DNA
Mr. Coleman
Biology
Why do we study DNA?
We study DNA for
many reasons, e.g.,
-its central importance
to all life on Earth,
-medical benefits such
as cures for diseases,
-better food crops.
DNA
DNA is often called
the blueprint of life.
In simple terms,
DNA contains the
instructions for
making proteins
within the cell.
Chromosomes and DNA
Proteins are made from
the blueprint that genes
provide.
Genes are on
chromosomes
in the cell’s nucleus.
Chromosomes are made
up of a chemical called
DNA.
The Shape of the Molecule
DNA is a very
long polymer.
The basic shape
is like a twisted
ladder or zipper.
This is called a
double helix.
A Little History of the Quest to Find the
Carrier of Our Genetic Heritage
In 1952 Alfred Hershey and
Martha Chase performed an
experiment using
radioactively labeled viruses
that infect bacteria.
These
viruses
were made
of only
protein
and DNA.
Hershey and
Chase labeled the
virus DNA with a
radioactive
isotope and the
virus protein with
a different isotope.
By following the infection of bacterial cells by the labeled
viruses, they demonstrated that DNA, rather than protein,
entered the cells and caused the bacteria to produce new
viruses.
In 1953, Rosalind Franklin first put forth the
possibility of DNA having a double helixical
shape. She based this on X-ray diffraction images
of DNA crystals she had produced in the
laboratory.
Also in 1953, Watson and Crick proposed that
DNA is made of two chains of nucleotides held
together by nitrogenous bases.
Watson and Crick
proposed that DNA is
shaped like a long zipper
that is twisted into a coil
like a spring.
Because DNA is composed of two strands twisted
together, its shape is called double helix.
The Double Helix
Molecule
The DNA double
helix has two
strands twisted
together.
One Strand of DNA
The backbone of the
molecule is
alternating
phosphate and
deoxyribose, a sugar,
parts.
The teeth are
nitrogenous bases.
phosphate
deoxyribose
bases
Nucleotides
O
O -P O
O
O
O -P O
O
One deoxyribose (or ribose)
together with its phosphate and
base make a nucleotide.
O
O -P O
O
Phosphate
O
C
C
O
C
Ribose
Nitrogenous
base
One Strand of DNA
One strand of DNA
is a polymer of
nucleotides.
One strand of DNA
has many millions
of nucleotides.
one
nucleotide
Four nitrogenous bases
DNA has four different bases:
• Cytosine
C
• Thymine T
• Adenine A
• Guanine G
Two Kinds of Bases in DNA
• Pyrimidines are
single ring bases.
• Purines are double
ring bases.
Thymine and Cytosine are
pyrimidines
Thymine and cytosine each have one
ring of carbon and nitrogen atoms.
Adenine and Guanine are
purines
Adenine and guanine each have two
rings of carbon and nitrogen atoms.
Two Stranded DNA
Remember, DNA
has two strands
that fit together
something like a
zipper.
The teeth are the
nitrogenous bases
but why do they
stick together?
Hydrogen Bonds
The bases attract each
other because of
hydrogen bonds.
Hydrogen bonds are
weak but there are
millions and millions
of them in a single
molecule of DNA.
Hydrogen Bonds
When making
hydrogen bonds,
cytosine always
pairs up with
guanine
and adenine
always pairs up
with thymine.
Important:
Adenine and Thymine always join
together
A T
Cytosine and Guanine always join
together
C G
DNA by the numbers
• Each cell has about 2 m
of DNA.
• The average human has
75 trillion cells.
• The average human has
enough DNA to go from
the earth to the sun
more than 400 times.
• DNA has a diameter of
only 0.000000002 m.
The earth is 150 billion m
or 93 million miles from
the sun.
1) In the Hershey Chase Experiment, DNA was labeled
with __________, and bacteriophage (virus) protein
was labeled with ____________.
A.
B.
C.
D.
radioactive phosphorous, radioactive sulfur
radioactive sulfur, radioactive phosphorous
codons, anticodons
DNA Polymerase, RNA polymerase
2) In the ladder analogy of the DNA molecule, the
"rungs" of the ladder are:
A. sugars
B. phosphates
C. paired nitrogenous bases
D. joined sugar and phosphate
3) Which of the following best describes the arrangement
of the sides of the DNA molecule?
A. twisted
B. antiparallel
C. bonded
D. alternating
4) If a DNA molecule is found to be composed of 40%
thymine, what percentage of guanine would be
expected.
A. 10%
B. 20%
C. 40%
D. 80%
5) A nucleotide consists of:
A. a phosphate and a base
B. a phosphate, and a sugar
C. a base and an amino acid
D. a phosphate, a sugar, and a base
6) The sugar in RNA is _____, the sugar in DNA is
_______
A. deoxyribose, ribose
B. ribose, deoxyribose
C. ribose, phosphate
D. ribose, uracil
7) Which of the following is found in RNA but not DNA?
A. uracil
B. deoxyribose
C. phosphate
D. adenine
8) DNA is a polymer of:
A. nucleosides
B. fatty acids
C. deoxyribose sugars connected by phosphodiester
bonds
D. nucleotides
• 9) Which of the following are pyrimidines?
A. adenine and cytosine
B. adenine and guanine
C. cytosine and guanine
D. cytosine and thymine
10) Which of the following are purines?
A. adenine and cytosine
B. adenine and guanine
C. cytosine and guanine
D. cytosine and thymine
11) A nucleic acid was analyzed and found to contain 32
percent A, 18 percent G, 17 percent C, and
33 percent T. The nucleic acid must be
A. single-stranded RNA
B. single-stranded DNA
C. double-stranded RNA
D. double-stranded DNA
12) What does DNA stand for?
A. Design of Natural Animals
B. Deoxyribonucleic acid
C. Doneoribonucleic acid
D. None of the above
13) Where in a cell is DNA located at?
A. Cytoplasm
B. Food vacuole
C. Nucleus
D. Cell membrane
14) DNA’s function in the cell is …
A. The instructions to the make-up to a living
organism.
B. To control what goes in and out of an organism.
C. To take over the mind as a back-up.
D. To give dreams and ideas in the mind.
15) The building blocks of DNA are called ……
A. Legos
B. Electrons
C. Neoculiotis
D. Nucleotides
16) The four DNA building blocks are …
A. Guanine, Adenine, Riginine, Jynine
B. Guanine, Adenine, Cynine, Thymine
C. Guanine, Adenine, Cytosine, Uracil
D. Guanine, Adenine, Cytosine, Thymine
17) A nucleic acid was analyzed and found to contain 37
percent A, 16 percent G, 22 percent C, and 25 percent U.
The nucleic acid must be:
A. single-stranded RNA
B. single-stranded DNA
C. double-stranded RNA
D. double-stranded DNA
18) A nucleotide consists of
A. a sugar, a protein, and adenine
B. a sugar, an amino acid, and a starch
C. a sugar, a phosphate group, and a nitrogencontaining base
D. a starch, a phosphate group, and a nitrogencontaining base
19) The part of the molecule for which deoxyribonucleic
acid is named is the
A. phosphate group
B. sugar
C. nitrogen base
D. none of the above
20) Who are the three people connected with the
discovery of the shape of DNA?
A. Franklin, Watson, and Creap
B. Franklin, Watson, and Crick
C. Francis, Watson and Crick
D. Francis, Watson, and Creap