• Deoxyribonucleic acid (DNA) (DNA)

– Stores info., copies itself

– Directs cell activities– hereditary material passed from cell → cell

• Nucleic Acid – polymer; monomer = nucleotidenucleotide.

– two kinds: DNA and RNA. .

Sections in a DNA mol. called genes.

Genes code for proteins; the hereditary info. in DNA tells cell how to make proteins

• Nucleotide:

three components (CP: 230) (Hon: 197)– 5 C sugar – phosphate group – nitrogenous base

(4 kinds in DNA)

• Nucleotide:

three components (CP: 230) (Hon: 197)– a 5-carbon sugar – a phosphate group – a nitrogenous base

(4 kinds in DNA)

Four Kinds of Nitrogenous Bases • PyrimidinesPyrimidines - single ring - single ring

bases.bases.– Thymine and CytosineThymine and Cytosine

• PurinesPurines - double ring - double ring bases.bases.– Adenine and GuanineAdenine and Guanine

• Base pairsBase pairs ((also called also called nucleotide pairsnucleotide pairs) ) are formed when a are formed when a purinepurine bonds with a bonds with a pyrimidinepyrimidine

• A-T and C-G (always)A-T and C-G (always)

C

C

C

C

N

N

OO

OO

ThymineThymine

C

C

C

C

C

N

N

OO

N

CytosineCytosine

C

C

C

C

N

N

N

AdenineAdenine N

N

C

C

C

C

C

N

NOO

N

GuanineGuanine N

N

C

DNA STRUCTURE• Shape is like twisted ladder.• Called a double helix -two

strands bonded together & twisted– The bases form the rungs

of the ladder • hydrogen bonds hold pairs

together; A-T, C-G

– Sugars and phosphates form sides of ladder.

The carbons in the sugar are labeled

DNA Animation

http://www.johnkyrk.com/DNAanatomy.html

http://207.207.4.198/pub/flash/24/menu.swf

Packaging DNA• Eukaryotic DNA:

many levels of packaging:– Fundamental

unit is Nucleosome –

• DNA wound around proteins called histones.

• (CP. 139)

• (Hon 151)

Nucleosome

Nucleosomes• Nucleosomes

• Lowest DNA packaging level

• Can be thought of as a length of thread wound around a spool, the thread representing DNA and the spool being histone proteins.

DNA - By The Numbers!DNA - By The Numbers!• Each cell has about

2 meters (6 ft) of DNA.• The average human has

60-75 trillion cells.• Avg human has enough

DNA to go from the Earth to the sun more than 400 times.

• DNA has a diameter of only 0.0000000002 meters (20Ǻ) [1Ǻ =10-10 m]

The earth is 150 billion metersor 93 million miles from

the sun.

Karyotypes

• Normal human male karyotype (the total set of chrom. of an organism)

Karyotypes

• Normal human female karyotype

The History of DNA

• Gregor Mendel-1866

– Determined “Unit characters” were the method of passing on traits for inheritance

• Friedrich Meischer - 1868

– Studied nuclei of pus cells obtained from discarded surgical bandages

– Detected a phosphorus-containing substance that he named nuclein.

• Frederick Griffith 1928 : Work with Bacteria– Found that DNA taken from a virulent

(disease-causing) strain of bacteria (Streptococcus pneumoniae)

– Transformed a non-virulent form of the bacterium into a virulent form.

Oswald Avery, Colin MacLeod, and Maclyn McCarty 1943 Continued the study of “Transformation” principle

Mendel Meischer Griffith

Avery McCartyMacLeod

Transformation Of BacteriaTwo Strains Of Streptococcus

Smooth Strain w/Capsule(Virulent)

Rough Strain(Harmless)

Capsule

Experimental

Transformation Of Bacteria -Griffith’s Experiment

Control

Control

Control

OUCH!

Rough

Smooth (virulent)

The History of DNA• Alfred Hershey and Martha

Chase - 1952– radioactive isotope tracer

experiment

– bacterial virus (bacteriophage T2) infects a host cell ( bacterium Escherichia coli)

– found that T2 virus DNA, not its protein coat, enters the host cell

– genetic information for replication of the virus

Using SUsing S3535Bacteria grown in normal non-radioactive media

T 2 grown in media containing S35 incorporate S35 into their proteins

Blending causes phage protein coat to fall off

T2 attach to bacteria and inject genetic material

Is protein the genetic material?

When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet.

The supernatant is radioactive, but the pellet is not.

Did protein enter the bacteria?

Using P32Bacteria grown in normal non-radioactive media

T2 grown in P32 containing media incorporate P32 into their DNA

Blending causes phage protein coat to fall off

T2 attach to bacteria and inject genetic material

Is DNA the genetic material?

When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet

The pellet is radioactive, but the supernatant is not.

Did DNA enter the bacteria?

The History of DNA Structure

• Erwin Chargaff- 1940 - “Chargaff’s rule”

– four bases may occur in varying proportions in DNA of different organisms

– # of A = # of T, w/ two hydrogen bonds

– = # of G and C are present w/ 3 hydrogen bonds

• Rosalind Franklin and Maurice Wilkins

– X-ray diffraction study concluded DNA fibers have two strands.

The History of DNA Structure

James Watson and Francis Crick - University of Cambridge -1953

Worked on problem of making a DNA molecule model that was double stranded but also had the specific A - T and G - C base equivalencies Solution-double helical structure for DNA.

Chargaff

Franklin

Wilkins

Watson and Crick