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KEY CONCEPT
DNA was identified as the genetic material through a series of
experiments.
DNA & RNA
Units of Life
A.
B.
C.
D.
E.
F.
History of DNA
DNA Discovery
RNA
Transcription
Translation
Mutations
DNA: Blueprint for Life
A. History of Discovery
1. Frederick Griffith: Mice Transformation
2. Avery: DNA Identified
3. Hershey-Chase: DNA and Viruses
4. Rosalind Franklin: X-ray Evidence
5. Chargaff’s Rules: Base Pairing
6. Watson and Crick:The Double Helix
Discovery of DNA: A
History
FREDERICK GRIFFITH (1928)
• Studied way in which bacteria cause
pneumonia and recognized process of
transformation.
• Showed through experiments that
one strain of bacteria could be
transformed into another.
• Hypothesized that there was a
transforming factor involved.
Avery identified DNA as the
transforming principle.
• Avery isolated and purified Griffith’s transforming
principle.
• Avery performed three tests on the transforming
principle.
– Qualitative tests showed DNA was present.
– Chemical tests showed
the chemical makeup
matched that of DNA.
– Enzyme tests showed
only DNA-degrading
enzymes stopped
transformation.
Griffith finds a ‘transforming principle.’
• Griffith experimented with the bacteria that cause
pneumonia.
• He used two forms: the S form (deadly) and the R
form (not deadly).
• A transforming material passed from dead S bacteria
to live R bacteria, making them deadly.
Section 12-1
Griffith’s Experiment
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Control
Disease-causing Harmless bacteria Heat-killed, disease(no growth)
bacteria (smooth (rough colonies) causing bacteria
colonies)
(smooth colonies)
Dies of pneumonia
Lives
Lives
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Section 12-1
Griffith’s Experiment
Heat-killed, diseasecausing bacteria
(smooth colonies)
Disease-causing
bacteria (smooth
colonies)
Dies of pneumonia
Harmless
bacteria
(rough
colonies)
Lives
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
DNA Discovery: A History
AVERY (1944)
• Repeated Griffith’s experiments and
identified DNA as the transforming
factor-identified DNA
• DNA-stores and transmits genetic
information from one generation to
another.
DNA Discovery: A History
HERSHEY-CHASE (1952)
• Experiments with bacteria-killing
viruses (bacteriophages)
• Confirmed again that DNA was the
molecule that contained the genetic
code.
Hershey and Chase confirm that DNA
is
the
genetic
material.
• Hershey and Chase studied viruses that infect
bacteria, or bacteriophages.
– They tagged viral DNA
with radioactive
phosphorus.
– They tagged viral
proteins with radioactive
sulfur.
•
Tagged DNA was found inside the bacteria; tagged proteins were not.
Hershey-Chase
Experiment
Bacteriophage
with phosphorus32 in DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage
with sulfur-35 in
protein coat
Phage infects
bacterium
No radioactivity inside
bacterium
Hershey-Chase
Experiment
Bacteriophage
with phosphorus32 in DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage
with sulfur-35 in
protein coat
Phage infects
bacterium
No radioactivity inside
bacterium
Hershey-Chase
Experiment
Bacteriophage
with phosphorus32 in DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage
with sulfur-35 in
protein coat
Phage infects
bacterium
No radioactivity inside
bacterium
Watson and Crick determined the
three-dimensional structure of DNA by
• They realized that
building models.
DNA is a double helix
that is made up of a
sugar-phosphate
backbone on the
outside with bases on
the inside.
DNA Discovery: A History
ROSALIND FRANKLIN and
MAURICE WILKINS (1950’S)
• Studied DNA molecule by using a
purified DNA sample and x-ray
pictures of molecule.
• Found it was a twisted “X”
structure.
•
Watson and Crick’s discovery built on the work of Rosalind Franklin and Erwin
Chargaff.
– Franklin’s x-ray images suggested that DNA was a double helix of even
width.
– Chargaff’s rules stated that A=T and C=G.
DNA Discovery: A History
ERWIN CHARGAFF (early 1950’s)
• Observed in any DNA sample, the
number of adenine molecules was equal
to the number of thymine; same for
guanine and cytosine.
