Prepared By: -
It is a ladder like structure which is made up of poly
nucleotide chains spirally coiled on a central axis.
The two strands are made up of polynucleotide held
together by Phosphodiester Bonds.
Each nucleotide is composed of a Phosphate Group, a
Deoxyribose Sugar and a Nitrogenous Base.
The steps of the ladder looking DNA are made up of
Nitrogenous Bases which are united by Hydrogen
Bonds.
Double Helical Structure of DNA
The two strands of polynucleotide are antiparallel to each other.
One strand runs from 5’ to 3’ direction
whereas the other strand runs from 3’ to 5’
direction.
The breaking of hydrogen bonds results in
separation of two strands.
Why does DNA replicate???
The fundamental properties of cells and organisms is their
ability to reproduce.
To give rise to new cells by undergoing DNA replication and
cell division.
Any organism grows from embryonic development until
death as a result of DNA replication.
The DNA replication results in growth of the cells, formation
of new cells and repair of the damaged tissues.
Lesson 1: The Replication Factory
Overview of the DNA replication.
Lesson 2: DNA replication Proteins
Terminology of all the proteins involved
in the DNA replication
Lesson 3: Strand Separation
Action of enzymes
Lesson 4: New Strand synthesis
Leading and lagging strand
Lesson 5: Replication in action
The entire process of DNA replication
Lesson 6: DNA repair
•D2.1 use appropriate terminology related to molecular genetics,
including, but not limited to: polymerase I, II, and III, DNA
ligase, helicase, Okazaki fragment, mRNA, rRNA, tRNA, codon,
anticodon, translation, transcription, and ribosome
subunits [C].
•D2.2 analyze a simulated strand of DNA to determine the
genetic code and base pairing of DNA
(e.g., determine base sequences of DNA for a
protein; analyze base sequences in DNA to recognize an
anomaly) [AI]
•D3.1 explain the current model of DNA replication,
and describe the different repair mechanisms
that can correct mistakes in DNA sequencing.
Important Terminologies:
DNA Helicase: - The enzyme that unwinds double-helical DNA by
disrupting hydrogen bonds.
Anneal: - The pairing of complementary strands of DNA through
hydrogen bonding.
Single-Stranded Binding Proteins (SSBs): - The protein that keeps
the separated strands apart.
DNA gyrase: - The bacterial enzyme that relieves the tension
produced by the unwinding of DNA during replication.
Important Terminologies:
Replication Fork: - The region where the enzyme replicating a DNA
molecule are bound to untwist single stranded DNA.
Replication Bubble: - The region where two replication forks are in
close proximity to each other producing a bubble in the replicating DNA.
Important Terminologies:
Leading Strand: - The new strand of DNA that is synthesized
continuously during DNA replication.
Lagging Strand: - The new strand of DNA that is synthesized in short
fragments which are later joined together.
Qkazaki Fragments: - Short fragments of DNA formed as a result of
the synthesis of lagging strands.
DNA Polymerase I: - Enzyme that removes RNA primer and replaces
them with the appropriate Deoxyribonucleoside.
DNA Ligase: - The enzyme that joins DNA fragments together by
catalyzing the formation of bond.
Newly synthesized DNA strand
Okazaki Fragments
DNA polymerase III add complementary nucleotide in 5’ to
3’ using RNA primers as starting points.
As the complementary sequence formation
completes; DNA polymerase III and DNA
polymerase I works as quality control
checkers. These enzymes check incorrectly
paired nucleotide on the template, excises it
and add correct nucleotide sequence on the
strand. These enzymes are known as
exonuclease.
These
enzymes
work
immediately to avoid mistakes during
replication.
Important Terminologies:
DNA polymerase III: - The enzyme responsible for synthesizing
complementary DNA strands of DNA during replication.
Primase: - The enzyme that builds RNA primers.
Deoxyribonucleoside Triphosphates: - Molecules composed of
deoxyribose bonded to three phosphate groups and a nitrogenous
base.
