GENETICS & DEVELOPMENT - Cell Division
AP BIOLOGYCELL UNITACTIVITY#6NAMEDATE HOURGENETICS & DEVELOPMENT - Cell DivisionPhysical Basis of Inheritability.Mechanisms of Cell Reproduction. egg & sperm cellscells reproduce identically, yet with variations (new traits)"All living cells arise from pre-existing cells"GENETICS asks. HOW? mechanisms at cellular & molecular levelDEVELOPMENT looks. at the LIFE CYCLE of organisms1. Reproduction mechanisms of organisms2. Growth of organism. zygote to adultcell differentiation - how one cell becomes different from anotherdifferential gene activity - genes are active at different timestotipotency & cloning - exact genetic copies of cellsMETHODS of CELL REPRODUCTION include.Fission - binary 2 equal halves (bacteria & cyanobacteria & protozoans)Budding - outgrowths detach new organism (unequal split)(hydra)Mitosis - asexually identical genetic copies [cytokinesis]genetically equal somatic cellsMeiosis - sexually produces sperm & egg cells with1/2 chromosome # & new gene combosMitosis - Asexual Reproduction Cell Cycle.results in copying & equal duplication of parental cell's DNAand the equal division of chromosomes into two daughter cells(rates liver cells 1x/yr - epithelial cells 1x/day)the Life cycle of a Cell. is referred to as the "CELL CYCLE".G1 growth and preparation of the chromosomes for replication;S synthesis of DNA and duplication of the centrosome;G2 preparation forM mitosis.When a cell is in any phase of the cell cycle other than mitosis, it is often saidto be in interphase.Cell Unit Activity #6 page 1
[3 Stages] - Cell Cycle is depicted as a circle 360o [G1 - S - G2 - M]Interphase - period between successive divisions of a cell3 parts G1 - before, DNA synthesis (S), & G2 period afterMITOSIS - nuclear division phase; separation & duplication of chromosomesCytokinesis - physical division of cell into two parts: animals/plantsProphase - chromatin condenses into chromosomesPrometaphase -chromosome MicroTubule's attach to kinetochoreseach homolog has 2 chromatidsMetaphase - chromosomes align at equatorhomologs align independently of each otherAnaphase MT attached to kinetochore; chromatids are pulledapart & poles move apartTelophase chromosomes at opposite poles;daughter cells form by cytokinesisNames and Numbers ChromosomesGenes occur in chromatin of nucleus,which condense into CHROMOSOMES(colored bodies) visible only during MITOSISbacteria have about 3,000 genes & 1 chromosome (DNA molecule)humans have some 20 to 25,000 genes & 46 chromosomesHumans have 46 chromosomes or 23 HOMOLOGOUS pairs23 maternal chromosomes23 paternal chromosomesCell Unit Activity #6 page 2
Control of Cell Division and the Cell CycleRegulated by "Growth Factors" - proteins that promote cell divisionTheir levels in the cell rise and fall with the stages of the cell cycle. Cyclinso a G1 cyclins (D cyclins)o S-phase cyclins (cyclins E and A)o mitotic cyclins (B cyclins)Cyclin-dependent kinases (Cdks)o a G1 Cdk (Cdk4)o an S-phase Cdk (Cdk2)o an M-phase Cdk (Cdk1)MPF - mitotic promoting factor. [ complex of two proteins cdk cyclin]MPF is a kinase enzyme, one that switches on/off target cell cycle proteins byphosphorylating them.inactive cycle protein active-protein-PATP ADPMPF promotes entrance into mitosis from the G2 phase by phosphorylating multipleproteins during mitosis including one that leads to destruction of cyclin itselfcdk - a cell division control protein - cyclin dependent kinase; active only whenbound to cyclin;cyclin - a protein whose amount varies cyclically; when in high concentrations,binds to cdk makes MPF.[cyclin cdk MPF]. favors MitosisCheckpoints: Quality Control of the Cell CycleThe cell has several systems for interrupting thecell cycle if something goes wrong. DNA damage checkpoints. These sense DNAdamage both before the cell enters S phase(a G1 checkpoint) as well as after S phase (aG2 checkpoint).o Damage to DNA before the cell entersS phase inhibits the action of Cdk2 thusstopping the progression of the cellCell Unit Activity #6 page 3
