Name: Date: Hour: Unit Four: Cell Cycle, Mitosis and Meiosis. Monomer Polymer Example Drawing Function in a cell DNA

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1 Unit Four: Cell Cycle, Mitosis and Meiosis I. Concept Review A. Why is carbon often called the building block of life? B. List the four major macromolecules. C. Complete the chart below. Monomer Polymer Example Drawing Function in a cell Glucose Protein DNA II. Structure of DNA Key Concept: DNA structure is the same in all organisms. A. Critical Reading: Highlight the main ideas Since the 1920s scientists have known the chemical parts of the DNA molecule. DNA is a very long polymer, or chain of repeating units. The units, or monomers, that make up DNA are called nucleotides. Each nucleotide has three parts: a phosphate group, a base, and a sugar. There are four different types of DNA nucleotides: cytosine (C), thymine (T), adenine (A), and guanine (G). All of the nucleotides contain a phosphate group and a deoxyribose sugar. They differ in their nitrogen-containing bases, as shown below. Thymine and Cytosine have a single ring structure and Adenine and Guanine have a double ring structure. Base Pairing Nucleotides always pair the same way. Each side of the DNA double helix is a long strand of phosphates and sugars connected by covalent bonds. The two sides of the double helix are held to each other by hydrogen bonds that form between the bases in the middle. Each individual hydrogen bond is weak, but togther they are strong enough to hold the shape of DNA. The bases of the two DNA strands always bond according to the base pairing rules: T pairs with A, and C pairs with G. The bases pair in this way because of hydrogen bonds. Notice that A and T form two hydrogen bonds, whereas C and G form three.

2 B. Color the diagram 1. Find the nucleotides at the top and color the phosphate group purple or pink. 2. Find the deoxyribose sugar and color it gray or black. 3. Find the four nucleotides: A, T, C and G. Use one of the following colors for each base and indicate which color it is in the key: Red, Yellow, Blue and Green. C. Reflect 1. What is a polymer? 2. What are the three different parts of a nucleotide? 3. How many types of nucleotides are present in DNA? List them. 4. Use the base pairing rules to write the sequence that would pair with the strands of DNA below: -TCACGTACTAG -CATTAGCAGTGAT D. Extension: Nucleus and Chromosomes DNA is stored in the nucleus of eukaryotic cells as chromosomes. A chromosome is one long piece of tightly coiled DNA. Humans have 46 chromosomes in each of their cells. DNA is condensed with the help of specialized proteins called histones. Histones and DNA combined form Chromatin. Chromosomes are made of chromatin and form an X shape made of two chromatids. The middle of a chromosome is called the centromere.

3 III. The Cell Cycle: How do living things grow and repair themselves? A. Critical Reading: Highlight the main idea and important information Living things grow and develop. At times they suffer injury or damage, or cells simply wear out. New cells must be formed for the organism to survive. The Cell Cycle The cell cycle is a regular pattern of growth, DNA replication, and cell division that occurs in eukaryotic cells, which contain a nucleus. There are four main stages in in the cell cycle: G1 or Gap 1, normal cell growth S or Synthesis, DNA is copied G2 or Gap 2, more growth M or Mitosis, nuclear cell division G1, S and G2 together are called interphase. In G1, also called the growth phase, the cell grows rapidly, while performing routine metabolic processes like cellular respiration. It also makes proteins needed for DNA replication and copies some of its organelles. A cell typically spends most of its life in this phase. In synthesis, a cell puts together or synthesizes a whole copy of its nuclear DNA. At the end of this stage, there are two complete sets of DNA in a cell s nucleus. There are two main parts to the M stage: mitosis and cytokinesis. Mitosis is the division of the cell nucleus and the DNA inside it. Cytokinesis is the division of the contents of the rest of the cell the cytoplasm. Regulation of the Cell Cycle How cell division is controlled is a very complex cellular mechanism. The cell can determine irregular levels of certain chemicals during the checkpoints of the cell cycle and terminate the cell should something be amiss. Cells which have errors that are not caught and go unregulated can result in cancer. Cancer is a disease that occurs when the cell cycle is no longer regulated and the cell is unable to break down when it is damaged (apoptosis). This may happen when a cell s DNA becomes damaged. Damage may result from exposure to harmful chemicals called carcinogens or hazards such as forms of radiation. B. Reflect 1. Where is mitosis in the cell cycle? 2. What three phases are part of interphase? 3. In which phase does a cell spend most of its life? What happens during this phase? 4. What is the S phase? What happens during this phase?