• Developed nitrogen base pairing rules
Percentage of Bases in
Four Organisms
Source of DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8
DNA Discovery: A History
WATSON-CRICK (1953)
• Tried to build 3D DNA model couldn’t quite solve it
• Used Franklin’s pictures to
develop the double helix model
• Double helix model explained much
about DNA structure, including
placement of nitrogen bases and
the formation of bonds.
• Received Nobel Prize along with
Wilkins (Franklin didn’t—why?)
DNA: Blueprint for Life
B. The Structure of DNA
1. Nucleotides – basic unit of DNA
2. Nitrogen Bases
3. DNA Replication
DNA is composed of four types of
nucleotides.
• DNA is made up of a long chain of nucleotides.
• Each nucleotide has three parts.
– a phosphate group
– a deoxyribose sugar
– a nitrogen-containing base
phosphate group
deoxyribose (sugar)
nitrogen-containing
base
•
The nitrogen containing bases are the only difference in the four
nucleotides.
Structure of DNA
DNA made of nucleotides, the basic unit
Nucleotide is made of three parts:
1. One Phosphate
2. One 5-Carbon Sugar (deoxyribose)
3. One Nitrogen base
Adenine(A), Guanine(G) – Purines
Thymine(T), Cytosine(C) – Pyrimidines
Structure of DNA
Sugar and Phosphate are the
“backbone” of DNA
Two parallel strands of sugarphosphate groups with pairs of
nitrogen bases linking the two
strands together with weak
hydrogen bonds, forming a
double helix.
WHY WEAK BONDS?
Nucleotides always pair in the same
way.
• The base-pairing rules
show how nucleotides
always pair up in DNA.
– A pairs with T
– C pairs with G
•
Because a pyrimidine (single ring)
pairs with a purine (double ring), the
helix has a uniform width.
G
A
C
T
Structure of DNA
Nitrogen Base Pairing ‘Rulz’:
A=T (one purine/ pyrimidine)
C=G (one purine/ pyrimidine)
DNA strands are complementary
because of base pairing rules
Nitrogen bases attached to sugars.
•
The backbone is connected by covalent bonds.
•
The bases are connected by hydrogen bonds.
hydrogen bond
covalent bond
DNA Nucleotides
Purines
Adenine
Guanine
Phosphate
group
Pyrimidines
Cytosine
Thymine
Deoxyribose
Structure of DNA
Nucleotide
Weak Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
DNA Replication
A Perfect Copy
When a cell divides, each daughter cell
receives a complete set of
chromosomes. This means that each
new cell has a complete set of the
DNA code. Before a cell can divide, the
DNA must be copied so that there are
two sets ready to be distributed to
the new cells.
DNA Replication
Complementary strands of DNA serve as a
pattern for a new strand.
DNA replication carried out by enzymes
which “unzip” the two strands by breaking
the hydrogen bonds.
Then, appropriate nitrogen bases are
inserted. Enzymes also proofread the
bases to make sure of correct base
pairing.
Chromosome Structure
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
DNA Replication
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Original
strand
Nitrogenous
bases
DNA Replication
Copied DNA C G G T A A C A T T A
DNA
G
C
C
A
T
T
G
T
A
A
T
enzymes
Copied DNA C G G T A A C A T T A
DNA
G C C A T T G T A A T
RNA: The Other Code
C. RNA and Protein Synthesis
A.The Structure of RNA
B. DNA and RNA Similarities/Differences
C. Transcription
D. Types of RNA
E. Protein Synthesis
F. Translation
RNA: The Other Code
A. RNA similar to DNA
•
•
long chain made of nucleotides
each nucleotide consists of:
 a sugar
 a phosphate
 a nitrogen-containing base
•
sugar and phosphate still backbone
of RNA
RNA: The Other Code
B. RNA different from DNA
• Different type of sugar (ribose)
• Single strand rather than a double strand
RNA molecule is a disposable copy of DNA
• Nitrogen base THYMINE found in DNA
replaced by a similar base URACIL (U) in RNA
ex. ( A - U ) and ( C - G )
Why RNA?
C. Why does DNA need to transfer genetic
information to RNA?
1. DNA is found in the nucleus.
Ribosomes are outside the nucleus.
2.DNA does not leave nucleus-too large for
nuclear pores.
3.Messenger must bring genetic information
from the DNA to the ribosomes to make
proteins/amino acid
4.Special molecule, messenger RNA
(mRNA), performs this task.
