Cell Division - Matawan-Aberdeen Regional School District

Cell Division - Matawan-Aberdeen Regional School District

Cell Cycle Why Cells Divide Why do cells need to divide? Cell Division - Purpose Provides a means of reproduction for organisms.

Provides a means of growth in multicellular organisms. Provides a means of repair in multicellular organisms. Reproduction Unicellular organisms divide in order to form new organisms. No Elizabeth, dont go!

Apologies to Gary Larson and the FAR SIDE Reproduction Multicellular organisms divide to reproduce special cells (gametes) that will carry out the formation of a new organism. Growth Multicellular

organisms are made of millions to trillions of microscopic cells rather than a few large cells. Growth mainly occurs by increasing the number of cells. Repair Many microscopic cells as

opposed to only a few large ones is also advantageous in the case of injury. How so? Is there any advantage to possessing many small cells as opposed to a few large cells? Examine the two cells below. The blue color represents the area of diffusion of glucose within the cell over equal periods

of time. Do you see a potential problem that might suggest an answer to the question above? nucleus Surface Area to Volume Ratio Relative size of the surface area of the plasma membrane and the volume of the cell reach a critical point. L W

H Analyze the Day 1 1 1 following cubic cell: one 1. Day 2 two 2

2 Nuclear Limitations 2. Limited capability of the nucleus -- there is a finite amount of genetic material because the genome size remains constant even as the cell grows.

Why Cells Divide What actually triggers or cues the cell about the need to divide? Most of it comes down to chemicals. Why Cells Divide Two irreversible points in cell

cycle replication of genetic material separation of sister chromatids REPLICATION (S phase) SEPARATION (anaphase) Why Cells Divide

Checkpoints process is assessed & possibly halted 3 major checkpoints: G1/S can DNA synthesis begin? G2/M

has DNA synthesis been completed correctly? commitment to mitosis spindle checkpoint are all chromosomes attached to spindle? can sister chromatids separate correctly?

Checkpoint control system Checkpoints cell cycle controlled by STOP & GO chemical signals at critical points signals indicate if key cellular processes have been completed correctly Why Cells Divide The decision to divide has

both external and internal chemical influences. Why Cells Divide EXTERNAL Cells can have direct contact with each other through cell junctions or surfaces. Certain chemicals can easily come in contact with adjacent cells in this way.

Why Cells Divide Cells can communicate with each other by secreting chemical messengers into the extracellular fluid. Paracrine signaling target is near the signaling

Hormonal signaling signal travels through source (ex. Adjacent cells) bloodstream from source to target (pituitary ovaries)

Synaptic signaling chemicals travel across small gap or synapse (neurotransmitters from neuron to neuron) Why Cells Divide 1. The signaling process consists of 3 stages: EXTERNAL Reception - Chemical

messengers interact with receptors, often those of the plasma membrane. Why Cells Divide INTERNAL 2. Transduction- This begins a chain of events in a chemical pathway within the cell, such as a phosphorylation cascade

Phosphorylation cascading refers to the transfer of phosphate groups from one protein molecule to the next, via a type of kinase enzyme, subsequently activating the molecules in the pathway. (Think Domino effect) Why Cells Divide 3. Response - cellular activity

Could be: Rearrangement of cytoskeleton Opening/closing ion channels Initiation of metabolic activity, such as cell division. Chemical Regulation of the Cell Cycle Once signaled, Kinase* proteins

give the go ahead signals at G1 and G2 checkpoints. *Kinase proteins are a family of related proteins that activate proteins which in turn activate certain cell processes such as cell division. These kinases (Cdks) themselves are not activated until they are attached to

cyclin (becoming MPFs) Cyclin concentrations fluctuate within a cell, slowly building up until cell division begins. The MPFs (Cdk-cyclin) cause nuclear membrane destruction and stimulate other kinases, setting the chain of events in motion

known as mitosis. The Cell Cycle (Internet click here)(click on the words above to go to website and ACQUIRE more information on the cell cycle.) Consists of phases characterized by important events in the

life of a cell After Mitosis MPFs (partially made of cyclin) levels must drop to allow the cell to enter interphase again.

Proteins such as ubiquitin*, regulate the cycle by causing the degradation of cyclin and kinases. This brings about the end of mitosis and the reforming of the nuclear membrane. Thus the new cells continue to interphase. *Ubiquitin common across most eukaryotic species; hence ubiquitous. Other Division Halting Processes

Density-dependent inhibition when the cell density reaches a certain maximum, many cells stop dividing. Anchorage dependence contact with a substratum may influence if a cell stops dividing. External signals Growth factors

coordination between cells protein signals released by body cells that stimulate other cells to divide density-dependent inhibition crowded cells stop dividing each cell binds a bit of growth factor not enough activator left to trigger division in any one cell

Degradation of protein growth factors also possible anchorage dependence to divide cells must be attached to a substrate touch sensor receptors Example of a Growth Factor

Platelet Derived Growth Factor (PDGF) made by platelets in blood clots binding of PDGF to cell receptors stimulates cell division in connective tissue heal wounds Other Division Halting Processes Necrosis and Apoptosis Necrosis death due to insult/injury

