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Molecular Biology
Griffith and Transformation
Fredrick Griffith isolated two different strains of
pneumonia bacteria from mice and grew them in
his lab.
The disease-causing strain of bacteria grew into
smooth colonies on culture plates.
The harmless strain grew into colonies with rough
edges.
The Central
Dogma of Biology
dog·ma
ˈdôɡmə/
noun
noun: dogma; plural noun: dogmas
1. A principle or set of principles laid
down by an authority as
incontrovertibly true.
"the Christian dogma of the Trinity“
Origin: mid 16th century: via late Latin
from Greek dogma ‘opinion,’ from
dokein ‘seem good, think.’
Translate dogma to
Use over time for: dogma
DNA  RNA Protein
Griffith's Experiments
Experiment 1:
Mice were injected with
the disease-causing
strain of bacteria.
The mice developed
pneumonia and died.
Experiment 2:
Mice were injected
with the harmless
strain of bacteria.
Harmless bacteria
(rough colonies)
These mice didn’t
get sick.
Lives
Experiment 3:
Griffith killed the
disease-causing
bacteria. He then
injected the heat-killed
bacteria into the mice.
Heat-killed diseasecausing bacteria (smooth
colonies)
The mice survived.
Lives
Experiment 4:
Heat-killed diseasecausing bacteria
(smooth colonies)
Griffith mixed
heat-killed,
diseasecausing
bacteria with
live, harmless
bacteria and
injected the
mixture into the
mice.
The mice
developed
pneumonia and
died.
Harmless bacteria
(rough colonies)
Live diseasecausing bacteria
(smooth colonies)
Dies of pneumonia
The heat-killed bacteria passed their
disease-causing ability to the harmless
strain.
Griffith called this process transformation
because the harmless strain had changed
into the disease-causing strain.
Griffith hypothesized that a factor must
contain information that could change
harmless bacteria into disease-causing
ones.
Avery and DNA
Oswald Avery determined which molecule
was most important for transformation.
Avery made an extract from the heat-killed
bacteria that they treated with enzymes.
Enzymes to destroy proteins
Then lipids
Then carbohydrates
Then other molecules including RNA.
Transformation still occurred.
Then DNA - NO transformation
Therefore, he concluded that 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.
The Hershey-Chase Experiment
Alfred Hershey and Martha Chase studied
viruses—nonliving particles smaller than a cell
that can infect living organisms.
Bacteriophages
A virus that infects bacteria is known as a
bacteriophage.
Bacteriophages are composed of a DNA or
RNA core and a protein coat.
Copyright Pearson Prentice Hall
They grew viruses in cultures containing
radioactive isotopes of phosphorus-32 (32P)
and sulfur-35 (35S).
If 35S was found in the bacteria, it would
mean that the viruses’ protein had been
injected into the bacteria.
Bacteriophage with
suffur-35 in protein coat
Phage infects
bacterium
No radioactivity
inside bacterium
If 32P was found in the bacteria, then it was
the DNA that had been injected.
Bacteriophage with
phosphorus-32 in DNA
Phage infects
bacterium
Radioactivity
inside bacterium
Nearly all the radioactivity in the
bacteria was from phosphorus (32P).
Hershey and Chase concluded that the
genetic material of the bacteriophage
was DNA, not protein.
Chargaff's Rules
Erwin Chargaff discovered that:
• The percentages of guanine [G] and cytosine [C]
bases are almost equal in any sample of DNA.
• The percentages of adenine [A] and thymine [T] bases
are almost equal in any sample of DNA.
Copyright Pearson Prentice Hall
DNA
A nucleotide is a monomer of
nucleic acids made up of:
•Deoxyribose – 5-carbon Sugar
•Phosphate Group
•Nitrogenous Base
There are four
kinds of bases
in DNA:
• adenine
• guanine
• cytosine
• thymine
X-Ray Evidence
Rosalind Franklin aimed
an X-ray beam at
concentrated DNA
samples and recorded
the scattering pattern of
the X-rays on film.
This gave her
information about the
structure of DNA.
The Double Helix
James Watson and Francis Crick stole Franklin’s
data and built a model that explained how DNA
carried information and could be copied.
Watson and Crick's model of DNA was a double
helix, in which two strands were wound around
each other.
DNA Double Helix
Watson and Crick discovered that
hydrogen bonds can form only
between certain base pairs—adenine
and thymine, and guanine and
cytosine.
This principle is called base pairing.
