Cell Division, Genetics, and Molecular Biology Cell Division, Genetics, and Molecular Biology

Ch 17_Bio_Alberta30 1/8/07 3:31 PM Page 552 3300 unit CC Cell Division, Genetics, Cell Division, Genetics, and Molecular Biology and Molecular Biology Cancer is a broad group of diseases associated with the uncontrolled,unregulated growth ofcells.Much more active than normal cells,cancer cells divide at rates that far exceed those of the parent cells from which they arose.Cancer cells also do not mature into specific cell types,as do normal cells.Cancer cells cannot carry out some ofthe functions ofnormal cells,which in turn can seriously affect a patient’s health. Cancer research aims at understanding how cells become cancer cells,and how they differ from normal cells. A research team at the University of Alberta, led by Dr.Mark Glover,is making significant contributions to our knowledge ofone form ofbreast cancer.People at risk ofdeveloping this form ofbreast cancer have a muta- tion in a particular gene,which in turn directs the production ofa mutant protein. Dr.Glover’s group created the first three-dimensional model ofthe part ofthis pro- tein that is involved in cancer development.This knowledge may lead to a method to screen patients for this type ofcancer early on. As you progress through the unit, thinkabout these focusing questions: • What cellularprocesses allow forreproduction and growth ofan organism? • What regulates the transmission ofgenetic information from one generation to the next? • How is DNA responsible forthe production ofproteins? UNIT30 C PERFORMANCE TASK Investigating Human Traits Genetics allows us to understand and predict the inheritance oftraits. This kind of information can be very important fortraits that cause health problems, such as cancer. How can human genetic traits be investigated? What do the patterns ofinheritance of some common traits tell us about the genes that determine those traits? At the end ofthis unit, you may apply yourskills and knowledge to complete this Performance Task. www.science.nelson.com GO 552 Unit 30 C NEL Ch 17_Bio_Alberta30 1/8/07 3:32 PM Page 553 Unit30 C GENERALOUTCOMES In this unit, you will • describe the processes ofmitosis and meiosis • explain the basic rules and processes associated with the transmission of genetic characteristics • explain classical genetics at a molecular level NEL Cell Division, Genetics, and MolecularBiology 553 Ch 17_Bio_Alberta30 1/8/07 3:32 PM Page 554 ARE YOU READY? Unit 30 C Cell Division, Genetics, and These questions will help you find out what you already know, and what you need to Molecular review, before you continue with this unit. Biology Knowledge 1. Identify the cell structures shown in Figure 1and explain the importance or function ofeach. Prerequisites Concepts 1 • DNA, genes, chromosomes • sexual reproduction 2 • asexual reproduction • adaptations and variations 3 • traits • nature versus nurture Skills • relate biological diversity to genetic diversity • probability 4 You can review prerequisite concepts and skills on the Nelson Web site and in the 5 Appendices. A Unit Pre-Test is also Figure 1 available online. 2. (a) Organize the following structures from largest to smallest:organ, www.science.nelson.com GO chromosome,organism,nucleus,tissue,DNA molecule,cell,gene. (b) Copy Figure 2.Use the listed structures in (a) as labels for your diagram. Figure 2 3. Ifa human muscle cell contains 46 chromosomes,indicate the number of chromosomes that you would expect to find in the cells shown in Figures 3,4,5, and 6,on the next page. 554 Unit 30 C NEL Ch 17_Bio_Alberta30 1/8/07 3:32 PM Page 555 Unit30 C Figure 3 Figure 4 Skin cell, 450(cid:1) Sperm cell, 1000(cid:1) Figure 5 Figure 6 Unfertilized egg cell, 2000(cid:1) Egg cell being fertilized by sperm cell, 5000(cid:1) 4. Provide examples ofhereditary traits that are (a) determined by genes (b) influenced by the environment 5. Many single-cell organisms divide by a process called binary fission.One cell divides into two cells identical to each other and identical to the original cell. More complex organisms form specialized sex cells.When sex cells combine from two different organisms,they form a fertilized egg or zygote. (a) Identify one advantage ofbinary fission as a means ofreproduction. (b) Identify and explain an advantage ofreproduction by the union ofsex cells from different individuals. 