DNA : GENETIC MATERIAL

What is a the important characters of Living Organism ?

• Reproduction and Metabolism is the symbol of Live

• Reproduction is the biological process by which new individual organisms are produced. Reproduction is a fundamental feature of all known life; each individual organism exists as the result of reproduction.

• Metabolism is the set of chemical reactions that occur in living organisms in order to maintain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments.

Chromosome determine the reproduction &

metabolism• 1865 Mendel : Gene determine the inheritance of plant

characters• 1882 Walther Flemming, investigating the structure of

cells, discovers a substance he calls chromatin. He notices that, during cell division, this substance separates into threadlike strings, which become known as chromosomes.

• 1902 William Sutton & Boveri : Mendel’s theory of genes is in accordance to chromosomes inheritance

• Conclusion: Genes reside on Chromosomes and take an important role in reproduction

• Eukaryote chromosomes consist of DNA and protein

• Which elements of chromosome take a role as genetic materials?

• What is the genetic material ?• DNA or Protein?

The Possibility of Proteinas genetic material ?

• It is easier to accept the protein than DNA as genetic materials, because the protein (enzyme) involve in metabolism process

• 1908 Archibald Garrod proposed that some human diseases (ex. alkaptonuria) are due to "inborn errors of metabolism" that result from the lack of a specific enzyme.

• 1941 Beadle and Tatum proved that mutation caused the change in metabolisms catalytic enzymes

The Possibility of DNA as genetic material• DNA is a specific chemical of chromosome, according

to cell staining technique• 1928 Fred Griffith discovered that some component of

heat-killed virulent bacteria can "transform" a non-virulent strain to become virulent.

• 1944 Avery, MacLeod and McCarthy showed that Griffith’s transforming agent is DNA. The results did not convinced everyone.

• 1952 Alfred Hershey and Martha Chase showed in bacteriophage labeling experiments that DNA is the molecule that mediates heredity,. The results really convinced everyone.

Griffith Experiment : Discovery of Transformation• Fred Griffith was a British medical officer, who

intended to develop vaccine of Pneumonia (human disease at Post World War I)

• It was used two strains of Streptococcus pneumonia,S strain →virulent and R strain →non-virulent

• It was discovered that some component of heat-killed virulent bacteria (S) can "transform" a non-virulent strain to become virulent (R ).

• It was concluded that the component (debris) of killed bacteria can enter into living bacteria cell, and transform the characters of recipient bacteria.

• This phenomenon is now called bacterial transformation.

Griffith Experiment : Discovery of Transformation

Living S

Living R

Heat killed S

Mixed of killed S+

and living R

Infected with bacteria isolated from dead mouse

Growing S

virulent

Non-virulent

Non-virulent

DNA is the agent of Griffith’s bacterial

transformation• 1944 Avery, MacLeod and McCarthy showed that

Griffith’s bacterial transformation agent is DNA• The experiment consisted of

– Extraction of chemical components of virulent strain of S. pneumonia (S strain) : DNA, RNA, protein and polysaccharide.

– Each component then was added to the culture of non-virulent strain (R strain), and was observed the appearance of virulent S strain from those cultures

– The result : the S strain appeared only in the culture of R strain that was added with DNA of S strain (it showed that only DNA could transform R strain to become S strain)

Avery, MacLeod and McCarthy Experiment

DNA RNA Protein Polysaccharide

S

R R R R

R R R RS

Bacteriophage illuminated the hereditary material

• 1943 Max Delbruck and Salvador Luriadiscovered bacteriophage (a type of virus that attacks bacteria)

• Phages have very simple structure, DNA and protein, making them ideal to resolve the nature of the hereditary material.

• Bacteriophages infect a cell by injecting DNA into the host cell, and after 25 minutes the host cell bursts, releasing hundreds of new bacteriophage .

The DNA (not protein) is the molecule that mediates heredity

in bacteriophage• 1952 Alfred D Hershey and Martha Chase proved that DNA

(not protein) was the hereditary material • By labeling the DNA and protein of bacteriophage with

different radioisotopes (the DNA was tagged with P32 and protein was tagged with S35) , they were able to determine which chemical (DNA or protein) was getting into the bacteria

• After infection of bacteria cells with labeled bacteriophage, Hershey and Chase found that the radioactive S remained outside the cell while the radioactive P was found inside the cell, indicating that DNA was the physical carrier of heredity.

