I. nucleotides: sub units „? DNA
B. 5-carbon sugar molecule (deoxyribose)
Chargaff „? base pairing rule: 1 = 3 and 2 = 4
II. Maurice Wilkins and Rosalind Frankilin „? X-ray diffraction photos of DNA molecule
– DNA molecules: tightly coiled helix and composed of two or three chains of nucleotides
III. Chargaff builds a model of the double helix: ?§a spiral staircase? of 2 strands of nucleotides twisting around a central axis.
A. alternating sugar and phosphate units
B. purine and pyrimidines paired up
– A can only form hydrogen bonds with T
– C can only for ?§ ?§ with G.
„? 2 strands that are complementary to each other
A. Replication: process of synthesizing a new strand of DNA.
B. Helices: open up the double helix by breaking the hydrogen bonds that link the complementary bases.
C. Two strands separated: additional enzymes and proteins attach to the individual strands and hold them apart „? twisting prevented
D. Replication fork : where double helix separates
1. DNA polymerases: enzymes that move along each strand „? adding nucleotides to the exposed bases.
„? one old and one new DNA strand
– genes hold info specifying how to build particular proteins
– affects the phenotype of an individual because of the activity of the protein that it specifies
– DNA encoded info that specifies particular proteins; each gene is made of a specific sequence of nucleotides
A. interruped by necleotides that have no coding info.
1. Introns:: noncoding sequences/ intervening
2. Exons :nucleotide segments that code for amino acids
-stitched together once all introns are removed
II. Multigene families: clusters of almost identical sequences;cells exist in mult

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