Mitotic Cell Division

Transcription

1 Mitotic Cell Division Types of cell division: Mitosis vs. Meiosis... 2 DNA forms: Chromosomes, Chromatin, and Chromatids... 2 The cell cycle... 2 TASK 1: THE CELL CYCLE and NUMBER of DNA MOLECULES present... 3 TASK 2: DIPLOID, HAPLOID AND POLYPLOID CELLS... 3 Mitosis: somatic cell division... 4 Stages of Mitotic Cell Division... 5 Differences between plant and animal mitosis... 5 TASK 3: PLANT MITOSIS IN ONION ROOT TIPS... 6 TASK 4: PLANT MITOSIS MODELS... 6 TASK 5: ANIMAL MITOSIS MODELS... 7 TASK 6: SUMMARY OF THE MITOTIC CELL CYCLE... 7 General Biology 1 Instructor: Jose Bava, Ph.D

2 Types of cell division: Mitosis vs. Meiosis Cell division is the process by which one cell gives origin to two new cells. Two different processes are involved; in one the nuclear content, the DNA, is divided in two new nuclei by means of a very specific sequence of events. In the second part, called cytokinesis, the cytoplasm of the cell is split in two and two new cells are produced from the original one. There are two types of nuclear division processes in eukaryotes: in mitosis or somatic cell division (soma=body), the original cell divides in two and each daughter cell has an exact (identical) copy of the DNA that was present in the original cell. The daughter cells are then diploid (2N) because each still has a complete set of DNA coming from the mother and one coming from the father. This type of cell division takes place in most parts of the body, hence the name somatic (soma = body). Meiosis is a variation of the normal process and takes place in the gonads (reproductive organs), so is meiosis is sex cell formation. The goal of meiosis is to generate cells with half of the original chromosomal number and to produce genetic variability by means of specific processes that take place in two stages of the this type of cell division. The daughter cells are then haploid (N) with half of the chromosomes and all cells contain a random combination of DNA from mother and father. Both mitosis and meiosis require the replication of the DNA previous to the nuclear division. DNA forms: Chromosomes, Chromatin, and Chromatids DNA in cells comes in big molecules called chromosomes during cell division. In humans, DNA comes in 46 molecules, of which 23 were passed by the father and 23 were passed by the mother. Each DNA molecule contains a certain number of genes, the segments of DNA that have the code for a given characteristic or trait in our body. DNA is not always present in the cells as chromosomes though, the 90% of the time a cell is not dividing (interphase) and the DNA is in the form of chromatin, which is the unpacked form of the DNA, while the chromosomes we see during the average 10% of division process constitute the packed version. When the cell is preparing for cell division, the DNA is replicated during the S (synthesis) part of interphase so each strand of DNA has an exact copy of the genetic information. The strand coils then around a type of proteins called histones. A tiny part of each long strand called centromere is not replicated though and binds the two identical strands, called sister chromatids. The DNA keeps condensing until it reaches the shape of the familiar chromosomes; at that moment the cell division process has already begun. In plants, multiple sets of DNA are possible sometimes and the plant can still survive, this condition is called polyploidy (poly=many, ploid=sets) The cell cycle Both mitosis and meiosis are part of what is called the cell cycle, the life cycle of any cell. The part of the life cycle when cell division is not actually happening, called Interphase, involves the generation of almost everything that is needed for the stage of cell division, including the replication of the DNA (synthesis). Keep in mind that the replication of the genetic material and the production of almost everything that is needed for cell division takes place before the actual process of cell division. A cell may spend an average of 90% of its lifetime in Interphase and the remaining 10% in the process of cell division. Mitotic cell division represents then the type of cell division that will produce genetically identical copies of cells, which in a human cell means 2 daughter cells having the same 46 chromosomes that were present in the original cell, 23 of which are chromosomes from the father and 23 are chromosomes from the mother. Your body is constantly replacing cells, with organs like the skin and the cells of the digestive system, and red blood cells among the ones that divide the most. Women also have a lot of mitotic cell division during the period, in which cells or different organs are undergoing mitotic cell division in preparation for a possible pregnancy. General Biology 2 Instructor: Jose Bava, Ph.D