DNA Structure Video
18 Things You Should Know
Quiz 8-1
Avery and other scientists discovered that
a. DNA is found in a protein coat.
b. DNA stores and transmits genetic
information from one generation to the next.
c. transformation does not affect bacteria.
d. proteins transmit genetic information from
one generation to the next.
The Hershey-Chase experiment was based on
the fact that
a. DNA has both sulfur and phosphorus in its
structure.
b. protein has both sulfur and phosphorus in
its structure.
c. both DNA and protein have no phosphorus
or sulfur in their structure.
d. DNA has only phosphorus, while protein
has only sulfur in its structure.
DNA is a long molecule made of monomers
called
a. nucleotides.
b. purines.
c. pyrimidines.
d. sugars.
Chargaff's rules state that the number of
guanine nucleotides must equal the number of
a. cytosine nucleotides.
b. adenine nucleotides.
c. thymine nucleotides.
d. thymine plus adenine nucleotides.
In DNA, the following base pairs occur:
a. A with C, and G with T.
b. A with T, and C with G.
c. A with G, and C with T.
d. A with T, and C with T.
DNA and Chromosomes
In prokaryotic cells, DNA is located in the cytoplasm.
Most prokaryotes have a single, circular DNA molecule
containing nearly all of the cell’s genetic information.
Chromosome
E. Coli Bacterium
Bases on the
Chromosomes
Many eukaryotes have 1000 times
the amount of DNA as
prokaryotes.
Eukaryotic DNA is located in the
cell nucleus inside chromosomes.
The number of chromosomes
varies widely from one species to
the next.
Chromosome Structure
•Eukaryotic chromosomes contain DNA and protein, tightly packed together to
form chromatin.
•Chromatin consists of DNA tightly coiled around proteins called histones.
•DNA and histone molecules form nucleosomes.
•Nucleosomes pack together, forming a thick fiber.
Chromosome
Nucleosome
DNA
double
helix
Coils
Supercoils
Histones
The two strands in
the DNA backbone
run in "anti-parallel"
directions to each
other.
That is, one of the
DNA strands is built
in the 5’  3’
direction, while the
complementary
strand is built in the
3’  5’ direction.
DNA Replication
Each strand of the DNA double helix has all the
information needed to reconstruct the other half
by the mechanism of base pairing.
In most prokaryotes, DNA replication begins at a
single point and continues in two directions.
DNA Replication Video
In eukaryotic chromosomes, DNA
replication occurs at hundreds of places.
Replication proceeds in both directions
until each chromosome is completely
copied.
The sites where separation and replication
occur are called replication forks.
Duplicating DNA
Before a cell divides, it duplicates its
DNA during “S” phase in a process
called replication.
Replication ensures that each
resulting cell will have a complete
set of DNA.
During DNA replication, the
DNA molecule separates into
two strands, then produces two
new complementary strands
following the rules of base
pairing. Each strand of the
double helix of DNA serves as a
template for the new strand.
New Strand
Original strand
Nitrogen Bases
Growth
Growth
Replication Fork
Replication Fork
DNA Polymerase
How Replication Occurs
DNA replication is carried out by enzymes that
“unzip” a molecule of DNA.
Hydrogen bonds between base pairs are
broken and the two strands of DNA unwind.
Copyright Pearson Prentice Hall
The principal enzyme involved in DNA
replication is DNA polymerase.
DNA polymerase joins individual free
nucleotides to produce a DNA molecule and
then “proofreads” each new DNA strand.
Quiz 8–2
In prokaryotic cells, DNA is found in the
a. cell membrane.
b. nucleus.
c. ribosome.
d. cytoplasm.
The first step in DNA replication is
a. producing two new strands.
b. producing DNA polymerase.
c. separating the strands.
d. correctly pairing bases.
A DNA molecule separates, and the sequence
GCGAATTCG occurs in one strand. What is the
base sequence on the other strand?
a. GCGAATTCG
b. GATGGCCAG
c. TATCCGGAT
d. CGCTTAAGC
In addition to carrying out the replication of DNA,
the enzyme DNA polymerase also functions to
a. “proofread” the new copies to minimize the
number of mistakes.
b. regulate the time copying occurs in the cell
cycle.
c. unzip the DNA molecule.
d. wrap the new strands onto histone proteins.
The structure that may play a role in regulating
how genes are “read” to make a protein is the
a. coil.
b. histone.
c. chromatin.
d. nucleosome.
