BIOL 1000 Lecture Notes - Lecture 21: Phosphodiester Bond, Heterochromatin, Guanine
5 Nov 2016
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Composed of: nitrogenous base, pentose sugar, phosphate group. 2 nucleotides linked through a phosphodiester bond in backbone. Nitrogenous bases are linked by hydrogen bonds. Adenine & guanine are double rings called purines. Thymine & cytosine are single ring- called pyrimidines. Sugar phosphate backbone on outside; bases on insides. Euchromatin: loosely packaged dna genes active & transcription occurring. Heterochromatin: densely packed dna genes inactive & transcription not occurring this packaging happens by histones. Histones pack dna at successive levels of organization. Many nonhistone proteins have key roles in regulation of gene expression. Period of growth followed by nuclear division & cytokinesis. Chromosomes: nuclear units of ge(cid:374)eti(cid:272) i(cid:374)fo that"(cid:396)e di(cid:448)ides & dist(cid:396)i(cid:271)uted (cid:271)(cid:455) (cid:373)itoti(cid:272) (cid:272)ell di(cid:448)isio(cid:374) Daughter cells are identical copies of parent cell. Each daughter cells contain exact same heritable material dna as parent cell. Replication of chromosomes is the s phase of interphase. Human dna takes only a few hours to copy.
