Chapter 9
Molecules of Heredity
Chapter 9 Outline
• 9.1 How Did Scientists Discover That Genes Are
Made of DNA?
• 9.2 What Is the Structure of DNA?
• 9.3 How Does DNA Encode Information?
• 9.4 How Does DNA Replication Ensure Genetic
Constancy During Cell Division?
• 9.5 How Do Mutations Occur?
9.1 Genes Are Made of DNA
• Known since the late 1800s:
1. Heritable information is carried in
discrete units called ________
2. Genes are parts of structures called
__________________
3. Chromosomes are made of
________________________ and
___________
Genes Are Made of DNA
• Transformed bacteria revealed the link
between ________ and ________
Genes Are Made of DNA
• F. Griffith worked with two strains of
Streptococcus pneumoniae bacteria
– _______ caused pneumonia when injected into
mice, __________ them
– ____ strain _______ cause pneumonia when
injected
Genes Are Made of DNA
• Griffith made a sample of heat-killed S
strain and mixed it with R strain
– Injection of combination into mice caused
____________________
Genes Are Made of DNA
• Deductions from Griffith’s experiment
(1920s)
– Living safe bacteria (R strain) were
__________ by something in the dead
(but normally disease-causing) S strain
– The living R strain bacteria were
_________________________________
________________________________
Genes Are Made of DNA
• Later findings by Avery, MacLeod, and
McCarty (1940s)
– The transforming molecule from the S
strain was ________
9.2 DNA Structure
• DNA is made of chains of small
subunits called _________________
DNA Is Composed of Four Nucleotides
•
Each nucleotide has three components:
1. __________________
2. ____________________
3. One of four nitrogen-containing bases
– ______________
– ______________
– ______________
– ______________
DNA Is Composed of Four
Nucleotides
•
In 1940, biochemist E. Chargaff
determined that:
– In a DNA molecule, amounts of
______________________
– “Chargaff’s Rule”
DNA Is a Double Helix
• In the 1940s several other scientists
investigated the structure of DNA
• Rosalind Franklin and Maurice Wilkins
studied DNA structure
_____________________
DNA Is a Double Helix
• From X-ray diffraction patterns they
deduced that DNA
– Is ___________
– Has a uniform diameter of ___________
– Is _____, and is _________ like a
corkscrew
– Consists of repeating subunits
DNA Is a Double Helix
• James Watson and Francis
Crick combined the X-ray
data with bonding theory to
deduce DNA structure:
– DNA is made of ____
_______ of nucleotides
– The deoxyribose and
phosphate portions make up
the ______________
backbone
Hydrogen Bonds
• Nitrogen-containing bases protrude
__________ from sugar-phosphate
backbone
Hydrogen Bonds
• ______________ hold
certain nitrogenous base
pairs together
– A bonds with __, G bonds
with ___
– Bonding bases called
_________________
base pairs
Hydrogen Bonds
• Ladder-like structure of the two DNA strands
are twisted into a _____________
9.3 How Does DNA Encode Information?
•
•
•
How can a molecule with only 4 simple parts
be the carrier of genetic information?
The key lies in the _________________, of
subunits
Within a DNA strand, the four types of bases
can be arranged in any ____________, and
this sequence is what encodes genetic
information
How Does DNA Encode Information?
•
The genetic code is analogous to languages,
where small sets of letters combine in various
ways to make up many different words
– English has 26 letters
– The binary language of computers uses only two
“letters” (0 and 1, or “on” and “off”)
How Does DNA Encode Information?
•
The sequence of only _______________ can
produce many different combinations
– A 10 nucleotide sequence can code for
greater than ___________ different
combinations
9.4 DNA Replication
• All cells come from __________ cells
• Cells reproduce by _______________
• Each of two daughter cells gets an
exact copy of parent cell’s genetic
information
• Duplication of the parent cell DNA is
called ___________________
DNA Replication
•
DNA replication begins
when _______________
separate the two strands
– Hydrogen bonds
between_______ are
broken
DNA Replication
• A second strand of new
DNA is synthesized
along each separated
strand by
__________________,
which position ______
nucleotides across
from ______________
nucleotides
DNA Replication
• Base pairing is the
foundation of DNA
replication
– An adenine on one
strand pairs with a
_______ on the other
strand; a cytosine pairs
with ___________
– If one strand reads ATG,
the other reads _______
DNA Replication
•
The two resulting DNA
molecules have one ___
___________ strand and
one ______________
(________________
replication)
9.5 How Do Mutations Occur?
Replication And Proofreading
• During replication, DNA polymerase
mismatches nucleotides once every
__________________
• DNA repair enzymes _________” each
new daughter strand, replacing
mismatched nucleotides
• However…
Mistakes Do Happen
DNA is damaged in a number of ways
• ___________ chemical breakdown
at body temperature
• Certain chemicals (some
components of _______________)
Mistakes Do Happen
• UV light from the
sun causes DNA
damage
– DNA damage
leads to
uncontrollable
_________ and
____________
Types of
Mutations
• ___________ individual
nucleotide in the
DNA sequence is
changed
Types of Mutations
• __________
mutation - one or
more nucleotide
pairs are inserted
into the DNA double
helix
Types of Mutations
• __________
mutation - one or
more nucleotide
pairs are removed
from the double helix
Types of Mutations
• ____________ piece of DNA is cut
out of a
chromosome,
turned around, and
re-inserted into the
gap
Types of Mutations
•
_______________ - chunk of DNA (often
very large) is removed from one
chromosome and attached to another