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AP Biology
AP Biology 2017
DNA
ReplicationMacromolecules: Nucleic Acids•Examples:•RNA (ribonucleic acid)•single helix
•DNA (deoxyribonucleic acid)•double helix
•Structure:•monomers = nucleotides
RNADNA
Nucleotides•3 parts •nitrogen base (C-N ring)•pentose sugar (5C)• ribose in RNA•deoxyribose in DNA
•phosphate (PO4) group
Are nucleic acidscharged molecules?
Nitrogen baseI’m the
A,T,C,G or Upart!
Types of nucleotides• 2 types of nucleotides
• different nitrogen bases
• purines• double ring N base
• adenine (A)
• guanine (G)
• pyrimidines• single ring N base
• cytosine (C)
• thymine (T)
• uracil (U)
Tall Cheerleaders make goodPyramids
All Good girls are Pure
Nucleic polymer• Backbone
• sugar to PO4 bond• phosphodiester bond
• new base added to sugar of previous base
• polymer grows in one direction• N bases hang off the
sugar-phosphate backbone
Dangling bases?Why is this important?
Pairing of nucleotides•Nucleotides bond between
DNA strands•H bonds•purine :: pyrimidine•A :: T•2 H bonds
•G :: C•3 H bonds
Matching bases?Why is this important?
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AP Biology
DNA molecule
•Double helix•H bonds between bases join the 2 strands•A :: T•C :: G
H bonds?Why is this important?
Directionality of DNA•You need to number the carbons!• it matters!
OH
CH2O
4
5
3 2
1
PO4
N base
ribose
nucleotide
This will beIMPORTANT!!
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
CH2O
base
O
PO
C
O–O
CH2
1
2
4
5
1
2
3
3
4
5
5
Sounds trivial, but…this will be
IMPORTANT!!
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
•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
Anti-parallel strands 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
3
AP Biology
Copying DNA•Replication•2 strands of DNA helix are
complementary•have one, can build other•have one, can rebuild the
whole
Matching halves?Why is this a good system?
When does a cell copy DNA?•When in the life of a cell does DNA have to be copied?•cell reproduction•mitosis
•gamete production•meiosis
But how is DNA copied?•Replication of DNA•base pairing suggests that it will allow each side to serve as a template for a new strand
Models of DNA Replication•Alternative models•become experimental predictions
conservative semiconservative
Can you designan experimentto verify this?
dispersive
1
2
P
DNA Replication • Large team of enzymes coordinates replication
Let’s meetthe team… Bidirectional Synthesis
•In prokaryotes, the circular DNA is opened up, and synthesis occurs in both directions
https://highered.mheducation.com/sites/9834092339/student_view0/chapter14/bidirectional_dna_replication.htmlhttps://highered.mheducation.com/sites/9834092339/student_view0/chapter14/bidirectional_dna_replication.html
4
AP Biology
Replication forks•In eukaryotes, the linear DNA has many replication forks, origins of replication.
Got Questions
?Ask them
Now!
Replication- Create a diagram that shows how the following components interact with each other (15 min)
• Lagging strand
• Helicase
• DNA polymerase 1
• DNA polymerase 2
• Single stranded binding protein
• Topoisomerase
• Replication fork
• RNA primer
• Leading strand
• DNA ligase
• RNA primase
• Okazaki fragments