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Nucleotides I. nucleotides: sub units DNA A. Phosphate group B. 5-carbon sugar molecule (deoxyribose) C. nitrogen base 1. Adenine 2. Guanine 3.

Thymine 4. Cytosine 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.

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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 IV. Copying of DNA: 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. 2.

Proofreading one old and one new DNA strand 8.3 The Structure of a Gene – 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 I. Genes in Eukaryotes A. interruped by necleotides that have no coding info. 1. Introns:: noncoding sequences/ intervening – must be removed 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 multiple copies A. Some are silent genes: don`t make protein B. Some are only active during embryonic or fetal development C.


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