Mitosis - Opener

Where did we come from?

What causes cancer?

What happens when we get old?

DNA is the blueprint of life!

Deoxyribonucleic acid, (DNA) is the hereditary material in humans and all other living organisms.Information is passed from cell to cell through DNA

What is DNA?

Chromosome Anatomy

Opener - Chromosomes

• What is the function of a Chromosome?• Diagram a Chromosome. • How many Chromosomes do we have? A

Fern?• If you could see and read human

chromosomes, what would this tell you?

Karyotypes!

• A KARYOTYPE is a map of chromosomes.• Karyotype can tell us vital information about

living organisms– Most commonly Genetic Disorders

Karyotypes - Opener

• What is a Karyotype?

• What can we do with Karyotypes?

• Where are we going with Karyotypes?

Cell Cycle

90 percent of a cells life is spent in INTERPHASE!

That would be 21 out of 24 hours in a day!

MitosisMitosis

When cells divide and pass on DNA

Mitosis occurs in 4 stagesProphaseMetaphaseAnaphaseTelophase

Cytokensis

Summary of Mitosis• Prophase:

• Chromosomes condense• Nuclear envelope disappears• Centrioles move to opposite sides of the cell• Spindle forms and attaches to chromosomes

• Metaphase• Chromosomes lined up on equator of spindle• Centrioles at opposite ends of cell

• Anaphase• Chromosomes divide• Chromosomes pulled to opposite poles by the

spindle• Telophase

• Nuclear envelope reappears• Cytokinesis: the cytoplasm is divided into 2 cells

Prophase

Prophase

• Chromosomes condense

• Nuclear envelope disappears

• Spindle forms and attaches to centromeres on the chromosomes

Metaphase

Metaphase

– The chromosomes are lined up at the equator

– The centrioles move to opposite sides of the cell and spindle fibers appear

Anaphase

• Anaphase

– The chromosomes divide.

– Then the spindle fibers contract, and the chromosomes are pulled to opposite poles.

Telophase

• Telophase– The cell pulls apart

– The spindle disintegrates

– Nuclear envelope begins to appear

– The cytoplasm is divided into 2 separate cells, the process of cytokinesis.

How does DNA get passed on?

• Your cells go through THREE steps!

1. DNA Replication

2. Mitosis

3. Cytokinesis

How is DNA replicated?

Opener 10/20/09

• Describe the function of DNA using the terms:– Gene and Chromosome

Chromosome Definitions

• You need to create Matchbooks on the following terms!– Homologous Chromosomes– Diploid– Haploid– Zygote– Autosomes– Sex Chromosomes– Kayrotype

Chromosome

Opener 3/22/2010

• Describe the function of Mitosis and how it occurs. Include the words:– Interphase, Prophase, Metaphase, Anaphase,

Telophase, Chromosomes and Cytokinesis

MitosisPoster• On your poster

you are going to show the steps of Mitosis!

Meiosis - opener

• What is the function of mitosis?

• What are chromosomes?

• How many chromosomes do we have in our cells?

• Where do we get out chromosomes from?

Cell replication

Chromosomes store DNA

23 pairs – 46 total

Half from mom, half from dad

Meiosis

• Meiosis is the production of gametes, or sex cells.– Sex cells only have HALF the number of

chromosomes, why?

mEiosis = sEx cells

Meiosis

• Meiosis has two parts

– Part one is the same as mitosis

– Part two is the same process, however the DNA is never duplicated.

– You end up with 4 daughter cells instead of 2!

Review!

Venn Diagram MeiosisMitosis

Meiosis

• Square dance

Cytokinesis• The organelles (other than the

chromosomes) get divided up into the 2 daughter cells passively: they go with whichever cell they find themselves in.

• Plant and animal cells divide the cytoplasm in different ways.

• In plant cells, a new cell wall made of cellulose forms between the 2 new nuclei, about where the chromosomes lined up in metaphase. Cell membranes form along the surfaces of this wall. When the new wall joins with the existing side wall, the 2 cells have become separate.

• In animal cells, a ring of actin fibers (microfilaments are composed of actin) forms around the cell equator and contacts, pinching the cell in half.

Chromosomes• The essential part of a chromosome

is a single very long strand of DNA. This DNA contains all the genetic information for creating and running the organism.

• The DNA is supported and neatly packaged by proteins bound to it. At different times, these proteins cause the DNA to be spread out like spaghetti in a bowl, or tightly condensed into the X-shaped chromosomes we can see in the microscope.

• Each chromosome has a central constricted region called a centromere 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 one chromatid. After replication, chromosomes have 2 sister chromatids, held together at the centromere. Each chromatid is one piece of DNA with its supporting proteins.

• In mitosis, the two chromatids of each chromosome separate, with each chromatid going into a daughter cell.

• Remember that diploid cells have two copies of each chromosome, one from each parent. These pairs of chromosomes are NOT attached together.

Cell Cycle• Some cells divide constantly: cells in the embryo, skin

cells, gut 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 “interphase” by the microscopists who first studied cell division. During interphase the cell increases in size, but the chromosomes are invisible.

• The 3 stages of interphase are called G1, S, and G2.

• The S phase (“Synthesis”) is the time when the DNA is replicated, when the chromosome goes from having one chromatid to having 2 chromatids held together at the centromere.

• G1 (“Gap”) is the period between mitosis and S, when each chromosome has 1 chromatid. Cells spend mot 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.

• G2 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 spindle, which is made of microtubules. The spindle fibers are attached to each centromere (which is part of the chromosome), and anchored on the other end to a centrosome (which is the organizing center for the spindle).

• There are 2 centrosomes, one at each end of the spindle. The chromosomes are lined up between the poles of the spindle.

• When the spindle fibers contract, the chromosomes are pulled to the opposing poles.

• The cell then divides to separate the two poles.

• Stages of mitosis: prophase, metaphase, anaphase, telophase.

Cancer• Cancer is a disease of uncontrolled cell division. It starts with a single cell

that loses its control mechanisms due to a genetic mutation. That cell starts dividing without limit, and eventually kills the host.

• Normal cells are controlled by several factors. – Normal cells stay in the G1 stage of the cell cycle until they are given a specific

signal to enter the S phase, in which the DNA replicates and the cell prepares for division. Cancer cells enter the S phase without waiting for a signal.

– 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 mortality: they are immortal and can divide endlessly.

– Normal cells that suffer significant chromosome damage destroy themselves due to the action of a gene called “p53”. Cancer cells either lose the p53 gene or ignore its message 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 “oncogenes”. The normal, unmutated versions of the oncogenes provide the control mechanisms for the cell. The mutations are caused by radiation, certain chemicals (carcinogens), and various random events during DNA replication.

• Once a single cell starts growing uncontrollably, it forms a tumor, a small mass of cells. No further progress can occur unless the cancerous mass gets its own blood supply. “Angiogenesis” 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 mass. Eventually some of the cancer cells will break loose and move through the blood supply to other parts of the body, where they start to multiply. This process is called metastasis. 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 remove the tumor, and radiation or

chemicals to kill actively dividing cells.• It is hard to remove all 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 actively dividing 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 resistant to the chemical, they will survive and multiply. 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.