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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

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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

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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