cycle until the damage can be repaired. If the damage is so severe that itcannot be repaired, the cell self-destructs by apoptosis.o Damage to DNA after S phase (the G2 checkpoint), inhibits the action ofCdk1 thus preventing the cell from proceeding from G2 to mitosis.A check on the successful replication of DNA during S phase. If replicationstops at any point on the DNA, progress through the cell cycle is halted untilthe problem is solved.Spindle checkpoints. Some of these that have been discoveredo detect any failure of spindle fibers to attach to kinetochores and arrestthe cell in metaphase until all the kinetochores are attached correctly (Mcheckpoint)o detect improper alignment of the spindle itself and block cytokinesis;SEXUAL CELL REPRODUCTION."MEIOSIS"nuclear division phase of sexually dividingcellsThe physical differences between nuclear divisions of MEIOSIS & MITOSISso the Distinct Differences are:meiosis 4 progeny cells [1 2 4]. thus 2 divisionsmitosis 2 daughter cells only. thus 1 cell divisionmeiosis one-half number of chromosomesmitosis same # of chromosomes as parent cellmeiosis new combinations of genes not in parents &chromosomes sort randomly of each othermitosis daughter cells are genetically identicalSexual Cell Reproduction (Meiosis)Where does meiosis occur during sexual cell cycle?Meiosis produces cells half chrm # 23 (sperm & egg - haploid)only specialized cells - gametes - can undergo meiosis.Fertilization (sperm egg) diploid life cycle (chrm # 46)Alternation of Generations & Human life CycleStages of Sexual Cell Divisionsame 3 phases. just as in asexual division(Interphase, Nuclear Division, Cytokinesis)but, 2 Divisions Meiosis I and Meiosis II1 cell 2 cell 4 cellsCell Unit Activity #6 page 4
Names of stages are same & have analogous functionsMeiosis I.Prophase I chromosomes condenseSYNAPSIS - homologs PAIR together tetradCROSSOVER - exchange occurs at a chiasmaMetaphase I chromosomes align at equatorAnaphase I chromosomes migrate toward polesTelophase I chromosome at poles - cell domains separateMeiosis I separates homologs of homologous pairMeiosis II. is just like mitosis [but without an S phase]separates chromatids of one homolog of the homologous pairjust as is done in mitosisIndependent Assortment - random alignment of homologous pairsCrossing Over - exchange of chromosome material1.2.3.4.5.6.7.8.Summary of MEIOSISNuclear division phase of sexual cell reproductionTwo successive divisions, results in 4 daughter cells.Meiosis 1 and Meiosis 2Reduction/division occurs. diploid haploiddaughter cells ½ number of parent cell chromosomesStages have same nomenclature as Mitosisprophase, metaphase, anaphase, telophase, M1 & M2Only one S phase, where DNA is duplicatedoften may be no interphase between M1 & M2Homologs separate in Meiosis 1Chromatids separate in Meiosis 2 (mitotic-like)Random Assortment occurs. homologs alignat equitorial plates independent of each otherCrossing over. may occur in Prophase I.synapsis close pairing homologs allows exchangechiasma point exchange of sister chromatidsCell Unit Activity #6 page 5
1.Briefly describe the physical differences between mitosis and meiosis.MitosisMeiosisPART I: COMPARING PLANT AND ANIMAL CELL MITOSIS2.Click on link to obtain a set of Mitosis Pictures.3.Examine the pictures comparing Plant and Animal Cell Mitosis4.What are the major differences between mitosis in animal cells and mitosis inplant cells?Animal Cell MitosisCell Unit Activity #6 page 6Plant Cell Mitosis
