Chapter 12
DNA AND RNA
HISTORICAL DEVELOPMENT

1928 – Griffith
 Discovered
bacteria
transferred something
between them that
changed them into a
new strain.
 Called this “bacterial
transformation”.
GRIFFITH’S EXPERIMENT
Section 12-1
Heat-killed, diseasecausing bacteria
(smooth colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
Lives
Lives
Control
(no growth)
Live, disease-causing
bacteria (smooth colonies)
Harmless bacteria
(rough colonies)
Dies of pneumonia
HISTORICAL DEVELOPMENT

1944 – Avery
 Determined
the
transforming factor
was DNA.
 He
destroyed different
parts of the bacteria,
and only when the DNA
was destroyed did
transformation not
occur.
HISTORICAL DEVELOPMENT

1952 – Hershey and Chase
 Using
a blender and bacteriophage, determined
that DNA, not protein, was the genetic material.
HERSHEY-CHASE EXPERIMENT
Section 12-1
Bacteriophage with
phosphorus-32 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
Section 12-1
Bacteriophage with
phosphorus-32 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
Section 12-1
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
HISTORICAL DEVELOPMENT

1952 – Rosalind
Franklin
 Used
x-ray
crystallography to show
the structure of DNA
was a helix.
HISTORICAL DEVELOPMENT

1953 – Watson and
Crick
 Determined
the
structure of DNA was a
double helix, and
proposed a model for
DNA replication.
DNA STRUCTURE

DNA is a chain (polymer) of nucleotides.
A
nucleotide consists of a sugar, phosphate and
nitrogenous base.
DNA NUCLEOTIDES
Section 12-1
Purines
Adenine
Guanine
Pyrimidines
Cytosine
Thymine
Phosphate group
Deoxyribose
DNA STRUCTURE

DNA is a double helix (twisted ladder).
 Two
nucleotide polymers are held together by weak
hydrogen bonds.
 Nitrogen bases always pair up this way:
 Adenine
with thymine A-T
 Cytosine with guanine C-G
 The
backbone of the ladder is alternating sugars
and phosphates.
 The steps of the ladder are the base pairs.
STRUCTURE OF DNA
Section 12-1
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
12-2
CHROMOSOMES AND DNA REPLICATION
DNA AND CHROMOSOMES

Prokaryotic cells (bacteria)
No nucleus
 Single circular chromosome
 Bacterial DNA is about 1.6mm long


Eukaryotic cells (all else)
1000X more DNA than bacteria
 DNA in nucleus (protected)
 Multiple chromosomes
 Human DNA (combined) is over 1 meter long

PROKARYOTIC CHROMOSOME STRUCTURE
Chromosome
E. coli bacterium
Bases on the chromosome
DNA AND CHROMOSOMES
Eukaryotic DNA is tightly packed and folded.
 It is wound about proteins called histones.

Chromosome Structure
of Eukaryotes
Section 12-2
Nucleosome
Chromosome
DNA
double
helix
Coils
Supercoils
Histones

DNA Packing
DNA REPLICATION

A cell copies its DNA before dividing.
 The
DNA uncoils.
 Then it “unzips” – the two strands separate along
the weak hydrogen bonds.
 Complimentary nucleotides are added with the help
of the enzyme DNA Polymerase.
 The result: two identical molecules of DNA.
DNA REPLICATION
Section 12-2
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication fork
Replication fork
New strand
Original
strand
Nitrogenous
bases
DNA REPLICATION

C:\Users\Carolyn\Videos\RealPlayer
Downloads\How DNA Copies Itself.mp4
12-3
RNA AND PROTEIN SYNTHESIS
BIG IDEA

DNA makes RNA makes Proteins makes You.
RNA STRUCTURE
Single-stranded chain of nucleotides
 No thymine - its replaced by uracil
 Sugar is ribose, not deoxyribose

TYPES OF RNA

Messenger RNA (mRNA)
 Carries
a copy of the genetic code (gene) for a
protein into the cytoplasm.

Ribosomal RNA (rRNA)
A
component of ribosomes where proteins are
made.

Transfer RNA (tRNA)
 Carries
amino acids to the ribosome for assembly
into proteins.
TRANSCRIPTION

The process of DNA making mRNA in the
nucleus is called transcription.
A
section of DNA (gene) unwinds and separates
 Enzymes add complimentary RNA nucleotides to
make mRNA.
 mRNA leaves the nucleus and goes to a ribosome
in the cytoplasm.
 What
is the complimentary nucleotide sequence for this
DNA sequence?

DNA = A-T-T-C-G-C-G
TRANSCRIPTION
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
RNA
DNA
TRANSCRIPTION

C:\Users\Carolyn\Videos\RealPlayer
Downloads\Transcription.flv
TRANSLATION

The process of mRNA being read on a ribosome to
make a protein is called translation.
mRNA attaches to a ribosome.
 tRNA carries amino acids to the ribosome.
 The mRNA codon (3 nucleotide sequence) matches up
with a complimentary tRNA anticodon (complimentary
sequence).
 The amino acid is dropped off and added the growing
polypeptide chain.

 What
is the amino acid sequence for the following mRNA
sequence? See the universal genetic code chart…

mRNA = AUAAGCGCU
THE GENETIC CODE
TRANSLATION
FIGURE 12–18 TRANSLATION (CONTINUED)
TRANSLATION

C:\Users\Carolyn\Videos\RealPlayer
Downloads\Translation.flv
TRANSCRIPTION AND TRANSLATION

C:\Users\Carolyn\Videos\RealPlayer
Downloads\From DNA to Protein.mp4
TRANSCRIPTION AND TRANSLATION

C:\Users\Carolyn\Videos\RealPlayer
Downloads\DNA Transcription and Protein
Assembly.mp4
GENES AND PROTEINS

Proteins are made of several polypeptide
chains folded together.
 The
shape is important to how the protein
functions.

One gene codes for the production of one
polypeptide.
 Therefore,
protein.
several genes are needed to make one
12-4
GENE MUTATIONS
KINDS OF MUTATIONS
Mistakes made when DNA is copied are called
mutations.
 Two kinds: gene and chromosome mutations

GENE MUTATIONS

Gene mutations affect only one gene.
 There
is a change in the sequence of bases in DNA.
 This causes the protein made by that gene to be
incorrect. (sometimes)
 Ex: lactose intolerance
CHROMOSOME MUTATIONS

Changes in the number or structure of
chromosomes are called chromosome
mutations.
 Ex:
An extra chromosome causes Down Syndrome.
MUTAGENS

Substances that can cause mutations are
called mutagenic agents.
 UV
light, chemicals, radiation
SIGNIFICANCE OF MUTATIONS
•

Inherited only if the mutation occurs in a sex cell.
Harmful mutations – cause many genetic
disorders.
 Ex:
cystic fibrosis
Neutral mutations – have no effect on gene
expression or protein function (most).
 Beneficial mutations – source of genetic
variability.

 Breeders
artificially select for these traits