dna the genetic material. big picture for most of the last century, no one knew what mendel’s...

DNA the Genetic Material

Big Picture

• For most of the last century, no one knew what Mendel’s “factors” were.

• Sutton first developed chromosomal theory in 1902, but only circumstantial evidence that factors were genes on chromosomes.

This is a story...

• About the process of science, as well as the structure and function of DNA.

• 14.1 What is the genetic material?The Hammerling Experiment: Cells Store Hereditary Information in the Nucleus Joachim Hammerling discovered that hereditary information in Acetabularia (unicellular green alga) resided in the foot region, which is also the location of the nucleus.

• (p. 280) How did he know? • By amputating differerent areas, grafting to

other alga, and seeing what parts would grow.• The form that was found in the foot region is

the one that would influence new growth.

• Transplantation Experiments: Each Cell Contains a Full Set of Genetic Instructions Later experiments in the mid-1950s showed that the nucleus of eukaryotic cells includes a full set of genetic information. (p. 281)

• By transplanting nuclei from one frog species into that of another.

• Totipotent- nucleus of adult cell carries instructions to create entire organism,

• The Griffith Experiment: Hereditary Information Can Pass Between Organisms

• 1928 Frederick Griffith - (p. 282)

• Non-pathogenic S. pneumoniae was transformed by dead pathogenic S. pneumoniae. Information specifiying the virulent surface protein had been delivered to the safe live form.

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Mice die; their bloodcontains live pathogenicstrain of S. pneumoniae

Mixture of heat-killedpathogenic and livenonpathogenic strainsof S. pneumoniae

+

Heat-killed pathogenicstrain of S. pneumoniae

Live pathogenicstrain of S. pneumoniae

Live nonpathogenicstrain of S. pneumoniae

Polysaccharidecoat

Mice liveMice die(1) (3) (4)

Mice live(2)

• The Avery and Hershey-Chase Experiments: The Active Principle Is DNA

• 1944- Oswald Avery provided conclusive evidence that DNA is the heredity material for the bacterial specimens under investigation. (p. 283)

• He removed as much protein and other material as possible, but still non pathogenic cells were transformed, so not protein, fat, or carb.

• Alfred Hershey and Martha Chase - (p. 283)

• Bacteriophage: simple nucleic acid with protein coat.

• Identified DNA by marking phosporous with 32P

• Identified protein by marking sulfur with 35S.

• Found that it was the DNA, marked with 32P, that was injected into the bacteria to cause disease.


Protein coat labeledwith 35S

DNA labeled with 32P

Bacteriophages infectbacterial cells.

T2 bacteriophagesare labeled withradioactive isotopes.

Bacterial cells are agitatedto remove protein coats.

35S radioactivityfound in the medium

32P radioactivity foundin the bacterial cells

Fig. 14.5(TE Art)

• 14.2 What is the structure of DNA?The Chemical Nature of Nucleic Acids Both DNA and RNA are formed of nucleotides joined together in series. Each nucleotide is composed of a five-carbon sugar, a phosphate group, and a nitrogen-containing base. (p. 284)

Chargaff's Rule - there are always equal proportions of purines and pyrimidines. (p. 285)

• A-T

• G-C

• Pure AGgie. (purines are A & G) • Do you remember how we numbered carbons

in sugar?• Start from right side. • Base attached to 1’, phosphate attached to 5’.

This comes up when we talk about replication, transcription, and translation. (We read from 5’ to 3’)

• Phosphodiester bond between nucleotides.

• The Three-Dimensional Structure of DNA Rosalyn Franklin was able to obtain the first glimpse of DNA using X-ray diffraction in 1953, while Watson and Crick theorized that DNA exists in a double-helical, antiparallel configuration. (pp. 286-287)

• Famous example of woman being scr’d.

• Could you guess the pattern by looking at the x-ray?

