1 AP Biology 2007-2008 DNA Replication AP Biology Watson and Crick 1953 article in Nature Double helix structure of DNA “It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.” Watson & Crick AP Biology Directionality of DNA You need to number the carbons! it matters! OH CH 2 O 45321PO 4 N base ribose nucleotide This will be IMPORTANT!! AP Biology The DNA backbone Putting the DNA backbone together refer to the 3and 5ends of the DNA the last trailing carbon OH O 3PO 4 base CH 2 O base O P O C O – O CH 2 12451233455Sounds trivial, but… this will be IMPORTANT!! Anti-parallel strands Nucleotides in DNA backbone are bonded from phosphate to sugar between 3& 5carbons DNA molecule has “direction” complementary strand runs in opposite direction 3553
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Watson and Crick DNA Replication · Watson and Crick 1953 article in Nature AP Biology Double helix structure of DNA “It has not escaped our notice that the specific pairing we
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1
AP Biology 2007-2008
DNA Replication
AP Biology
Watson and Crick 1953 article in Nature
AP Biology
Double helix structure of DNA
“It has not escaped our notice that the specific pairing we have postulated
immediately suggests a possible copying mechanism for the genetic
material.” Watson & Crick AP Biology
Directionality of DNA
You need to
number the
carbons!
it matters!
OH
CH2
O
4
5
3 2
1
PO4
N base
ribose
nucleotide
This will be
IMPORTANT!!
AP Biology
The DNA backbone
Putting the DNA
backbone together
refer to the 3 and 5
ends of the DNA
the last trailing carbon
OH
O
3
PO4
base
CH2
O
base
O
P
O
C
O –O
CH2
1
2
4
5
1
2
3
3
4
5
5
Sounds trivial, but…
this will be IMPORTANT!!
AP Biology
Anti-parallel strands
Nucleotides in DNA
backbone are bonded from
phosphate to sugar
between 3 & 5 carbons
DNA molecule has
“direction”
complementary strand runs
in opposite direction
3
5
5
3
2
AP Biology
Bonding in DNA
….strong or weak bonds?
How do the bonds fit the mechanism for copying DNA?
3
5 3
5
covalent
phosphodiester
bonds
hydrogen
bonds
AP Biology
Base pairing in DNA
Purines
adenine (A)
guanine (G)
Pyrimidines
thymine (T)
cytosine (C)
Pairing
A : T
2 bonds
C : G 3 bonds
AP Biology
Copying DNA
Replication of DNA
base pairing allows each strand to serve as a template for a new strand
new strand is 1/2 parent template & 1/2 new DNA
semi-conservative copy process
AP Biology
DNA Replication Large team of enzymes coordinates replication
Let’s meet the team…
AP Biology
Replication: 1st step
Unwind DNA
helicase enzyme
unwinds part of DNA helix
stabilized by single-stranded binding proteins
single-stranded binding proteins replication fork
helicase
I’d love to be helicase & unzip
your genes…
AP Biology
DNA
Polymerase III
Replication: 2nd step
But… We’re missing
something! What?
Where’s the ENERGY
for the bonding!
Build daughter DNA
strand
add new
complementary bases
DNA polymerase III
3
AP Biology
energy
ATP GTP TTP CTP
Energy of Replication
Where does energy for bonding usually come from?
ADP AMP GMP TMP CMP
modified nucleotide
energy
We come with our own
energy!
And we leave behind a nucleotide!
You remember
ATP! Are there other ways
to get energy out of it?
Are there other energy nucleotides?
You bet!
AP Biology
Energy of Replication The nucleotides arrive as nucleosides
DNA bases with P–P–P P-P-P = energy for bonding
DNA bases arrive with their own energy source for bonding