DNA and its Structure
Let’s get ready to take some notes…
DNA
Deoxyribonucleic Acid
Determines
an
organism’s traits by
determining the
structure of proteins
Background
 1950’s: many
scientists believed that
proteins were the genetic material
 1952: Alfred Hershey and Martha
Chase
 Their
experiment determined that
DNA is the genetic material
 Video clip
Background continued
 1953: Watson
and Crick proposed
that DNA is made of two chains
of nucleotides held together by
hydrogens bonds between the
nitrogenous bases
 They also said that DNA is shaped
like a twisted ladder, or double
helix
The Structure of Nucleotides
DNA
is a polymer
made of repeating
subunits, or
monomers, called
nucleotides
Nucleotides are made of three
parts.
5
Carbon sugar Deoxyribose
Phosphate group
Nitrogenous base
Phosphate
Sugar
Nitrogenous
Base
Nitrogenous Base
Carbon ring structure
4 types
Adenine
purines
Guanine
Cytosine
Thymine
pyrimidines
Therefore
There
are four
possible nucleotides
because there are four
nitrogenous bases
Nucleotides
bond
together by the
phosphate of one to
the sugar of the next
Adenine
only bonds with
Thymine
Held together by two
hydrogen bonds
Thymine
Adenine
Guanine
only bonds with
Cytosine
Held together by three
hydrogen bonds
Cytosine
Guanine
The importance of nucleotide
sequence
 All
organisms have
DNA made of the
same four nucleotides
 The
differences in
organisms is because
of the difference in
the sequence of
nucleotides
Chagraff’s Rule
 Adenine
will always pair with
Thymine
 Guanine will always pair with
cytosine
Fact Check
Let’s get our boards ready…
 Who
established the structure of
DNA?
a) Darwin and Virchow
b) Watson and Crick
c) Hooke and Schwann
d) Rutherford and Millikan
 The
structure of DNA is
a) A square
b) A pentagon
c) A helix
d) A double helix
 How
many hydrogen bonds hold
guanine to cytosine?
a) One
b) Two
c) Three
 DNA
was established as the genetic
material because
a) Radioactive sulfur was found inside
cells infected by bacteriophages
b) Radioactive phosphorous was
found inside cells infected by
bacteriophages
 The
sugar in DNA is called
a) Sucrose
b) Ribose
c) Lactose
d) Deoxyribose
 How
many hydrogen bonds hold
adenine to thymine?
a) One
b) Two
c) Three
 A, C, G, and T
Helium
b) Hydrogen
c) Oxygen
d) Nitrogen
a)
are ______ bases
 Adenine
pairs up with cytosine.
True or false
 Guanine
pairs up with cytosine.
True or false
 In
the picture of a DNA
backbone on the right, the
pentagons represent ___
and the circles represent
___.
a) Deoxyribose, phosphate
b) Phosphate, deoxyribose
 Adenine
pairs up with thymine.
True or false
 The
DNA strand that
would pair with the strand
on the right would read
(from top to bottom)
a) GAC
b) CTG
c) TCG
d) ACT
 Snake
DNA and human DNA
consist of the same four
nucleotides, just in different
sequences.
True or false
 DNA
is double-stranded.
True or false
 DNA
is a monomer.
True or false
 What
kind of bond holds
together the sides of the DNA
double helix?
a) Hydrogen
b) Covalent
c) Ionic
 DNA
is a macromolecule. The
subunits that make it up are called
a) Monosaccharides
b) Fatty acids
c) Amino acids
d) Nucleotides
 Each
a)
b)
c)
d)
nucleotide consists of
A phosphate group
A sugar
A nitrogen base
All of the above
 The
a)
b)
c)
d)
purines are
Adenine and thymine
Thymine and cytosine
Cytosine and guanine
Guanine and adenine
 The
a)
b)
c)
d)
pyrimidines are
Adenine and thymine
Thymine and cytosine
Cytosine and guanine
Guanine and adenine