Why Do Cells Divide?

►To repair injured tissues

►For growth (to add bulk)

►To replace dead cells

►Depending on their function, some cells divide every few hours/days/weeks, others not at all

Types of Cell ReproductionAsexual

Reproduction►Involves one

parent cell that divides into two

►Daughter cells are identical to the parent cell (clones)

►Mitosis produces clones

►AKA binary fission in some single celled organisms (bacteria)

Sexual Reproduction

►Involves two parents (an egg cell and a sperm cell)

►Daughter cells are genetically different than either parent

►Meiosis produces egg and sperm cells

►Some organisms can reproduce either sexually or asexually

Cell Division Types

Words to KnowChromatin ► Long stretched

out rods of DNA►Everyday life of

cell, DNA able to be read by cell to do work

Chromosomes►Condensed DNA ►Occurs in

preparation for mitosis

Words to Know

Sister Chromatids

►Chromosomes replicate before mitosis

►The two identical copies are attached by a centromere

Words to Know

Homologous Chromosomes

You have two copies of every chromosome (one from mom, one from dad) in each of your cells

►They are similar (same genes in the same location on specific numbered chromosomes) but not necessarily identical (hair color: brown gene from mom, black gene from dad)

Homologous Chromosomes

More Background/Words to Know

► Each of your body cells contains 46 chromosomes, 23 from your mom and 23 from your dad AKA diploid (2n)

► Body cells are called somatic cells► Chromosome pairs #1-22 are called autosomes► Chromosome pair #23 are called sex

chromosomes ► XX = female, XY = male

► Each of your sex cells contain 23 chromosomes, only one of each chromosome AKA haploid (n)

► Sex cells are called gametes (sperm in males, eggs AKA ova in females)

► They are created in the gonads (testes in males, ovaries in females

The Cell Cycle►The life cycle of the

cell is known as the cell cycle

► It is divided into Interphase and the Mitotic phase

The Cell Cycle

Interphase is divided into 3 sections:

G1: everyday life of cell, the cell performs its job in the body

S: DNA replicatesG2: all organelles

replicate

Mitotic phase has 4 phases:

ProphaseMetaphaseAnaphaseTelophase------------------------------

-Cytokinesis (begins

in late anaphase, completed at the end of telophase)

Interphase

►Early Interphase►The cell performs its normal functions

(G1)►DNA is in the form of chromatin so that

genes (directions) can be read to make proteins needed by the cell

►Late Interphase►At this point, both

the chromosomes and the organelles have replicated (S and G2)

►Cell size has increased

►Sister chromatids joined by centromeres are present

Interphase

Prophase► Nuclear membrane

breaks down exposing chromosomes

► Nucleolus disappears► Centrioles migrate to

opposite sides of the nucleus

► The spindle forms between the centrioles. It is made of microtubules

► Chromosomes attach to spindle using their centromere

Metaphase

►The spindle fibers pull the chromosomes by their centromeres until they line up down the middle AKA equator of the spindle

Anaphase

►The centromeres of the sister chromatids split and the individual chromatids separate, being pulled by the spindle fibers to opposite ends (poles) of the cell

►Cytokinesis begins in late anaphase

Telophase

►The spindle breaks down

►Nuclear membrane returns

►Nucleolus reappears►Centriole returns to

its normal spot just outside the nucleus

►Cytokinesis is completed, 2 daughter cells are now formed

Cytokinesis

►This is the process by which the rest of the cell begins to divide

►The cell membane begins to pinch in (microfilaments do this) until the cell is completely divided into two cells

Cytokinesis

►Begins in late anaphase►Is completed as telophase ends

Mitosis+ Cytokinesis

Cell Division

Mitosis Summary & Animationhttp://www.youtube.com/watch?v=s4PaOz7eWS8

Mitosis Review

Which Phase Is It?

Meiosis pp. 196-197►Has two parts:

Meiosis I and Meiosis II

►Meiosis I is slightly different than mitosis in two ways:*two homologous sister chromatid pairs line up on each spindle fiber (see p. 196)*crossing over occurs in Prophase I

►Meiosis II is simply a mitotic division

►It is called a reduction division because…

►Daughter cells reduce the # of chromosomes from diploid (2n) to haploid (n)

Crossing Over

►Occurs in Prophase I

►Homologous pairs form a tetrad (4)

►They exchange genes AKA genetic recombination

►This results in increased genetic diversity of the offspring

Meiosis Summary & Animationhttp://www.youtube.com/watch?v=D1_-mQS_FZ0

Mitosis vs. MeiosisMitosis Meiosis

Location Somatic Cells (body cells)

Gonads (ovaries or testes)

Parent Cell Diploid (2n) Diploid (2n)

Daughter Cells

Diploid (2n) somatic cells

Haploid (n) sex cells (gametes)

# of Daughter Cells?

2 4

Crossing Over?

