Chromosomes and Cell Division DNA Limits Cell Size

Chromosomes and Cell Division

DNA Limits Cell Size n n Cell cannot survive unless there is enough DNA to support the protein needs of the cell In some really large cells are multinucleated – More nuclei = more DNA = quick, efficient protein manufacturing to meet large cell needs

Prokaryote Cell Division n n Bacteria Circular DNA Reproduce by binary fission = 2 daughter cells DNA copied Know steps

n Cell division—making 2 new cells from 1 parent cell n New cells are (and have to be) Genetically IDENTICAL n Why? When? Who? How? n n n Cell Reproduction

Eukaryotes —the Who n Somatic cells—mitosis – Growth & replacement of lost, dead or damaged

Cell Cycle n n • G 1: 1 st growth phase major part n. S: "synthesis" DNA replicates; 2 copies G 2: 2 nd growth phase; microtubules made M: mitosis C: cytokinesis 2 daughter cells

• G 1 checkpoint—cell growth—are conditions favorable to divide (yes—S phase; no—rest or stop) • G 2 checkpoint— enzymes edit and repair mistakes made during replication • M checkpoint— triggers exit from mitosis to begin G 1

I P M A I—I n P—put n M—my n A—arm n T—there n C—’cuz n T C

n n double stranded negative charge wraps around histones (+ proteins) chromatid + centromere = chromosomes DNA

Chromosomes n n n During mitosis Super-coiled DNA 46 in somatic (body) cells Contains 1000 s of nucleotides Contains 100 s of genes Small mistakes have major complications

Interphase Not mitosis… n n n set up for mitosis centrioles replicate DNA replicates & condenses

Prophase n n n Chromosomes 1 st visible Centrioles move to poles & form spindle fibers Nuclear envelope breaks down

Prophase in plants… Spindle fibers Disappearing nuclear envelope Doubled chromosome

Metaphase n n n "middle" centromere replicates Chromosom es line up along the equator

Metaphase in Plants… Centromere Sister chromatids

Anaphase n n chromatids pulled to poles Pulled by spindle fibers

Anaphase in Plants…

Telophase and Cytokinesis n n nuclear membrane reforms spindle fibers disassembles uncoiling of chromosomes cleavage; membrane pinches in

Telophase in Plants… Cell plate forms Nuclear envelope reappears Two daughter cells are formed

Differences in plants—cell plate forms n have asters not centrioles n

Plant Mitosis

Why is mitosis important? What’s its purpose? n Growth and replacement of dead, lost and damaged cells n Ensures each daughter cell gets an complete and exact copy of the genetic material from the parent cell in the quickest, most efficient manner

n Mitosis