DNA:
Structure and Function
Chapter 12
Section 1
The
First
three-dimensional
LifeMolecule
Instruction
Deoxyribose
Nucleic
The
Blueprint
of Manual
Life Acid
The
of
Heredity
xerox machine
The Architect of Life
DNA
Why Study DNA?
To truly understand genetics, biologists first had
to discover the chemical structure of the gene
This would then help them understand how genes
control the inherited characteristics of living things
Gene expression is what
enables cells of the same
organism to take on so many
different sizes, shapes and
functions
(even though just about every
cell in an individual contains
the same DNA)
Review
1. What organelle is known as the
control center of the cell?
nucleus
2. What structures are found in the nucleus?
chromosomes
3. What are short segments of chromosomes?
genes
4. What are genes/chromosomes composed of?
DNA
5. How do genes/chromosomes control the
activity of the cell? produce proteins that
regulate cell functions and become cell structures
Review
History
1869 - Friedrich Miescher – “discovered” DNA in
nucleus
1928 - Frederick Griffith – Identified DNA as source of
genetic material using bacteria
1930’s - Oswald Avery, Colin MacLeod and Maclyn
McCarty - Confirmed that genes made of DNA
1950 - Alfred Hershey and Martha Chase confirmed
DNA is the biochemical of heredity using
radioactive markers bacteriophages
1952- Maurice Wilkins and Rosalind Franklin X-rayed
DNA to show repeatingX-ray
nucleotide
structure
of double
helix
1953- James Watson and Francis Crick combined data
Oswald Avery
Maclyn McCarty
to
create
a
3-D
model
of
structure
called the
Rosalind Franklin
Alfred Hershey
double helix
Martha
Chase
James
Watson
Francis Crick
Frederick Griffith
Watson-Crick
Model
DNA Structure
• Is a polymer of 1000’s of
nucleotide monomers
• Is a double strand of
covalently bonded
nucleotides in twisted ladder shape
•twisted ladder shape = double helix
DNA Shape
Double helix: 2 spirals wound around
each other
But joined in
the middle
DNA Structure
• Is a polymer of 1000’s of
nucleotide monomers Sugar
• Is a double strand of Phosphate
Backbone
covalently bonded
nucleotides in twisted ladder shape
twisted ladder shape = double helix
• ‘Rungs’ of ladder = nitrogen bases
• ‘Sides’ of ladder = sugar & phosphate
groups (also called the DNA backbone)
Nucleotide
•Nucleotide- Individual unit of DNA.
•Made of three parts:
•Deoxyribose (5-carbon sugar)
•Phosphate group
•A nitrogen-containing base
adenine
A
base with a
double-ring
structure
(T)
base with a
adenine
A
single-ring
basestructure
with a
Bases
sugar
(deoxyribose)
double-ring
structure
•Four nitrogen-containing bases
•Adenine
•Guanine
•Cytosine
•Thymine
sugar
(deoxyribose)
guanine
adenine
(G)
A a
base with
base with a
double-ring
double-ring
structure
structure
adenine
A
base with a
double-ring
structure
guanine
(G)
base with a
double-ring
structure
sugar
(deoxyribose)
thymine
(T)
base with a
single-ring
structure
guanine
thymine
adenine
cytosine
(G) (T)
A
(C)
base with
a
with
base
cytosine
base
with
base with
aaa
double-ring
(C)
single-ring
base with a
double-ring
single-ring
structure
single-ring
structure
structure
structure
structure
Bases

Adenine
double ringed = purines

Guanine

Thymine
single ringed = pyrimidines

Cytosine
Nucleotide
Deoxyribose (like ribose)
P
base
is a sugar with 5 carbon
atoms in a ring
sugar
Oxygen is one of the ring
members
In Deoxyribose, one of the OH groups is missing
and replaced with hydrogen
Thus deoxy =
- 1 oxygen
H
OH
Nucleotide
P - the Phosphate group
P
Is important because it
links the sugar on one
sugar
nucleotide with the phosphate
of the next nucleotide to make
a polynucleotide
Nucleotides are connected to each other
via a covalent bond
base
‘Base Pairing Rule’
• Bases are paired together in specific
manner
 Because of chemical structure and shape
•Adenine only pairs with Thymine
•Guanine only pairs with Cytosine
 Exactly enough room for only one purine
and one pyramide base between the
two strands of DNA
‘Base Pairing Rule’
•Bases held together in ‘rungs’ by
weak hydrogen bonds
•2 hydrogen bonds between A & T
•3 hydrogen bonds between C & G
DNA
DNA Function
• Scientists wondered how DNA worked.
They knew genes do these critical things:
• Carry information from one generation to
another
• Put information to work to determine an
organism’s characteristics
• Can be easily copied
• Store and transmit genetic information
needed for all cell functions
• In order to do these things it had to be a
special molecule!
Understanding DNA
• Our knowledge of DNA put to use:
• Inheritance/ Genetic Counseling
• Cell function/protein synthesis
• Embryonic development/gene regulation
• Evolution/ phylogenetic relationships
• Medicine/genetic diseases
• Genetic engineering/ recombinant DNA
Structure of DNA Review
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Structure of DNA Review
Pyrimidines
Purines
Adenine
Guanine
Cytosine
Thymine
Bases
Phosphate group
Deoxyribose
DNA’s Size
To get an idea of the size of the human genome
present in each of our cells, consider the following
analogy: If the DNA sequence of the human
genome were compiled in books, the equivalent
of 200 volumes the size of a Manhattan telephone
book (at 1,000 pages each) would be needed to
hold it all. It would take about 9.5 years to read
out loud (without stopping) the 3 billion bases in
one person's genome sequence, calculated on
a reading rate of 10 bases per second, equaling
600 bases/minute, 36,000 bases/hour,
864,000 bases/day, 315,360,000 bases/year.
Human Genome Project
A
DNA
How Am I
Packaged?
• Nitrogen bases
1. Are like letters in the code
2. Put them in different order
make a different gene
DNA
A
Package
HAT
CAT
DOG
• Genes
1. Are like words made up of letters
2. A group of nitrogen bases that
makes sense
3. Tells the cell to do something
The cat sat.
DNA
Package
One dog ate.
The big hat.
• DNA strand
1. Are like sentences made up of words
2. A long line of genes on each DNA
strand
DNA
Package
• Chromosomes
1. Are like books full of sentences
2. DNA strand twists around and
around itself
DNA
Package
• Nucleus
1. Is like a bookcase
2. Inside the cell, where all the
chromosomes are stored
DNA
Package
• So what would a library full of rows and
rows of bookcases represent?
many cells together
which is a tissue