Since DNA contains Phosphorous (P) but no Sulfur (S), then the DNA was tagged with radioactive Phosphorous-32.

Protein lacks P but does have S, thus it could be tagged with radioactive Sulfur-35

Hershey and Chase “Blender experiment”

proved that hereditary material

is DNARadioactive S remained outside the cell while the radioactive P was found inside the cell. It is indicating that DNA was the physical carrier of heredity.

Komponen RNA menentukan jenis protein kapsul TMV

Tipe baku

Tipe HR

Hibrid RNA baku

Protein HR

Tipe baku

The Search for DNA Structure• 1869 Johann Friedrich Miescher extracts what

comes to be known as DNA from the nuclei of white blood cells

• During the 1920s, P.A. Levene found that the DNA contained four nitrogenous bases: cytosine, thymine, adenine, andguanine; deoxyribose sugar; and a phosphate group.

• 1950 Erwin Chargaff discovers regularity in proportions of DNA bases for different species. In all organisms he studies, the amount of adenine (A) approximately equals that of thymine (T), and guanine (G) equals cytosine (C).

• 1952 Alfred D Hershey and Martha Chase proved that DNA (not protein) was the hereditary material

• 1953 James D. Watson and Francis H. C. Crick proposed the structure DNA as two long chains of AT & CG base pairs would likely form a double helix.

DNA Component

• He concluded that the basic unit (nucleotide) was composed of a base attached to a sugar and that the phosphate also attached to the sugar

• During the 1920s, Phoebus .A. Levene found that the DNA contained four nitrogenous bases: cytosine, thymine, adenine, andguanine; deoxyribose sugar; and a phosphate group

Levene (unfortunately) also erroneously concluded that the proportions of bases were equal and that there was a tetranucleotide that was the repeating structure of the molecule.

Chargaff Rule• 1950 Erwin Chargaff discovered in all organisms, the

amount of adenine (A) approximately equals that of thymine (T), and guanine (G) equals cytosine (C).

Organism Bases composition(%) Bases ProportionA T G C A/T G/C A+T/G+C

Human 30.9 29.4 19.9 19.8 1.05 1.00 1.52Goat 29.3 28.3 21.4 21.0 1.03 1.02 1.30Wheat 27.3 27.1 22.7 22.8 1.04 1.00 1.19Yeast 31.3 32.9 18.7 17.1 0.95 1.09 1.79E coli 24.7 23.6 26.0 25.7 1.04 1.01 0.93Brucella abortus 21.0 21.1 29.0 28.9 1.00 1.00 0.72

• This result ultimately led to a rule in molecular biology (Chargaff Rule) that A pair with T and G pair with C

• Chargaff also founded that the proportion of A+T/G+C varied among different species. The result showed that DNA have a length variation and also showed that Levene proposal on DNA structure was incorect

DNA Structure is Double Helix

• 1953 James D. Watson and Francis H. C. Crick proposed the structure DNA as two long chains of AT & CG base pairs would likely form a double helix.

• Based on Chargaff’s data Watson and Crick concluded that DNA consisted of two polynucleotide strands, and there were pairing base A with T and G with C (called Chargaff rule)

• The two strand of DNA take an anti-parallel position• Based on crystallographic studies (Conducted by Rosalind

Franklin) they concluded that the two strand of DNA formed double helix

Nucleotides : Component of DNA

Polynucleotide chain

5’P end

3’OH end

Sugar-phosphate backbone

Nitogenous Bases

Phospho-diesther bond

Anti-parallel pairing of DNA strands

The bases pairing are maintained by hydrogen bonds

AdenineThymine cytosine Guanine

2 bonds 3 bonds

A hydrogen bond results from a dipole-dipole force between an electronegative atom and a hydrogen atom bonded to nitrogen, oxygen or fluorine

Crystalographic data led to the doubles helix structure

3.4 Ao

diffraction

34 Ao

diffraction

Rosalind Franklin took X-ray diffractionphotomicrographs of crystalline DNA extract , and the data led Watson and Crick to conclude that the structur of DNA is a double helix

Double Helix Structure of DNA

3.4 Ao

34 Ao

20 Ao

Keragaman Heliks Ganda

DNA-ZDNA-B

STRUKTUR KROMOSOM EUKARIOT

DNAHiston

Matriks Protein Nirhiston

Nukleosom

Solenoid

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