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?

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.

Cancer Is One Outcome of A Runaway Cell Cycle

Licentious division - prostate cancer cells during division.

The Knit of Identity - Mitosis Precisely and Evenly Divides Duplicated Chromosomes

Precisely dividing the duplicated chromosomes has the consequence of providing each new cell with an identical and complete set of genetic instructions.

interphase prophase metaphase

Mitosis Precisely and Evenly Divides Duplicated Chromosomes

Cytokinesis is the process of cell division and it is distinct and separable from mitosis.

Mitosis in Action

Blue shows DNA, green shows spindle fibers.

In Animal Cells, a Cleavage Furrow Forms and Separates Daughter Cells

Cleave furrow in a dividing frog cell.

The Plant Cell Wall Forces Cytokinesis to Play by Different Rules