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Lecture 27

BIO 201 Lecture 27: Mitosis

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Biological Sciences
BIO 201
Lara Hutson

BIO 201 Dr. Lara Hutson Lecture 27 Notes 4/14/17 DNA Condensation: Histones and Nucleosomes ● M-phase: duplicated DNA is condensed ● Must be condensed more than bacterial DNA because we have more of it 1. All Eukaryotic DNA wrapped around histone proteins a. DNA histone complex is a nucleosome (proteins) and an octomer b. Make up ~50% of total mass of chromosomes 2. During interphase, nucleosomes and DNA and further coiled into chromatin (30 nm) 3. During mitosis, chromatin is even further condensed (700 nm) a. Final degree of condensation triggered by histone phosphorylation by Cdk1 How Much Condensation? ● Degree of condensation needed to fit DNA into nucleus: 17,000x condensation!!! Chromosome Terminology ● Homologous chromosomes: the same chromosome inherited from either the father or mother ○ Not identical - contain same genes but different alleles ● Sister chromatids: 2 copies of replicated chromosome ● Centromere: location on chromosome where sister chromatids are held together after DNA replication ● Kinetochore: protein complex at centromere that holds sister chromatids together Mitosis 1. Beginning of M: centrosomes often already duplicated 2. Condensation of chromosomes* and formation of the spindle from microtubules* 3. Nuclear envelope breaks down* and beginning of chromosome alignment 4. Alignment of chromosomes at metaphase plate 5. Segregation of sister chromatids and cell lengthening 6. Cytokinesis and reformation of nuclear envelope * Targets of Cdk1! Mitotic Spindle ● Array of microtubules responsible for alignment and segregation of chromosomes ● Formation ○ In early metaphase, MTs polymerize from centrosome → grows randomly in all directions ○ Some MTs run into kinetochore and bind tightly → become kinetochore MTs ○ MTs that run into membrane become astral MTs ○ MTs run into MTs coming from other centrosomes → become pola
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