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 DemandsCoordination 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 0.000005 meters in diameter.

chromatin

duplicatedchromosome

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 CycleEvents that occur in the life of a cell.Includes 3 major stages:1. Interphase 2. Mitosis3. Cytokinesis

1. Interphase (Cell is not dividing)

G1 Phase – carries out basic functions & performs specialized activities.duration is extremely variablecontains restriction checkpoint ~ cell “decides” to:divideenter a quiescent phase (G0)

die

1. Interphase (Cell is not dividing)G0 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 proteinsanimal cells replicate centrioles as well

1. Interphase (Cell is not dividing)G2 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

Review of the M-phase

Review of the M-phase

Review of the M-phase

Review of the M-phase

Review of the M-phase

Review of the M-phase

Review of the M-phase

Review of the M-phase

Review of the M-phase

Cancer Is One Outcome of A Runaway Cell Cycle

Licentious division - prostate cancer cells during division.