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Mitosis
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Genes and Proteins
• _________ do the work of the cell: growth, maintenance, response to the environment, reproduction, etc.
• Proteins are chains of ____________. The sequence of amino acids in each protein is coded in the _______ as a specific sequence of A, C, G and T bases: a gene.
• Each _________ codes for a different protein.
• Key points:– All ________ within an organism have the same ____________.– What makes cells different from each other is that different
genes are ___________ and ______________ in different cells.
• The DNA must be _________ and then _______ exactly so that each cell gets an identical copy.
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Mitosis• Cells divide to make ________. While
all the other organelles can be randomly separated into the daughter cells, the _______________ must be _____________ so that each daughter cell gets exactly the _____________.
• Mitosis is normal cell division, which goes on throughout life in _______ of the body. Meiosis is the special cell division that creates the _______ and ________, the gametes. We will discuss meiosis separately.
• Mitosis and meiosis occur in ____________. Prokaryotes use a different method—”fission” to divide.
• Humans have _____ chromosomes, ______ from each parent. Every cell has the same 46 chromosomes Each species has a characteristic number of chromosomes: corn ahs 20, house flies have 10, chimpanzees have 48.
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Chromosomes• The essential part of a
chromosome is a single very long strand of _________. This DNA contains all the ________ information for creating and running the organism.
• The DNA is supported and neatly packaged by _______ bound to it. At different times, these proteins cause the DNA to be __________ like spaghetti in a bowl, or tightly condensed into the __________ chromosomes we can see in the microscope.
• Each chromosome has a central constricted region called a _____________ that serves as an attachment point for the machinery of mitosis.
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More Chromosomes• Chromosomes exist in 2 different
states, before and after they replicate their DNA. Before replication, chromosomes have _____________. After replication, chromosomes have __________
• ___________, held together at the ________. Each chromatid is one piece of DNA with its supporting proteins.
• In mitosis, the two chromatids of each chromosome ________, with each chromatid going into a ___________________.
• Remember that diploid cells have ____ copies of each chromosome, one from each parent. These pairs of chromosomes are ______ attached together.
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Cell Cycle• Some cells divide constantly: cells in the ________,
_____ cells, ____ lining cells, etc. Other cells divide rarely or never: only to replace themselves.
• Actively dividing cells go through a cycle of events that results in mitosis. Most of the cycle was called “________” by the microscopists who first studied cell division. During interphase the cell increases in ________, but the chromosomes are __________.
• The 3 stages of interphase are called ___, __, and ____.
• _____ (“Gap”) is the period between mitosis and S, when each chromosome has ___________. Cells spend most of their time in G1: it is the time when the cell grows and performs its normal function. Control of cell division occurs in G1: a cell that isn’t destined to divide stays in G1, while a cell that is to divide enters the S phase.
• The ________ (“Synthesis”) is the time when the DNA is replicated, when the chromosome goes from having one ________ to having 2 __________ held together at the centromere.
• _______ is the period between S and mitosis. The chromosome have 2 chromatids, and the cell is getting ready to divide.
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Machinery of Mitosis• The chromosomes are pulled
apart by the ________, which is made of microtubules. The spindle fibers are attached to each ___________ (which is part of the chromosome), and anchored on the other end to a _________ (which is the organizing center for the spindle).
• There are 2 centrosomes, one at _________ of the spindle. The chromosomes are lined up between the poles of the spindle.
• When the spindle fibers _______, the chromosomes are pulled to the ________________.
• The cell then ________ to separate the two poles.
• Stages of mitosis: prophase, metaphase, anaphase, telophase.
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____________• In prophase, the cell begins the process
of ____________. • 1. The chromosomes _________. The
proteins attached to the DNA cause the chromosomes to go from long thin structures to short fat one, which makes them easier to __________.
• 2. The ______________________. The double membrane that surround the nucleus dissolves into a collection of small vesicles, freeing the ___________ to use the whole cell for division
• 3. The ___________ move to _______ poles. During interphase, the pair of centrosomes were together just outside the nucleus. In prophase they separate and move to opposite ends of the cell.
• 4. The _________starts to form, growing out of the ______________ towards the ___________________.