4 C. True or False 1. Cell division is basically the same in prokaryotic and eukaryotic cells. 2. Cytokinesis is the division of the cytoplasm. 3. Mitosis is the process in which the nucleus of the cell divides. 4. A cell spends most of its life in growth phase 1 of the cell cycle. 5. The correct order of phases of the cell cycle is G1 S G2 M. 6. Interphase consists of mitosis and cytokinesis. 7. In prokaryotic cells, all organelles, such as the Golgi apparatus and endoplasmic reticulum, divide prior to cell division. 8. Organelles are made during growth phase In eukaryotic cells, DNA is replicated during the S phase of the cell cycle. 10. If the cell cycle is not regulated, cancer may develop. 11. Mitosis occurs in both prokaryotic and eukaryotic cells. D. Enrichment: Visit and play the cell game. Describe what needed to be done in order to keep your cell alive. IV. Mitosis: Cells divide during mitosis and cytokinesis A. Critical Reading: Highlight the main ideas Chromosomes and Mitosis Chromosomes are coiled structures made of DNA and proteins, and are a form genetic information takes during cell division. During other phases of the cell cycle, DNA is not coiled into chromosomes. DNA coils into the familiar X shaped form of a chromosome only after it has replicated during synthesis. Because it has already replicated, each chromosome actually consists of two identical copies. The two copies are called sister chromatids. They are attached to one another at a region called the centromere. The DNA of a chromosome is encoded with genetic instructions for making proteins. These instructions are organized into units called genes. Most genes contain the instructions for a single protein and there can be hundreds to thousands of genes on a single chromosome. Replication By the end of interphase, a cell is ready to divide. Mitosis divides the DNA, and cytokinesis divides the rest of the cell. The result is two identical cells. Mitosis happens in all of your body cells except cell that form eggs or sperm. Your cells divide for growth, development, and repair. Mitosis and cytokinesis are continuous processes; they do not happen in steps. However, there are four main phases of mitosis: prophase, metaphase, anaphase, and telophase; a.k.a., PMAT. Cytokinesis begins at the end of anaphase or in telophase. In prophase, chromatin condenses into tightly coiled duplicated chromosomes and the nuclear membrane breaks down. In metaphase the chromosomes line up in the middle of the cell. In anaphase, sister chromatids are pulled to opposite sides of the cell. Finally in telophase, nuclear membranes start to form again and chromosomes begin to uncoil. B. Critical Writing: Describe the structure of a chromosome, using proper vocabulary. Discuss when and why a chromosome forms.

5 B. Color the diagram. 1. Color all the genetic information purple or blue. 2. Color the nucleus orange or yellow. 3. Color the centrioles and spindle fibers red or pink. C. Application: Onion Cell Root Using a microscope, count the number of onion cells you can find in each stage of cell division in a single viewing area of the slide. Draw what each stage looks like in the space below. 1. Interphase: cells 2. Prophase: cells 3. Metaphase: cells Microscope Analysis 1. What phase is the most abundant? Why? 4. Anaphase: cells 2. Which phases are least abundant? Why? 5. Telophase: cells 3. Why would the sample of dividing cells come from an onion root instead of skin?