RNA: The Other Code
RNA - The Other Part of the Code
A. RNA –“messenger” between the
DNA in the nucleus and the
ribosomes. (mRNA)
B. Ribosomes –organelles outside the
nucleus that make proteins from
amino acids.
C. Proteins/Amino Acids –used to
build and repair cells.
• Discovery education streaming
• Standard Deviants School Biology:
The Cell –RNA Polymerase segment
RNA Synthesis
Transcription- process by which one
strand of DNA is copied into a
complementary strand of mRNA in
the nucleus.
enzymes
mRNA C G G U A A C A U U A
DNA G C C A T T G T A A T
Copied DNA C G G T A A C A T T A
enzymes
mRNA G C C A U U G U A AU
enzymes
Transcription
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
Types of RNA
Transfer RNA (tRNA)
A. Carries amino acids to ribosome
B. Single strand looped back on itself
C. Anticodon-three nucleotides on tRNA are
complementary to the three on the mRNA.
D. Matching of codon (mRNA) to
anticodon (tRNA) allows the correct
amino acid to be put in place.
Ribosomal RNA (rRNA)
A. makes up majority of ribosome
Types of RNA
RNA
can be
Messenger RNA
also called
Ribosomal RNA
which functions to
mRNA
Carry instructions
also called
which functions to
rRNA
Combine
with proteins
from
to
to make up
DNA
Ribosome
Ribosomes
Transfer RNA
also called
which functions to
tRNA
Bring
amino acids to
ribosome
Protein Synthesis
A. Nucleotides in DNA have all the
information to make proteins.
B. DNA code copied into mRNA
C. Proteins are made of amino acids
which are coded from mRNA.
D. mRNA code is read in triplet
form called a CODON which
specifies certain amino acids using
a decoder (p.201)
Protein Synthesis:
Translation
Only 20 amino acids make all life as we
know it! How can this be?
*AUG - codes for amino acid methionine
or be an “initiator codon” and will
always start mRNA
*Some are “stop” codons which end
mRNA
Translation -the decoding of mRNA code
into an amino acids--proteins
Translation
Nucleus
Messenger RNA
Messenger RNA is transcribed in the nucleus.
Phenylalanine
tRNA
mRNA
Transfer RNA
Methionine
The mRNA then enters the cytoplasm and
attaches to a ribosome. Translation begins
at AUG, the start codon. Each transfer RNA
has an anticodon whose bases are
complementary to a codon on the mRNA
strand. The ribosome positions the start
codon to attract its anticodon, which is part
of the tRNA that binds methionine. The
ribosome also binds the next codon and its
anticodon.
Ribosome
mRNA
Lysine
Start codon
Translation (continued)
The Polypeptide “Assembly Line”
The ribosome joins the two amino acids—
methionine and phenylalanine—and breaks
the bond between methionine and its tRNA.
The tRNA floats away, allowing the
ribosome to bind to another tRNA. The
ribosome moves along the mRNA, binding
new tRNA molecules and amino acids.
Lysine
Growing polypeptide chain
Ribosome
tRNA
tRNA
mRNA
Completing the Polypeptide
mRNA
Ribosome
Translation direction
The process continues until the
ribosome reaches one of the
three stop codons. The result is a
growing polypeptide chain.
The Genetic Code
Decoder
BACK
Translation
DNA T A C T T T G T A A C T
mRNA A U G A A A C A U U G A
enzymes
Determining the
Sequence
of a Gene
•DNA contains the code of
instructions for cells.
•Sometimes, an error occurs when
the code is copied.
•Such errors are called mutations.
Mutations
• Mutations can occur on individual
chromosomes by way of gene
mutations.
– Base sequence gets rearranged and may
cause insertion, deletion, or substitution
of genes
• Mutations can also occur with
entire chromosomes.
Gene Mutations:
Substitution, Insertion, and Deletion
Deletion
Substitution
Insertion
• Original
The fat cat ate the wee rat.
•
•
•
•
•
The fat hat ate the wee rat.
The fat caa tet hew eer at.
The fat __ ate the wee rat.
The fat cat xlw ate the wee rat
The fat tar eew eht eta tac.
Point Mutation
Frame Shift
Deletion
Insertion
Inversion
Chromosome Mutations
Deletion
Duplication
Inversion
Translocation
Mutagen.
