Lab 10 Mitosis. Background. Mitosis. Prokaryotic fission. Prophase During prophase, the chromatin. Eukaryotic cell division

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1 Lab 10 Mitosis Background Reproduction means producing a new organism from an existing organism. The new offspring must receive hereditary information and enough cytoplasmic material to maintain its own metabolism. The process of mitosis is responsible for ensuring that both cells receive the correct genetic information and cytoplasm. Prokaryotic fission Prokaryotic cells do not contain organelles. Therefore, their genetic chromosome is located in the cytoplasm. First the chromosome is replicated so the cell then contains two exact copies of all the genetic material. Each chromosome is attached at one point to a protein located in the cell membrane. This attachment ensures that each daughter cell will contain a copy of the chromosome as the cell splits into two. Eukaryotic cell division Cells that contain organelles, eukaryotic cells, exhibit a much more complex process during cell division. Not only do eukaryotic cells, have to contend with their genetic material locked in the nucleus, but they also have multiple chromosomes that need to be separated to each daughter cell. Cell division involves two processes: mitosis (nuclear division) and cytokinesis (cytoplasmic division). Mitosis ensures that the genetic material is evenly divided. Cytokinesis ensures that each new cell contains enough of the cytoplasmic components required to sustain cellular metabolism. Cell Cycle Cells pass through a sequence of events call the cell cycle. The cell cycle is composed of two stages the interphase and mitotic phase. A cell will spend 95% or more of its life cycle in interphase. Interphase is further subdivided into three phases called: G 1, S, and G 2. During the G 1 phase, the cell increases in volume. G 1 is the longest phase in the cell cycle. Indeed, some cells may opt out of the cell cycle during G 1 and enter a stationary phase called G 0. Cells continuing in the cell cycle will, after G 1, enter the S phase. During the S phase the chromosomal DNA (the genetic material) is replicated. Following the S phase, during the Lab 10 Page 1 G 2 phase the cell will prepare for mitosis by translating the necessary proteins. This is the shortest phase of interphase. Mitosis Mitosis is responsible for ensuring that the genetic material is equally divided between the daughter cells. While mitosis is divided up into four phases, to the cell all the phases blend together. Prophase During prophase, the chromatin condenses into visible structures called chromosomes. In animal cells, the centrioles, which replicated during interphase, move to opposite sides of the cell. (The centrioles are too small to be seen with a light microscope.) However, you can identify their location by the star burst pattern of microtubules that surround the centrioles. The microtubules located between the centrioles produce a structure called the spindle. Some of these microtubules attach to the chromosomes. Simultaneously, the nuclear envelope begins to disappear. Prophase is the longest phase of mitosis. Therefore when you are looking at rapidly dividing cells you will see many cells in prophase. Metaphase As the microtubules grow they push against each other. This tug-of-war places the chromosomes in a line along the center of the microtubule spindle. This line of visible chromosomes is called the metaphase plate. This is the most recognizable phase of mitosis. Anaphase During anaphase the paired replicated chromosomes split apart. The microtubules begin to pull the chromosomes in opposite directions. The key to identifying this phase if that the moving chromosomes look like Vs. You can also see the poles of the cell pushed apart. This is the shortest phase of mitosis so you will have to look longer to find a cell in anaphase. Telophase This phase of mitosis begins as soon as the chromosomes stop moving. Now it looks like prophase in reverse. The chromosomes uncoil, two nuclear envelopes re-form, nucleoli reappear, and the microtubules breakdown.

