DNA REPL

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DNA REPLICATION

MISS SOFIA PAZ

WHEN A CELL DIVIDES A COMPLETE SET OF GENETIC INSTRUCTIONS IS GENERATED FOR EACH NEW CELL.

Template mechanismBased on the specific pairing rules of complementary bases.

REPLICATION: The process of copying the DNA molecule

What is to replicate something???

HOW does cells replicate DNA???

By a TEMPLATE MECHANISM!! (photo negative)

REPLICATION

• DNA is copied semi-conservatively. This means that each old strand of DNA pairs with a strand made from new nucleotides.

• Replication starts at a fixed point and is bidirectional (replicates in both directions).

Replication takes place in the nucleus

Enzyme separates the strands

Polymerase joins a complementary base to the new strand.

The TEMPLATE FOR Ther leading strand: Replication fork moves from 3’ to 5’

STEP EVENTS Key words

Step1

BREAKING HYDROGEN BONDS between bases of the two antiparallel strands with Helicase Enzyme forming the Replication Fork

Origin of replicationHelicaseHyodrogen bondsReplication Fork

Step2

BINDING OF DNA PRIMASE in the the initiation point of the 3'-5'

parent chain DNA Primase attract RNA nucleotides which bind to the DNA nucleotides of the 3'-5‘RNA nucleotides are the primers (starters) for the binding of DNA nucleotides

DNA Primase3'-5' strand RNA nucelotidesRNA primers (starters)

Step3

THE ELONGATION PROCESS ( Leading strand 5'-3' template different process thanLagging strand 3'-5' template)

A)Leading Strand (5'-3' Template) DNA Polymerase delta can "read" the template and continuously adds nucleotides

Leading strand (5'-3' template)Lagging strand (3'-5' template)DNA Polymerase delta

Step3

B)Lagging Strand (3'-5'Template): cannot be "read" by DNA Polymerase sigma. more RNA Primers. DNA polymerase epsilon reads the template and lengthens the bursts. The gap between two RNA primers is called "Okazaki Fragments"

Lagging strandRNA primersOkazaki FragmentsDNA Polymerase epsilon

Step4

TERMINATION DNA Polymerase reaches to an end of the strands

DNA Polymerase

Step5

MECHANISM OF REPAIR It fixes possible errors caused during the replication (nucleases remove the wrong nucleotides and the DNA Polymerase fills the gaps)

NucleasesDNA polymerase

STEPS

Helicase is the enzyme that splits the two strands

The unwounding of the two strands is the starting point

The initiation point where the splitting starts is called "origin of replication"

The structure that is created is

known as "Replication Fork"

1. FIRST STEP

The first step of DNA Replication is BREAKING HYDROGEN BONDS between bases of the two antiparallel strands

The splitting happens in places of the chains which are rich in A-T (because there are only two bonds between Adenine and Thymine

Key Words:Origin of replicationHelicaseHyodrogen bondsReplication Fork

DNA primase can attract RNA nucleotides which bind to the DNA nucleotides of the 3'-5' strand due to the hydrogen bonds between the bases

RNA NUCLEOTIDES ARE THE PRIMERS (STARTERS) for the binding of DNA nucleotides 

2. SECOND STEPIs THE BINDING OF DNA PRIMASE in

the the initiation point of the 3'-5' parent chain. 

Key words:DNA Primase3'-5' strand RNA nucelotidesRNA primers (starters)

Leading Strand : DNA Polymerase delta  can "read" the template and continuously adds nucleotides (complementary to the nucleotides of the template, for example adenine opposite to thymine etc)

3. THIRD STEP

IS THE ELONGATION PROCESSDifferent For The 5'-3' And 3'-5' Template

KEY WORDS:Leading strand (5'-3' template)Lagging strand (3'-5' template)DNA Polymerase delta and epsilon

The TEMPLATE FOR Ther leading strand: Replication fork moves from 3’ to 5’

-3'-5' TEMPLATE CANNOT BE "READ" BY DNA POLYMERASE DELTA.

-IN THE LAGGING STRAND DNA PRIMASE ADDS MORE RNA PRIMERS. DNA POLYMERASE EPSILON READS THE TEMPLATE AND LENGTHENS THE BURSTS. THE GAP BETWEEN TWO RNA PRIMERS IS CALLED "OKAZAKI FRAGMENTS".

-THE RNA PRIMERS ARE NECESSARY FOR DNA POLYMERASE EPSILON TO BIND NUCLEOTIDES TO THE 3' END OF THEM.

-THE DAUGHTER STRAND IS ELONGATED WITH THE BINDING OF MORE DNA NUCLEOTIDES.

3. THIRD STEP

ELONGATION PROCESSDifferent For The 5'-3' And 3'-5' Template

KEY WORDS:Leading strand (5'-3' template)Lagging strand (3'-5' template)DNA Polymerase delta and epsilon

DNA POLYMERASE REACHES TO AN END OF THE STRANDS

EUKARYOTES LINEAR CHROMOSOMES, DNA REPLICATION IS UNABLE TO REACH THE VERY END OF THE CHROMOSOMES

ENDS AT THE TELOMERE REGION OF REPETITIVE DNA AT THE END → SHORTENS THE TELOMERE OF DAUGHTER DNA STRAND.

SOMATIC CELLS, NORMAL PROCESS, CAN ONLY DIVIDE A CERTAIN NUMBER OF TIMES

GERM CELL LINE(PASSES DNA TO THE NEXT GENERATION) TELOMERASE EXTENDS THE REPETITIVE SEQUENCES OF THE TELOMERE REGION TO PREVENT DEGRADATION

4. FOURTH STEP

TERMINATION KEY WORDS:DNA PolymeraseLinear chromosomesTelomere regionTelomerase

IT FIXES POSSIBLE ERRORS CAUSED DURING THE REPLICATION

NUCLEASES REMOVE THE WRONG NUCLEOTIDES AND THE DNA POLYMERASE FILLS THE GAPS)

5. FIFTH STEPMECHANISM OF

REPAIR

KEY WORDS:NucleasesDNA polymerases

http://www.youtube.com/watch?v=8kK2zwjRV0M

http://www.youtube.com/watch?v=dIZpb93NYlw

http://www.youtube.com/watch?v=2iVltkYy0jg

http://www.youtube.com/watch?v=gW3qZF9cLIA

http://www.youtube.com/watch?v=1L8Xb6j7A4w