T. H. Morgan's group showed that genes exist as parts of chromosomes: DNA and protein.

Biochemists identified proteins as a class of macromolecules w/ great heterogeneity & hereditary material

He used two strains of bacterium, one pathogenic & one nonpathogenic to study streptococcus pneumonia

Two Strains: S (smooth/with capsule) strain caused pneumonia & R (rough/no capsule) strain are nonpathogenic.

Conclusion: living R bacteria transformed into pathogenic S bacteria by unknown, heritable substance from dead S cells that enabled R cells to make capsules.

Transformation: A change in genotype and phenotype due to the assimilation to external DNA by a cell.

Virus DNA/RNA enclosed by a protective coat, that is protein.

Could quickly turn E. Coli cell into a T2 producing factory that released many copies of new phages when cell ruptures.

Hershel & Chase found that the phage DNA entered the host cells but the protein did not.

Results: DNA inside the cells played an ongoing role during injection process.

Concluded that the DNA injected by the phage must be the molecule carrying the gene info that makes the cells produce new viral DNA & proteins.

1) Mixed radioactively labeled phages w/bacteria. The phages infected the bacterial cells.

2. Agitated the mixture in a blender to free phage parts outside the bacteria from the cells.

3. Centrifuged the mixture so that bacteria formed a pellet at the bottom of test tube; free phages & phage parts, which are lighter, remained suspended in the liquid.

DNA: Nitrogenous Base, Pentose Sugar called deoxyribose & a phosphate group.

Bases can be adenine (A), thymine (T) guanine (G), or cytosine (C)

EX: Sea urchins = 32.8 % base A, Human DNA = 30.4 % bass A nucleotides, only 24.7% bacterium E. Coli have base A.

In Chargaff's analysis, sea urchin percentages: A = 32.8%; T=32.1%; G = 17.7%; C= 17.3%

Each DNA nucleotide monomer consists of a nitrogenous base (T, A, G or C, sugar deoxyribose (blue) & a phosphate group (yellow).

Phosphate group of one nucleotide is attached to the sugar of the next by a covalent bond, forming a "backbone" of alternating phosphates & sugars from which base projects.

A polynucleotide strand has directionality from 5' end to 3' (w/the -OH group of the sugar), 5' and 3' refer to the #s assigned to the carbons in the sugar ring.

Spots & Smudges in the image were by the X-Rays that were diffracted as they passed thru aligned fibers of purified DNA

The two sugar-phosphate backbones are antiparallel running in opposite directions.

Adenine & Guanine are purine (Nitrogenousbases w/organic rings)

Cytosine & thymine are pyrimidine (Nitrogenous Bases w/a single ring).

Each Chain acts as a template for the formation on to itself of a new companion chain so the two pairs of chains exist.

When DNA is copied, each strand serves as a template for ordering nucleotides into a new, complementary, strand.

Watson's & Crick's model represents that when a double helix replicates, each of the two daughter molecules will have one old strand, from the parent molecule & one new strand.

The conservative Model: Two parent strands reassociate after acting as templates for new strands, thus restoring the parent double helix.

Semiconservative Model: Two strands of the parental molecule separate & each functions as a template for synthesis of a new complementary strand.

Dispersive Model: Each strand of both daughter molecules contain a mixture of old & synthesized DNA.

Proteins that initiate DNA replication recognize this sequence & attach to the DNA, separating the 2 strands & opening up a replication "bubble".

Replication bubble has a replication fork at each end (y-shaped region where DNA are being unwound).

Helicases untwist double helix at replication forks, making parental strands as template strands.

single-stranded binding proteins bind to unpaired DNA strands to keep them from repairing

The untwisting of double helix causes a tighter twist & strain on Y-Fork.

Topoisomerase:enzyme helps relieve strain by breaking swiveling & rejoin strands.

Multiple replication bubbles form & fuse. Speeding up the copying of the very long DNA molecules.

Eukaryotic DNa replication proceeds in both directions of each origin.

Replication Fork at each end (Yshaped region where DNA are being unwound).

Helicases untwist double helix at the replication forks, making parental strands as template strands.

single-stranded binding proteins bind to unpair DNA strands to keep them from repairing.

The untwisting of the double helix causes tighter twist & strain on Y-Fork

Topoisomerase: enzyme helps relieve strain by breaking, swiveling, and rejoin strands

Initial Nucleotide Chains: RNA chain called a primer & synthesized by primase

Primase begin w/a single nucleotide & adds RNA nucleotide one at a time using parental DNA strand as template.

DNA polymerases catalyze synthesis of new DNA by adding nucleotides to 3' end of a preexisting chain.

leading strand: only one primer is required for DNA pol iii to synthesize the entire leading strands.

DNA pol III must work along template strand in direction "away" from Y-fork.

lagging strand: strand elongating in direction; okazaki fragments are segments of the lagging strands.

DNA polymerase catalyzes the addition of a nucleotide to the 3' end of a growing DNA strand, with release of two phosphates

Synthesis of the leading strand during DNA replication

1. After RNA primer is made, DNA pol III starts to synthesize the leading strand.

2. The leading strand is elongated continuously in the 5 ---> 3 direction as the fork progresses.

Function: Unwinds parental double helix at replication forks

Function: Binds to and stabilizes single-stranded DNA until it is used as a template

F: Relieves overwinding strain ahead of Y-Forks by breaking, swiveling, and rejoining DNA strands

F: Synthesizes an RNA primer at 5' end of leading strand and at 5' end of each Okazaki fragment of lagging strand

F: Using parental DNA as a template, synthesizes new DNA strand by adding nucleotides to an RNA primer or a pre-existing DNA strand

F: Removes RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides added to 3' end of adjacent fragment.

F: Joins Okazaki fragments of lagging strand; on leading strand, joins 3' end of DNA that replaces primer to rest of leading strand DNA.

consists of multiple repetitions of one short nucleotide sequence

EX: 6-nucleotide sequence TTAGGG is repeated b/w 100 and 1,000times

telomeric DNA prevent the staggered ends of the daughter molecule from activating the cell's systems for monitoring DNA damage.

telomeric DNA acts as a buffer zone to protect against the organism's genes shortening.