How do cells grow & reproduce?

In the Beginning – One Cell

• Most of the organisms start out as one cell• Humans start out as a single cell, the zygote, formed

by uniting a sperm and egg• The zygote divides to make trillions of cells• During the process of dividing, cells become

specialized to function in the various tissues and organs of the body = differentiation

• Mitosis is the process of cell division in eukaryotic cells

The Cell Cycle =

Sequences of growth and division of a cell

Two main parts:1. Interphase – growth phase; takes most of the time

2. Mitosis – cell division phase

G1G1

MM

G2G2

SS

Interphase

G1G1

MM

G2G2

SS

The Cell Life Cycle

Gap 1 - Doubling of cell size, increase in the number of organelles, regular cellular activities

S - Synthesis of DNA

Gap 2 - Final preparation for division

Mitosis - Cell division

G1, S, & G2 = Interphase =

busy time

S phase – DNA replication

Fig. 3.26

INTERPHASE:

nuclear envelope is clearly visible

chromatin = uncoiled DNA

http://www.fed.cuhk.edu.hk/~johnson/photomicrographs/mitosis/animal/animal_interphase.htm

nucleolus is still visible

Interphase

• Metabolic phase• Cell growth• DNA replication• Protein synthesis• Visible nucleus with

CHROMATIN

Stages of Mitosis

Interphase

Anaphase

Telophase

Metaphase Mitotic spindle

Prophase

Nucleus with chromatin

Equator of the cell

Condensed chromosomes

Disappearing nuclear membrane

Poles of the cell

Mother cell

Two daughter

cells

PROPHASE

chromosomesbecome visible

nuclear envelopedisappears

nucleolusdisappears

http://www.ac-dijon.fr/pedago/svt/documents/mitose/prophase.gif

Prophase

• Centrioles move to the opposite sides of cell

• Spindle fibers from centrioles connect with chromosomes

Prophase

METAPHASE

http://iccbweb.med.harvard.edu/mitchisonlab/Pages/mt.html

METAPHASE

http://www.chembio.uoguelph.ca/educmat/chm736/cycletx.htm

chromatids

spindle

centriole

Chromosomes line up at the equator of the cell

Each chromatid is attached to a separate spindle fiber by its centromere

Metaphase

Nature (408. 423, 2000).

chromatids spindle

centriole

http://www.blc.arizona.edu/courses/181gh/Lectures_WJG.01/mitosis_F.01/mitosis.html

ANAPHASE

http://www.univ-orleans.fr/SCIENCES/BIOCHIMIE/MMC/accueil.htm

Conly Rieder http://www.wadsworth.org/BMS/SCBlinks/WEB_MIT2/HOME.HTM

ANAPHASE

early late

http://www.blc.arizona.edu/courses/181gh/Lectures_WJG.01/mitosis_F.01/mitosis.html

ANAPHASE

Chromatids separate and migrate to opposite poles

Anaphase

TELOPHASE

Daughter Nucleus

Daughter Nucleus

Spindles dissolve

Telophase

• Chromosomes uncoil

• Two identical nuclei are formed (DNA is in the chromatin form)

• Nuclear membrane & nucleolus reappear

Cytoplasmic Division: Cytokinesis

• Division of a cell’s cytoplasm to form two identical cells

• Usually begins in late anaphase• Interphase begins when cytokinesis is

complete

Replication

Chromosomes, Chromatids & Centromeres

Centromere

Chromosome arm

Chromosome arm

Identical chromatid(sister chromatid)

Chromatid

Anaphase

A packaged chromosome

Two identical chromosomes

DNA doubling during S-phase

Joins sister chromatids

Results of Mitosis:

Two new diploid cells with chromosomes that are identical to those of the parent cell

Hmm…

Why is it necessary for a cell’s chromosomes to be distributed to its daughter cells in such a

precise manner?