RNA Primer: - Sequence of 10 to 60 RNA bases that is annealed to
a region of singe-stranded DNA for the purpose of initiation of DNA
replication.
SSB Protein
Leading Strand
Helicase
Lagging Strand
Gyrase
Exonuclease
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During DNA Replication, each strand of the original DNA
becomes the template for the new strand of DNA. Note,
however, that each strand is not a duplicate of itself, but
the compliment of itself. It will not look like the template
it is copying from, but rather the antiparallel strand of the
double helix. For example, this is how the original
template and the newly strand will appear:
Original Strand: AATTCCG
Copied Strand: TTAAGGC
So the original strand and the copied strand will anneal
forming a double helix of an old and new strand of DNA.
Because each new strand contains one original strand and
one copied strand, it is called semi-conservative
replication.
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Inquiry based gizmo activity on DNA Building and
Replication.
Students would think critically and follow the process of
DNA replication.
Students would be asked to complete the lab attached
along with the gizmo and would be marked on it.
Link to the gizmo:
http://www.explorelearning.com/index.cfm?method=cR
esource.dspDetail&ResourceID=439
Here is a link to the
video
demonstration of
the entire process
of DNA Replication:
http://www.wiley.com/col
lege/pratt/0471393878/s
tudent/animations/dna_re
plication/index.html
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After the entire lesson for DNA Replication,
the class would be divided into groups of 45 students.
Each student in each group would be
assigned one enzyme involved in the DNA
Replication process.
Each group would be provided with two
strands of DNA and then the groups would
organize their information into step by step
manner and put all the pieces of the process
together to complete the jigsaw.
Every group would present the information
to the class.
Objective
Students will model the semi-conservative
replication of DNA.
Materials
For each group
1.DNA patterns (see preparation)
2.Paper
3.Pencil
4.Scissors
Preparation
Create and duplicate sample
patterns of the following parts of
the DNA molecule: the four bases
(A, C, T, G), a sugar (S), and a
phosphate (P).
Instructions
1.
Ask students to use the DNA patterns to trace and
cut out 16 each of sugar and phosphate, and 8 of
each base.
2.
Have students build a model of a segment of a
DNA molecule. The segment should contain 4
base "rungs." Any bases can be used for the
sequence, as long as the appropriate
complementary bases are used for the pairs.
3.
Once students have made their models, ask them
to separate the models down the middle so that
there are now two single strands of DNA.
4.
Have students create new double-stranded DNA
by matching complementary nucleotides to the
bases on each single strand.
Discussion Questions
1. Compare the two new strands of DNA. Are
they the same or different? (The same.) Why?
(Because each strand contains complementary
pairs, so that each daughter molecule consists
of one-half of the original DNA chain, and
one-half new material.)
2.
How does the structure of a DNA molecule
help account for the great variety of life that
exists on earth? (The seguence of the base
pairs determines how the organism will form.
The variety in the sequence of the base pairs
accounts for the variety of life forms.)
Misconception 1: Students always have a
confusion about the direction of the formation of
the new DNA strands.
Resolution: The new strands of DNA are always
built from the 5’ direction to the 3’ direction.
Misconception 2: When does DNA replication
occurs in a cell?
Resolution: DNA replication always occurs at the
beginning of the process of cell division.
Misconception 3: Why are the RNA Primers made
first on the replicated DNA strands when the
process itself is DNA Replication
Resolution: The RNA Primers that are built, are
used for the initiation of the formation of the new
DNA strand on the template.
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This process can
be used in genetic
engineering such
as in creating
clones.
This process is also
used to create
genetically
modified foods and
organisms using
the Recombinant
DNA technology.
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The students would have a chance of working on a
culminating project on the topic DNA Replication and
they can present in any way possible such as a PPT
presentation, Bristol board, Oral / verbal
presentation, through role plays or skits,
communicating through songs or videos or using a
case study etc.
The student’s understanding would also be assessed
through a unit test which would be an Assessment of
learning.
The choice of the way of the presentations by the
students would act as a mode of assessment for
learning.