[PPT]DNA Replication - Ms. Mulder's Science Classroommulderscience.yolasite.com/resources/Biology/molecular... · Web viewTitle DNA Replication Author Cheryl Massengale Last modified

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DNA DNA StructureStructure

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DNA NucleotideDNA Nucleotide

O=P-O O

PhosphatePhosphate GroupGroup

NNitrogenous baseNitrogenous base (A, G, C, or T)(A, G, C, or T)

CH2

O

C1C4

C3 C2

5

SugarSugar(deoxyribose)(deoxyribose)

O


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Pentose SugarPentose Sugar• Carbons are numbered

clockwise 1’ to 5’CH2

O

C1C4

C3 C2

5



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DNADNA

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A


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Antiparallel Antiparallel StrandsStrands

• One strand of DNA goes from 5’ to 3’ (sugars)

• The other strand is opposite in direction going 3’ to 5’ (sugars)


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DNA DNA ReplicatiReplicati

onon


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Replication FactsReplication Facts• DNA has to be copied DNA has to be copied

before a cell dividesbefore a cell divides• DNA is copied during DNA is copied during

the the SS or synthesis phase or synthesis phase of of interphaseinterphase

• New cells will need New cells will need identical identical DNA strandsDNA strands


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Synthesis Phase (S Synthesis Phase (S phase)phase)

• S phase during interphase of the cell cycle

• Nucleus of eukaryotes

Mitosis-prophase-metaphase-anaphase-telophase

G1 G2

Sphase

interphase

DNA replication takesDNA replication takesplace in the S phase.place in the S phase.


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DNA ReplicationDNA Replication• Begins atBegins at Origins of ReplicationOrigins of Replication• Two strands open forming Two strands open forming

Replication Forks (Y-shaped Replication Forks (Y-shaped region)region)

• New strands grow at the forksNew strands grow at the forks

ReplicationReplicationForkFork

Parental DNA MoleculeParental DNA Molecule

3’

5’

3’

5’copyright cmassengale

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DNA ReplicationDNA Replication• As the 2 DNA strands open at As the 2 DNA strands open at

the origin, the origin, Replication Replication BubblesBubbles form form

• Prokaryotes (bacteria) have a single bubble

• Eukaryotic chromosomes have MANY bubbles

Bubbles Bubbles


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DNA ReplicationDNA Replication• Enzyme Enzyme HelicaseHelicase unwinds unwinds

and separates the 2 DNA and separates the 2 DNA strands by breaking the strands by breaking the weak hydrogen bondsweak hydrogen bonds

• Single-Strand Binding Single-Strand Binding ProteinsProteins attach and keep the 2 DNA strands separated and untwisted


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DNA ReplicationDNA Replication• DNA polymeraseDNA polymerase can only add can only add

nucleotides to the nucleotides to the 3’ end3’ end of of the DNA the DNA

• This causes the This causes the NEWNEW strand to strand to be built in a be built in a 5’ to 3’ direction5’ to 3’ direction

RNARNAPrimerPrimerDNA PolymeraseDNA PolymeraseNucleotideNucleotide

5’

5’ 3’

Direction of ReplicationDirection of Replicationcopyright cmassengale

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Remember HOW the Remember HOW the Carbons Are Numbered!Carbons Are Numbered!

OO=P-O O

PhosphatePhosphate GroupGroup

NNitrogenous baseNitrogenous base (A, G, C, or T)(A, G, C, or T)

CH2

O

C1C4

C3 C2

5



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Remember the Strands are Remember the Strands are AntiparallelAntiparallel

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A


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Synthesis of the New Synthesis of the New DNA StrandsDNA Strands

• The The Leading StrandLeading Strand is synthesized as a single single strand strand from the point of origin toward the opening replication fork

RNARNAPrimerPrimerDNA PolymeraseDNA PolymeraseNucleotidesNucleotides

3’5’

5’


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Synthesis of the New DNA Synthesis of the New DNA StrandsStrands

• The The Lagging StrandLagging Strand is is synthesized discontinuouslydiscontinuously against overall direction of replication

• This strand is made in MANY short segments It is replicated from the replication fork toward the origin

RNA PrimerRNA Primer

Leading StrandLeading Strand

DNA PolymeraseDNA Polymerase

5’

5’

3’3’

Lagging StrandLagging Strand

5’

5’

3’

3’ copyright cmassengale

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Lagging Strand Lagging Strand SegmentsSegments

• Okazaki FragmentsOkazaki Fragments - - series of short segments on the lagging strandlagging strand

• Must be joined together by Must be joined together by an an enzymeenzyme

Lagging Strand

RNARNAPrimerPrimer

DNADNAPolymerasePolymerase

3’

3’

5’

5’

Okazaki FragmentOkazaki Fragment


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Replication of Replication of StrandsStrands

Replication Fork

Point of Origin


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Proofreading New Proofreading New DNADNA

• DNA polymerase initially DNA polymerase initially makes about makes about 1 in 10,0001 in 10,000 base base pairing errorspairing errors

• EnzymesEnzymes proofread and proofread and correct these mistakescorrect these mistakes

• The new error rate for DNA The new error rate for DNA that has been proofread is that has been proofread is 1 1 in 1 billionin 1 billion base pairing errors base pairing errors


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Semiconservative Model Semiconservative Model of Replicationof Replication

• Idea presented by Idea presented by Watson & CrickWatson & Crick• TheThe two strands of the parental

molecule separate, and each acts as a template for a new complementary strand

• New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA

Parental DNA

DNA Template

New DNA


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DNA Damage & DNA Damage & RepairRepair

• Chemicals & ultraviolet radiation damage the DNA in our body cells

• Cells must continuously repair DAMAGED DNA

• Excision repair occurs when any of over 50 repair enzymes remove damaged parts of DNA

• DNA polymerase and DNA ligase replace and bond the new nucleotides together


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Question:Question:•What would be the

complementary DNA strand for the following DNA sequence?

DNA 5’-CGTATG-3’DNA 5’-CGTATG-3’copyright cmassengale

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Answer:Answer:

DNA 5’-CGTATG-3’DNA 5’-CGTATG-3’DNA 3’-GCATAC-5’DNA 3’-GCATAC-5’


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[PPT]DNA Replication - Ms. Mulder's Science Classroommulderscience.yolasite.com/resources/Biology/molecular... · Web viewTitle DNA Replication Author Cheryl Massengale Last modified