6 D. Vocabulary: Match the word from the word bank to the proper definition. 1. Division of the nucleus 2. Region of the chromosome where sister chromatids are attached. 3. Division of the cytoplasm 4. Phase of mitosis in which spindle fibers attach to the centromere 5. Coiled structures made of DNA and proteins 6. Phase in which sister chromatids separate and the centromeres divide 7. A segment of DNA with the genetic instructions to make a protein 8. Two copies of replicated DNA that make a chromosome 9. The first and longest phase of mitosis 10. Uncoiled DNA 11. Phase in which the chromosomes begin to uncoil and form chromatin Word Bank Anaphase Centromere Chromatid Chromatin Chromosome Cytokinesis Gene Metaphase Mitosis Prophase Telophase E. Multiple Choice Practice: Circle or highlight the correct answer 1. Why is it necessary for DNA to replicate prior to cell division a. so that each daughter cell will have 23 chromosomes b. so that each daughter cell will have a complete copy of the genetic material c. so that each daughter cell will have 2 sister chromatids 2. Why do chromosomes have an X-shape? a. because they are made of two sister chromatids b. because they are made of two sister chromosomes c. because they are made of two sister centromeres 3. Chromosomes form during what part of the cell cycle? a. prophase of mitosis b. the end of the G2 phase c. right after S phase and DNA replication 4. How many chromosomes are in a normal human cell? a. 23 b. 32 c The correct order of phases during mitosis is a. telophase, prophase, metaphase, anaphase b. prophase, anaphase, metaphase, telophase c. prophase, metaphase, anaphase, telophase 6. Which cells undergo nuclear cell division? a. prokaryotic cells only b. eukaryotic cells only c. both prokaryotic and eukaryotic

7 V. Meiosis: Gamete Cell Division A. Critical Reading: Highlight or underline the main ideas. Sexually-reproducing organisms have a second form of cell division that produces reproductive cells with half the number of chromosomes. This process is called Meiosis. The cells that are the product of meiosis are known as haploid cells. During meiosis, homologous chromosomes separate, and the haploid cells that form have only one chromosome from each pair. Two cell divisions occur during meiosis, and a total of four haploid cells are produced. These two divisions are known as meiosis I and meiosis II. The overall process involves the chromosomes replicating once, and dividing twice. Meiosis I begins after DNA replicates during interphase. Cells undergo meiosis to create haploid sex cells that have the potential to combine with other haploid cells to create a new organism. Chromosome Math Humans have 46 chromosomes in each of their normal or somatic cells. During Meiosis I there are 92 chromosomes present in the dividing cell. After dividing in Cytokinesis I, there are 46 chromosomes in each cell. During Meiosis II, the 46 chromosomes are split so each of the four daughter cells contains 23 chromosomes. B. Color and label the Diagram 1. Outline all of the cells undergoing meiosis I in red 2. Outline all of the cells undergoing meiosis II in blue 3. Color the genetic information found in each cell purple or pink. 4. Color the nuclear membrane orange or yellow. Based on you knowledge of Mitosis, label each part of Meiosis as Prophase, Metaphase, Anaphase, Telophase, Cytokinesis, with a I or II. 1a. 1b. 1c. 1d. 1e. 2a. 2b. 2c. 2d. 2e.

8 C. Connection: Karyotypes A Karyotype is a photograph taken of a cell during mitosis or meiosis. From that image the individual chromosomes can be separated and organized into pairs. Humans have 23 pairs of chromosomes, 22 autosomal and 1 pair of sex chromosomes. Humans are diploid organisms, meaning they have two copies of every chromosome, one from each parent. In some rare cases, chromosomes do not separate into sister chromatids during meiosis which can result in aneuploidy or an abnormal number of chromosomes, too many or not enough. 1. Research one disorder that results from an abnormal number of chromosomes and describe it below. D. Reflect: Answer questions with proper terms and complete thoughts. 1. Define Meiosis. 2. Is the DNA replicated after meiosis I? Why or why not? 3. Describe the main difference between metaphase I and metaphase II. 4. State the phase where each of the following processes occurs: a. sister chromatids separate b. homologous chromosomes form pairs c. Two haploid cells form d. homologous chromosomes separate 5. Compare and Contrast Mitosis to Meiosis Mitosis Similarities Meiosis 6. Hedgehogs have 88 chromosomes in their diploid cells (more than humans!). How many chromosomes will a cell have? a. before meiosis I b. after meiosis I c. after meiosis II

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