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_______________
• Metaphase is a short _________ period where the chromosomes are ______ on the ______ of the cell, with the centrosomes at opposite ends and the spindle fibers attached to the centromeres. Everything is _______ for the rest of the division process to occur.
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_____________
• In anaphase, the ___________ divide. At this point, each individual chromosome goes from:– __ chromosome with ___
chromatids – to:– ___ chromosomes with
_____ chromatid each.
• Then the spindle fibers _________, and the chromosomes are pulled to ____________, towards the __________.
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Telophase
• In telophase the cell actually ____________.
• The chromosomes are at the ______ of the spindle.
• The spindle __________.• The nuclear envelope __-
________ around the two sets of chromosomes.
• The _____ is divided into 2 separate cells, the process of ___________.
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Cytokinesis• The _____________ (other than the
chromosomes) get divided up into the 2 daughter cells __________: they go with whichever cell they find themselves in.
• Plant and animal cells divide the cytoplasm in different ways.
• In ______ cells, a new cell wall made of _______ forms between the 2 new nuclei, about where the chromosomes lined up in metaphase. Cell ___________ form along the surfaces of this wall. When the new wall joins with the existing side wall, the 2 cells have become separate.
• In _______ cells, a ring of ______ fibers (microfilaments are composed of actin) forms around the cell equator and contacts, pinching the cell in half.
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Summary of Mitosis• __________:
• Chromosomes condense• Nuclear envelope disappears• centrosomes move to opposite sides of the cell• Spindle forms and attaches to centromeres on the chromosomes
• __________:• Chromosomes lined up on equator of spindle• centrosomes at opposite ends of cell
• __________:• Centromeres divide: each 2-chromatid chromosome becomes
two 1-chromatid chromosomes• Chromosomes pulled to opposite poles by the spindle
• _________:• Chromosomes de-condense• Nuclear envelope reappears• Cytokinesis: the cytoplasm is divided into 2 cells
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Cancer• Cancer is a disease of _____________________. It starts with a
single cell that loses its control mechanisms due to a genetic mutation. That cell starts _________________, and eventually kills the host.
• _________ cells are controlled by several factors. – Normal cells stay in the ____ stage of the cell cycle until they are given
a specific signal to enter the S phase, in which the DNA ________ and the cell prepares for division. Cancer cells enter the S phase without ____________________.
– Normal cells are mortal. This means that they can divide about 50 times and then they lose the ability to divide, and eventually die. This “clock” gets re-set during the formation of the gametes. Cancer cells escape this process of ________: they are immortal and can divide endlessly.
– Normal cells that suffer significant chromosome _________ destroy themselves due to the action of a gene called “______”. Cancer cells either _____________ gene or ______________ and fail to kill themselves.
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Cancer Progression• There are many different forms of cancer, affecting
different cell types and working in different ways. All start out with mutations in specific genes called “_________”. The normal, unmutated versions of the oncogenes provide the control mechanisms for the cell. The mutations are caused by ____________, certain chemicals (___________), and various random events during _______________.
• Once a single cell starts growing uncontrollably, it forms a ________, a small mass of cells. No further progress can occur unless the cancerous mass gets its own blood supply. “___________” is the process of developing a system of small arteries and veins to supply the tumor. Most tumors don’t reach this stage.
• A tumor with a blood supply will grow into a large ________. Eventually some of the cancer cells will ____________ and move through the blood supply to other parts of the body, where they start to multiply. This process is called _________. It occurs because the tumor cells lose the proteins on their surface that hold them to other cells.
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Cancer Treatment• Two basic treatments: surgery to ____________, and __________
or ____________ to kill actively dividing cells.• It is hard to remove _______ the tumor cells. Tumors often lack
sharp boundaries for easy removal, and metastatic tumors can be very small and anywhere in the body.
• Radiation and chemotherapy are aimed at killing ______________ cells, but killing all dividing cells is lethal: you must make new blood cells, skin cells, etc. So treatment must be carefully balanced to avoid killing the patient.
• Chemotherapy also has the problem of natural selection within the tumor. If any of the tumor cells are __________ to the chemical, they will _____________. The cancer seems to have disappeared, but it comes back a few years later in a form that is resistant to chemotherapy. Using multiple drugs can decrease the risk of relapse: it’s hard for a cell to develop resistance to several drugs at the same time.