DNA: THE MOLECULE OF
HEREDITY
CHAPTER 9
Big Idea
• The Big Idea!
• The structure of DNA, the molecule of
heredity, enables the molecule to copy itself.
•
Enduring Understanding
• Students will understand that:
• -DNA carries the code for the building blocks
of a living organism.
• -Mutations can lead to changes and there is
potential to changes those mutations.
• -We have the technology to manipulate DNA:
Essential Questions
• What is DNA and where is it found?
• How can knowledge of DNA help us to
understand the way organisms are related to
each other?
• How and why does DNA copy itself?
• How is the discovery of DNA an example of
cooperation, competition, and
Intrnationalism?
Knowledge
• DNA is composed of nucleotides and is shaped like a
double helix, with strands running antiparallel
• Bases always form complementary base pairs (adenine
with thymine and cytosine with guanine)
• Complementary base pairing enables DNA to replicate,
or copy itself
• DNA replication involves three steps and each step
uses a specific enzyme
• There is a leading strand and a lagging strand for each
replication fork
• The lagging strand is made from Okazaki fragments
Students know
• The “ tranforming principle” from the
experiment conducted by Griffith.
• DNA is the genetic material
• Watson and Crick model of DNA
• DNA is composed of four types of nucleotides
• Nucleotides always pair in the same way.
• Replication copies the genetic information
Vocabulary
•
•
•
•
Nucleotide
Adenine
Thymine
Cytosine
• Transformation
• Replication
• Chromosomes
Tour of the basics, from Learn.Genetics.
• http://learn.genetics.utah.edu/content/begin/
tour/
• This is a very useful link which will enable you
to learn about DNA, Chromosomes, gene,
protein, trait, all at your own pace. Make sure
you make best use of this link.
Griffith’s Experiment
http://www.youtube.com/watch?v=vQOdDGM5vSg
Griffith’s Experiment
• Transformed Bacteria
The DNA Song
http://www.youtube.com/watch?v=FUA6_Ucw3i4
History Behind The Discovery of DNA
• Internet Search Activity
• DNA timeline
• Make sure you post brief information and also
the picture of the scientists.
Prokaryotic and Eukaryotic DNA
Prokaryotic and Eukaryotic DNA
• genetic material DNA in prokaryotes is not bound within a
nucleus whereas in Eukaryotes the genetic material DNA is
bound within the nucleus.
• In prokaryotes, DNA is a single loop/arranged in a circular
shape. In Eukaryotes, DNA is organized into chromosomes.
• Eukaryotic DNA is complexed with proteins called
“histones” and is organized into chromosomes; prokaryotic
DNA is “naked” meaning that it has no histones associated
with it, and it is not formed into chromosomes.
• In prokaryotic DNA there is only one replication origin
when replication starts. By contrast, in eukaryotic DNA
there are as many as 1000 replication origins.
•
What is the Structure of DNA?
• How does DNA encode genetic information?
• How is DNA duplicated so that information
can be accurately passed from one cell to its
daughter cells?
• The secrets of DNA function, and therefore of
heredity itself, can be found in the three
dimensional structure of the DNA molecule.
Contribution made by Maurice Wilkins
and Rosalind Franklin
• Wilkins and Franklin used X.ray diffraction to study
DNA with X-rays recorded how the X-rays bounced off
the DNA molecules.
• They deduced a lot of information about DNA from the
pattern
• A molecule of DNA is long and thin, with a uniform
diameter of 2 nanometers.
• DNA is helical; that is it is twisted like a corkscrew.
• The DNA molecule consists of repeating subunits.
• Based on this James Watson and Francis Crick
proposed a model for the structure of DNA
Structure of DNA
• DNA is composed of Four Nucleotides
DNA
• Structure of DNA
Structure of DNA
• DNA is a double-helix: it has two strands that twist
around each other.
• Each strand is a polymer of linked nucleotides.
• Within each strand, the phosphate group of one
nucleotide bonds to the sugar of the next nucleotide in
the strand.
• This bonding pattern produces a “backbone” of
alternating covalently bonded sugars and phosphates.
• Each strand is made of single units called nucleotides.
• The nucleotide bases protrude from this sugarphosphate backbone.
• Each nucleotide in DNA consists of three parts: a phosphate
group, a sugar called deoxyribose, and one of four possible
nitrogen-containing bases – adenine (A), guanine (G),
thymine (T), or cytosine (C).
• All of the nucleotides within a single DNA strand are
oriented in the same direction. Therefore, the two ends of a
DNA strand differ; ne end has a ‘free’ or unbonded sugar,
and the other end has a “free” or unbonded phosphate
Nitrogenous Bases
Hydrogen Bonds Between Complementary
Bases Hold the Two DNA Strands Together
• Watson and Crick proposed that two DNA strands are held together by
hydrogen bonds that form between the two protruding bases of the
individual DNA strands.
