Download DNA Replication

The Meaning Of Life
The Central Dogma

Dogma is a principle or set of principles laid down by
an authority as incontrovertibly true
In biology:
 DNA – hereditary code that contains the instructions
to make RNA (1 ‘gene’ at a time)

RNA – code carrying the instructions to make
proteins

proteins (you) – the building blocks of you OR the
worker bees that run you
DNA  RNA  protein
The Structure of DNA and RNA
DNA – deoxyribonucleic acid
 RNA – ribonucleic acid
 both are made of nucleotides:

P
P – phosphate (PO43-)
S
ribose sugar (C5H10O5)
B
nitrogenous base
Nucleic Acids




the phosphate molecule is 1 phosphate (gr. 10
nomenclature)
in RNA, the sugar is ribose, a pentose sugar with
5C, 10H and 5O
however in DNA, one oxygen is removed and hence
the name deoxy ribo; 5C, 10H and 4O
the real difference is in the nitrogenous bases, there
are 5 of them
Nucleic Acids
adenine and guanine have a double ring structure
and are called purines
 thymine, cytosine and uracil are single rings called
pyrimidines
 in the DNA structure, a purine can only match up
with a pyrimidine and specifically, A-T and G-C
(more on uracil later)

DNA Structure





DNA’s overall structure is a double helix
it is like a twisted ladder where the sides are made
up of the sugar and phosphate
the ‘rungs’ are made
up of the bases
which are paired up
A always pairs with T
and G always pairs
with C
the pairs of bases are
held in place by
hydrogen attractions
(bonds) (3 bonds
between G-C and two
between A-T)
DNA Structure
We know that to function as a genetic material,
DNA has to be able to do three things:
1) replicate (duplicate) itself so that it can be
transmitted to future generations
2) store information
3) undergo mutations (changes) that provide
genetic variability (to account for the variety
in living things)
 Before
a cell divides, DNA must replicate or make an
exact copy of itself.
 Each of the two new cells that will be produced after
cell division occurs, will receive one complete set of
DNA.
 Each strand serves as a template for the building of a
new strand
 Each original strand produces a new strand of DNA
beside itself by complementary base pairing
 The result is two new DNA double helices, identical
to each other and to the original DNA molecule (two
copies)
DNA Replication


DNA replication is semiconservative
each new strand is half original strand and half
newly made strand
Parent
DNA
DNA is
Parental (old)
DNA molecule
making an
exact copy
of itself
Daughter
(new) strand
Daughter
DNA molecule
(double helices)
Figure 10.6
DNA
replication begins at multiple sites along
the DNA called origins of replication:
1. DNA unwinds and unzips. Each strand will now
serve as a template (blueprint or mold)
The enzyme
gyrase unwinds
the strand

2. Free nucleotides present in the nucleus
are fitted into place beside each original
strand following the complementary base
pairing rule
The enzyme
helicase
unzips the
strand
Nucleotides are
added to the
open side of each
strand by
enzymes

3. These new nucleotides are joined
together into a strand by an enzyme
called DNA polymerase.
Nucleotides are
added to the
open side of each
strand by
enzymes

4. When the process is completed the
result is two identical DNA molecules
being formed.
The two
daughter strands
are each part old,
part new
Origin of
replication
Replication Fork
Parental strand
Daughter strand
Bubble
Two identical daughter DNA molecules
http://www.dnatube.com/video/365/DNA-Replication
Figure 10.8
The Discovery of DNA
Levene (1920s) – determined that DNA was made of a
series of subunits called nucleotides
Chargaff (1940s) – determined that in any species the
amount of adenine and thymine were virtually the
same, as was the amount of guanine and cytosine.
Franklin (1951)– used X-ray crytallography to
photograph the DNA molecule; showed that DNA was
coiled in a helix.
The Hershey Chase Experiment (1952) – identified
that the molecule DNA was responsible for carrying
genetic information, not protein
Watson and Crick (1953) – created a scale model of
DNA that explained all the prior knowledge of DNA.
DNA DANCE

Activity
If
the sequence of DNA bases on one
strand of the double helix is CGT-AATCGC-TTA, what will be the
complementary sequence on the other
side of the double helix?
Plenary…
1.
2.
3.
What are the three major groups of
chemicals in DNA?
If DNA is only composed of three types
of chemicals, why are living things so
different from each other?
What are the base pairs in DNA?
But…what’s so important about
DNA?

In a cell all functions are carried out by proteins:
control of cell reproduction, production of energy,
production of hormones, production of digestive
enzymes, etc.

DNA contains genes: the blueprints for those
proteins

Each gene is an assembly guide (think IKEA) on how
to put the protein together

… tomorrows lesson
Your Task


Draw a diagram illustrating the process of DNA
replication.
Include in your diagram:
1. The correct structure of DNA (labeled)
2. The steps involved in DNA replication (labeled)
3. Show how the free nucleotides in the nucleus pair
up with their complementary base on each template
strand of DNA
4. Read p. 228-233 #1b, 2-5 … and …
Describe Rosalind Franklin’s contributions to the
understanding of the DNA structure.