Cell Division

Cellular Reproduction Organism’s life begins as one cell

Rudolf Virchow (1858) stated: All cells come from cells

Prokaryotes divide only to reproduce

Asexual repro: 1 parent 2 daughters

AKA Binary fission (“dividing in half”)

One set of DNA duplicates, cell divides

Eukaryotic cells divide for reproduction, growth, and replacement of cells

Other organisms (plants & animals especially) reproduce through sexual reproduction

Sperm + Egg

offspring

Offspring gets two

sets of genetic

information, one

from each parent

The Chromosome DNA is contained in structures called chromosomes within the nucleus of the cell

“chroma” color, “soma” body

Most of the time, chromatin fills the nucleus

Tangled mass of fibers of DNA & protein

When a cell begins to divide, the chromatin condenses and coils into chromosomes

Each chromosome has one long DNA molecule containing thousands of genes

The Chromosome Before a cell divides, it must duplicate its chromosomes

DNA replication!

Once duplicated, the chromosomes have sister chromatids with identical genes, joined at a centromere

When the cell divides, half goes to each daughter cell

The Cell Cycle Sequence of events from the time a cell divides to when it forms two daughter cells

Serves to double the cell’s parts, then splits

Stages:

Interphase 90%

Mitotic phase 10%

Mitotic Phase Unique to eukaryotes

Ends with 2 identical cells

Sub-stages of Mitosis:

Prophase

Metaphase

Anaphase

Telophase

Cytokenisis

Prophase Sister chromatids are attached at centromere

Centrioles separate and extend spindle fibers

Nucleolus disappears and nuclear envelope breaks down

Kinetochores form on each chromatid, spindle fibers attach

Metaphase Centrosomes at poles

Chromosomes lined up at metaphase plate (cell’s equator)

Kinetochores of sister chromatids face opposite poles

Anaphase Spindle fibers pull sister chromatids apart forming daughter chromosomes

Chromosomes move centromere first towards opposite poles

Cell elongates

Telophase & Cytokenisis

Cell continues to elongate

Daughter nuclei appear at poles

Nuclear envelopes reform

Spindle fibers disappear

Cytoplasms separate, new cell membranes form

Cytokenisis Cell pinches into two cells

Called a cleavage furrow

Plants are a little different

Vesicles save materials from cell wall

Form a plate at center of dividing cell

Cell plate fuses to cell wall, 2 cells

Factors that Affect Cell Division

Most reasons are unknown

“Growth Factors”

Proteins need for division; if not present it stops

Cell-cycle control system

A system of proteins in the cell that trigger & coordinates major events in the cell cycle

Make checkpoints

Factors that Affect Cell Division

Anchorage dependence

Cells must be in contact with a solid surface

Density-dependant inhibition Division will slow as the population grows more dense

When It All Goes Wrong Cell-cycle control system malfunctions

Cells divide excessively and in the wrong places; creates tumors

Benign: normal cells

Malignant: cancerous, invasive

Will divide indefinitely if not treated

When It All Goes Wrong Types of Cancers

Carcinoma

Skin, stomach lining

Sarcoma

Supporting tissues, bones

Leukemia & Lymphoma

Blood producing tissues, bone marrow

Treatments Aim to stop the spread of cancerous cells by stopping division

Chemotherapy (meds) and/or Radiation