• Ultraviolet light, nuclear radiation,
and certain chemicals can damage
DNA by altering nucleotide bases so
that they look like other nucleotide
bases
Environmental Impact
• Ultraviolet light, nuclear radiation, and certain
chemicals can damage DNA by altering
nucleotide bases so that they look like other
nucleotide bases.
Mutagens are environmental agents that can
cause mutations in the genetic code.
• High energy radiation from radioactive elements, X-rays, gamma
rays, microwaves, and ultraviolet light (please use sunscreen and
wear a hat).
• Industrial chemicals such as PCB's (support the ban).
• Pollutants such as cigarette smoke (please don't smoke and if you do
work hard to quit)
• Pesticides (eat organic).
• Food Additives (read food labels).
• Drugs (use only when necessary).
• Viruses (wash your hands and practice safe sex).
Mutagen
• An agent, such as a chemical, ultraviolet light, or a
radioactive element, that can induce or increase the
frequency of mutation in an organism.
• Spontaneous DNA replication and repair errors, spontaneous
modification of nucleotides
• All types of mutations produced UV irradiation
• Pyrimidine dimers induce error prone repair (SOS) Mainly G-C to
A-T transitions, but all other types of mutations including deletions,
frameshifts, and rearrangements
Impact of Genetics
Autosome
Disorders
caused by
Recessive
alleles
Dominant alleles
Codominant
alleles
include
include
include
Huntington’s
disease
Sickle cell
disease
Galactosemia
Albinism
Cystic
fibrosis
Phenylketonuria
Tay-Sachs
disease
Achondroplasia
Hypercholesterolemia
Pedigrees
A circle
represents a
female.
A horizontal line
connecting a male and
female represents a
marriage.
A half-shaded
circle or square
indicates that a
person is a carrier
of the trait.
A completely
shaded circle
or square
indicates that a
person
expresses the
trait.
A square
represents a male.
A vertical line and a
bracket connect the
parents to their
children.
A circle or square
that is not shaded
indicates that a
person neither
expresses the
trait nor is a
carrier of the trait.
Blood Groups
A. Four major blood groups: A, B, O, AB
B. Each type carries certain Antigens
C. Antigens are markers on surface of
cells that identify the type of cell.
Allows antibodies to attack if they
aren’t identified correctly.
D. Antibodies found in the body, they
provide protection from diseases and
foreign substances. As you are
exposed to diseases, your body
builds up antibodies—resistance.
Blood Groups
E. Blood Type
A
B
AB
O
Antigen
A
B
AB
none
Antibodies
b
a
none
a and b
F. Type O blood is the universal donor blood
Why?
There are no markers (but O can only
receive O)
G. Type AB is the universal recipient blood
Why?
Carry both markers; lack antibodies
Blood Groups
Phenotype
(Blood Type
Genotype
Antigen on
Red Blood Cell
Safe Transfusions
To
From
Blood Groups-Rh Factor
• Rh factor identified in rhesus monkey
and later found in human blood.
• Rh+ is dominant over Rh• If you have Rh+ blood (O+, A+, etc)=
O+O+, A+O- , B+O+, etc
• If you have Rh- blood (O-, B-, etc)=
O-O-, B-O- ,A-O- , etc
Blood Types-Rh Factor
• Blood types must match up correctly
when getting blood or death results.
• Important during pregnancy:
if mom is Rh- and has Rh+ fetus,
mom’s antibodies don’t recognize Rh+
and begin to attack. Could result in
death. This can be detected early
and treated with blood supplements.
• What was the dad’s Rh type?
Nondisjunction
Homologous
chromosomes
fail to
separate
Meiosis I:
Nondisjunction
Meiosis II
Nondisjunction
Homologous
chromosomes
fail to
separate
Meiosis I:
Nondisjunction
Meiosis II
Nondisjunction
Homologous
chromosomes
fail to
separate
Meiosis I:
Nondisjunction
Meiosis II
Sex-Linked Traits:
Colorblindness
Father
(normal vision)
Normal
Colorblind vision
Male
Female
Mother
(carrier)
Daughter
(normal
vision)
Son
(normal
vision)
Daughter
(carrier)
Son
(colorblind)
Sex-Linked Traits:
Colorblindness
Father
(normal vision)
Normal
Colorblind vision
Male
Female
Daughter
(normal vision)
Son
(normal vision)
Mother
(carrier)
Daughter
(carrier)
Son
(colorblind)