Download Molecular Biology BCH 361

Lecture no. 2
RNA Hypothesis
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Lecture no. 2
Life on Earth Probably Began with RNA
• Living systems have definable characteristics and requirements. Catalysis
and biological information are particularly important requirements for
any life form.
• The first molecule that fulfilled the requirements of catalysis and
biological information may have been a self-replicating RNA, according to
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the RNA world hypothesis.
The RNA World
• The RNA world hypothesis was first
proposed as a stage in evolution. The
hypothesis describes a living system
(or set of living systems) based on RNA.
• In this system, a variety of RNA
enzymes could catalyze all of the
reactions needed to synthesize the
molecules required for life from
simpler molecules available in the
environment.
• The “RNA organism,” out of equilibrium
with its surroundings, would have to be
defined by a boundary.
RNA is the only currently
used macromolecule
that is both a carrier of
genetic information and
an enzyme.
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Lecture no. 2
Four more-recent lines of evidence have added much
breadth and depth to the plausibility of the proposal
• The first was the discovery (early 1980s) of catalytic RNAs, or
ribozymes- enzymes that are made of RNA instead of protein.
• The second and third discoveries that in ribosomes, the large
ribonucleoprotein complexes that translate RNA into protein, the
RNA is the active component with the capacity to catalyze
protein synthesis.
• Another supportive research demonstrated that artificially
constructed RNA molecules can catalyze almost any imaginable
reaction needed in a living system.
• Finally, and most recently, RNA sequences capable of simple
forms of self-replication have been discovered.
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Lecture no. 2
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Rnase P- ribozyme
that cleaves tRNA
precursors
Self-splicing
introns
Possible remnants of the RNA
World
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Self-cleaving viral
RNAs
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Peptidyl
transferase in the
ribosome
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Nucleotides (ribo)
involved in
metabolism,
Signalling..etc
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Lecture no. 2
Biochemical Unity Underlies Biological Diversity
 LUCA, the last universal common ancestor of all life now present on
earth, can be studies by identifying the common characteristics of living
organisms and defining the minimal complement of genes necessary to
support a living cell.
 On the basis of their biochemical characteristics, the diverse organisms
of the modern world can be divided into three fundamental groups
called domains: Eukarya (eukaryotes), Bacteria, and Archaea .
The universal tree of life. A
current version of the tree is
shown, with branches for the
three main groups of known
organisms: bacteria, archaea, and
eukaryotes.
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Lecture no. 2
The Modern Era: The Impact of Molecular
Biology
 The molecular biology revolution in the middle of the Twentieth
Century provided the means to study the role of genes in
development.
 The key technological advance for the study of gene control of
development was the ability to isolate and clone genes.
 The patterns of expression of individual genes could be
followed by tracing the products of their expression.
 Molecular biology obtained a very powerful tool to facilitate the
study of nucleic acids when the polymerase chain reaction
(PCR) was developed, which amplify specific sequences of DNA
many-fold from a minute amount of starting material.
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Lecture no. 2
Molecular Biology Timeline
 The term molecular biology first appeared in mid 1800s in a report
prepared for the Rockefeller Foundation by Warren Weaver.
 Two studies performed in the 1860s provided the foundation for
molecular biology.
Gregor Mendel’s (1865) Three Laws of Inheritance
Friedrich Miescher (1869) identified DNA & called it nuclein
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Mendel's Laws of Heredity are usually stated as:
1) The Law of Segregation:
Each inherited trait is
defined by a gene pair.
Parental genes are randomly
separated to the sex cells so
that sex cells contain only
one gene of the pair.
Offspring therefore inherit
one genetic allele from each
parent when sex cells unite
in fertilization.
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Continue…
2) The Law of Independent
Assortment:
Genes
for
different traits are sorted
separately from one another
so that the inheritance of
one trait is not dependent on
the inheritance of another.
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Continue…
3) The Law of Dominance: An
organism with alternate forms of
a gene will express the form that
is dominant.
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Thomas H. Morgan (1910) discovers genes on chromosomes
Beadle & Tatum (1941) One gene-one enzyme
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Avery, Mcleod & McCarty (1944) DNA is genetic material
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Edwin Chargaff (1950) find C complements G and A
complements T
Watson, Crick, Franklin, Wilkins(1953) Structure of DNA
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Brenner, Jacob & Meseleson (1961) Discovery of mRNA
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1956
Central Dogma; Crick & Gamov
1966
Finished unraveling the code; Nirenberg & Khorana
1972
Recombinant DNA made in vitro; P. Berg
1973
1973
DNA cloned on a plasmid; H. Boyer & S. Cohen
Discovery of reverse transcriptase; H. Temin
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Lecture no. 2
1977
1977
1982
1986
Rapid DNA sequencing; F. Sanger & W. Gilbert
Discovery of split genes; Sharp, Roberts et al.
Discovery of ribozymes; T. Cech & S. Altman
Creation of PCR; K. Mullis et al.
Lecture no. 2
Molecular Biology 2000- Present
2000- The fly Drosophila melanogaster is one of
the most intensively studied organisms in
biology and serves as a model system for the
investigation of many developmental and
cellular
processes
common
to
higher
eukaryotes, including humans. Scientists have
determined the nucleotide sequence of nearly
all
of
the
approximately
120-megabase
euchromatic portion of the Drosophila genome
using a whole-genome shotgun sequencing
strategy.
The genome sequence of
Drosophila melanogaster.
Science. 287:2185-95.
2000.
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Lecture no. 2
Continue…
2001- The Human Genome Project (HGP) began in October 1990 with
a primary goal of determining the sequence of chemical base pairs
which make up DNA, and of identifying and mapping the approximately
20,000–25,000 genes of the human genome from both a physical and
functional standpoint.
Due to widespread international cooperation and advances in the field
of genomics (especially in sequence analysis), as well as major
advances in computing technology, a 'rough draft' of the genome was
finished in 2000 (announced jointly by U.S. President Bill Clinton and
the British Prime Minister Tony Blair on June 26, 2000).
http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml
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Lecture no. 2
Continue…
2003- The Human Genome Project (HGP). Mouse genome
is sequenced.
2004- Rat genome sequenced.
2010- Understanding the function of all genes within their
cellular, organismal and evolutionary context of
Arabidopsis thaliana
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Nobel Prize Laureates in
Physiology or Medicine from 2006
to present
Lecture no. 2
 2006 - ANDREW Z. FIRE, and CRAIG C. MELLO for their
discovery of RNA interference - gene silencing by doublestranded RNA.
 2007- MARIO R. CAPECCHI, SIR MARTIN J. EVANS, and
OLIVER SMITHIES for their discoveries of principles for
introducing specific gene modifications in mice by the use of
embryonic stem cells.
 2009- ELIZABETH H. BLACKBURN, CAROL W. GREIDER, and
JACK W. SZOSTAK for the discovery of how chromosomes are
protected by telomeres and the enzyme telomerase
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Lecture no. 2

We are in the midst of a "Golden Era" of biology,
and the revolution is mostly about treating biology
as an information science, and not only as specific
biochemical technologies
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http://www.dnai.org/timeline/index.html
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Homework:
Can you identify the most
important terms that you have
gone through a lecture today
and find a scientific definition
for it.
Remember this will be your next
lecture, so be prepared.
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