BIOL 3510 1st Edition Lecture 4 Outline of Last Lecture I The Functions of Different Proteins II Enzymes and their Actions a Lysozyme III Protein Regulation IV Antibodies and their Uses Outline of Current Lecture I Nucleotides and the Composition of DNA II Genome III Chromosome packing IV Inside of the Nuclear Envelope Current Lecture DNA and Chromosomes Nucleotides are composed of a base sugar and a phosphate group In deoxyribonucleic acid DNA the sugar is deoxyribose Nucleotides are linked via phosphodiester bonds to form nucleic acids Phosphodiester bonds form via condensation reactions DNA nucleotides can be purines G A or pyrimidines T C DNA strands have a polarity 5 versus 3 and DNA strands are negatively charged Double stranded DNA consists of two complementary chains of nucleotides in an anti parallel conformation The DNA strands are held together by hydrogen bonds The DNA double helix contains 10 base pairs per turn There are major grooves and minor grooves The entirety is 2 nm in width Most genes contain information to make proteins gene A on the double helix RNA A protein A where RNA A and protein A is the gene expression Genome is all the information contained within an organism s DNA Eukaryotic DNA is divided into chromosomes These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute Homologous chromosomes homologous one pair of chromosomes one maternal and one paternal Karyotype display of the mitotic chromosomes These questions would be determined by using karyotyping a If the individual genetically is female or male b Do any of the chromosomes contain pieces that belong to other chromosomes c Does the individual have an extra chromosome The human genome drafted in 2001 finished in 2004 22 autosomes and 2 sex chromosomes 3 2 billion base pairs Approx 25 000 genes 1 5 of the genome encodes exons The duplication and segregation of chromosomes occurs through an ordered cell cycle Three DNA sequence elements ensure chromosomes can be replicated replication origin and telomere and segregated centromere The chromosomes in a cell are condensed Mitotic chromosomes most condensed 1 micrometer Interphase chromosomes less condensed 10 micrometers Chromatin DNA and its associated proteins Nucleosomes are the basic unit of chromatin packing Consist of 4 pairs of histones 8 total Histones highly conserved small positively charged proteins 147 base pairs in a piece of DNA Nucleosomes are further packed into 30 nm fibers via 1 Interactions between histone tails 2 Binding of histone H1 Nucleosome wrapped DNA is accessible to other DNA binding proteins via 1 Nucleosome structure is fluid and dynamic 2 Chromatin remodeling complexes slide DNA in nucleosomes in an ATP dependent manner 3 Modification of histone tails by modifying proteins Disrupts stability of the 30 nm fibers and higher order packing Recruits proteins that condense or decondense chromatin The pattern of histone modification indicates the status of the nearby chromatin heterochromatin formation gene silencing or gene expression There are two levels of interphase chromatin condensation 1 Heterochromatin Most condensed Induced by tail modifications including methylation of lysine 9 on the histone H3 tail Gene poor regions centromeres and telomeres Genes are not expressed Example X inactivation see fig 5 30 in Essential Cell Biology 4th ed 2 Euchromatin Less condensed Gene rich regions see fig 5 28 in Essential Cell Biology 4th ed Genes undergoing transcription are found in areas of chromatin with the least amount of condensation 1 Folded 30 nm fiber looped domain proteins forming chromosome scaffold Histones modifying enzymes chromatin remodeling complexes or RNA polymerase 2 High level expression of genes in loop Chromatin structure is inherited epigenetic inheritance 1 Parental nucleosomes with modified histones 2 Only half of the daughter nucleosomes have modified histones 3 Parental pattern of histone modification re established by proteins that recognize the same modifications they catalyze DNA is contained within the nucleus of eukaryotic cells Nuclear envelope two co centric lipid bi layers Nuclear pores allow exchange between the cytoplasm and nucleus Nuclear lamina mesh of intermediate filaments that support the nucleus Chromosomes occupy discrete territories within the nucleus There are biochemical neighborhoods within a nucleus as well Nucleolus example of a biochemical neighborhood contains genes that encode ribosomal RNAs
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