2 Cytokinesis While the first part of the mitotic phase, mitosis, is broken up into sub sub phases, the second part of the mitotic phase, cytokinesis has no sub phases. Mitosis ensures that the daughter cells obtain equal amounts of the genetic material. Cytokinesis, on the other hand, is responsible for separating the cytoplasm and begins in late anaphase. In animal cells, microfilaments attached to the cell membrane constrict in a ring around the middle of the cell and pinch the cell into two cells. Each new cell contains a new nucleus from mitosis. This invagination is called cleavage furrowing. Do not underestimate the importance of cytokinesis. It is important for the daughter cells to receive enough cytoplasm and organelles to maintain metabolism until more cytoplasm and organelles can be produced. Exercise 10.1 Animal Cell Mitosis 1. Under high power in your microscope identify and draw below all four phases of mitosis from the White Fish blastula. Mitosis in Plant Cells Plants grow at the ends of their stems and roots by adding new cells. These special regions are called meristems and are the sites of very active nuclear and cell division In addition, plants will increase their girth through cell division growth. In animals, cell division occurs continually throughout the body. Besides location plant cells exhibit a few more differences in mitosis. Plant cells do not contain centrioles. Instead, the microtubule bundle is anchored on opposing cell walls. Since plant cells contain a hard cell wall, they do not form a cleavage furrow. Instead plant cell cytokinesis involves the formation of a cell plate. Vesicles originating from the Golgi apparatus migrate to the spindle equator and fuse with each other. The contents of the vesicles include material for making new the cell wall (cellulose) and new cell membrane components. The vesicles fuse to from the cell plate which will divide the two daughter cells. Exercise 10.2 Plant Cell Mitosis 1. Under high power in your microscope identify and draw below all four phases of mitosis from the meristem of the Allium root tip. Meiosis The chromosomes in eukaryotic cells exist in pairs of homologous chromosomes. They contain similar, but not identical genetic information. One homologue is inherited from your dad and the other from your mom. Therefore your cells are diploid (2n) since they have both homologues in the same nucleus. For sexual reproduction the germ cells must contain only one of the homologues and are called haploid (1n). To obtain a haploid state cells under go meiosis which resembles the mitotic phase done twice (meiosis I and meiosis II). Since meiosis follows the S phase, there are essentially four copies of each chromosome. Unlike mitosis, in meiosis prophase I the duplicated homologous chromosomes attach to each other until metaphase I where they separate. Exercise 10.3 Meiosis 1. Using four different colors depict two pairs of condensed homologous chromosome through each stage of meiosis. Lab 10 Page 2

3 Exercise 10.1 Report Animal Cell Mitosis Prophase Name Anaphase Metaphase Telophase Exercise 10.2 Report Plant Cell Mitosis Prophase Anaphase Metaphase Telophase Lab 10 Page 3

4 Exercise 10.3 Report Name Meiosis I Meiosis II Prophase II Prophase I Metaphase II Metaphase I Anaphase I Anaphase II Telophase I Telophase II Exercise 10.4 Report DNA sequence name: Species DNA matches to: Lab 10 Page 4

5 BLAST The comparison of nucleotide or protein amino acid sequences from the same or different organisms is a very powerful tool in molecular biology. By finding similarities between sequences, scientists can infer the function of newly sequenced genes, predict new members of gene families, and explore relationships between genes and organisms. Now that whole genomes are being sequenced, sequence similarity searching can be used to predict the chromosomal location and function of protein-coding and transcription-regulation regions in genomic DNA. BLAST is an anagram that stands for Basic Local Alignment Search Tool. BLAST is a computer program that takes a user submitted sequence and finds a related sequence from a database. The researcher or student can submit either DNA/RNA nucleotide or protein amino acid sequence. This process allows a user to identify the gene and species of an unknown sequence providing the sequence is in the database. Currently one of the largest data bases is located at the National Center for Biotechnology Information (NCBI, check the URL (address) you must type in the exercise below.) which is part of the National Institute of Health (NIH) which is funded by the Federal Government. Exercise 10.4 Using a computer that is connected to the internet and open a browser. Navigate to Dr. Engle s web page (DrEngle.net) and make your way to the Biology I web page. Scroll down the page to the Additional Resources section. Click on the Week 10 Laboratory DNA sequence list link. Scroll down and randomly click on any link on the page. Be sure to copy the name of the file you are clicking on to the report on page 4 of this lab. You should now see a DNA sequence on your screen. Select the entire sequence and copy it to the clipboard (Edit -> Copy) Open a new tab or window and point a browser to: Under the Basic BLAST section click on the nucleotide blast link. Paste your DNA sequence into the first entry box labeled Enter Query Sequence: Enter accession number(s), gi(s), or FASTA sequence(s) In the next section of that same page titled Choose Search Set selects which data base to search. We don t want to search the Human genomic database so click on the radio button labeled Others (nr etc.) Now click on the blue BLAST button near the bottom of the page. When the results page comes up (you may have to wait a few seconds) scroll down to find the first identifiable species in the list and report that organism in the lab report on page 4. Lab 10 Page 5