2. WHEN A CELL DIVIDES A COMPLETE
SET OF GENETIC INSTRUCTIONS IS
GENERATED FOR EACH NEW CELL.
Template mechanism
Based 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)
3. 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).
4.
5. Replication takes place
in the nucleus
Enzyme separates the
strands
Polymerase joins a
complementary base
to the new strand.
6. The TEMPLATE FOR Ther leading strand: Replication fork moves
from 3’ to 5’
7. STEP EVENTS Key words
Step1 BREAKING HYDROGEN BONDS between bases of the two
antiparallel strands with Helicase Enzyme forming the Replication
Fork
Origin of replication
Helicase
Hyodrogen bonds
Replication 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
Step3 THE ELONGATION PROCESS( Leading strand 5'-3' template
different process thanLagging strand3'-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 strand
RNA primers
Okazaki Fragments
DNA Polymerase
epsilon
Step4 TERMINATION DNA Polymerase reaches to an end of the
strands
DNA Polymerase
Step5 MECHANISM OF REPAIR It fixes possible errors caused Nucleases
8. 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
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
Key Words:
Origin of
replication
Helicase
Hyodrogen bonds
Replication Fork
9. 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 STEP
Is THE BINDING OF DNA PRIMASE in the the
initiation point of the 3'-5' parent chain.
10. 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 PROCESS
Different For The 5'-3' And 3'-5' Template
KEY WORDS:
Leading strand (5'-3'
template)
Lagging strand (3'-5'
template)
DNA Polymerase delta and
11. The TEMPLATE FOR Ther leading strand: Replication fork moves
from 3’ to 5’
12. -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 PROCESS
Different For The 5'-3' And 3'-5' Template
KEY WORDS:
Leading strand (5'-3'
template)
Lagging strand (3'-5'
template)
13. 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 Polymerase
Linear chromosomes
Telomere region
Telomerase
14. IT FIXES POSSIBLE ERRORS CAUSED DURING THE
REPLICATION
NUCLEASES REMOVE THE WRONG NUCLEOTIDES
AND THE DNA POLYMERASE FILLS THE GAPS)
5. FIFTH STEP
MECHANISM OF
REPAIR
KEY WORDS:
Nucleases
DNA polymerases
