Mitosis

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.

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.

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.

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.

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.

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.

____________• 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 ___________________.

_______________

• 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.

_____________

• 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 __________.

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 ___________.

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.

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

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.

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.

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.