Mitosis and Cell Division

How do you grow? Give examples and be specific. Cell Division (Mitosis)

2What if there was no more Mitosis?

Start the explore by saying we used wound healing to introduce mitosis. Ask the students what Mitosis is? (Process of cellular division/replication)In order to have them think about why mitosis is important and all of its functions, ask what if there was no more mitosis? What would be the consequences?(Allow for student response) Expected responses: -Wounds would not heal-Growth could not happen-Zygote division would not occur-Cell replacement and repair would not happen3Reasons for Mitosis:Generate new cells for:GrowthRepairMaintenance

Emphasize these three main functions of mitosis. Relate these to the previous slide and why organisms could not complete these tasks without mitosis. 4DNADeoxyribonucleic acid

During mitosis, DNA gets reorganized from messy, spaghetti-like CHROMATIN into organized, neat CHROMOSOMES!

Humans have 46 chromosomes (23 from your mom, 23 from your dad)

Relaxed chromatinNeat & tidy chromosomeChromosome

What initiates cell division?A cell or cells that need to undergo cell division receive a signal to begin division

QUESTION: What do you think are examples of division signals?

Students need to understand that cells do not undergo cell division at all times, only when a division signal is received. Ask students what they think are examples of division signals/when they occur?Expected answers:Inflammation from wound or cutPuberty General growth signalsFertilization of an eggDevelopment of an embryoHair growth Etc..

8Preparation - Interphase. Interphase: the preparation stage for a cell going through divisionDuring interphase, 3 main preparations occur:Growth DNA replication (4692 Chromosomes)*IN HUMANSNew organelles and cellular materials are made (proteins made in ribosomes!)

There is a preparation stage before mitosis that ensures a cell is properly prepared to undergo mitosis. Students need to understand why all of these preparations are necessary and must happen before mitosis can be completed. Emphasize the 3 main preparations that occur during interphase growth, DNA replication, and new organelles and cellular materials. The steps of interphase are outline in the next slide. 9InterphaseG1SG1: Growth 1S: SynthesisG2: Growth 2As demonstrated in the pie chart, cells spend much more time in interphase preparing for mitosis rather than actually undergoing mitosis. Explain that this is because the preparation is so important for a cell to divide and it needs to be done efficiently and accurately. Explain what happens during G1 (growth and production of new organelles and material), S (DNA synthesis or replication) and G2 (additional growth and production of organelles and material)

*emphasize that new organelles, plasma membrane, cytoplasm, etc. all needs to be made 10Why is interphase so important?A cell must prepare accurately in order to divide into two identical cellsDNA must be replicated properly so that both cells have the same genetic material (46 92 46) *IN HUMANSThe cell must grow and make new organelles/cellular material in order to give half to the new cell

11Preparation complete!The cell is now ready to undergo mitosis!

12Steps of Mitosis

Prophase-Microtubules start to form-Nuclear envelope starts to disappear 2. Metaphase-Chromosomes align at the center of the cell (metaphase plate)-Spindles attach to the chromosomes (each chromatid)Steps of Mitosis

4. Telophase-Nuclear envelope starts to reform -Cell elongates

3. Anaphase-Spindle fibers shorten to pull sister chromatids apartProphase

Late Metaphase

Anaphase

Telophase

What happens during mitosis?Chromosome alignment.The replicated chromosomes (DNA) move towards the middle This alignment allows the chromosomes to be separated equally between the two cellsProteins move and align the chromosomes

Explain that as the cell goes through mitosis, it is sorting or aligning the chromosomes that allows the DNA to divide and be sorted evenly between the two cells.Also emphasize that it is the proteins that move and align the chromosomes.

The new curriculum does not place an emphasis on the names of the mitosis phase, therefore try to get the students to see and understand more of what is actually going on in the cell rather than the specific phases. 19What is the point of alignment?A.B.What would be the result of these two cells dividing?Have students draw in their notes the different products for A and B. Then draw the results on the board and discuss why chromosome alignment is so important. 20Mitosishttp://labs.bio.unc.edu/Salmon/

What happens during mitosis?Physical division (Cytokinesis).Not only is the DNA divided equally, but the new organelles and cellular material must be divided equally as well Cytokinesis: The cell pinches or furrows in the middle then physically separates into two identical cells. (cleavage)

Discuss briefly how cytokinesis occurs, pinching then physically separating into two identical cells. 22What is the result of mitosis?Two identical cells (the original and a new cell)Think of a photocopier machine:

Original(46 chromosomes)Copy(46 chromosomes)(Interphase, mitosis, cytokinesis)Use the analogy of a photocopier machine. The original is copied but still exists. Therefore, it is not two new cells rather the original cell and a copy of that cell. Students often get confused by the term daughter cells which is why it has been omitted. Focus on the original cell still existing but producing a new cell as well. 23Plant Cell DivisionPlant cells divide just like animal cells EXCEPT they do not have centrioles and their cell wall causes cytokinesis to occur differently

A new cell wall forms in between the two new cells in plant cells rather than furrowing/cleavageThis could be a good time to review the stages since they are not labeled. 24SCAB UNDERLYING BLOOD VESSELUNWOUNDED SKIN CELLS BLOOD (BLOOD CELLS)

Mitosis in action! Cross section of a woundThe purpose of this slide is to show how cell division aids in the healing of wounds. Ask the students to imagine that this is a cross section of the finger wound they saw earlier in the YouTube.

The site starts off with a gaping hole in the layer of skin cells. The underlying vessel is broken and blood fills the gap. As the blood clots/dries, certain fibers within it attempt to contract the wound site. Cells at the perimeter of the cut realize they no longer have a neighbor and are chemically signaled (yellow explosion clip art) to divide. The goal is for the cells to continually divide in the direction of the green arrows in order to close the gap/heal! (Its only the cells on the basal layer that are actually dividing and sending new cells up. For the sake a simplicity this will suffice, I think.) The developing scab acts as a mechanical barrier to protect the healing process occurring just beneath it. When this process is complete the scab usually falls off to reveal the newly created skin tissue. If the scab is pulled off too early then the healing process may be stunted and therefore take longer.

*the newly created cells are a shade lighter for two reasons: 1) so students can visualize the newly created cells and 2) represents the tendency of scars to have a slightly different appearance from the uninjured tissue around it.

**see if students can guess which cells will be signaled to divide by, at least, the last round of mitosis. From this you can see if they understand that only cells without their neighbor will be signaled to undergo mitosis, in this scenario.25-Growth

-DNA Replication

-More Organelles MadeAlert! Cell receiving division signalCell undergoing mitosisZooming in on one cell in the cross sectionAs the preview slide shows, there is an exterior signal for the cells to divide due to the wound. ALERT! Skin is wounded and needs to be repaired! More cells are needed!The first thing that occurs is Interphase, where the cell grows and increases its supply of organelles, and most importantly, copies its DNA. Mitosis will begin, and the replicated chromosomes will align on the metaphase plate26Once aligned, the cell continues to go through Mitosis then Cytokinesis, and separate to create two identical cells. This increases the population of cells, filling the gap in the skin to heal the wound.27