3 TASK 1: THE CELL CYCLE and NUMBER of DNA MOLECULES present Using the diagram below with the cell shown in G0 as reference, draw the DNA molecules as they would appear in G1 and G2 and complete the missing information. This is the terminology to be used for this exercise Every stick with a dot in the center represents an unduplicated chromosome, and every chromosome (stick) with a different length is a different type of DNA from the others. Then, and knowing that humans have 46 chromosomes in all somatic (body) cells How many different chromosomes do you have in this example?.. How many total chromosomes are present in a human lung cell?. How many different chromosomes are present in a human lung cell?. 2 sticks connected by a dot represent a duplicated chromosome. The dot represents the centromeres, the part of DNA that connects two sister chromatids in a chromosome Every stick also represents a molecule of DNA. How many chromosomes do you have in this example?.. How many different types of chromosomes are present in this example?. Is this example a diploid or haploid cell?... How can you tell the previous? ) Using the following picture of the cell cycle, draw sticks (chromosomes) for a cell 2N=6 durign G1 and G2. Use two different colors for mom and dad chromosomes and different sizes for each different type of chromosome 2) How # Chromosomes and DNA molecules are present in a human somatic cell during G1? / ) How # Chromosomes and DNA molecules are present in a human somatic cell during G2? /..... General Biology 3 Instructor: Jose Bava, Ph.D

4 TASK 2: DIPLOID, HAPLOID AND POLYPLOID CELLS Using the diagram below (modified from Wu, Biology 101 Lab manual from Fullerton College), determine A= if the cell is haploid, diploid, or polyploid B= if the chromosomes are duplicated or unduplicated C= the total number of DNA molecules present in the cell D= number of different chromosomes A B C D Mitosis: somatic cell division As soon as fertilization takes place, cells in the embryo begin dividing by mitosis, so the very first reason mitosis is needed is growth. However, as we live our lives cells in our body die by the millions because of aging, and need to be replaced, so mitosis is also used for maintenance. The body may produce by cell division as many as 50 millions cells per second in order to replace old ones, or those that have been damaged due to an injury for example. When we heal as a result of a wound, we are in fact replacing millions of cells, we are repairing our body. 4) Indicate with and X which ones of the following processes in a human body will use mitotic cell division to reproduce cells Embryo growing into and adult individual... Replacing skin as a result of a wound Creating sperm or eggs for sexual reproduction Healing a broken bone... Creating red blood cells when recovering from a surgery 5) What body parts will have a higher amount of cell division in an adult individual? General Biology 4 Instructor: Jose Bava, Ph.D

5 Stages of Mitotic Cell Division Refer to the picture below for the different stages that take place in a typical plant cell mitotic cell division 1. Interphase or metabolic phase. The DNA is not condensed in the form of chromosomes and is called chromatin. The cell has the normal metabolic activities and the DNA is replicated during the S (synthesis) part of interphase 2. Prophase. DNA organizes into chromosomes. In animal cells, centrioles migrate to the poles of the cell, dragging along the spindle fibers, an arrangement of proteins that will be used by the chromosomes to migrate to opposite poles of the cells. In plant cells, spindle fibers also extend but centrioles are absent. The nuclear membrane completely disappears at the end of this phase and the chromosomes are free in the cytoplasm of the cell 3. Metaphase. Spindle fibers extend from pole to pole. In animal cells, centrioles are located at opposite poles of the cell. Each chromosome attaches by the centromere to one fiber at the equatorial plane 4. Anaphase. Each chromosome s centromere replicates and the sister chromatids separate and migrate to opposite poles, ensuring that the two new cells will have an exact copy of the original DNA. 5. Telophase. The nuclear membrane is reconstructed around each set of chromosomes. The spindle fibers disappear and the DNA uncoils and becomes chromatin. Cytokinesis starts during the last part of telophase. So, as the nucleus is reformed, the cell is splitting in two 6. Cytokinesis or cell splitting overlaps in time with telophase. In plant cells, a cell plate forms in between the two new nucleai and eventually grows towards the outside completing the cell splitting into two new cells Differences between plant and animal mitotic cell division Plant cells show two differences during the cell division process when compared to animal cells. The first one is during mitosis: centrioles are only present in animal cells; even if absent in plant cells, the spindle fibers still extend from pole to pole in the same way than in animal cells. The second difference is during cytokinesis and has to do with a structural dfference between both types of cells: plant cells are not flexible as animals cells are because of the presence of the rigid cell wall made of cellulose. Cytokinesis cannot happen in the same way. A cell plate appears in the center of the cell during telophase and extends to the sides of the cell eventually forming a new cell wall that splits the original cell in two new ones. Cytokinesis in plants happens then from the center of the cell towards the outside, as opposed to what happens in animal cells. In animal cells with just the cell membrane, the cell simply pinches in two during cytokinesis General Biology 5 Instructor: Jose Bava, Ph.D

