Cell Division

Chapter 9

Why do you think cells in all plants and organisms need to divide?

To replace damaged tissue To increase in size To reproduce

Repair

• Cells are constantly repairing themselves• If a cell can’t be repaired new ones are

produced to fill the void

Growth

• Cells are also what create our size• As we grow our cells are constantly

reproducing • If the reproduction rate is faster than normal

we grow

ReproductionAsexual

• Done by somatic or body cells

• Creates identical daughter cells

Sexual

• Done by sex cells• Creates genetically

different daughter cells

What do we need for cell division?

• Chromatin: a mass of DNA found in the nucleus

What do we need for cell division? • Chromosome: a compacted

piece of chromatin that is used for cell division

• Sister Chromatids: A pair of identical Chromosomes

• Centromere: The center section where the sister chromatids are connected

Sister chromatids

Centromere

TEM

36,

600

DNA supercoil

LE 8-4

Sister chromatids

CentromereTE

M 3

6,60

0

Sister chromatids

Chromosomedistribution

todaughter

cells

Chromosomeduplication

How do cells divide?

• Cell Cycle: an orderly sequence of events where cells divide

• The cell cycle consists of two major phases– Interphase (90% of the time)– Mitotic Phase (10% of the time)

The Cell Cycle

In humans and other mammals, cells that reproduce daily have a cell cycle that usually lasts 10 to 20 hours.

The Cell Cycle: series of events that cells go through from “birth” to reproduction

Interphase

• Phase where all metabolic processes and functions happen– Ex:

• Cellular respiration• Protein creation• Movement• Growth• Other desired function

Interphase

• Interphase is also when the cell prepares for cell division– Ex:

• Increases proteins• Duplicates organelles• Grows in size• Duplication of DNA

Mitotic Phase

• The division phase of the cell• There are two main parts of M phase

– Mitosis – Cytokinesis

Mitotic phase

• Mitosis– The division of a cells nucleus and DNA into two

equal parts– Creates two daughter nuclei

• Cytokinesis– The division of the cells cytoplasm

• Together they create two identical daughter cells

Mitosis

• Prophase:– Sister chromatids are formed– Formation of spindle– Nuclear envelope breaks down

• Metaphase:– Sister chromatids line up– Spindle is formed and attaching to chromosomes

LE 8-6a

INTERPHASE PROPHASE PROMETAPHASE

KinetochoreFragmentsof nuclearenvelope

CentrosomeEarly mitoticspindleChromatin

Centrosomes(with centriole pairs)

LM 2

50

Nucleolus Nuclearenvelope

Plasmamembrane

Chromosome, consistingof two sister chromatids

Centromere Spindle microtubules

Mitosis

• Anaphase:– Separation of sister chromatids– Spindle pulls chromosomes to either side of the cell

• Telophase:– Spindle breaks down– Nuclear envelopes form (2)– Chromosomes loosen to become chromatin

• Cytokinesis:– Cell pulls apart to create two identical cells

LE 8-6b

METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS

Metaphaseplate

Spindle Daughterchromosomes

Nuclearenvelopeforming

Cleavagefurrow

Nucleolusforming

Cytokinesis in animal cells

Animal

• Formation begins with indentation

• Cell is pulled/ pinched until it breaks apart

Plants

• Formation begins with a disc containing cell wall materials

• A cell plate forms between the two nuclei

Cleavage furrow

Cleavagefurrow

Daughter cells

Cleavagefurrow

Contracting ring ofmicrofilaments

SEM

14 0

Cytokinesis in plant cells• Formation begins with a disc containing cell wall materials• A cell plate forms between the two nuclei

Cell wall New cell wall

Daughter cellsCell plateVesicles containingcell wall material

Benign vs. malignant tumor• Benign tumor:

– abnormal mass of normal cells Malignant tumor:

• Masses of cells that result from the reproduction of cancer cells

• Cancer – Disease caused by cells that loose their ability to

control rate of division

Meiosis

• Organisms that reproduce sexually have specialized cells called gametes

• Gametes are the result of a type of cell division called meiosis

Diploid and haploid• Almost all human cells are diploid or containing two

homologous sets of chromosomes 2n = 46• Eggs and sperm cells (gametes) are haploid or

containing a single set of chromosomes n = 23

HUMAN KARYOTYPE

A display of all the 46chromosomes of an Individual.

9.5 page 2

ORGANISM (Genus species) NUMBER OF CHROMOSOMES Homo sapiens (human)______________________________46 Mus musculus (house mouse)_________________________40 Drosophila melanogaster (fruit fly)_____________________8 Caenorhabditis elegans (microscopic roundworm)_________12 Saccharomyces cerevisiae (budding yeast) ______________32 Arabidopsis thaliana (plant in the mustard family) ________10 Xenopus laevis (South African clawed frog)______________36 Canis familiaris (domestic dog)________________________78 Gallus gallus (chicken) ______________________________28 Zea mays (corn or maize)____________________________20 Muntiacus reevesi (the Chinese muntjac, a deer) _________23 Muntiacus muntjac (its Indian cousin) __________________6 Myrmecia pilosula (an ant) ___________________________2 Parascaris equorum var. univalens (parasitic roundworm)___2 Cambarus clarkii (a crayfish)__________________________200 Equisetum arvense (field horsetail, a plant)______________216

Horsetail

MITOSIS

Meiosis

In the human life cycle a haploid egg and sperm fuse and form a diploid zygote. Mitosis produces an embryo with numerous cells that continue to multiply and develop.

haploid egg and sperm

diploid zygote

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120074/bio17.swf::Comparison%20of%20Meiosis%20and%20Mitosis

2n

2n 2n

MITOSISMEIOSIS

Original diploid cell

2 diploid daughter cells

Genetic variation is a result of two processes that occurr during meiosis:

• Independent assortment of chromosomes, and • Crossing over

• During metaphase I, the independent assortment of chromosomes that end up in the resulting cells occurs randomly

• Crossing over: exchange of genetic material between homologous chromosomes during prophase I of meiosis

• Genetic recombination: new combination of genetic information in a gamete as a result of crossing over during prophase I of meiosis

(pages 195, 200, & 201) MITOSIS MEIOSIS

TYPE OF CELL (that undergoes this division)

# OF CELL DIVISIONS

Starts/ends as diploid or haploid cell

# OF DAUGHTER CELLS

# OF CHROMOSOMES AFTER DIVISION

EXCHANGE OF DNA (Y/N)

UNIQUE OR IDENTICAL CELL AFTER DIVISION

Development of egg and sperm

Onion Root Cell Observations

• Using the largest magnification (X400), find a section of the onion root (towards the tip works better).

• Count only the cells in one of the quadrants.• Try to find the different stages of cell division, and fill out

the table bellow as accurately as you can.

Phase # of cells % Time/min.

Interphase

Prophase

Metaphase

Anaphase

Telophase

Total # of cells