Why is DNA Interesting?
• DNA is a nonliving molecule.
• There are 6 feet of it in every cell.
• Each length of DNA comprises 3.2 billion letters of coding –
enough to produce 10 3,480,000,000 possible combinations.
• It will take 5,000 average size books to print that figure.
• DNA is guaranteed to be unique against all conceivable odds.
• DNA controls all the activities in the cell from the nucleus.
• DNA is unable to communicate directly with cellular
organelles.
Why is DNA interesting?
What do you know about DNA?
Figure 12–2 Griffith’s Experiment
Section 12-1
Heat-killed,
disease-causing
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)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Figure 12–2 Griffith’s Experiment
Section 12-1
Heat-killed,
disease-causing
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)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Avery and DNA
Oswald Avery repeated Griffith’s work in an effort to determine which
molecule in the heat-killed bacteria was important for transformation.
Avery treated an extract made from heat-killed bacteria with enzymes
that destroyed proteins, lipids, carbohydrates, RNA, and other molecules.
Transformation still occurred.
Avery repeated the experiments with enzymes that destroyed DNA.
Transformation did not occur.
DNA was the transforming factor.
Avery and other scientists discovered that the nucleic acid DNA stores and
transmits the genetic information from one generation of an organism to
the next.
Figure 12–4 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
Figure 12–4 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
Figure 12–4 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
The Components and Structure of DNA
How could DNA do the three critical things that genes were
known to do?
Genes had to carry information from one generation to the
next.
Genes had to put that information to work by determining
the heritable characteristics of organisms.
Genes had to be easily copied, because all of a cell’s
genetic information is replicated every time a cell divides.
Figure 12–5 DNA Nucleotides
Section 12-1
Purines
Adenine
Guanine
Phosphate
group
Pyrimidines
Cytosine
Thymine
Deoxyribose
Percentage of Bases in
Four Organisms
Section 12-1
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
Chargaff’s Rules states that [A] = [T] and [G] = [C] in any
sample of DNA.
Discovering the Role of DNA
Rosalind Franklin (1952) – studies the DNA molecule using X-ray
diffraction. Works with Maurice Wilkins.
James Watson and Francis Crick (1953) – develop the double-helix model
of the structure of DNA. They along with Maurice Wilkins win the Nobel
Prize for their discovery.
Sydney Brenner (1960) – along with other scientists shows the existence
of messenger RNA.
Walter Gilbert, Allan Maxam, and Frederick Sanger (1977) – develop the
Sanger method to sequence DNA.
Human Genome Project (2000) – the entire human genome is sequenced.
Figure 12–7 Structure of DNA
Section 12-1
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Prokaryotic Chromosome Structure
Section 12-2
Chromosome
E. coli bacterium
Bases on the chromosome
Figure 12-10 Chromosome Structure
of Eukaryotes
Section 12-2
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
Figure 12–11 DNA Replication
Section 12-2
New strand
Original
strand
DNA
polymerase
Growth
DNA
polymerase
Growth
Replication
fork
Replication
fork
New strand
Nitrogenous
bases
Original
strand
During replication the new nucleotides are added to the 3’ end of the new
DNA strand.
The deoxyribose is at the 3’ end and the phosphate group is at the 5’ end.
Figure 12–5 DNA Nucleotides
Section 12-1
Purines
Adenine
Guanine
Pyrimidines
Cytosine
Thymine
5’
3’
Phosphate
group
Deoxyribose
RNA and Protein Synthesis
Genes are coded DNA instructions that control the production of
proteins within the cell.
The first step in decoding the DNA instructions is to copy part of the
nucleotide sequence from DNA into RNA = TRANSCRIPTION.
In most cases, an RNA molecule is a copy of a single gene.
Like DNA, RNA consists of a long chain of nucleotides. Each RNA
nucleotide has a 5-carbon sugar, a phosphate group, and a
nitrogen base.
In most cells, the primary job of RNA is protein synthesis.
Comparison of RNA and DNA
RNA
DNA
Sugar - ribose
Sugar - deoxyribose
Usually single-stranded
Usually double-stranded
Nucleotides: adenine, cytosine, Nucleotides: adenine, cytosine,
guanine, uracil
guanine, thymine
Types of RNA
Section 12-3
RNA
can be
Messenger RNA
also called
Ribosomal
RNA
which functions to
also called
which functions to
rRNA
Combine
with proteins
Carry
instructions for
making a protein
mRNA
made during
from
to
to make up
DNA
Ribosome
Ribosomes
transcription
Transfer
RNA
also called
tRNA
which functions to
bring
amino acids to
ribosome during
translation and
protein synthesis
Transcription
RNA molecules are produced by copying part of the nucleotide
sequence of DNA into a complementary sequence of RNA. This
process is called transcription and produces mRNA.
RNA polymerase is the enzyme that carries out transcription.
RNA polymerase binds to DNA and separates the DNA strands.
One of the strands is then used as a template for the new strand of
RNA.
RNA polymerase binds to regions of DNA called promoters which
have specific base sequences that act as a signal for where to start
transcription.
Similar sequences in DNA signal to the RNA polymerase to stop
transcription.
Figure 12–14 Transcription
Section 12-3
Adenine (DNA and RNA)
Cystosine (DNA and RNA)
Guanine(DNA and RNA)
Thymine (DNA only)
Uracil (RNA only)
RNA
polymerase
DNA
RNA
RNA Editing
Eukaryotic genes contain introns and exons. The introns do not
code for proteins. Exons code for proteins.
When mRNA is made, both the introns and exons are copied from
the DNA. The introns are cut out while the mRNA is still in the
nucleus. The exons are then spliced together to form the final
mRNA.
Some mRNA may be cut and spliced in different ways to produce
different mRNA molecules. This allows for a single gene to produce
different forms of mRNA.
Intron sequences may be involved in regulation of expression of
genes.
Gene Structure & Protein Synthesis
The Genetic Code
Proteins are made by joining amino acids into long chains called
polypeptides. There are 20 different amino acids. The properties of
the protein are determined by the order of amino acids.
The genetic code is read three letters at a time so that each “word”
is three bases long. Each three letter “word” is a codon.
A codon consists of three consecutive nucleotides that specify a
single amino acid that is to be added to the polypeptide.
There are 64 possible codons. Some amino acids can be specified
by more than one codon.
There is a start codon, AUG (methionine). There are three stop
codons.
Figure 12–17 The Genetic Code
Section 12-3
Figure 12–18 Translation
Section 12-3
Anticodon
Figure 12–18 Translation (continued)
Section 12-3
Gene Mutations
Section 12-4
Deletion
Substitution
Substitution
Insertion
Insertion
Deletion
Insertions and deletions are frameshift mutations.
Figure 12–20 Chromosomal Mutations
Section 12-4
Deletion
Duplication
Inversion
Translocation
Typical Gene Structure
Section 12-5
Regulatory
sites
Promoter
(RNA polymerase
binding site)
Start transcription
DNA strand
Stop transcription