DNA caries genetic information of organisms. This presentation covers the discovery of DNA as genetic material, structure of DNA, Nucleotides and nucleosides. Watson and crick DNA model.
2. Which molecule can be called as Genetic Material?
It must have 4 crucial characteristics
1. Replication
2. Storage of information
3. Expression of information
4. Variation by Mutation
3. Protein as Genetic Material
• Early 19th century both protein and nucleic acid were major candidates
for the role of genetic material
• Until 1944 observations favoured protein as genetic material
For two major reasons:
I. Proteins are diverse and abundant in the cell
II. Much more known about the chemistry of Protein than Nucleic Acid
4. DNA Study
• DNA was 1st studied in 1869 by a Swiss Chemist Friedrick Miescher
• He isolated cell nuclei and derived an acidic substance (now known to
contain DNA), that he called nuclein
• In 1910 Levene observed that DNA contain approximately equal amount of 4
similar molecules called Nucleotides
• In 1940 Erwin Chargaff showed that Levene’s proposal was incorrect
• when he Studied that most organisms do not contain precisely equal
proportions of the four nucleotides
5. DNA as Genetic Material
• In 1944 Oswald Avery, Colin MacLeod, and Maclyn McCarty
studied transforming principle” in bacteria
• The first direct experimental proof that DNA, and not protein, is the
biomolecule responsible for heredity
• Frederick Griffith, a medical officer
• He performed experiments with several different strains of the
bacterium Streptococcus pneumoniae
6.
7. Griffith concluded that the heatkilled IIIS bacteria somehow converted live avirulent IIR cells into
virulent IIIS cells
(Transformation)
8. Transformation Early Studies
After Frederick Griffith many biologists studied Transformation
Dawson and his co-workers showed that transformation could occur
in vitro
Therefore Mice was not necessary
9. The Avery, MacLeod, and McCarty Experiment
• In 1944, after 10 years of work, Avery, MacLeod, and McCarty
published their results
• They reported that they had obtained the transforming principle in a
purified state and it was DNA
10.
11. The Hershey–Chase Experiment
2nd Evidence (1952)
They studied bacterium E.coli and Bacteriophage T2
The virus consists of protein coat surrounding a core of DNA
15. RNA as Genetic Material
• In Some Viruses RNA core is present rather than DNA
• So in these Viruses RNA serves as genetic material
16. Understanding DNA Structure
• DNA is Nucleic Acid
• Building blocks of Nucleic Acid are Nucleotides
Nucleotide
Nitrogenous Base
Pentose Sugar
Phosphate Group
19. Understanding Nucleotide Structure
Nucleoside: If a molecule is composed of a purine or pyrimidine base
and a ribose or deoxyribose sugar, the chemical unit is called a
nucleoside
Nucleotide: If a phosphate group is added to the nucleoside, the
molecule is now called a nucleotide
20. Names of the Nucleosides and Nucleotides of RNA and
DNA.
21. Types of Nucleosides
• Nucleotides are also define by the term nucleoside nonophosphate
(NMP)
• NDP nucleoside diphosphate
• NTP nucleoside triphosphate
Examp:
adenosine triphosphate (ATP) and guanosine triphosphate (GTP)
22. Structures of nucleoside diphosphates and triphosphates. Deoxythymidine diphosphate
and adenosine triphosphate
23. Polynucleotides
The 2 mononucleotides are linked with a phosphate group & two
sugars by the help of Phosphodiester bond
Short chains consisting of up to approximately 30 nucleotides linked
together are called oligonucleotides
Chains consisting of large number of nucleotides are called
Polynucleotides
24. Structure of DNA
• From 1940 to 1953, many scientists were interested in solving the
structure of DNA
• In 1953, James Watson and Francis Crick proposed that the structure
of DNA is in the form of a double helix
25. The Watson–Crick Model
Major Features of Model
Two long polynucleotide chains are coiled around a central axis,
forming a right-handed double helix
Both the chains are antiparallel, their C-5´to-C-3´ orientations run in
opposite directions
Nitrogenous bases of opposite chains are paired as a result of
hydrogen bonding
In DNA, only A pairs with T and G pairs with C occur
The double helix has a diameter of 20 Å (2.0 nm
26.
27. Differences b/w DNA and RNA
DNA
• Double Stranded
• Pentose Sugar Deoxyribose
• Thymine is present
• Genetic material of all the
individuals except Viruses
RNA
• Single Stranded
• Oxyribose sugar is present
• Uracil is present
• Genetic material of some viruses
28. Types of RNA
rRNA:
Constitutes about 80 percent of all RNA in an E. coli cell
Important structural components of ribosomes, which function as
nonspecific workbenches where proteins are synthesized
mRNA:
Carries genetic information from the DNA to the ribosome
About 5 percent of RNA is mRNA in E. coli
tRNA:
Carries amino acids to the ribosome during translation
29. Analytical Techniques Which can be Used for
Analysis of DNA and RNA
Absorption of Ultraviolet Lights:
Nucleic acids absorb ultraviolet (UV) light most strongly at
wavelengths of 254 to 260 nm
In aqueous solution, peak absorption by DNA and RNA occurs at 260
nm
Thus, UV light can be used in the localization, isolation, and
characterization of molecules that contain nitrogenous bases
30. Denaturation and Renaturation of Nucleic Acids
Heat or other stresses can cause a complex molecule like DNA to denature
DNA lose its function due to the unfolding of its three-dimensional
structure
The hydrogen bonds of the duplex (double-stranded) structure break
The helix unwinds, and the strands separate
The viscosity of the DNA decreases
UV absorption Increases
If DNA that has been denatured thermally is cooled slowly, random
collisions between complementary strands will result in their reassociation
H bonds will reform