Introduction to Molecular
Genetics
Rowan University
Spring Semester
Mrs. Patricia Sidelsky
2008
Regulatory RNAs
http://www.dnalc.org/ddnalc/dna_today/episodes/5/episode5.html
Molecular Genetics
 Molecular genetics and molecular
biology are almost synonomous terms
 A “ hybrid” science
 The change in the understanding of
life has led to a revolution in the field
of Biology
Molecular Genetics
 The result of an amalgam of a variety of
physical and biological sciences
 Genetics, microbiology, biochemistry,
physical chemistry, and physics
 Driven by the need to understand the
underlying principles of life and the
reactions of life
Max Delbruck
Ilustrates the blend in scientific disciplines
 German immigrant
 Originally trained in physical chemistry
and theoretical physics
 Converted to molecular genetics
 Collaborated with Salvador Luria on the
characterization and genetics of
bacteriophages
Molecular Genetics - Origins
 Thomas Hunt Morgan- Columbia University
 The physical nature of the gene
 A discovery in 1910 changed the course of
genetics
 Developed experimental model for the study
of modern genetics- the fruit fly – Drosophila
melanogaster
 The white eyed male mutant appeared in a
culture of flies in the fly room and this was
the beginning of a search for mutants
White and Wild type
 Easy to cultivate
 Prolific progeny
 Small and
inexpensive
 Large polytene
chromosomes
 Diploid number 8
 Many mutations
Hermann Joseph Muller
 X rays cause
mutations
 Produced a variety
of flies with
phenotypes such
asvestigial
Alfred Sturdevant produced the first
genetic map from linkage experiments
 Genes were related
to position on the
chromosome map
 Mutants were
related to
differences in the
appearance of the
polytene
chromosomes due
to staining
DNA as Genetic Material
Transformation
 Griffith in 1928 observed the change of
non-virulent organisms into virulent
ones as a result of “transformation”
 MacLeod and McCarty in 1944 showed that
the transforming principle was DNA
Figure 11.1
Transforming principle
Avery, McLeod, and McCarty
Proof of the Transforming Principle
 Chemical analysis of sample containing the
transforming principle showed that the major
component was a deoxyribose -containing nucleic
acid
 Physical measurements show that the sample
contained a highly viscous substance having the
properties of DNA
 Incubatyion with trypsin or chymotrypsin, enzymes
that catalzye protein hydrolysis or with ribonuclease(
RNase), an enzyme that catalyzes RNA hydrolysis did
not affect the transforming principle
Incubation with DNase, an enzyme that catalyzes
DNA hydrolysis inactivates the transforming principle
Transfection
DNA as Genetic Material
( of viruses)
 Hershey and Chase, 1952
 used bacteriophage T2 infection as model
 DNA labeled with 32P;protein coat labeled with
 Only DNA entered cell but both new DNA and
35S
protein coats synthesized and incorporated into
new viruses indicating that DNA had the genetic
information for synthesis of both of these viral
components
T2 phage
Chargaff’s Rule
 Analyzed DNA from a variety of sources
and improved both the separation and
quantitation of the DNA bases
 [C] = [G] and [A] = [T]
 Today this is applied to the G=C or G.C
pairs. Scientists describe the G+C
content in organisms
G+C
 Now used as a means of classifying
bacteria
 G+C content varies in Gram Positive
Bacteria
 G+C content ranges from .27 in
Clostridium to .76 for Sarcina
 Most Eukaryotes have a value close to
50%
G+C content
 G+C content = [G] +[C] / all bases in
DNA
The Race for the Double Helix
 Rosalind Franklin and
Maurice Wilkins at
Kings College
 Studied the A and B
forms of DNA
 Rosalind’s famous xray crystallography
picture of the B form
held the secret, but
she didn’t realize its
significance
Rosalind Franklin
 Technically and
scientifically a
gifted scientist
 Focused on the A
form of DNA and
missed the double
helix
The Race for the Double Helix
 Watson and Crick
formed an unlikely
partnership
 A 22 year old PhD and
a thirty + PhD “want
to be” embarked on a
model making venture
at Cambridge
 Used the research of
other scientists to
determine the nature
of the double helix
Nucleic Acid Composition
DNA and RNA

a.
b.
c.
d.
DNA – Basic Molecules
Purines – adenine and guanine
Pyrmidines – cytosine and thymine
Sugar – Deoxyribose
Phosphate phosphate group
http://www.dnai.org/index.htm - DNA background
Nucleotides
 Sugar
 Phosphate
 Base
 Adenine and guanine are
purines
 Thymine and Cytosine are
pyrimidines
Deoxyribose in DNA
Double Helix
 Two polynucleotide strands joined by
phosphodiester bonds( backbone)
 Complementary base pairing in the center of the
molecule
A= T and C
G – base pairing. Two
hydrogen bonds between A and T and three
hydrogen bonds between C and G.
A purine is bonded to a complementary pyrimidine
 Bases are attached to the 1’ C in the sugar by a
glycosidic linkage
 At opposite ends of the strand – one strand has
the 3’hydroxyl, the other the 5’ hydroxyl of the
sugar molecule
DNA
Structure
http://www.johnkyrk.com/DNAanatomy.html - DNA structure
Double helix( continued)
 The double helix is right handed – the