RNA and Protein Synthesis
•Genes are coded DNA instructions that
control the production of proteins.
•Genetic messages can be decoded by
copying part of the nucleotide sequence
from DNA into mRNA.
•mRNA contains coded information for
making proteins.
The Structure of RNA
There are three main differences between
RNA and DNA:
•The sugar in RNA is ribose instead
of deoxyribose.
•RNA is generally single-stranded.
•RNA contains uracil in place of
thymine.
Types of RNA
There are three main types of RNA:
• messenger RNA (mRNA)
• ribosomal RNA (rRNA)
• transfer RNA (tRNA)
Transcription & Translation Video
Messenger RNA (mRNA) carries copies of
instructions for assembling amino acids
into proteins.
Ribosome
Ribosomal RNA
Ribosomes are made up of proteins and
ribosomal RNA (rRNA).
Amino acid
Transfer RNA
During protein construction, transfer RNA
(tRNA) transfers each amino acid to the
ribosome.
DNA
molecule
DNA strand
(template)
5
3
TRANSCRIPTION
mRNA
5
3
Codon
TRANSLATION
Protein
Amino acid
Transcription
DNA is copied in the form of RNA
This first process is called transcription.
The process begins at a section of DNA called
a promoter.
RNA Editing
Some DNA within a
gene is not needed
to produce a protein.
These areas are
called introns.
The DNA sequences
that code for
proteins are called
exons.
The introns are
cut out of RNA
molecules.
Exon Intron
DNA
Pre-mRNA
The exons are
the spliced
together to form
mRNA.
mRNA
Cap
Tail
The Genetic Code
The genetic code is the
“language” of mRNA
instructions.
The code is written using four
“letters”
(the bases: A, U, C, and G).
A codon consists of three consecutive
nucleotides on mRNA that specify a
particular amino acid.
Translation
Translation is the decoding of an mRNA
message into a polypeptide chain
(protein).
Translation takes place on ribosomes.
During translation, the cell uses information
from messenger RNA to produce proteins.
Nucleus
mRNA
The ribosome binds new tRNA molecules
and amino acids as it moves along the
mRNA.
Phenylalanine
Methionine
Ribosome
mRNA
Start codon
tRNA
Lysine
Protein Synthesis
The process continues until the
ribosome reaches a stop codon.
Polypeptide
Ribosome
tRNA
mRNA
Codon
Codon Codon
DNA
Single strand of DNA
Codon Codon Codon
mRNA
mRNA
Alanine Arginine Leucine
Protein
Amino acids within
a polypeptide
Quiz 8-3
The role of a master plan in a building is similar
to the role of which molecule?
a. DNA
b. messenger RNA
c. transfer RNA
d. ribosomal RNA
A base that is present in RNA but NOT in DNA is
a. thymine.
b. cytosine.
c. uracil.
d. adenine.
The nucleic acid responsible for bringing
individual amino acids to the ribosome is
a. messenger RNA.
b. DNA.
c. transfer RNA.
d. ribosomal RNA.
A region of a DNA molecule that indicates to an
enzyme where to bind to make RNA is the
a. intron.
b. exon.
c. codon.
d. promoter.
A codon typically carries sufficient information to
specify a(an)
a. single base pair in RNA.
b. single amino acid.
c. entire protein.
d. single base pair in DNA.
Mutations
Mutations are changes in the genetic
material.
Kinds of Mutations
•Gene Mutations
• Mutations that produce
changes in a single gene.
•Chromosomal Mutations
• Mutations that produce
changes in whole
chromosomes.
Gene Mutations
Gene mutations involving a change
in one or a few nucleotides are
known as point mutations because
they occur at a single point in the
DNA sequence.
Point mutations include
substitutions, insertions, and
deletions.
DNA Mutations Video
Substitutions
usually affect
no more than
a single
amino acid.
The effects of insertions or
deletions are more dramatic.
The addition or deletion of a
nucleotide causes a shift in the
grouping of codons.
Changes like these are called
frameshift mutations.
In an insertion,
an extra base is
inserted into a
base sequence.
In a deletion, the loss of a single
base is deleted and the reading
frame is shifted.
Chromosomal Mutations
•Chromosomal mutations
involve changes in the number
or structure of chromosomes.
•Chromosomal mutations
include deletions, duplications,
inversions, and translocations.
Deletions involve the loss of all or
part of a chromosome.
Duplications produce extra copies
of parts of a chromosome.
Inversions reverse the direction of
parts of chromosomes.
