DNA
Life’s Instruction Manual
of
What Genes are Made Of
DNA
(Deoxyribonucleic Acid)
DNA Video
The Genetic Book of Life
• Genome: Book
• Chromosome:
Chapter
• DNA Strands:
Sentences
• Genes: words
• Base pairs: letters
Important Scientists
in Cellular Biology
Unit 6-DNA Structure and Replication
• Introduction to DNA
Matthias Schleiden
1804–1881
• Contributed to cell
theory (All living
things are composed
of cells.); worked with
Theodor Schwann;
studied plant tissues
and determined that
plants are made of
cells; also realized the
importance of the
cell’s nucleus and felt
it might relate to cell
division
Theodor Schwann
1810–1882
• Contributed to cell
theory (All living
things are composed
of cells.); worked with
Matthias Schleiden;
discovered “Schwann
cells” in the nervous
system; studied
animal cells/tissues
especially muscular
and nervous tissues;
considered the
founder of histology
Rudolf (Rudolph) Virchow
1821–1902
• Contributed to cell
theory (All cells
arise from existing
cells.); considered
father of pathology;
was an advocate for
public health;
applied cell theory
to the spread of
diseases in the
human body
Frederick Griffith & Oswald
Avery
1879–1941
• Griffith did experiments
trying to find a vaccine for
pneumonia; he discovered
that when harmless
bacteria and a virulent
(actively poisonous) bacteria
were mixed some of the
harmless bacteria became
virulent, he called this
transformation; Avery
continued Griffith’s
experiments and tried to
find out what substance
caused the transformation,
he determined it was DNA
that caused the
transformation
1877–1955
Rosalind Franklin
- X-ray photo
of DNA.
(1952)
Alfred Hershey & Martha Chase
1908–1977
• Conducted
experiments (the
“Hershey-Chase”
experiments) to
confirm the
transformation
principle;
determined that
DNA is the genetic
molecule of
inheritance not
proteins.
1927–2003
Erwin Chargaff
1905–2002
• Adenine and
Thymine always join
together
•
A
T
• Cytosine and
Guanine always join
together
•
C
G
James Watson & Francis Crick
1928 - living
• Discovered the
double-helix
structure of DNA
(with the help of
previous X-ray
diffraction
experiments by
Rosalind Franklin
and Maurice
Wilkins).
• animation
1916–2004
Watson & Crick proposed…
•DNA was made of 2 long stands of
nucleotides arranged in a specific
way called the “Complementary Rule”
•DNA had specific pairing between the
nitrogen bases:
ADENINE – THYMINE
CYTOSINE - GUANINE
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.
15
The Double Helix Molecule
• The DNA
double helix
has two
strands
twisted
together.
16
DNA
• DNA is often called
the blueprint of life.
• In simple terms,
DNA contains the
instructions for
making proteins
within the cell.
17
What can DNA do?
• 1. Can replicate before cell division.
• 2. Can direct protein synthesis. It tells the
RIBOSOME to make a protein.
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.
19
Genetic material of cells…
• GENES – units of
genetic material that
CODES FOR A
SPECIFIC TRAIT
• Called NUCLEIC
ACIDS
• DNA is made up of
repeating molecules
called NUCLEOTIDES
DNA Nucleotide
Phosphate
Group
O
O=P-O
O
5
CH2
O
N
C1
C4
Sugar
(deoxyribose)
C3
C2
Nitrogenous base
(A, G, C, or T)
One Strand of DNA
• The backbone of
the molecule is
alternating
phosphates and
deoxyribose
sugar
• The teeth are
nitrogenous
bases.
phosphate
deoxyribose
bases
23
Nucleotides
One deoxyribose together with
its phosphate and base make
a nucleotide.
Nitrogenous
base
Phosphate
Deoxyribose
24
One Strand of DNA
nucleotide
• One strand of DNA
is a polymer of
nucleotides.
• One strand of DNA
has many millions
of nucleotides.
25
Four nitrogenous bases
DNA has four different bases:
• Cytosine
C
• Thymine T
• Adenine A
• Guanine G
26
Two Kinds of Bases in DNA
N
NC
• Pyrimidines are
single ring bases. O C C
NC
• Purines are
double ring
bases.
N
NC
C CN
NC
NC
27
Thymine and Cytosine are
pyrimidines
• Thymine and cytosine each have one
ring of carbon and nitrogen atoms.
O
N C
OC
CC
N C
thymine
N
N C
O C
C
N C
cytosine
28
Adenine and Guanine are
purines
• Adenine and guanine each have two
rings of carbon and nitrogen atoms.
N
O
N C
N C
N C
C
C
C
N
N
N C
N C
C
Guanine
N
AdenineN C
29
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?
30
O
• 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.