6. Explain why the duplication ofgenetic material is essential prior to division. Skills Table 1 Events in the Cell Cycle 7. Table 1shows the events in a typical cell cycle.Draw and label a Event Time (h) circle graph to represent the data. rapid growth 15 8. A couple are expecting their third child.After the birth oftwo boys, growth and DNA replication 20 they reason that the next child will be a girl. preparation fordivision 10 (a) Determine the probability ofhaving three boys in a row. mitosis 5 (b) Determine the probability that the next child will be a girl. NEL Cell Division, Genetics, and MolecularBiology 555 Ch 17_Bio_Alberta30 1/8/07 3:32 PM Page 556 11chap7t7er CCeellll DDiivviissiioonn In this chapter All life depends on the ability to grow and reproduce.Both these processes involve cell Exploration: Observing division.Organisms that reproduce asexually produce offspring that are identical to the Daphnia parents.Sexually reproducing organisms exchange genetic information,so that the off- Investigation 17.1: spring have a unique combination oftraits.The genetic material determines the proteins Frequency ofCell Division that make up cells,which ultimately give rise to physical traits. Daphnia(Figure 1,next page) is a truly remarkable animal.Females can produce off- Mini Investigation: Cloning from a Plant spring without a mate since they can produce eggs that require no fertilization.Upon Cutting development,these eggs become females,which in turn produce females,all ofwhich are identical to each other and to the parent.Then,in response to some environmental cue, Explore an Issue: The Ethics ofStem Cell Daphniabegin producing eggs that develop as either males or females.The males and Research females produce sex cells.Sexual reproduction occurs when the sperm cells fertilize the egg cells,producing many offspring with a variety oftraits.Asexual reproduction occurs Web Activity: Stem Cell Cord Blood when food is plentiful,while sexual reproduction is triggered during times ofenviron- mental stress. Investigation 17.2: All of the cells in Daphniaarise from one single cell.To develop into the complex Identification ofa CancerCell organism in Figure 1,that single cell must divide many times.In this chapter,you will explore the events that occur during cell division in order to produce cells ofthe body Mini Investigation: and specialized cells involved in reproduction. Gamete Formation in Grasshoppers Investigation 17.3: STARTING Points Comparing Mitosis and Meiosis Answerthese questions as best you can with yourcurrent knowledge. Then, using Web Activity: Comparing the concepts and skills you have learned, you will revise youranswers at the end of Life Cycles ofPlants the chapter. Web Activity: Dr. Renée Martin 1. Make a list ofthe advantages ofbeing multicellular. 2. Suggest possible advantages ofreproducing Web Activity: Modelling (a) asexually Mitosis and Meiosis (b) sexually 3. If22chromosomes are found in the muscle cell ofa mouse, predict the numberof chromosomes found in each cell ofthe following types: (a) brain cell (b) sperm cell (c) fertilized egg cell Explain yourpredictions. CareerConnection: Geneticist 556 Chapter17 NEL Ch 17_Bio_Alberta30 1/8/07 3:32 PM Page 557 heart brood pouch eye antennae intestine Figure 1 Daphniais also known as a waterflea, but it is a crustacean, not an insect. Exploration Observing Daphnia Materials:prepared slide ofDaphnia, concave depression slide, • Place the slide on an ice cube for3 min, then dry the bottom glycerin, coverslip, Daphniaculture, medicine dropper, ofthe slide with a papertowel and observe once again under microscope, ice cubes, cotton swab low-powermagnification. • Ifavailable, lookat a prepared slide ofDaphnia. Take note of (a) Why did you smearglycerin on the slide? the Daphnia’s general appearance and the location ofcertain (b) Why did you put the slide