Cell Division and Genetics – Mechanisms for a Knit of Identity and Thread of Distinction

DNA and Its Faithful Replication – The Knit of Identity Because DNA stores genetic information and is faithfully replicated, information is passed largely unaltered from cell-to-cell, generation-to- generation.

Proteins and Their Production – The Primary Reason for DNA

Cell Division Demands Coordination of DNA Replication, Mitosis and Cytokinesis What’s so important about cell division (3 reasons)?

Cell division requires coordinated division of chromosomes (mitosis) ….. …… and division of the cytoplasm (cytokinesis).

DNA Replication – Simple in Principle, Complicated in Practice

DNA is Packaged into Chromosomes DNA in the cell is virtually always associated with proteins. The packaging is impressive – 2 meters of human DNA fit into a sphere about meters in diameter. chromatin duplicated chromosome

The Link Between DNA Replication and Chromosome Duplication

DNA is Condensed into Visible Chromosomes Only For Brief Periods in the Life of a Cell 95% of the time, chromosomes are like this. Easily visible chromosomes are apparent perhaps 5% of the time in an actively growing cell and less in a non-growing cell.

A Karyotype is an Arranged Picture of Chromosomes At Their Most Condensed State A normal human karyotype Boy or girl? Note that almost all chromosomes come in homologous pairs.

From Birth to Rebirth, a Cell Progresses Through Characteristic Stages That Constitute the Cell Cycle In multicellular organisms like us, progress through the cell cycle is carefully regulated.

The Cell Cycle Events that occur in the life of a cell. Includes 3 major stages: 1.Interphase 2.Mitosis 3.Cytokinesis

1. Interphase (Cell is not dividing)  G 1 Phase – carries out basic functions & performs specialized activities.  duration is extremely variable  contains restriction checkpoint ~ cell “decides” to:  divide  enter a quiescent phase (G 0 )  die

1. Interphase (Cell is not dividing)  G 0 Phase – cell maintains specialized characteristics, but does not divide Ex. neurons & muscle cells

1. Interphase (Cell is not dividing)  S Phase – cell replicates chromosomes & synthesizes proteins  animal cells replicate centrioles as well

1. Interphase (Cell is not dividing)  G 2 Phase - cell synthesizes additional proteins (ex. tubulin) & assembles/stores membrane material

2.Mitosis (M phase) – Equal distribution of replicated genetic material.  Four steps:  Prophase  Metaphase  Anaphase  Telophase

2.Mitosis – Prophase  replicated chromosomes condense  centrosomes separate & migrate toward opposite sides of cell  mitotic spindle forms (microtubules grow out from centrosomes)  nucleolus and envelope disappear

2.Mitosis – Late Prophase (prometaphase)  nuclear membrane breaks down  spindle fibers attach to centromeres of chromosomes

2.Mitosis – Metaphase  chromosomes are lined up single-file along equator of mitotic spindle

2.Mitosis – Anaphase  Centromeres part, sister chromatids (now called chromosomes) separate  chromosomes move toward opposite poles  ?

2.Mitosis – Telophase  mitotic spindle breaks down  chromosomes decondense  nuclear membranes reform around two nuclei  nucleoli reappear

3.Cytokinesis  Distribution of cytoplasm to daughter cells  begins during anaphase or telophase  differs in animal & plant cells

3.Cytokinesis in animal cells  Cleavage furrow (slight indentation) forms around equator of cell  Actin & myosin microfilaments act like a drawstring to pinch the cell in two  Usually an equal division

In Animal Cells, a Cleavage Furrow Forms and Separates Daughter Cells Cleave furrow in a dividing frog cell.

Review of the M-phase

Cancer Is One Outcome of A Runaway Cell Cycle Licentious division - prostate cancer cells during division.