1 chapter 15 expression of biological information

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Chapter 15

EXPRESSION of BIOLOGICAL

INFORMATION

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DNA & Genetic InformationObjectives

• to describe the structure of DNA based on the Watson & Crick model

• to explain DNA as the carrier of genetic information• to explain the concept of one gene one polypeptide

DNA STRUCTURE

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• Watson and Crick Model

• Monomer : NUCLEOTIDE

• Component : Deoxyribose (pentose sugar)

Phosphate group

Nitrogenous base : Adenine (A) Thymine (T)

Guanine (G) Cytosine (C)

*Base pairing rule : A-T and C-G

DNA NUCLEOTIDE

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WATSON AND CRICK MODEL

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• DNA : 2 polynucleotide chain

• Arrange in double helix

• Nucleotide link by alternating sugar-phosphate backbone : phosphodiester bond

• Antiparallel (3’ to 5’) and (5’ to 3’)• Each polynucleotide chain attach to another polynucleotide chain by hydrogen bond

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DNA as carrier of genetic information

• Experiments are conducted by Frederick Griffith (1928) and Avery (1944)

• Griffith: Identify transformation process

• Avery et.al. : identify the transformation agent

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• Griffith (1928) - studied Streptococcus pneumoniae ; bacterium that causes pneumonia to mammals

• two strains (varieties) of S. pneumoniae :

• R (rough) strain

• mutant strain• non-capsulated• non-virulent (non-pathogenic)

• S (smooth) strain• capsulated• virulent (pathogenic / causing disease)

DNA: The Carrier of Genetic Information

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1 2


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Transformation occur


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• the transformed bacteria reproduce forming S strain daughter cells (heritable)

• transformationtransformation occur; live R strain is transformed into live S strain by hereditary material obtained from the dead strain-S cells

• the hereditary substance was unknown


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Definition

• a change in genotypes and phenotypes of an individual

• due to the assimilation of foreign DNA by a cell.

R strainS strain


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• In 1944, Oswald Avery, Maclyn McCarty and Colin McLeod proved that DNADNA was the transforming substance.

• Two models of the experiment were carried out.

Transformation agent


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• heat-killed the S strain bacteria culture• purify the culture; remove proteins, carbohydrates, lipids, RNA and DNA• add proteins, carbohydrates, lipids, RNA and DNA to different cultures of living R strain

ObservationObservation : After a few days, colonies of : After a few days, colonies of SS strain strain grewgrew in the in the RR strain culture that was strain culture that was added with added with DNADNA

• Experiment 1Experiment 1


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• Experiment 1Experiment 1 The observationThe observation

• After a few days, colonies of the S strain grew in the R strain culture which had DNA added.


15.1 DNA: The Carrier of Genetic Information

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S colonies

extracts are added to different cultures of R strain

no change no change no change no change

carbohydrate lipid protein RNA

S strain found

DNA



Transformation

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• Experiment 2Experiment 2 Enzyme Treatment Enzyme Treatment

1. The purified DNA of the S strain bacterium was mixed with the R strain colonies.

The Procedures The Procedures

2. 2. Different enzymesDifferent enzymes were added to the different mixture.

3. Bacteria colony was grown in different culture.



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The enzymes added:

• proteaseprotease - degrades proteins• ribonucleaseribonuclease - RNase

- degrades RNA• deoxyribonucleasedeoxyribonuclease- DNase

- degrades DNA

• Experiment 2Experiment 2 Procedures Procedures



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R Strain

R colonies

DNA fromheat-killed

S cellsno colonies

Living R Strain

+DNA fromheat-killed

S cells

+Serum that

precipitates R cells from

mixture S colonies(transformation)

Experiment 2Experiment 2

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R strain+

DNA fromheat-killed

S cells+

Serum thatprecipitates R cells from

mixture

+protease

transformation

R strain+DNA fromheat-killed

S cells+


mixture

+ RNase

transformation

R strain+

DNA fromheat-killed

S cells+


mixture

+ DNase

NO colonies

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2

3

Experiment 2Experiment 2

S colonies

S colonies

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• The protease and the RNase failedfailed to stop the transformation of the R strain into the S strain by the purified DNA.

• The DNase destroyeddestroyed the transforming activity of the purified DNA preparation.

• Experiment 2Experiment 2 The Inferences The Inferences



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• Experiment 2Experiment 2 The Conclusion The Conclusion


• DNA isis the carrier of genetic information

• DNA from the capsulated bacteria (S strain) carries the gene that encode the production of capsule

• During transformation, the DNA is assimilated by DNA of R strain; enables R strain to synthesize capsule


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• George Beadle and Edward Tatum (1941) • study the relationship between genes and enzymes • by using Neurospora crassa (bread mold) • fungi (Ascomycota / sac fungi)

Fungi that produce spores in structures called sacs

Gene concept: One-Gene-One-Polypeptide

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Minimal mediumMinimal medium

consists of agar, glucose, inorganic salts and vitamin biotin

Complete mediumComplete medium

consists of agar, glucose, inorganic salts, vitamin biotin and 20 amino acids.

Medium needed:

Beadle & Tatum experiment


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• some conidia (asexual spores) were exposed to X-ray; to induce mutation


Procedures

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• conidia (mutant) were transferred to complete complete mediummedium and grown; mycelia formed

• mycelia (from mutant conidia) were crossed with mycelia (from wild type conidia). wild type conidia are NOT exposed to X-ray


Procedures

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• producing asci (sin. ascus) that consist of eight ascospores (four ascospores from each parental mycelia – mutant and wild type)


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• the ascospores were dissected out and transferred to complete medium. ALL grew and formed mycelia

• mycelia were placed on minimal medium NO growth occur


Procedures

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• mycelia which did no grow were unable to synthesize certain amino acids

• to determine which amino acids were synthesized, mycelia were transferred to minimal media each containing a different amino acid amino acid test


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• the medium in which growth occur, contain the amino acid which the mutant Neurospora unable to synthesize


Observations

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• does not have the enzyme to synthesize arginine

• due to lacks of gene that encodes the enzyme

• results in the mutant could ONLY grow with the supply of arginine

“ One GENE ; One ENZYME ”

• the mutant Neurospora was defective in biochemical pathway to synthesize arginine


Conclusion

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• proteins that AREN’T enzymes also encoded by genes

• NOT all proteins are enzymes e.g keratin (structural protein) insulin (peptide hormone)

“ One GENE ; One PROTEIN ”

• proteins are composed of different polypeptide chains (e.g hemoglobin)

• each polypeptide chain is encoded by gene “ One GENE ; One POLYPEPTIDE ”

Restatement

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• the defect is in the biochemical pathways that normally synthesize arginine

From further experiments From further experiments

Beadle and Tatum concluded that


1 chapter 15 expression of biological information

Documents

experiments gene concept

structure of dna

dna nucleotide

transformation occurdna

different polypeptide

watson crick model

definitionr strains

polypeptidedna structure