chains turn counter-clockwise.
As the strand turn around each other they
form a major and minor groove.
The is a distance of .34nm between each
base
The distance between two major grooves
is 3.4nm or 10 bases
The diameter of the strand is 2nm
Complementary Base Pairing
 Adenine pairs with
Thymine
 Cytosine pairs with
Guanine
The end view of DNA
 This view shows the
double helix and the
outer backbone with
the bases in the
center.
 An AT base pair is
highlighted in white
Double helix and anti-parallel
 DNA is a directional molecule
 The complementary strands run in
opposite directions
 One strand runs 3’-5’
 The other strand runs 5’ to 3’
( the end of the 5’ has the phosphates
attached, while the 3’ end has a
hydroxyl exposed)
Prokaryote DNA
 Tightly coiled
 Coiling maintained by molecules similar to the




coiling in eukaryotes
Circular ds molecule
Borrelia burgdoferi ( Lyme Disease )has a
linear chromosome
Other bacteria have multiple chromosomes
Agrobacterium tumefaciens ( Produces Crown
Gall disease in plants) has both circular and
linear
Prokaryote chromosomes
Circular DNA
Mitochondria
 Mitochondrial DNA(




mt DNA)
16,500 base pairs
37 genes
24 encode RNA
Defects lead to
diseases that are
related to energy
Chloroplast DNA
 Chloroplast DNA( cp DNA) is larger than
mitochondrial DNA
 195,000 bp
 Genes for photosynthesis
 Cp ribosomal RNAs
Heavy and Light N
Meselson and Stahl experiment
 In the first
generation of E. coli,
all the DNA was
heavy
 After one
generation, the DNA
was half heavy and
half light
DNA Replication –Semi
Conservative
DNA Replication
 DNA opens at an Ori ( origin of
replication)
 Combination of many enzymes
coordinate the replicative process
 Template strand used to make the copy
 DNA polymerases read the template
and match the complementary base
Degradation of DNA
 Endonucleases cleave DNA and RNA, by
cutting between individual bonds
 Some endonucleases cleave one
strand some cleave both strands at
a specific point or sequence(
restriction nucleasess)
The Flow of Genetic Information
 from one generation to the next
 DNA stores genetic information
 Information is duplicated by replication and
is passed on to next generation
The Flow of Genetic Information
within a single cell
 Process called gene expression
 DNA divided into genes
 transcription yields a ribonucleic acid (RNA) copy
of specific genes
 translation uses information in messenger RNA
(mRNA) to synthesize a polypeptide
 Also involves activities of transfer RNA (tRNA) and
ribosomal RNA (rRNA)
Flow of Genetic Information in
Cells
Nucleic Acid Structure
Ribonucleic Acid (RNA)
 Polymer of nucleotides
 Contains the bases adenine,
guanine, cytosine and uracil
 Sugar is ribose
 Most RNA molecules are single
stranded
RNA
Types of RNA
a. Messenger
b. Transfer
c. Ribosomal
d. micro RNAs ( regulatory RNAs)
Messenger RNA
16s rRNA
Ribosomal RNA
tRNA
RNA viruses
 Reoviruses
 Retroviruses
 Enteroviruses
Genomics of RNA viruses
Genomes
 - + RNA
 - RNA
 segmented RNA
 Ds RNA
Polio virus
Polio Virus- + ss RNA virus
Viroids
 Infectious agents that causes disease
in higher plants
 Small circular loops of RNA
 The viroid RNA is infectious and its is
not surrounded by a capsid
 Viroids RNA replicates autonomously
Viroids
 PSTV
 Potato SpindleTuber Viroid
Proteins are polymers
 Proteins are polymers of amino
acids. They are molecules with diverse
structures and functions.
 Polymers are made up of units called
monomers
 The monomers in proteins are the 20
amino acids
Protein Facts
 Proteins: Polymers of Amino Acids
 Proteins are polymers of amino acids.
They are molecules with diverse structures
and functions.
 Each different type of protein has a
characteristic amino acid composition and
order.
 Proteins range in size from a few amino acids
to thousands of them.
 Folding is crucial to the function of a protein
and is influenced largely by the sequence of
amino acids.
Proteins: Polymers of Amino
Acids
 Each different type of protein has a
characteristic amino acid composition
and order.
 Proteins range in size from a few amino
acids to thousands of them.
 Folding is crucial to the function of a
protein and is influenced largely by the
sequence of amino acids.
Proteins are complex molecules
 They have levels of structure
 Structure based upon the sequence of
the amino acids
Polar side chains
Non Polar Hydrophobic side
chains
Electrical charged hydrophilic
Function of Proteins - continued
 Enzymes – Biological catalysts
 Transport of small molecules – Albumin and




haptoglobin
Transport of oxygen – hemoglobin and
myoglobin
Membrane proteins – to assist in support
Channels in membranes – to allow the
passage of molecules or ions
Electron carriers in electron transport in the
production of ATP
Functions( continued)i





Clotting proteins
Immune proteins to fight infectious agents
Histones – DNA binding proteins
Toxins to repel or kill other organisms
Bacteriocins – molecules produced by
bacteria against bacteria
Functions of proteins
 Hormones – Growth hormone
 Receptors – to Receive information so that
cell can communicate with other cells
 Neurotransmitters – messenger molecules –
to send information between neurons
 Cytoskeleton – actin, myosin, and collagen –
the structure of connective tissue and
muscles
 Antibodies – Immunoglobulins to fight
disease
Four levels of Protein Structure
 There are four levels of protein structure:
primary, secondary, tertiary, and quaternary.
 The precise sequence of amino acids is called
its primary structure.
 The peptide backbone consists of repeating
units of atoms: N—C—C—N—C—C.
 Enormous numbers of different proteins are
possible.
The causes of Tertiary structure