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 Sexual Reproduction ► Involves two parents► Involves one parent cell that divides into (an egg cell and a two sperm cell) ► Daughter cells are► Daughter cells are identical to the parent genetically different cell (clones) than either parent ► Meiosis produces► Mitosis produces clones egg and sperm cells ► Some organisms can► AKA binary fission in some single celled reproduce either organisms (bacteria) sexually or asexually
Words to KnowChromatin► Long stretched out rods of DNA► Everyday life of cell, DNA able to be read by cell to do workChromosomes► Condensed DNA► Occurs in preparation for mitosis
Words to KnowSister Chromatids► Chromosomes replicate before mitosis► The two identical copies are attached by a centromere
Words to Know Homologous ChromosomesYou 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)
More Background/Words to Know► Each of your body cells ► Each of your sex cells contains 46 chromosomes, contain 23 chromosomes, 23 from your mom and 23 only one of each from your dad AKA chromosome AKA haploid diploid (2n) (n)► Body cells are called ► Sex cells are called somatic cells gametes (sperm in males,► Chromosome pairs #1-22 eggs AKA ova in females) are called autosomes ► They are created in the► Chromosome pair #23 are gonads (testes in males, called sex chromosomes ovaries in females► XX = female, XY = male
The Cell Cycle► The life cycle of the cell is known as the cell cycle► Itis divided into Interphase and the Mitotic phase
The Cell CycleInterphase is divided into Mitotic phase has 4 phases: 3 sections: Prophase MetaphaseG1: everyday life of cell, Anaphase the cell performs its Telophase job in the body -------------------------------S: DNA replicates Cytokinesis (begins in lateG2: all organelles anaphase, completed at replicate the end of telophase)
Interphase► Early Interphase ► Late Interphase► The cell performs its ► At this point, both the normal functions (G1) chromosomes and the► DNA is in the form of organelles have chromatin so that replicated (S and G2) genes (directions) can ► Cell size has increased be read to make ► Sister chromatids proteins needed by the joined by centromeres cell are present
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
Meiosis pp. 196-197► Has two parts: Meiosis ► Meiosis II is simply a I and Meiosis II mitotic division► Meiosis I is slightly different than mitosis ► It is called a in two ways: reduction division *two homologous because… sister chromatid pairs line up on each spindle ► Daughter cells reduce fiber (see p. 196) the # of chromosomes *crossing over from diploid (2n) to occurs in Prophase I 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
Chromosomal Mutations ► Otherchromosomal► Down Syndrome is mutations include: caused by a trisomy of chromosome #21 Duplication► This is due to a Deletion (part of nondisjunction of chromosome breaks off) sister chromatids Inversion (breaks off, during anaphase of reattaches upside down) meiosis when they are supposed to separate 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)
Normal Cells vs. Cancer Cells Normal Cells Cancer CellsGenetic factors (tumor Other genetic factors calledsuppressor genes) can oncogenes can encouragekeep cell cycle in check. cell cycle/mitosis and therefore lead to cancer.Cell cycle regulated by many Cancer cells either make theirproteins/chemicals (called own regulatorygrowth factors) so that cell proteins/chemicals (growthdivision is staggered (not all factors) or don’t respond tocells going through cell the regular ones and godivision at one time). At any through cell divisiongiven time, some cells are repeatedly without any regarddoing their job! to what other cells are doing/the job to be performed.
Normal Cells vs. Cancer Cells Normal Cells Cancer CellsNormal cells show density Cancer cells do not showdependent inhibition density dependentwhich means that they stop inhibition which means theydividing once they hit/touch continue to divide even whenother cells. 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 CellsNormal cell growth/division is also Cancer cells are able to recruitlimited by their resources…they blood vessels, hogging resourcesneed energy to do these things and that allow the tumor to grow biggerthat requires nutrients and oxygen while at the same time deprivingfrom the blood supply which is other nearby cells of nutrients. Thisshared among all cells. is called angiogenesis.Normal cells show anchorage Cancer cells in malignant tumorsdependence which means they are able to metastasize. Thismust be attached to their neighbors means that they are able to detachin order to grow/survive/divide 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 OptionsSurgery Localized removal of cancerous cells (tumor)Radiation therapy Used to kill cancer cells60-75% of all cancer over a more diffuse areapatients undergo RT and/or to kill any cancerwith many severe side cells left after surgicaleffects removal of a tumorChemotherapy 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 Enhances body’s naturalEffective only for some immune response tocancers, not all kill/suppress cancer cellsHormonal Therapy Uses strong steroids to suppress hormones thatEffective only for some stimulate specific cancerscancers, not all (ex: tamoxifen for breast cancer)Proton Therapy A type of radiationFDA approved only since therapy that targets2001, research on tumor cells more directlyeffectiveness and side than RT, reducing theeffects continues, $$$$ 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.