• The DNA strands are not straight, they are twisted about each other to
form a double helix.
• The two strands in a DNA double helix are oriented in opposite direction.
• Complementary Base Pairs:
• Adenine forms hydrogen bonds only with thymine and that guanine forms
hydrogen bonds only with cytosine.
• The presence of complementary base pairs expalians Chargaff’s resultsthat the DNA of a given species contains equal amounts of adenine and
thymine, as well a equal amounts of cytosine and guanine.
• Within a DNA strand, the four types of bases can be arranged in any linear
order, and this sequence is wht encodes genetic information.
Complementary Base Pairs:
• Adenine forms hydrogen bonds only with
thymine and that guanine forms hydrogen bonds
only with cytosine.
• The presence of complementary base pairs
expalains Chargaff’s results-that the DNA of a
given species contains equal amounts of adenine
and thymine, as well a equal amounts of cytosine
and guanine.
• Within a DNA strand, the four types of bases can
be arranged in any linear order, and this
sequence is what encodes genetic information.
• All of the nucleotides within a single DNA
strand are oriented in the same direction.
Therefore, the two ends of a DNA strand
differ; ne end has a ‘free’ or unbonded sugar,
and the other end has a “free” or unbonded
phosphate
Nitrogenous bases
• Nitrogenous bases are of two types
Purines and Pyramidines
• Purines – Adenine (A) and guanine (G)
• Pyramidines - thymine (T) and Cytosine ( C)
How to extract your own DNA?
• http://m.gizmodo.com/5889997/how-toextract-your-own-dna-using-household-items
• I am sure you will have fun.
• Watch the video and the demonstration and
follow the steps carefully and extract your
own DNA.
• Awesome to watch your own DNA!!!!.
The order of Nucleotides in DNA can Encode vast amounts of
Information
• Consider the many characteristics of just one organism.
• How can the color of a bird’s feathers, the size and
shape of its beak, the ability to make a nest, its song,
and its ability to migrate all be determined by a
molecule with just four simple parts?
• It’s not the number of different subunits but their
sequence that’s important.
• Within a DNA strand, the four types of bases can be
arranged in any linear order, and this sequence is what
encodes genetic information.
The Discovery of the Double Helix
• Read page number 154 in your text book and
you can also refer to other Biology text book
and form a time line for the discovery of DNA.
Differences between DNA and RNA
DNA
RNA
a double- stranded molecule with a long
chain of nucleotides
A single-stranded molecule and has a shorter
chain of nucleotides
A-T(Adenine-Thymine), G-C(GuanineCytosine)
A-U(Adenine-Uracil), G-C(Guanine-Cytosine)
Found in nucleus
Found in nucleus and cytoplasm
Sugar is deoxyribose. nitrogenous bases are
A,T,C,G
Sugar is ribose. Nitrogenous bases are
A,U,C,G
Transmission of hereditary material
The main job of RNA is to transfer the
genetic code need for the creation of
proteins from the nucleus to the ribosome
DNA REPLICATION
• Key concept
• DNA replication copies the genetic
information of a cell.
• Replication copies the genetic information
• Proteins carry out the process of replication
• Replication is fast and accurate
The Replication of DNA is a critical event in a
cell’s life
• Nearly every cell of our body contains identical genetic
information-the same genetic information present in the
fertilized egg.
• During the process of cell division, two daughter cells are
formed from a single parent cell. Each daughter cell
receives a nearly perfect copy of the parent cell’s genetic
information.
• As a result, the parent cell must synthesize two exact copies
of its DNA through a process known as DNA Replication.
• DNA replication produces two identical double helices, one
of which will be passed to each of the new daughter cells.
Replication Process
1. Enzymes called DNA helicases begin to unzip the
double helix at numerous places along the
chromosomes called origins of replication. That is,
the hydrogen bonds connecting base pairs are
broken, the original molecules separates, and the
bases on each strand are exposed.
• 2. now DNA strands complimentary to the two
parental strands must be synthesized. One by
one, free nucleotides pair with the bases exposed
nucleotide pair in the template strand.
• DNA polymerases bond the nucleotides together
and form new strands complementary to each
template.
• DNA polymerase also connects these free
nucleotides with one another to form two new
DNA strands, each complementary to one of the
parental DNA strands.
• When replication is complete, one parental DNA
strand and its newly synthesized, complementary
daughter DNA strand wind together into one
double helix. At the same time, the other
parental strand and its daughter strand wind
together into a second double helix.
• In forming a new double helix, the process of
DNA replication conserves one parental DNA
strand and produces one newly synthesized
strand. Hence, the process is called
semiconservative replication
Semiconservative DNA Replication
http://www.mcb.harvard.edu/losick/images/trombonefinald.swf