Cell division

Mitosis

“multiply and divide”

•  Figure typifies what students learn •  Mitosis (so different from meiosis!) •  Chromosome = colored body. •  Most of what cells do is when they are

NOT dividing! -- •  Introduce cell cycle

cell-cycle - Understand:

•  2n is diploid, •  prophase, metaphase, anaphase. •  interphase is when the cell actually functions - •  unwound chromatin vs. condensed

chromosomes •  cell cycle:interphase G1, S, G2, mitosis •  G = gap, S = synthesis •  arrest in G1 if postmitotic •  these are the cells which age

Some cells do not divide

•  brain (CNS Neurons) and heart (myocardial cells) - do not divide,

•  why stroke and heart attack are so damaging (no new cells replaced by mitosis)

•  vs. in intestines, cells are constantly replaced by mitoses from stem cells

•  in that milieu, cells digest themselves.

Information

•  homologues do not line up (contrast with meiosis, next lecture),

•  DNA had already doubled (S=synthesis) •  Terms to know •  prophase, centrioles, spindle •  Centromere (on chromosome) = kinetochore

(where microtubules attach) •  later (metaphase) chromosomes line up at

metaphase plate

Information

•  centromeres divide •  anaphase, chromosomes separate •  telophase when cells separate •  followed by cytokinesis. •  Cell division in eukaryotes to make

genetically identical daughter cells •  FUNDAMENTAL: multicellular, all cells

have same genes (except germ cells)

Human chromosomes •  observe at metaphase block w colchicine •  (they are duplicated - sister chromatids.) •  Karyotype •  different centromere location, size, & bands •  46 chromosomes (23 pairs [diploid, 2n]) •  one from father and one from mother •  22 pairs of autosomes & 2 sex chromosomes,

XX female, XY male •  there are two homologues in a pair

cell cycle is controlled

•  Very specific molecules control progress through cell cycle.

•  Many of the signal transduction cascades control this cell cycle.

•  When things go wrong with these controls, cancer occurs.