA
structure
•http://www.umass.edu/molvis/tutorials/dna/dnapairs.htm
manipulate DNA
Why does DNA need to be
replicated?
Growth – new cells - reproduction
How does this process
happens?
REPLICATION IN 3 STEPS
 DNA
replication
results in two
new strands,
each
containing
one new
strand
(yellow) and
one original
strand (blue)
 Weak bonds
 Hydrogen bonds
 Comes apart
easily
 Comes together
easily
Overview of DNA
replication
 DNA separates
 Complementary
nucleotides are
linked along
separated strands
initiate
 Initiator protein
guides
unzipper
protein
(helicase) to
correct position
on DNA
untwister
 Untwister
(topoisomerase)
unwinds the
DNA double
helix in advance
of the unzipper
unzip
• Unzipper
separates
DNA strands,
breaking
weak bonds
between the
nucleotides
assemble
• Builders
(polymerases)
assemble new
DNA strand by
joining
nucleotides to
their matching
complements on
the exposed
strands
straightners
 Straighteners
(single-strand
DNA binding
proteins)
keep single
strand of
DNA from
tangling
Phosphate provides
energy
• Phosphate bond
energy from the
new nucleotides
is used to make
the new bonds
Leading vs. Lagging
strand
 Leading (top)
strand is built
continuously as
the builder
follows behind
the unzipper,
but the Lagging
(lower) strand
builds in the
opposite
direction
Lagging strand
 Lagging
(lower)
builder
makes a
loop with the
DNA strand
and builds in
opposite
direction
Lagging strand
 Built in small
sections
 Sections
linked by
enzyme ligase
Repairs of DNA
 Erasers (Repair
Nuclease): find
poorly matched
or damaged
nucleotides and
cut them out
Repairs of DNA
 Builders
(Polymerase):
fill gaps using
other DNA
strand as a
guide
Repairs of DNA
 Stitchers
(Ligase): uses
ATP to restore
continuity of
backbone of
repaired strand
Big picture of DNA
replication
Replication review
REPLICATION IN 3 STEPS
 DNA
replication
results in
two DNA
molecules,
each with
one new
strand
(yellow)
and one
old strand
(blue)
DNA replication animations
 http://www.youtube.com/watch?v=4jtmO
ZaIvS0
 http://www.youtube.com/watch?v=gW3qZ
F9cLIA
 http://www.youtube.com/watch?v=oNW_
ykH3AvA
 http://www.youtube.com/watch?v=hC_8y
8fNkCw
TED talk – DNA replication –
Chromosomes- malaria
 http://www.youtube.com/watch?v=dMPX
u6GF18M