Chapter 05: DNA and Chromosomes PDF

Chapter 05 DNA and Chromosomes Mendel Sutton Morgan •Before biologists understood the structure of DNA, they knew that traits and associated genes were linked with chromosomes •Chromosomes contain DNA and protein. But which carries the hereditary info? Figure 5-1 DNA is inherited; protein i...

Chapter 05 DNA and Chromosomes Mendel Sutton Morgan •Before biologists understood the structure of DNA, they knew that traits and associated genes were linked with chromosomes •Chromosomes contain DNA and protein. But which carries the hereditary info? Figure 5-1 DNA is inherited; protein is not Hershey-Chase --Cold Spring Harbor 1952 05_05_Hershey_Chase.jpg Pyrimidines -- Thymine (Uracil), Cytosine OH in RNA A, G, T, C are present in DNA A, G, U, C are present in RNA See panel 2.7 Five prime end 3’-5’ Phosphodiester bond Ester -- formed from an organic acid and an alcohol, usually with elimination of water Nucleotide Three prime end 02_25_nucleotide residues.jpg Figure 2-28 Shapes of bases only allow H-bonds between A & T and G & C •antiparallel •complementary 05_06_compl_pairs.jpg See Figure 5-4 DNA synthesis 5’ 3’ G C C 3’ G 5’ Spiral staircase 05_07_base pairing.jpg Fig 5-4 The double helix Hydrophobic and van der Waal forces •major vs. minor groove See Fig. 5.5 DNA structure A chromosome is a long strand of DNA Double helix Gene expression Genes contain information to make RNA, some of which encode proteins Figure 5-7 Human chromosomes have been “painted” with fluorescent DNA probes to allow identification Figure 5-8 Abnormal chromosomes are associated with some inherited genetic defects and many cancers Figure 5-9 Replication and segregation of chromosomes occurs in the cell cycle of proliferating cells --Chromosomes exist in different forms throughout the life of the cell -- during interphase, the cell expresses many of its genes; during one part of this phase, it also duplicates the chromosomes Figure 5-13 3 DNA sequence elements needed to produce chromosome that can be replicated and segregated in mitosis • Origins for initiation of DNA replication • The centromere • The two ends (telomeres) 3 DNA sequence elements needed for duplication and segregation Double-helix Figure 5-14 Interphase chromosomes are organized in the nucleus --Different “territories” within nucleus Figure 5-16 Levels of organization of chromatin •chromatin = DNA + proteins •histones - basic AA •nucleosomes - repeating subunits of DNA and histones •Local modification of histones determines whether chromatin in that region is transcribed Compaction during mitosis Figure 5-26 Heterochromatin consists of chromosome regions that do not uncoil after mitosis •euchromatin is uncoiled and active in interphase; ~60% of chromosome •heterochromatin found in centromeres and telomeres; ~40% of chromosome (50% permanently condensed; remainder “silenced” Figure 5-17 Chromatin structure varies along a single interphase chromosome Figure 5-29 09_25_Chromosome22.jpg Figure 9-31