• 14.3 How does DNA replicate?The Meselson-Stahl Experiment: DNA Replication Is Semiconservative Matthew Meselson and Franklin Stahl demonstrated that DNA replication is semiconservative because each strand of the original duplex becomes one of the two strands in each new duplex. (p. 288)

• Also figured out by using isotopes, this time 14N.

• What would the F1 generation look like if completely new DNA were synthesized, rather than semi-conservative?

• It would be heavy as in test tube #2 in diagram.


4. The DNA was suspendedin a cesium chloridesolution.

Centrifugation

1 2 3 4

Control group(unlabeled DNA)

Labeled parentDNA (both strandsheavy)

F1 generation DNA(one heavy/light hybridmolecule)

F2 generation DNA(one unlabeled molecule,one heavy/light hybridmolecule)


OH

CH2

O

4

5

3 2

1

PO4

Base

• The Replication Process Replication of E. coli begins at a specific origin, proceeds bidirectionally, and ends at a specific terminus. (p. 290)

• OriC is beginning point.

• Contains many A-T pairs, which are double bonded, easy to open.

• Leading and lagging strand, why so named?

• One side is synthesized continuously, but the other limited to short segments (Okizaki fragments).


DNApolymerase III

DNA double helix

Lagging strand

Primer

Okazakifragment

Leadingstrand

59

39

• DNA primase -creates a short RNA primer complementary to a DNA template;

• DNA helicase, which unwinds the helix DNA polymerase, which then synthesizes new DNA by adding nucleotides to the growing strands; and DNA ligase, which creates phosphodiester bonds between adjacent Okazaki fragments. (pp. 292-293)

• Each of these has a name that gives away its job.

• These are the only enzymes you are responsible for.

• Replication fork- Open area of DNA where replication takes place. Replication can be divided into three stages: initiation, elongation, and termination. (p. 294)

• Initiation- there are two OriC’s, one on each strand.


Leadingstrand

Laggingstrand

DNA ligaseDNA polymerase I

Okazakifragment

RNAprimer

First subunit ofDNA polymerase III

Single-strand binding proteins

Second subunit ofDNA polymerase III

PrimaseHelicase

ParentalDNA helix

• Eukaryotic DNA Replication The major difference between prokaryotic and eukaryotic replication is that eukaryotic chromosomes have multiple replication origins, whereas prokaryotic chromosomes have a single point of origin. (p. 295)

•14.4 What is a gene?The One-Gene/One-Polypeptide Hypothesis Beadle and Tatum concluded that genes produce their effects by specifying the structure of enzymes, and that each gene encodes the structure of one enzyme. Today, this is commonly referred to as the one-gene/one-polypeptide relationship. (p. 297)

• How did they figure this out?

• Using bread mold nutrient mutants- mutants that lack the ability to make a certain aa, and must be supplied with it to grow.

• Found that each enzyme that was disabled corresponded to a defect in a specific gene.


Wild-typeNeurospora

Minimalmedium

Products ofone meiosis

Select one ofthe spores

Grow oncomplete medium

Minimalcontrol

Nucleicacid

CholinePyridoxine RiboflavinArginine

Minimal media supplemented with:

ThiamineFolicacid

NiacinInositolp-Aminobenzoic acid

Test on minimalmedium to confirmpresence of mutation

Growth oncompletemedium

X rays or ultraviolet light

Asexualspores

Meiosis

• How DNA Encodes Protein Structure

• Sanger sequenced the amino acids of insulin, first time to sequence a protein. Then Ingram found that a single aa substitution Valine instead of Glutamic acid, caused sickle cell anemia.

Over 50 years of research has yielded clear evidence that DNA is the molecule responsible for the

inheritance of traits from one generation to the next, and that DNA is divided into functional subunits, or genes, located on

chromosomes. (p. 298)

The question is answered

dna the genetic material. big picture for most of the last century, no one knew what mendel’s...

Documents

structure of dna

pneumoniae heat

function of dna

hereditary information

protein coats

pidentified protein

set of genetic information

pathogenic cells