Translocations occurs when part of
one chromosome breaks off and
attaches to another.
Significance of Mutations
•Many mutations have little or no
effect on gene expression.
•Some mutations are the cause of
genetic disorders.
•Polyploidy is the condition in which
an organism has extra sets of
chromosomes.
Polyploidy
Down’s Syndrome
Turner’s Syndrome
Quiz 8-4
A mutation in which all or part of a chromosome
is lost is called a(an)
a. deletion.
b. duplication.
c. inversion.
d. point mutation.
A mutation that affects every amino acid
following an insertion or deletion is called a(an)
a. point mutation.
b. frameshift mutation.
c. chromosomal mutation.
d. inversion.
A mutation in which a segment of a chromosome
is repeated is called a(an)
a. deletion.
b. inversion.
c. duplication.
d. point mutation.
The type of point mutation that usually affects
only a single amino acid is called
a. a deletion.
b. a substitution.
c. an insertion.
d. a frameshift mutation.
When two different chromosomes exchange
some of their material, the mutation is called
a(an)
a. inversion.
b. deletion.
c. substitution.
d. translocation.
• Gene Regulation: An Example
• E. coli provides an example of how gene
expression can be regulated.
• An operon is a group of genes that
operate together.
• In E. coli, these genes must be turned on
so the bacterium can use lactose as
food.
• Therefore, they are called the lac operon.
How are lac genes turned
off and on?
–The lac genes are
turned off by
repressors and turned
on by the presence of
lactose.
On one side of the operon's three genes are
two regulatory regions.
• In the promoter (P) region, RNA
polymerase binds and then begins
transcription.
The other region is the operator (O).
When the lac repressor binds to the O
region, transcription is not possible.
• When lactose is added, sugar binds to the
repressor proteins.
Gene Regulation: An
changes shape
and
Example
• The repressor protein
falls off the operator and transcription is
made possible.
• Many genes are regulated by
repressor proteins.
• Some genes use proteins that
speed transcription.
• Sometimes regulation occurs at
the level of protein synthesis.
• trp Operon
• lac vs. trp Operons
How are most eukaryotic
genes controlled?
• Eukaryotic Gene Regulation
–Operons are generally not found in
eukaryotes.
–Most eukaryotic genes are
controlled individually and have
regulatory sequences that are much
more complex than those of the lac
operon.
• Many eukaryotic genes have a sequence
called the TATA box.
Upstream
enhancer
TATA
box
Promoter
sequences
Introns
Exons
Direction of transcription
• The TATA box seems to help position
RNA polymerase.
Upstream
enhancer
TATA
box
Promoter
sequences
Introns
Exons
Direction of transcription
• Eukaryotic promoters are usually found
just before the TATA box, and consist of
short DNA sequences.
Upstream
enhancer
TATA
box
Promoter
sequences
Introns
Exons
Direction of transcription
• Genes are regulated in a variety of ways
by enhancer sequences.
• Many proteins can bind to different
enhancer sequences.
• Some DNA-binding proteins enhance
transcription by:
• opening up tightly packed chromatin
• helping to attract RNA polymerase
• blocking access to genes.
• Development and Differentiation
• As cells grow and divide, they
undergo differentiation, meaning
they become specialized in
structure and function.
• Hox genes control the
differentiation of cells and tissues
in the embryo.
• Careful control of expression in
hox genes is essential for
normal development.
• All hox genes are descended
from the genes of common
ancestors.
• Hox Genes
Fruit fly chromosome Mouse chromosomes
Fruit fly embryo
Mouse embryo
Adult fruit fly
Adult mouse
Quiz 8-5
–Which sequence shows the typical organization
of a single gene site on a DNA strand?
a. start codon, regulatory site, promoter, stop
codon
b. regulatory site, promoter, start codon, stop
codon
c. start codon, promoter, regulatory site, stop
codon
d. promoter, regulatory site, start codon, stop
codon
– A group of genes that operates together is
a(an)
a. promoter.
b. operon.
c. operator.
d. intron.
– Repressors function to
a. turn genes off.
b. produce lactose.
c. turn genes on.
d. slow cell division.
–Which of the following is unique to the
regulation of eukaryotic genes?
a. promoter sequences
b. TATA box
c. different start codons
d. regulatory proteins
–Organs and tissues that develop in various
parts of embryos are controlled by
a. regulation sites.
b. RNA polymerase.
c. hox genes.
d. DNA polymerase.