• The bonds between
cytosine and guanine are
shown here with dotted
lines
C N
C
C N
N
C N
C
N
Hydrogen Bonds
N
C N
C
C O
31
Hydrogen Bonds, cont.
• When making
hydrogen bonds,
cytosine always
pairs up with
guanine
• Adenine always
pairs up with
thymine
• Adenine is bonded
to thymine here
O
N C
OC
CC
N C
32
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.
33
DNA Double Helix
“Rungs of ladder”
Nitrogenous
Base (A,T,G or C)
“Legs of ladder”
Phosphate &
Sugar Backbone
DNA Double Helix
5
O
3
3
O
P
5
O
C
G
1
P
5
3
2
4
4
2
3
1
P
T
5
A
P
3
O
O
P
5
O
3
5
P
Nitrogenous Bases
• PURINES
1. Adenine (A)
2. Guanine (G)
A or G
• PYRIMIDINES
3. Thymine (T)
4. Cytosine (C)
T or C
Chargaff’s Rule
• Adenine must pair with Thymine
• Guanine must pair with Cytosine
• Their amounts in a given DNA molecule will be
about the same.
T
A
G
C
BASE-PAIRINGS
H-bonds
G
C
T
A
Genetic Diversity…
• Different
arrangements of
NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among
living organisms.
The Code of Life…
• The “code” of the chromosome is the
SPECIFIC ORDER that bases occur.
A T C G T A T G C G G…
DNA is wrapped tightly around
histones and coiled tightly to form
chromosomes
• DNA Replication
video
• DNA Replication
Animation
• DNA Animation
DNA Replication
• DNA must be copied
• The DNA molecule produces 2
IDENTICAL new complementary
strands following the rules of
base pairing:
A-T, G-C
•Each strand of the
original DNA serves as
a template for the new
strand
DNA Replication
Watson and Crick
showed: the two strands
of the parental molecule
separate, and each
functions as a template
for synthesis of a new
complementary strand.
1.
.
DNA Template
Parental DNA
New DNA
Replication Quiz
1. Why is replication necessary?
A---?
G---?
2. Describe how replication works. C---?
T---?
3. Use the complementary rule to
A---?
create the complementary
G---?
strand:
A---?
G---?
C---?
A---?
G---?
T---?
Replication Quiz
A---T
1. Why is replication necessary?
G---C
So both new cells will have the correct
C---G
DNA
T---A
2. Describe how replication works.
A---T
Enzymes unzip DNA and complementary
G---C
nucleotides join each original strand.
A---T
3. Use the complementary rule to
G---C
create the complementary strand:
C---G
A---T
G---C
T---A
Animation Time…
• DNA replication animation take
2
• DNA Replication Process
(1961)
Watson & Crick proposed…
• …DNA controlled cell function by
serving as a template for PROTEIN
structure.
• 3 Nucleotides = a triplet or CODON
(which code for a specific AMINO ACID)
See p.303
• AMINO ACIDS are the building blocks
of proteins.
DNA Transcription
• DNA can “unzip”
itself and RNA
nucleotides match
up to the DNA
strand. See p.301
• Both DNA & RNA
are formed from
NUCLEOTIDES and
are called NUCLEIC
acids.
DNA Translation
• The cell uses
information from
“messenger” RNA
to produce proteins
See p.304-305
We will
discuss details
of this on a
later date
1.
2.
3.
4.
5.
6.
Transcription/Translation Quiz
Why is transcription necessary?
Describe transcription.
Why is translation necessary?
Describe translation.
What are the main differences
between DNA and RNA.
Using the chart in your journal,
identify the amino acids coded for by
these codons:
UGGCAGUGC
1. Why is transcription necessary?
Transcription makes messenger RNA (MRNA)
to carry the code for proteins out of the
nucleus to the ribosomes in the cytoplasm.
2. Describe transcription.
RNA polymerase binds to DNA, separates the
strands, then uses one strand as a template to
assemble MRNA.
3. Why is translation necessary?
Translation assures that the right amino acids
are joined together by peptides to form the
correct protein.
4. Describe translation.
The cell uses information from MRNA to
produce proteins.
5. What are the main differences between
DNA and RNA.
DNA has deoxyribose, RNA has ribose;
DNA has 2 strands, RNA has one strand;
DNA has thymine, RNA has uracil.
6. Using the chart on page 303, identify the
amino acids coded for by these codons:
UGGCAGUGC
tryptophan-glutamine-cysteine
AMAZING DNA FACTS…
• DNA from a single human
cell extends in a single
thread for almost 2 meters
long!!!
• It contains information
equal to some 600,000
printed pages of 500 words
each!!!
(a library of about 1,000 books)
LET’S REVIEW DNA…
1. Summarize the relationship between
genes & DNA.
2. Describe the overall structure of the
DNA molecule.
3. What are the 4 kinds of bases?