6 TASK 3: PLANT MITOSIS IN ONION ROOT TIPS Get a prepared slide of allium sp (onion root tips), find and sketch a cell in interphase and cells in the four stages of mitosis. Label what you observe on each one (i.e. chromatin, chromosomes, nucleus, etc.) Interphase prophase Metaphase Anaphase Telophase / cytokinesis TASK 4: PLANT MITOSIS MODELS Your lab instructor has placed several models corresponding to different stages of plant cell division on the table; each model is identified by a number. The numbers are in order but that is not the right order for the cell division process. Your goal is to identify the right order and write it in the space provided below. 6) Order the PLANT MITOSIS stages on display in the correct order (INDICATE THE NUMBERS) Now, consider the four first models having and asterisk (*) next to the number, give the name for the stage (interphase, prophase, metaphase, anaphase, telophase, cytokinesis) and briefly explain what thing/s present in the model allow/s you to define in what stage the cell actually is. Note: you may use the term early or late if you consider the situation shown in the model is actually between two stages. 7) Number 1. Indicate the name of the stage:.. Justify your choice General Biology 6 Instructor: Jose Bava, Ph.D

7 8) Number 2. Indicate the name of the stage:.. Justify your choice 9) Number 3. Indicate the name of the stage:.. Justify your choice 10) Number 4. Indicate the name of the stage:.. Justify your choice TASK 5: ANIMAL MITOSIS MODELS Your lab instructor has placed several models corresponding to different stages of animal cell division on the table; each model is identified by a number. The numbers are in order but that is not the right order for the cell division process. Your goal is to identify the right order and write it in the space provided below. 11) Order the ANIMAL MITOSIS stages on display in the correct order (INDICATE THE NUMBERS) Now, consider the five different models having and asterisk (*) next to the number, give the name for the stage (interphase, prophase, metaphase, anaphase, telophase, cytokinesis) and briefly explain what thing/s present in the model allow/s you to define in what stage the cell actually is. Note: you may use the term early or late if you consider the situation shown in the model is actually between two stages. 12) Number 1. Indicate the name of the stage:.. Justify your choice 13) Number 2. Indicate the name of the stage:.. Justify your choice 14) Number 3. Indicate the name of the stage:.. Justify your choice 15) Number 4. Indicate the name of the stage:.. Justify your choice TASK 6: SUMMARY OF THE MITOTIC CELL CYCLE In the diagram provided, use the cell presented at the top to draw the DNA as it would appear on each stage of the mitotic cell division process and fill in the information for the number of chromosomes and DNA molecules present on each stage. Use 2 different colors to represent mother and father chromosomes for each pair General Biology 7 Instructor: Jose Bava, Ph.D

8 Diploid parental cell 2N = 6 # of chromosomes:.. # of different chromosomes:.. DNA duplication # of chromosomes:.. # of chromosomes:.. # of chromosomes:.. # of chromosomes in one daughter cell:.. General Biology 8 Instructor: Jose Bava, Ph.D

9 16) What two things allow you to confirm that the first cell in the diagram is actually in G1 interphase? ) What allows you to confirm that the second cell in the diagram has to be in prophase?... 18) The cell cycle of an eukaryotic cell is composed of a part where the cells is not dividing called ( %) and one where the cells are dividing called. ( %) 19) The genetic material (DNA) is replicated during..., a part of the cell cycle that happens ( BEFORE / DURING / AFTER ) the nuclear division or mitosis 20) DNA is organized as chromatin during and as chromosomes during. 21) Chromosomes are first visible during the stage. 22) Centrioles replicate and nuclear membrane dissolves during the stage. 23) Centrioles are located in two opposite poles in the cell during the stage 24) Chromosomes align at the equatorial plane during the stage. 25) Sister chromatids separate and migrate to the poles during 26) Spindle fibers disappear during.. 27) What else happens during the same stage? 28) Cytokinesis refers to the process by which.. 29) The closest mitotic phase to cytokinesis is 30) Mitotic cell division generates (DIPLOID / HAPLOID) cells 31) In human mitotic cell division, the daughter cells will be all (IDENTICAL / DIFFERENT), each cell having a total of. chromosomes 32) The main differences between plant and animal mitosis are General Biology 9 Instructor: Jose Bava, Ph.D