Apoptosis programmed cell death What benefits would there be for an organism to destroy its own cells? http://virtuallaboratory.colorado.edu/Biofundame ntals/lectureNotes/Topic5-4_CellDeath.htm Cancer

Transformation Alterations in genes implicated with cell cycle begin the conversion of a normal cell to cancerous cell. Oncogenes Tumor Supressor genes Tumor mass of abnormal cells Benign tumor remains at site Malignant Becomes invasive enough to interfere with organ function

Metastasis cancer cells spread to other sites Development of Cancer Cancer develops only after a cell experiences ~6 key mutations (hits) unlimited growth turn on growth promoter genes

ignore checkpoints turn off tumor suppressor genes (p53) escape apoptosis turn off suicide genes immortality = unlimited divisions

turn on chromosome maintenance genes promotes blood vessel growth turn on blood vessel growth genes overcome anchor & density dependence turn off touch-sensor gene

p53 master regulator gene NORMAL p53 p53 allows cells with repaired DNA to divide. p53 protein DNA repair enzyme p53 protein

Step 1 Step 2 Step 3 DNA damage is caused by heat, radiation, or chemicals. Cell division stops, and p53 triggers enzymes to repair damaged region.

p53 triggers the destruction of cells damaged beyond repair. ABNORMAL p53 abnormal p53 protein Step 1 Step 2

DNA damage is caused by heat, radiation, or chemicals. The p53 protein fails to stop cell division and repair DNA. Cell divides without repair to damaged DNA. cancer cell

Step 3 Damaged cells continue to divide. If other damage accumulates, the cell can turn cancerous. Explain the purpose of meioisis. Compare and contrast the processes of mitosis and meiosis. Distinguish between male and female

gametogenesis in humans. Define tetrad, homologous chromosome, synapsis. Describe the process of crossing-over. Identify the composition of a eukaryotic chromosome. Explain the results of a duplication, deletion, inversion and translocation of chromosomes. Define nondisjunction and provide examples of several genetic disorders resulting from nondisjunction.

Genomes and Chromosomes A Closer Look at Reproduction Genomes and Chromosomes An organism is determined by its organisms genetic material or genome. In order to maintain life, any new cells created must

possess the same exact genome. Genome and Chromosomes The mitotic portion of the cell cycle ensures that the genome is transferred correctly to the new cells created.

Genes and Chromosomes http://images.sciencedaily.com/ 2009/10/091005110401-large.jpg Chromosomes are the condensed version of the DNA-protein complex called chromatin. http://www.damours.iric.ca/Site/Projects_files/Chromatin_Nucleosomes Genes and Chromosomes

Once the chromatin is replicated during the S phase of the cell cycle a cell is ready to divide. Kinetochor e

Mitosis vs. Meiosis Mitosis Meiosis Both Mitosis vs. Meiosis Mitosis Chromosome Replication

Cell division end cell # Chromosome Result Both Meiosis During S phase

Once two Same as original: Diploid Twice four Half of the originalhaploid Meiosis

For what purposes would HALF the chromosome material be appropriate? For the union of two cells (gametes) sexual reproduction. Meiosis I Homologous Chromosomes pair up forming a tetrad in a process called synapsis.

At certain points the chromatids of the homologs may crisscross, forming a chiasmata. Meiosis I As the cell transists from metaphase to anaphase it is the homologs which are separated rather than the chromatids.

Meiosis I Cytokinesis occurs, resulting in two haploid cells. Depending on the type of gamete, meiosis II may proceed directly or be carried out at a later date. Meiosis II Proceeds

much like the process of mitosis, however, the end results differ due to Meiosis I. 4 haploid cells are created. Meiosis Humans Spermatogenesis 4 viable

haploid sperm produced. Oogenesis 1 viable haploid egg and 3 non-functional polar bodies produced. What is the advantage of producing one LARGE egg as opposed to 4 smaller on http://legacy.owensboro.kctcs.edu/gcaplan/anat2/notes/gametogenesis.jpg Meiosis Plants produce spores

which then mitotically divide to form gametophyte. This produces gametes which then fuse to form sporophyte. Genetic Variation Does not exist in cells produced by mitosis, unless some mutation arises. Sexual reproduction

provides a recombination of genetic material in 3 ways. Genetic Variation Independent assortment of homologues. Genetic Variation Random joining of gametes.

Getting here is only HALF the race Boys! Genetic Variation Crossing over, as demonstrated in lab activity, involves the exchange of genetic material between nonsister

chromatids, during prophase I Genetic Variation Deletion and duplication see lab activity Inversion see lab activity CHROMOSOMES, KARYOTYPES, AND SEXUAL LIFE

CYCLES KARYOTYPE CARTOONIZE D Ideogram of chromosome after staining. The short arm of the chromosome is referred to




OF CENTROMERE USED FOR IDENTIFICATION. KARYOTYPES What can you determine about this individual? KARYOTYPES What can you

determin e about this individu al? KARYOTYPES What about this individua l?


Many organisms, other than animals, sexually reproduce. Sexual reproduction is a way to increase variety within a population. This can then lead to evolution of the populations themselves. The sexual life cycle itself, has been subject to evolutionary changes.

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