5. Click on link for Mitotic Phase Identification Cards. Determine the phaserepresented in the picture and indicate if the cell is plant or animal.Slide#Mitotic PhaseAnimal orPlantSlide#172839410511612Mitotic PhaseAnimal orPlantPART II: TIME FOR CELL REPRODUCTIONIt is hard to imagine that you can estimate how much time a cell spends in eachphase of cell replication from a slide of dead cells. Yet this is precisely what youwill do in this part of the activity. You will count the number of cells in each phaseand they infer the percent of time each cell spends in each phase.6.Examine the cells in Microscopic Field #1 of the Mitosis Pictures.Determine the cell cycle phase for each cell present in the field of view.Record the numbers in the Time for Mitosis Data Table.7.Repeat step 6 for each of the eight microscopic fields.8.Calculate the total number of cells in each phase and the total number ofcells viewed. Record the totals in the Time for Mitosis Data Table.9.Calculate the percentage of cells in each phase.10.It takes, on average, 24 hours (1,440 minutes) for onion root-tip cells tocomplete the cell cycle. Using this information you can calculate the amountof time spent in each phase of the cell cycle using the percent of cells in thatstage. (Percent of cells in phase times 1,440 minutes). Calculate the timespent in each phase and record your results in the data table.Cell Unit Activity #6 page 7
Time for Mitosis Data TableField# of CellsinInterphase# of CellsinProphase# of CellsinMetaphase# of CellsinAnaphase# of CellsinTelophase123456Total% of TotalCellsCountedTime inEachPhase11.Based on the data you collected, what can you infer about the relative lengthof time an onion root-tip cell spends in each stage of cell division?Cell Unit Activity #6 page 8
PART IV: QUESTIONSUse the drawings below to answer the questions that follow.12.BADCEFGKHIa.JWhat phase is shown in cell A?b. What mitotic phase is shown in cells B, C, D, and E?c. What mitotic phase is shown in cell F?Cell Unit Activity #6 page 9
d. What mitotic phase is shown in cells G and H?e. What mitotic phase is shown in cells I and J?f. What phase is shown in cell K?13.Are the cells pictured in Question 23 animal or plant?How do you know?14.In what way are the newly formed cells, which result from mitosis, similar tothe mother cell?15.How are the new cells different?16.Why is it necessary for DNA to replicate before mitosis begins?17.Examine the diagrams below.Cell #1Cell #2Cell #3Cell #4Name the structure indicated by letter a in cell #1.Name the structure indicated by letter b in cell #3.Name the structure indicated by letter c in cell #4.What is the correct order of the diagrams?Cell Unit Activity #6 page 10
18.Match the structure with the correct letter from the diagram.Cell oremicrotubulesNonkinetochoremicrotubule19.Match the description/event with the correct mitotic phase. Use the keybelow to indicate your answers.A AnaphaseP ProphaseT TelophaseM MetaphasePM PrometaphaseNucleoli disappearChromatin coils & folds (condenses)Mitotic spindle formsCentrosomes separate and move to opposite poles of cellNuclear envelope fragmentsKinetochore microtubules attach to kinetochoresChromosomes move to metaphase plateCentromeres of each chromosome “break” and move apartSister chromatids separate and are referred to as chromosomesSpindle fibers move the chromosomes to opposite polesNonkinetochore microtubules elongate the cellDaughter nuclei form at each poleCell Unit Activity #6 page 11
Nuclear envelopes form around each set of chromosomesNucleoli reappearChromatin uncoils (decondenses)Chromosomes line up along the metaphase plate20.Match the event or description with the correct cell cycle phase.MitosisDNA replicationCytokinesisCell grows in sizeOrganelles replicateInterphaseDivision of nuclear contentsDivision of cytoplasmG1 (gap 1)G2 (gap 2)S phaseCell prepares for cell mes condense (coil and fold)Chromosomes uncoilChromosomes pulled to opposite poles of cellChromosomes line up along the equator of the cellCell Unit Activity #6 page 12