on an ice cube? features (e.g., eyes, antennae, heart) so that you will be able (c) Make and label a scientific drawing ofa Daphnia. to identify them more easily in the Daphniaculture. (d) Do you thinkthat Daphniaare composed ofmany cells? • Remove the prepared slide. Obtain the othermaterials. Using a Describe any features that you observe that demonstrate this fact. cotton swab,smearsome glycerin into the depression on the (e) Try viewing the Daphniaundermedium power. (Hint: You slide. Then, using a medicine dropper, place a small drop of may have to adjust the diaphragm.) Draw what you see. Daphniaculture onto the glycerin. Prepare a wet mount by adding a coverslip. Examine the slide underlow-power magnification. Pay attention to the movement and heart rate ofthe organism. NEL Cell Division 557 Ch 17_Bio_Alberta30 1/8/07 3:32 PM Page 558 1177..11 The Cell Cycle Learning Tip All the estimated 100 trillion cells that make up your body arose from a single fertilized egg.As with the frog egg shown in Figure 1,this fertilized egg cell underwent a series DNA, the cell’s hereditary ofdivisions that increased the number ofcells,thus increasing the size and complexity information, is found in the ofyour body until eventually you reached your current size.Cell division also maintains chromosomes ofa cell. In eukaryotic cells (cells with a a fully grown individual.All multi-cellular eukaryotic organisms grow in size and main- nucleus), the chromosomes tain the cells of their body (the somatic cells) by a sequence of events called the are found in the nucleus. cell cycle. Review this information in Section 6.5 ofthis book. one division several divisions Figure 1 Early stages ofcell division ofa fertilized frog egg cell cyclethe sequence ofstages The cell cycle is often described as taking place in phases (Figure 2,next page).However, through which a cell passes from the cycle is a continuous process and does not pause after each phase.During the divi- one cell division to the next sion phase (mitosis,or M),the components ofthe cytoplasm and the components ofthe nucleus ofthe parent cell are divided to give rise to two identical daughter cells by two mitosis (M)a type ofcell division processes,mitosis and cytokinesis.Mitosis ensures the equal distribution ofthe nuclear in which a daughtercell receives the same numberofchromosomes contents.This process includes the duplication ofchromosomes,so that each daughter as the parent cell cell ends up with the same number of chromosomes as the parent cell.Cytokinesis divides the cytoplasm and its constituent organelles of the parent cell roughly equally cytokinesisthe division of between the daughter cells. cytoplasm For most cells,the nuclear division that occurs during mitosis marks only a small interphasethe time interval part oftheir cycle.The stage between division phases,called interphase,is marked by between nucleardivisions when a a period of rapid growth (gap 1,or G1),the duplication of chromosomes (synthesis, cell increases in mass, roughly or S),another period ofgrowth (gap 2,or G2),and preparation for further divisions.Cells doubles the cytoplasmic carry out their particular functions during interphase. components, and duplicates its chromosomes Chromosome Structure Before looking at the details of mitosis,you will need to know something about the structure of chromosomes.In animals such as humans,the DNA is divided among a number ofchromosomes.Chromosomes contain both DNA and a number ofproteins. 558 Chapter17 NEL Ch 17_Bio_Alberta30 1/8/07 3:32 PM Page 559 Section 17.1 D I V I S I O N PHASE M: mitosis and cytokinesis G2: G1: growth and cell phase of preparation for cycle rapid cell cell division growth S: Figure 2 synthesis of DNA The cell cycle. The circle represents for duplication of the entire life cycle ofthe cell, chromosomes which can be divided into two majorphases: interphase and the INTER P H A S E division phase. Most cells spend the majority oftheirtime in interphase. This combination ofDNA and proteins is called chromatin.As the cell moves through chromatinthe complexofDNA the cell cycle,chromosomes may be either uncondensed