RNA HypothesisRNA Hypothesis

1

Lecture no. 2

Life on Earth Probably Began with RNALife on Earth Probably Began with RNA

2

Lecture no. 2

• 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 the RNA world hypothesis.

The RNA WorldThe 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.

3

RNA is the only RNA is the only currently used currently used macromoleculemacromoleculethat is both a carrier of that is both a carrier of genetic information andgenetic information andan enzyme.an enzyme.

Four more-recent lines of evidence have added much breadth and depth to the plausibility of the

proposal

4

Lecture no. 2

• 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.

5

Possible remnants of the RNA Possible remnants of the RNA WorldWorld

Self-splicing introns

Rnase P- ribozyme that cleaves tRNA

precursors

Self-cleaving viral RNAs

Peptidyl transferase in the ribosome

Nucleotides (ribo) involved in metabolism, Signalling..etc

2 1

3 4 5

Lecture no. 2

Biochemical Unity Underlies Biological DiversityBiochemical 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 .

6

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.

Lecture no. 2

The Modern Era: The Impact of Molecular The Modern Era: The Impact of Molecular BiologyBiology

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.

7

Lecture no. 2

Molecular Biology TimelineMolecular 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.

8

Gregor Mendel’s (Gregor Mendel’s (18651865) Three Laws of ) Three Laws of InheritanceInheritance

Friedrich Miescher (Friedrich Miescher (18691869) identified DNA & called it ) identified DNA & called it nucleinnuclein

Lecture no. 2

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.

9

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.

10

Continue…

3) The Law of Dominance: An organism with alternate forms of a gene will express the form that is dominant.

11

12

Thomas H. Morgan (Thomas H. Morgan (19101910) discovers genes on ) discovers genes on chromosomeschromosomes

Beadle & TatumBeadle & Tatum ( (19411941) ) One gene-one One gene-one enzymeenzyme

Lecture no. 2

1313

Avery, Mcleod & McCarty ((19441944) ) DNA is genetic material

Lecture no. 2

141414

Watson, Crick, Franklin, Wilkins((19531953) ) Structure of DNA

Edwin Chargaff ((19501950) ) find C complements G and A complements T

Lecture no. 2

15151515

Brenner, Jacob & Meseleson ((19611961) ) Discovery of mRNA

Lecture no. 2

16

Central Dogma; Crick & Gamov

1956

Recombinant DNA made in vitro; P. Berg

1972

DNA cloned on a plasmid; H. Boyer & S. Cohen

1973

Discovery of reverse transcriptase; H. Temin

1973

Finished unraveling the code; Nirenberg & Khorana

1966

Lecture no. 2

Rapid DNA sequencing; F. Sanger & W. Gilbert

1977

Discovery of split genes; Sharp, Roberts et al.

1977

Discovery of ribozymes; T. Cech & S. Altman

1982

Creation of PCR; K. Mullis et al.

1986

Lecture no. 2

Molecular Biology 2000- PresentMolecular 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.

18

The genome sequence of Drosophila melanogaster.

Science. 287:2185-95. 2000.

Lecture no. 2

Continue…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).

19

http://www.ornl.gov/sci/techresources/Human_Genome/home.shtml

Lecture no. 2

20

Continue…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

20

Lecture no. 2

Nobel Prize Laureates in Nobel Prize Laureates in Physiology or Medicine from 2006 Physiology or Medicine from 2006

to present to present

2006 - ANDREW Z. FIRE, and CRAIG C. MELLO for their discovery of RNA interference - gene silencing by double-stranded 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

21

Lecture no. 2

We are in the midst of a "Golden EraGolden Era" of biology,and the revolution is mostly about treating biology as an information science, and not only as specific biochemical technologies

22

Lecture no. 2

23

http://www.dnai.org/timeline/index.html

Lecture no. 2

24

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.

Lecture no. 2