Nucleotides

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 …

…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