L09 GRQs Mitosis, Development, and cancer PDF

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Unit 2: Genetics Guided Reading Questions

LO9 Mitosis, Development and Cancer Guided Reading Qs (Reading from textbook: Chapter 8 introduction-8.10 AND one article posted about breast cancer) Reading Objectives:  Contrast asexual and sexual reproduction in outcome and types of organisms/cells that use each.  Recognize/describe the stages of mitosis, contrasting animal and plant cells.  Articulate how the cell cycle differs in normal, dividing cells compared to nerve cells or cancer cells.  Explain the significance of a mutated BRCA-1 gene in terms of risks and consequences. Chapter 8 reading: 1. What are the options for a woman with stage 0 breast cancer? -DCIS (ductal carcinoma in situ) = stage 0 breast cancer. Cancer cells have not spread beyond the milk ducts of the breast. -Options for a woman with DCIS = a lumpectomy (removal of part of the breast), single or double mastectomy (removal of most of all of one or 2 breasts), and radiation therapy. What does it mean when cells are cancerous? -Cancer cells start out as normal cells, but genetic mutations cause them to lose the ability to regulate their division. Cancer cells become unconstrained in their multiplying at an alarming rate, dividing and spreading quickly, so that they invade other tissues and disrupt organ function, killing the host. 2. Contrast asexual from sexual reproduction. -Asexual: reproducing with only yourself via cell division (single-celled prokaryotes). The creation of genetically identical offspring by a single parent, without the participation of sperm and egg. -Sexual: eggs and sperm are produced by a particular type of cell division (multicellular organisms). Requires gametes, egg, and sperm. -gamete: has only half as many chromosomes as the parent cell that gave rise to it, and these chromosomes contain unique combinations of genes. -in sexual reproduction, offspring are not identical to their parents, although they generally resemble their parents more than other organisms of the same species -Because of this, sexual reproduction can produce great variation What does cell division have to do with human embryonic development? -Cell division: two “daughter” cells result from one “parent” cell and all 3 are genetically identical to each other. -Cell division is necessary in the production of gametes -Also, cell division enables sexually reproducing organisms to develop from a single cell – the fertilized egg, or zygote – into an adult organism

-All of the cells that make up our bodies right now came to be through repeated cell divisions that began as a single fertilized egg cell in your mother’s womb -Once we are fully grown, cell division occurs to replace damaged cells (ex: skin cells continuously shedding and creating new skin cells) 3. When prokaryotes divide, which is called __binary fission (type of cell division that means dividing in half) _______, what needs to be divided to daughter cells? -The parent cell is what divides into the two daughter cells -Binary fission: the (singular) chromosome that is coiled in the cell first duplicates, then the 2 copies are separated as the cell is elongated, then it divides into 2 daughter cells 4. True or false? Correct false statements:     

Prokaryotes have one circular chromosome. FALSE – prokaryotes have one chromosome, but it is not circular – it is coiled tightly Eukaryotes have more genes than prokaryotes. TRUE Humans are smarter and more complex than hedgehogs, therefore we have more chromosomes. FALSE – these are not related, but even still, hedgehogs have more chromosomes than we do Each human chromosome has one gene on it. FALSE – each human body cell has 46 chromosomes, and each chromosome consists of one long DNA molecule, which has hundreds to thousands of genes on it Humans have over 100,000 genes. FALSE – human cells carry just under 21,000 genes

5. How is DNA compaction/coiling analogous to moving to a new apartment? Before you move into an apartment, you wouldn’t just leave all your stuff around. You would pack it up tightly into tight boxes so that it is easier to move all at once. Similarly, as a cell prepares to divide, its chromatin coils up, forming tight, distinct chromosomes. Before a cell can undergo division, it must compact all of its DNA into manageable packages. 6. A chromosome replicates and stays joined to its replicated partner. These are now called __sister_____ chromatids. Once they separate from each other to move into different daughter cells, each will be known as a ___chromosome___ again. 7. You find a cell that is currently replicating its DNA. What part of the cell cycle is it in? S phase aka “synthesis” (occurs during interphase) What will happen next? Next, is G2 phase where the cell completes its preparations for division. After that iis the mitotic phase (M phase) where the cell physically divides. 8. You view an animal cell through a microscope and observe dense, duplicated chromosomes lined up in the middle of the cell. Which stage of mitosis are you looking at? _Metaphase_________ -Five stages of mitosis: prophase, prometaphase, metaphase, anaphase, and telophase

