I. nucleotides: sub units „³ DNA A. Phosphate group B. 5-carbon sugar molecule (deoxyribose) C. nitrogen base 1. Adenine 2. Guanine 3. Thymine 4. Cytosine Chargaff „³ base pairing rule: 1 = 3 and 2 = 4 II. Maurice Wilkins and Rosalind Frankilin „³ 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 …showed first 75 words of 312 total…

…showed last 75 words of 312 total…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. Some encode the two chains of