chapter 6

Chapter 6Expression

of Biological Information

Concepts review

Expression of Biological

Information

DNA & Genetic Information

DNA as genetic material

Gene hypothesi

s

Abilities of DNA

Forming new DNA

Produce polypeptide

ReplicationProtein

synthesis

Operon

Griffith (1931)

Avery et. al

(1944)

Beadle & Tatum (1944)

Hershey & Chase

At the end of the lesson, you At the end of the lesson, you should be able to :should be able to :

Explain DNA as the carrier of genetic information.Explain gene concept : One gene one polypeptideDescribe the semi-conservative replication of DNA

DNA as genetic material

Carrier of Carrier of genetic genetic

information information

DNA as genetic material…DNA as genetic material…Frederick Griffith (1931)

Streptococcus pneumoniae

mouse

Two types

Mutant typeRough, non-

virulent(IIR)

Wild typesmooth, virulent

(IIIS)

DNA as genetic material…DNA as genetic material…

Sample 1Frederick Griffith

(1931)

DNA as genetic material…DNA as genetic material…

Sample 2Frederick Griffith

(1931)

DNA as genetic material…DNA as genetic material…

Sample 3Frederick Griffith

(1931)

DNA as genetic material…DNA as genetic material…

Sample 4Frederick Griffith

(1931)

Living S cells found in the

blood

DNA as genetic material…DNA as genetic material…Frederick Griffith

(1931)conclusion

Living R cells are converted Living R cells are converted to S cells.to S cells.

Transformation occurred.Transformation occurred.

What is the transforming agent?

DNA as genetic material…DNA as genetic material…Concepts of transformation

Transformation is a types of genetic transfer found in bacteria.

Bacteria can take up the externally DNA.

DNA as genetic material…DNA as genetic material…

Oswald T. Avery

DNA as transforming agent

Colin MacLeod

Maclyn McCarty

DNA as genetic material…DNA as genetic material…

S strain(killed)

R strain(living)+

Protein destroye

d

RNA destroye

d

DNA destroye

d

Lipid eliminate

dLiving

S cells

Living S

cells

Living S

cells

Living R

cellsNo transformation

DNA as transforming agent

protease

RNase DNase centrifugation

DNA as genetic material…DNA as genetic material…Avery et. al (1944)

conclusionThe strain without DNA caused no transformation occur.So, the transformation agent is DNA!

DNA as genetic material…DNA as genetic material…Hershey and Chase

Prove that DNA is the molecules that responsible as genetic information, not protein.

Bacteriophages

Gene Hypothesis

One gene one One gene one polypeptidepolypeptide

Gene Hypothesis…

Edward Tatum

George Beadle

Gene Hypothesis…

George Beadle and Edward Tatum experiment: connection between genes &

metabolism.

Neurospora crassa as experimental organism.

- short life-cycle, easily grown.

Since it is haploid for much of its life cycle, mutations would be immediately

expressed.

Gene Hypothesis… Neurospora crassa able to synthesize all of

the amino acids and other chemicals needed for growth

Mutations will affect a single genes and single enzymes in specific metabolic pathways.

Gene Hypothesis…Beadle & Tatum

Experiment

Minimal Nutrient

Gene

Enzyme

Minimal Nutrient

Amino acid

Mutant neurospora

Wild type neurospora

Case 1Case2Case 3Amino acid

How to make sure ONE genes is only code ONE polypeptide???

Gene A

Gene B

Gene C

Precursor

Ornithine

Citrulline

Arginine

Enzyme A

Enzyme B

Enzyme C

+Ornithine

+Citrulline

+Arginine

X X

X X

X X

Is the gene A only produce enzyme A

only?

Is the gene B only produce enzyme B

only?

Is the gene C only produce enzyme C

only?

Gene Hypothesis…Beadle & Tatum

Experimentconclusion

Each gene will produce certain enzyme (polypeptide)

One gene one polypeptide.

DNA Replication Model

Meselson and Meselson and StahlStahl

DNA Replication Model…

Proposed by Matthew Meselson (left) and Franklin W. Stahl (right) in 1958.

DNA Replication Model…

DNA Replication

Process of copying a double stranded DNA strand which is the two

resulting double strands are identical and each of them consist of one

original and one newly synthesize strand.

DNA Replication Model…

Watson and Crick suggest that each strands of DNA molecule could serve as template for the synthesis of opposite strand.

Each half-helix could pair with their complementary nucleotides to replace its missing partner.

Will result two DNA double helices, each identical to the original.

DNA Replication Model…Meselson & Stahl

(1958)Studied the replication in E. coli

3 hypotheses

conservative semiconservative

dispersive

Which one is the model of DNA replication?

DNA Replication Model…Meselson & Stahl

(1958)

Both parent strand remain together and

all new copies is made.

Hypothesis 1conservative

DNA Replication Model…Meselson & Stahl

(1958)

The 2 strand of the parental molecule separate and each

functions as a template for

synthesis of a new complementary

strand

Hypothesis 2semiconservative

DNA Replication Model…Meselson & Stahl

(1958)

Each strand of both daughter molecules contains a mixture of old and newly synthesized parts

Hypothesis 3dispersive

DNA Replication Model…Meselson & Stahl

(1958)

DNA Replication Model…Meselson & Stahl

(1958)

Second replication

First replication

Result

DNA Replication Model…Meselson & Stahl

(1958)

Second replication

First replication

Result

DNA Replication Model…Meselson & Stahl

(1958)

Second replication

First replication

Result

DNA Replication Model…Meselson & Stahl

(1958)

Second replicatio

n

First replicatio

n

DNA Replication Model…Meselson & Stahl

(1958)conclusion

DNA replication is take place by DNA replication is take place by semiconservative.