No Yes, in Prophase I

Genetic Recombinatio

n?

No Yes

Mitosis vs. Meiosis

Egg Cell vs. Sperm Cell Production(#, size, motility)

3 Polar bodies

1 Ovum (egg)

4 evenly sized sperm with flagella (tails)

Sexual Reproduction

Haploid (n)

Gamete Ova (egg)

Haploid (n)

Gamete Sperm

+ =

Diploid (2n) Zygote AKA Junior!

Chromosomal Mutations

►Down Syndrome is caused by a trisomy of chromosome #21

►This is due to a nondisjunction of sister chromatids during anaphase of meiosis when they are supposed to separate

►Other chromosomal mutations include:

Duplication

Deletion (part of chromosome breaks off)

Inversion (breaks off, reattaches upside down)

Translocation (breaks off, reattaches on another chromosome)

Diagnosis

►An amniocentesis takes cells from the developing fetus (dead skin cells floating in the amniotic fluid)

►A picture of the chromosomes called a karyotype is taken

►Chromosomal abnormalities can be seen (not individual genes)

Karyotypes

Normal Cells vs. Cancer CellsNormal Cells Cancer Cells

Genetic factors (tumor suppressor genes) can keep cell cycle in check.

Other genetic factors called oncogenes can encourage cell cycle/mitosis and therefore lead to cancer.

Cell cycle regulated by many proteins/chemicals (called growth factors) so that cell division is staggered (not all cells going through cell division at one time). At any given time, some cells are doing their job!

Cancer cells either make their own regulatory proteins/chemicals (growth factors) or don’t respond to the regular ones and go through cell division repeatedly without any regard to what other cells are doing/the job to be performed.

Normal Cells vs. Cancer CellsNormal Cells Cancer Cells

Normal cells show density dependent inhibition which means that they stop dividing once they hit/touch other cells.

Cancer cells do not show density dependent inhibition which means they continue to divide even when they are crowding other cells, leading to the formation of a tumor. This prevents nearby cells from doing their jobs well. Tumors are classified as either benign or malignant (actively diving/growing).

Normal Cells vs. Cancer CellsNormal Cells Cancer Cells

Normal cell growth/division is also limited by their resources…they need energy to do these things and that requires nutrients and oxygen from the blood supply which is shared among all cells.

Cancer cells are able to recruit blood vessels, hogging resources that allow the tumor to grow bigger while at the same time depriving other

nearby cells of nutrients. This is called angiogenesis.

Normal cells show anchorage dependence which means they must be attached to their neighbors in order to grow/survive/divide

Cancer cells in malignant tumors are able to metastasize. This means that they are able to detach from their parent tissue, enter the blood stream and travel to a new site, reattach and continue growing in the new area, disrupting the activity of multiple areas/tissues of the body, keeping cells from doing their jobs well.

Traditional Cancer Treatment Options

Surgery Localized removal of cancerous cells (tumor)

Radiation therapy60-75% of all cancer patients undergo RTwith many severe side effects

Used to kill cancer cells over a more diffuse area and/or to kill any cancer cells left after surgical removal of a tumor

Chemotherapy The use of strong chemicals to kill rapidly dividing cells. This includes both cancer cells and some normal cells (hair follicles)

Other Cancer Treatment OptionsImmunotherapy Effective only for some cancers, not all

Enhances body’s natural immune response to kill/suppress cancer cells

Hormonal Therapy

Effective only for some cancers, not all

Uses strong steroids to suppress hormones that stimulate specific cancers (ex: tamoxifen for breast cancer)

Proton TherapyFDA approved only since 2001, research on effectiveness and side effects continues, $$$$

A type of radiation therapy that targets tumor cells more directly than RT, reducing the impact on normal cells

Helpful Resource:

►http://www.cancerquest.org/cell-division-mitosis.html This website has great animations and

explanations comparing/contrasting typical cell division with cancer cell division.