The BasicsWithin the nucleus are chromosomes

Chromosomes occur in pairsone from mother, one from fathereach member of the pair is basically identicalhomologous chromosomes

most of an organism's cells are diploid (2n)

produced through mitosis

somatic cells or body cells (not sex cells)

Diploid

an organism's sex cells are haploid (n)

contain ½ the number of chromosomes

produced through meiosis

germ cells, gametes (egg and sperm)

Haploid

The Cell Cycle

The lifespan of a cellgrowth, replication, and division (reproduction) occurDivided into 2 basic phases:

Interphase (cell doing job) G1- growth of cell, doubles organelles, accumulates materials

S- DNA is copied (synthesized), chromatids form

G2- proteins that assist in cell division formed, mitotic spindle

Mitosis (cell division)

Not all cells divide (nerve, muscle cells), stay in stage Go

Checkpoints are found at the end of G1 and G2 that allow the cell to progress

Cyclins- proteins that allow cell division to progress

p53 controls checkpoint and will stop cell division in damaged cells

All cancer cells have multiple mutations

Mutations in checkpoints (esp. p53) allow cell to divide when damaged

Apoptosis (preprogrammed cell death) stops, telomeres (chromosome tips) do not shorten, or proteins bind that prevent checkpoint from stopping cell division

All can lead to cancer.

Mitosis and Cancer

MITOSIS

Mitosis is 1:2 cell division

Parent cells divide to form daughter cells which are identical to parent cells

Composed of 4 phasesProphaseMetaphaseAnaphaseTelophase

early prophasenucleolus and nuclear

envelope disappearcentrioles migrate to

opposite poles (animal cells)chromatin thickens into full

chromosomes

Prophase

late prophaseasters form and

spindle fibers become visible

kinetochore (spindle fibers) attach to centromeres

chromosomes line up along equatorial plane by their centromeres

they are perpendicular to each pole

Metaphase

centromeres of each chromosome divide in half

sister chromatids detach sister chromatids move

toward opposite poles as spindle fibers pull them

Anaphase

spindle fibers disappear centrioles return to

normal position nucleolus and nuclear

envelope reform chromosomes unravel

back into chromatin

Telophase

division of the cytoplasm plasma membrane furrows and

cleaves (divides in ½) 2 identical daughter cells are

produced in plants, the new cell wall begins

as a cell plate does not have to occur in all cells

of all organisms ie. Multi-nucleated tissue

Cytokinesis

primary means of asexual reproduction (binary fission, budding)all tissue growth takes place through mitosisreplacement of old, damaged, or malfunctioning cellsrepair of damaged tissueAllows cell specialization to occur

Functions of Mitosis

MEIOSIS

Meiosis is special kind of cell division

it occurs only in certain reproductive organs/cells

cells undergoing meiosis are called germ cells

gametes (egg or sperm) result

gametes are haploid

gametes are not genetically identical to the parent cell

meiosis is a 1:4 cell division

one diploid cell divides to produce 4 non-identical haploid cells

produces haploid gametes

ensures that offspring receive a full set of chromosomes

introduces genetic variability into the gametes and offspring

Functions

more complicated than mitosis

interphase with G1, S, and G2 is the same

M phase is now meiosisit is divided into 2 sets of cell divisions: meiosis I and II

reduction division

Differences from Mitosis

nuclear envelope and nucleolus disappear centrioles migrate to opposite poles spindle fibers appear as asters

Prophase I

synapsis homologous chromosomes physically paired

homologues tetrads (bivalents)

crossing over (crossover) non-sister chromatids exchange segments of

themselves with each other chiasmata Allow for more variation

Unique processes

tetrads line up along the equatorial plane homologous chromosomes in each tetrad

line up on random sides of each other independent assortment promotes genetic diversity

spindle fibers attach to centromeres

Metaphase I

homologous chromosomes separate and move to opposite poles

Anaphase I

nuclear envelope and nucleolus reform centrioles return to normal position spindle fibers disappear

Telophase I

cell cleaves into two daughter cells have 2 non-identical, diploid cells at the

end of meiosis I

Cytokinesis

essentially the same as mitosis each haploid daughter cell divides again independent separation of sister

chromatids

have 4 non-identical, haploid gametes at the end of meiosis II

these 4 came from one diploid germ cell

Meiosis II