21.What directs the sequential events of the cell cycle?22.What is the significance or importance of the checkpoints in the cell cycle?23.For many cells, what seems to be the most important checkpoint?What happens to the cell if it meets the requirements of this checkpoint?What happens to the cell if it fails to meet the requirements of thischeckpoint?24.Define or describe each of the following:ProteinKinaseCyclinCdksMPF25.Explain how MPF is involved in the control of the cell cycle.Cell Unit Activity #6 page 13
26.Describe how the concentration of each of the following changes during thecell cycle:CdkCyclinMPF27.What is the role of proteolytic enzymes in the cell cycle?28.What internal and external cues help regulate the cell cycle?29.Define or describe the following:Growth eCell Unit Activity #6 page 14
30.How are cancer cells different from normal cells?Cancer Cells31.Define the following:TransformationTumorBenign TumorMalignant TumorMetastasisCell Unit Activity #6 page 15Normal Cells
Chromosomes Genes occur in chromatin of nucleus, which condense into CHROMOSOMES (colored bodies) visible only during MITOSIS : bacteria have about 3,000 genes & 1 chromosome (DNA molecule) humans have some 20 to 25,000 genes & 46 chromosomes Humans ha
Somatic cell genetics. Books Recommended: 1. Genetics - Gardener 2. Molecular Genetics of Bacteria 2nd edition 1995, Jeremy W.Dale.-John Wiley and sons. 3.Cell biology (1993)-David E.Sadva (Jones and Barrette) 4.Modern genetics (2nd edition,1984)-A.J.Ayala and W.Castra(Goom Helns,London) 5. Genetics by P.K Gupta. 6. Genetics by Verma and Agarwal 7.
Genetics – A Continuity of Life – Daniel Fairbanks, Ralph Anderson. Concepts of Genetics – Klug and Cummings. Principles of Genetics – Hartt and Jones. GN 5 B 07 : CORE COURSE VII Medical Genetics Total – 54 hrs Unit- 1: Principles of Human Genetics (2 hrs) History, Origin of medical genetics, classification of genetic disease .
of the cell and eventually divides into two daughter cells is termed cell cycle. Cell cycle includes three processes cell division, DNA replication and cell growth in coordinated way. Duration of cell cycle can vary from organism to organism and also from cell type to cell type. (e.g., in Yeast cell cycle is of 90 minutes, in human 24 hrs.)
HUMAN GENETICS AND PEDIGREES 7.4 . Key Concept A combination of methods is used to study human genetics . Human Genetics Human genetics follows the patterns seen in other organisms The basic principles of genetics
Class-XI-Biology Cell Cycle and Cell Division 1 Practice more on Cell Cycle and Cell Division www.embibe.com CBSE NCERT Solutions for Class 11 Biology Chapter 10 Back of Chapter Questions 1. What is the average cell cycle span for a mammalian cell? Solution: The average cell cycle span o
The Cell Cycle The cell cycle is the series of events in the growth and division of a cell. In the prokaryotic cell cycle, the cell grows, duplicates its DNA, and divides by pinching in the cell membrane. The eukaryotic cell cycle has four stages (the first three of which are referred to as interphase): In the G 1 phase, the cell grows.
In unicellular organisms, division of one cell reproduces the entire organism Cell division enables multicellular eukaryotes to develop from a single cell and, once fully grown, to renew, repair, or replace cells as needed Cell division is an integral part of the cell cycle, the life of a cell from its formation to its own division
cycles of growth and division allow a single cell to form a structure consisting of millions of cells. 10.1 CELL CYCLE Cell division is a very important process in all living organisms. During the division of a cell, DNA replication and cell growth also take place. All these processes, i.e., cell division, DNA replication, and cell growth .