or condensed.Uncondensed and protein that make up chromosomes chromosomes are long,thin strands that cannot be seen under a light microscope.A condensed chromosome can be seen under a light microscope and may resemble the centromerethe structure that diagram in Figure 3.Condensed chromosomes may be either unduplicated or dupli- holds chromatids together cated.In a duplicated chromosome,the original chromosome and its duplicate are attached to each other by a structure called the centromere.While attached to one sisterchromatidsa chromosome another,the two chromosome duplicates are called sisterchromatids.Since sister chro- and its duplicate, attached to one anotherby a centromere until matids contain identical genetic information,the pair,attached at the centromere,is separated during mitosis still considered to be one chromosome. one chromosome one chromosome (unduplicated) (duplicated) centromere Figure 3 An unduplicated and a duplicated sisterchromatids chromosome NEL Cell Division 559 Ch 17_Bio_Alberta30 1/8/07 3:32 PM Page 560 Interphase Cells spend most oftheir lives in interphase.In this phase ofthe cell cycle,cells are not actively dividing.Interphase includes the G1,S,and G2 phases ofthe cell cycle.Cells in interphase grow and undergo the various metabolic processes needed for their func- tioning during G1,S,and G2. Chromosomes are uncondensed throughout interphase (Figure 4).During G1,cells undergo a period ofrapid growth,and the chromosomes are unduplicated.During the S phase,cells begin to prepare for division during interphase by duplicating its chro- mosomes.At the end ofthe S phase,all the chromosomes are therefore duplicated chro- mosomes.During G2,the cell again grows and it completes the preparations for division (mitosis,or the M phase). Late Prophase Chromosomes continue to condense. The centrioles assemble and spindle fibres attach to the centromeres ofthe chromosomes. The nuclearmembrane starts to dissolve. Early Prophase The chromosomes condense, becoming shorter and thicker. The centrioles move to opposite poles of the cell and spindle fibres start to form. Interphase The cell replicates its DNA and prepares fornucleardivision. In humans, each ofthe 46 chromosomes duplicates itself. The result is 46 duplicated chromosomes, or46 pairs of chromatids. Figure 4 Interphase and mitosis in an animal cell. Interphase includes the G1, S, and G2phases ofthe cell cycle. Mitosis and cytokinesis occurduring the M phase. 560 Chapter17 NEL Ch 17_Bio_Alberta30 1/8/07 3:32 PM Page 561 Section 17.1 The Stages of Mitosis Prophase Prophase is the first phase ofmitosis.The chromosomes in the nucleus become visible under a microscope as they shorten and thicken (Figure 4).In animal cells,a small body in the cytoplasm separates and its parts move to opposite poles ofthe cell as the chromosomes become visible.These tiny structures,called centrioles,provide attachment for the centriolesmall protein body found spindle fibres,which serve as guide wires for the attachment and movement ofthe chro- in the cytoplasm ofanimal cells that provides attachment forspindle mosomes during cell division.Collectively,the centrioles and spindle fibres make up the fibres during cell division spindle apparatus.Most plant cells do not have centrioles,but spindle fibres still form and serve a similar purpose.The centromere joining the two chromatids helps anchor spindle fibreprotein structure that the chromosomes to the spindle fibres.When viewed under a microscope during prophase, guides chromosomes during cell the nuclear membrane appears to fade;in effect,it is dissolving to allow the separation of division chromosomes and cell organelles. Metaphase Anaphase Chromosomes line up The centromeres divide and at the equatorial plate. the resulting chromosomes, The nuclearmembrane formerly chromatids, move to completely dissolves. opposite poles ofthe cell. An identical set ofchromosomes moves to each pole. Telophase Chromosomes lengthen again, the spindle fibres dissolve, and a nuclear membrane forms around the chromosomes. In humans, each new nucleus contains 46 unique chromosomes. NEL Cell Division 561