Nucleic Acid-Based Cellular Activities: DNA Replication Flashcards
(29 cards)
3 DNA REPLICATION MODELS
1.Semiconservative Replication Model
2.Conservative Replication Model
3. Dispersive Replication Model
Proposed by James Watson and Francis Crick
Semiconservative Replication Model
Each strand of the parental DNA molecule serves as a
template for the synthesis of a new complementary strand.
1.Semiconservative Replication Model
in the semiconservative replication model what is the resulting dna molecule
After replication, each resulting DNA molecule consists of one
old (parental) strand and one newly synthesized strand
The parental DNA molecule remains intact, and an entirely
new copy is synthesized
Conservative Replication Model
The original double-stranded DNA serves as a template for
the formation of an entirely new double-stranded DNA
molecule.
Conservative Replication Model
Proposed as an alternative to the semiconservative model.
Dispersive Replication Mode
The parental DNA molecule is broken into fragments, and
each fragment serves as a template for the synthesis of a
new DNA fragment
Dispersive Replication Mode
Dispersive Replication Mode result
The parental DNA molecule is broken into fragments, and
each fragment serves as a template for the synthesis of a
new DNA fragment
STEPS IN DNA REPLICATION
- initiation
- elongation
- termination
Synthesizes short RNA primers complementary
to the DNA template strand.
RNA primase
must have a free 3’ -hydroxyl to which the
growing chain can attach
RNA primer
Starting point for DNA synthesis.
RNA primer
leading and lagging srand of dna primer
Leading strand- 1 primer
Lagging strand- 1 primer for each Okazaki
fragment
synthesizes a new DNA strand by adding complementary nucleotides to the 3’ OH end of the
RNA primer.
DNA Polymerase III
D NA Polymerase III
can only add nucleotides in the
can only add nucleotides in the 5’ to 3’ direction
what is the lagging and leading strand in Okazaki fragments
Leading strand- synthesized continuously in the 5’ to 3’
direction.
Lagging strand- synthesized discontinuously in short
fragments called Okazaki fragments
direction of synthesis is opposite to the moving
direction of the replication fork.
Semidiscontinuous DNA Replication Mechanism
5’ end of each of these Okazaki fragments is
closer to the replication fork than the 3’ end
Semidiscontinuous DNA Replication Mechanism
DNA polymerase I (RNAse H)
activities
5’ to 3’ Polymerase activity- fills in the gap with
deoxynucleotides
5’ to 3’ Exonuclease activity- removes the RNA
primer, remove short stretches of nucleotides
during repair
3’ to 5’ Exonuclease activity- proofreading,
removes incorrect nucleotides
joins the Okazaki fragments on the lagging strand,
creating a continuous DNA strand.
DNA ligase
DNA ligase
joins the Okazaki fragments on the lagging strand,
creating a
continuous DNA strand
Primer Removal and Fragment Ligation
ELONGATION
Primer Synthesis
INITIATION
