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DNA AND ITS STRUCTURE
DNA is located inside the
nucleus
DNA is stored in chromosomes,
and chromosomes are found in
the nucleus
Female and Male Sex
Chromsomes
A karyotype is a picture of all the
chromosomes in a cell. Humans have
22 pairs of chromosomes and two sex
chromosomes
What is DNA?
DNA
Heredity material
for life
Known as
Deoxyribonucleic
Acid
Double helix
Molecule
• What makes DNA so exciting is that it
shows how living organisms store
information in biological molecules
• The structure of DNA is nicely suited for
this task
• The structural backbone creates a simple,
consistent chain upon which many, many
bases can be laid out in an orderly
sequence
DNA
• Your DNA contains a set of instructions for
building a human. It is responsible for all
inherited characteristics.
• It directs all the cell’s activities
• These instructions are inscribed in the
structure of the DNA molecule through a
genetic code
• DNA shows us how living organisms can
pass down information to their offspring
• For example, it tells us how a child can be
born with “his mother’s eyes” or “his
father’s nose”
• DNA is compact, yet complex enough to
carry all the information needed to guide
the development of an entire organism
• But there is so much information that
needs to be stored about us. How is DNA
able to provide enough information for a
living organism?
• The simple answer is that DNA molecules
are very, very long
• Did you know a simple bacteria, E. Coli is
4 million nucleotides sequences long! This
corresponds to the information storage
capacity of an 8 MB hard drive! Lots of
information for a tiny bacteria!
• Genes carry information about making all
the proteins required by all organisms
• Interesting, DNA makes proteins, and it is
also containing them as well…
Francis Crick and James
Watson
• The first scientists to discover the shape
DNA
DNA- a double helix molecule made up of four
nucleotide bases,phosphate, and the sugar,
deoxyribose
The human genome is approximately 3
billion nucleotides long! The information
storage capacity of a 3GB hard drive!
We can think of DNA as a “genetic
database” for living organisms …okay,
let’s move on
• DNA is made of a long sequence of
smaller units strung together.
• There are four basic types of unit:
Adenine, thymine, guanine, and cytosine
The Nitrogen Bases
• These bases make up the “rungs” of the
ladder:
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
DNA is made up of a long sequence of
these units strung together.
• The capital letters represent the bases:
Adenine= A
Thymine= T
Guanine= G
Cytosine= C
• Know that adenine only pairs up with
thymine and cytosine only pairs with
guanine in the DNA molecule
Pairing of the
Nucleotide
Bases
Adenine
always pairs
with thymine
Guanine
always pairs
with cytosine
The back bone of DNA
• Made up of phosphate and a sugar called
deoxyribose
A codon is a group of three
base pairs that code for a
specfic amino acid
DNA Replication
• Base pairs are complementary to each
other because each base only bonds with
the other base pair
• CCGA will bond to the sequence GGCT
DNA Replication
STEP 1
• First, in replication, a DNA molecule is split
down the middle (figure 5)
• The bases on each side of the molecule
are used as a pattern for a new strand
• As new bases on the original molecule are
exposed, complementary nucleotides are
added
• Proteins help to unwind, copy, and rewind
the DNA molecule
Half of each of the molecules is
old DNA and half is new DNA
Mutations
• A change in the nucleotide- base
sequence of DNA
• Caused by random errors in the copying of
DNA
• Also, can be caused by things in the
environment
• A physical or chemical agent that causes a
mutation is called a mutagen
Do Mutations Matter?
• Changes in DNA can cause an improved
trait, no change, or a harmful trait
• If the mutation does not change the
protein that the gene makes then there will
be no change to the trait
Can you think of a mutation that could
benefit an organism?
A mutagen might have caused
this frog to develop six legs
Known Harmful Mutagens
2. What is a mutation? Is a mutation always
harmful?
The change in the nucleotide- base
sequence of DNA. No they are not always
harmful- sometimes beneficial, other times
no change
*Does a mutation always produce a
change in the individual? Explain.
No, only if it changes a protein that a gene
codes for will there be a change in a trait
What is the human genome project?
• A project designed by the U.S. department of
Energy and National Institute of Health to:
• Identify all the approximately 30,000 genes in
human DNA
• Determine the sequence of the 3 billion chemical
base pairs (nucleotides)
• Store the information in databases
• improve tools for data analysis
• Transfer data to private sector
• Address ethical issues stemming from the
project’s findings
DNA Extracted From
Strawberries
What are some practical benefits to
learning about DNA?
• Knowledge of the variations of DNA among
individuals can help diagnose, treat and
someday prevent thousands of disorders that
affect us
• Useful in crime solving cases and paternity
suits
• Help us understand the natural capabilities of
our non- human friends- that can be applied in
solving challenges in agriculture, health care,
energy production, etc
Questions for guess who?
• That’s right…for you!
Questions
1.Which two scientists are well known for
discovering the structure of the DNA
molecule?
Francis Crick and James Watson
3.The nitrogen base pairing pattern is key
to understanding how______occurs.
DNA replication
• DNA replication ensures that each
daughter cell will have____________.
All of the genetic information it needs to
carry out its activities
4.DNA replication begins
when_____________________________
__________________________.
the two sides of the DNA molecule unwind
and separate, like a zipper unzipping.
6.The molecule separates between
the__________on each rung.
paired nitrogen bases
Place the steps of DNA replication
in order
1. The nitrogen bases that are floating in
the nucleus pair up with the bases on each
half of the DNA molecule
2.The two sides of the ladder unwind and
separate, like a zipper unzipping
3.The new bases are attached
4.The order of the bases in each new DNA
molecule will match the order of the old
DNA
• 2, 1, 3, 4
Warm-up
If this was a sequence of nitrogen bases in
a DNA strand, what would its matching
strand look like?
A T G C G A T C
T A C G C T A G
Warm Up
1. List three facts about DNA (book pages
57-59).
• DNA is shaped like a twisted ladder. This
shape is known as a double helix.
• The two sides of the DNA ladder are made
up of molecules of sugar, called
deoxyribose, alternating with molecules
called phosphates
• The rungs of the ladder are made of
nitrogen bases