For a spindle to form in which chromosomes move along its microtubules, what cellular structure must dissolve during prophase and prometaphase? The nuclear envelope that was housing the chromatids How would you know if a cell was in anaphase? The two centromeres of each chromosome come apart, separating the sister chromatids. The separated chromosomes start to move to opposite poles of the cell 9. Why does cytokinesis differ between plant and animal cells? (think about differences in structure!) Plant cells have a strong cell wall while animal cells do not. Animal cells can contract but plant cells cannot contract with such a strong wall -In animal cells: cytokinesis occurs by cleavage (pinching in of the plasma membrane – makes a cleavage shape between the two cells) -In plant cells: membranous vesicles containing cell wall material collect at the middle of the parent cell and they fuse to form a membranous disk called the cell plate, which grows outward, accumulating more cell wall materials and eventually fuses with the plasma membrane to become ½ of each of the two daughter cell’s inner cell walls. 10. Scientists have learned how to grow cells outside of the body in plastic trays (although not all cells of the body cooperate and divide). You may find yourself in a lab in the future asked to “maintain cells in tissue culture”. This is what we call this technique. Describe, not simply list, three factors (chemical or physical) that influence how normal cells divide, based on what scientists have learned from these cell cultures. -Culture = laboratory growth medium outside of the body -Anchorage dependence (physical): most animal cells must be in contact with a solid surface, such as the inside of a culture dish or the outside of a tissue in your body -Density-dependent inhibition (physical): a phenomenon in which crowded cells stop dividing, or they need more open space in order to continue dividing -Growth factors (chemical): most mammalian cells will only divide if certain proteins, called growth factors are present. Dozens have been discovered and different cells only respond to certain ones. 11. How are nerve cells and muscle cells different from many other cells of the human body relative to the cell cycle? Muscle cells and nerve cells never divide, unlike cells like skin cells and cells lining you digestive tract that divide almost every day / constantly. Because of this, when they are damaged, they don’t recover as easily (ex: loss of feeling can be permanent or paralysis). They are in the G0 phase permanently. 12. If the cell cycle is carefully controlled by proteins that are present only temporarily to help turn on the cell cycle (i.e. growth factors) and other proteins that halt the cycle (checkpoint proteins), what do you suppose would happen if a cell was continuously exposed to growth factors? The cell would divide and multiply rapidly and without stopping and become cancerous. What do you supposed would happen to a cell in which checkpoints were faulty?

If checkpoints were faulty, cells would likely continue growing rapidly with no restraint. At these checkpoints, the default action in most animal cells is to halt the cell cycle unless overridden by specific go-ahead signals in the form of growth factor proteins. Checkpoint errors would make it fail in its ability to stop growth when needed. How does all of this relate to one of our major themes—interactions within and between systems? -Other things outside the cell are what give the cell its directions to either continue dividing or stop dividing. Growth factor proteins received by the cell through its receptor proteins are what cause the cell to continue dividing. Checkpoint give signals to the cell to stop dividing (unless a signal overrides it, telling it to divide). The control system also receives messages from the general environmental conditions to signal whether or not to continue. -A growth factor only does something if there is a receptor protein there to receive it and continue the message 13. What makes a tumor malignant? Unlike a benign tumor, when the abnormal cells remain at their original site, a malignant tumor is a mass that can spread into neighboring tissues and invade other parts of the body, with potential to harm the existing tissues. What does the word immortal mean in cell biology? “Immortal” cells are cells like cancerous cells that can go on dividing infinitely, as long as they have a supply of nutrients 14. Are the words tumor and cancer interchangeable? Why or why not? No – not all tumors are cancerous because only tumors that spread into nearby tissues and invade space are cancerous 15. Scientific thinking: Is the described study a prospective or retrospective observational study? The described study is a prospective observational study. The study followed 108,000 women for 20 years to count their deaths and personal data. It started with them and followed them, rather than inquiring about 108,000 random women who had already died. What scientific question did scientists hope to answer with the study? The scientists hope to answer the question: do age at diagnosis, ethnicity, and socioeconomic status impact success in cancer treatment? What did they find? They found that women diagnosed when they are less than 35 and black women are more at risk to die 20 years after diagnosis. How does the knowledge they discovered affect women in society? Doctors know that women in those groups should pursue the most aggressive form of cancer. It also shows that cancer treatment is not a one size fits all and should be personalized for each patient.

16. Go to http://www.myriad.com/patients-families/disease-info/breast-cancer/ People with a gene mutation in either BRCA-1 or BRCA-2 genes are at what risk of developing breast cancer by age 70? __87___ How does this compare to the general population (people without these mutations?) The general population is only at an 8% risk Carrying a defective BRCA gene affects your risk of breast cancer, but also significantly increases your risk of what other kind of cancer in women? ___ovarian cancer____ Who is a good candidate for gene testing? (i.e. what are the risk factors?) People who had breast cancer before age 50, have ever had ovarian cancer, are of Ashkenazi Jewish descent and have a personal or family history of breast cancer, or any of those things were in your family. 16. Read the “Breast Cancer” New York Times article on our sakai site. Deb Lindner’s mother who had breast cancer had a defective BRCA-1 gene. When Deb was awaiting her results, what was the chance (%) that she was going to find out that she was a carrier of this defective gene too? _50% chance of inheriting it from her mom_______

How old was Deb’s mother when she was diagnosed with breast cancer? __48_____

4. What was Deb’s more immediate decision (at age 33) after finding out she was indeed a BRCA-1 mutation carrier? To get preventative breast removal surgery so that she does not develop breast cancer What will she do before she turns 40? She will have her ovaries removed...