1CH 10 – CELL CYCLE & CELL DIVISIONhttps://biologyaipmt.com/CELL CYCLE AND CELL DIVISION Growth and reproduction are characteristics of living cells and organisms.Cell Cycle – The sequence of events by which a cell duplicates its genome, synthesizes the other constituentsof 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 coordinatedway.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.)Cell cycleInterphase Phase between two successive M phases.Lasts for 95% of total duration of cellcycle.Also called resting phase but Cell prepareitself for division by undergoing both cellgrowth and DNA replication.M phase (mitosis phase) The actual cell division or mitosis occursLasts for 95% of total duration of cellcycleStarts with nuclear division and endswith cytoplasmic division.Interphase It is divided into 3 further phases G1, S, and G2.G1 phase (Gap 1 Phase)Corresponds to the interval between mitosis and initiation of DNA replication.During G1 phase the cell is metabolically active and continuously grows but does not replicateits DNA.S phase (synthesis phase)period during which DNA synthesis or replication takes place.During this time the amount of DNA per cell doubles. (only amount of DNA is doubled, no ofchromosomes remain same.)In animal cells, during the S phase, DNA replication begins in the nucleus, and the centrioleduplicates in the cytoplasm.Prepared by –Dr. Anurag mittal
2CH 10 – CELL CYCLE & CELL DIVISIONhttps://biologyaipmt.com/ G2 phase (Gap 2 Phase)Proteins are synthesised in preparation for mitosis while cell growth continues.Some cells do not exhibit division like heart cells, nerve cells etc. these cells enter in an inactive phasecalled G0 or quiescent phase from G1 phase.Cells in this phase are metabolically active but they do not divide unless they are called on to do so.Mitosis or M phase In animals, mitotic cell division is only seen in the diploid somatic cells while in the plantsmitotic divisions can be seen in both haploid and diploid cells.it is also called as equational division as the number of chromosomes in the parent andprogeny cells are the same.Mitosis is divided into the following four stages: Prophase Metaphase Anaphase TelophaseProphase It follows the S and G2 phases of interphase.The centrioles now begin to move towards opposite poles of the cell.In prophase Chromosomal material condenses to form compact mitotic chromosomes.Initiation of the assembly of mitotic spindle with the help of the microtubules.Cell organelles like Golgi complexes, endoplasmic reticulum, nucleolus and the nuclearenvelope disappear.Metaphase Start of metaphase is marked by the complete disintegration of the nuclear envelope.The chromosomes are spread through the cytoplasm of the cell.condensation of chromosomes is completed and they can be observed clearly under themicroscope.Prepared by –Dr. Anurag mittal
3CH 10 – CELL CYCLE & CELL DIVISIONhttps://biologyaipmt.com/ This is the stage at which morphology of chromosomes is most easily studied.At this stage, metaphase chromosome is made up of two sister chromatids, which are heldtogether by the centromere.centromere serve as the sites of attachment of spindle fibres to the chromosomes.chromosomes are moved into position at the centre of the cell.the metaphase is characterised by all the chromosomes coming to lie at the equator with onechromatid of each chromosome connected by its kinetochore to spindle fibres from one poleand its sister chromatid connected by its kinetochore to spindle fibres from the opposite pole.The plane of alignment of the chromosomes at metaphase is referred to as the metaphaseplate or equatorial plate.Anaphase At the onset of anaphase, each chromosome arranged at the metaphase plate is splitsimultaneously and the two daughter chromatids begin to move towards the two opposite poles.As each chromosome moves away from the equatorial plate, the centromere of eachchromosome is towards the pole and hence at the leading edge, with the arms of thechromosome trailing behindTelophase At the beginning of telophase, the chromosomes at their respective poles decondense and formchromatin network.Nuclear envelope assembles around the chromatin network.Nucleolus, Golgi complex and ER etc cell organelles reform.Cytokinesis After karyokinesis the cell itself is divided into two daughter cells by a separate process calledcytokinesis.In an animal cell, this is achieved by the appearance of a furrow in the plasma membrane.The furrow gradually deepens and ultimately joins in the centre dividing the cell cytoplasm intotwo.Plant cells undergo cytokinesis by cell plate method. In cell plate method wall formation starts inthe centre of the cell and grows outward to meet the existing lateral walls.The formation of the new cell wall begins with the formation of a simple precursor, called thecell-plate that represents the middle lamella between the walls of two adjacent cells.At the time of cytoplasmic division, organelles like mitochondria and plastids get distributedbetween the two daughter cells.In some organisms karyokinesis is not followed by cytokinesis as a result of which multinucleatecondition arises leading to the formation of syncytium (e.g., liquid endosperm in coconut).(should be coenocytic)Prepared by –Dr. Anurag mittal
4CH 10 – CELL CYCLE & CELL DIVISIONhttps://biologyaipmt.com/Significance of mitosis(1) Mitosis results in the production of diploid daughter cells with identical genetic complementusually.(2) The growth of multicellular organisms is due to mitosis.(3) Cell growth results in disturbing the ratio between the nucleus and the cytoplasm. Therefore, celldivide to restore the nucleo-cytoplasmic ratio.(4) mitosis is important in cell repair. The cells of the upper layer of the epidermis, cells of the liningof the gut, and blood cells are being constantly replaced.(5) Mitotic divisions in the meristematic tissues – the apical and the lateral cambium, result in acontinuous growth of plants throughout their life.Fig: Different stages of MitosisPrepared by –Dr. Anurag mittal
5CH 10 – CELL CYCLE & CELL DIVISIONhttps://biologyaipmt.com/Meiosis The specialised kind of cell division that reduces the chromosome number by half results in theproduction of haploid daughter cells called meiosis.It is responsible for formation of haploid gametes, which during sexual reproduction form diploidzygote by fusion.Meiosis involves two sequential cycles of nuclear and cell division called meiosis I and meiosis IIbut only a single cycle of DNA replication.Interphase of meiosis is similar to interphase of mitosis.Meiosis IProphase I Prophase of the meiosis I division is typically longer and more complex than prophase of mitosis.It has been further subdivided into the following five phases based on chromosomal behavior.Prophase ILeptoteneChromosomes become gradually visible under the lightmicroscope. (Bouquet phase)ZygoteneHomologous chromosomes start pairing together and formsynaptonemal complex or tetrad by synapsis.PachyteneAppearance of recombination nodules.Crossing over occurs between non-sister chromatids of thehomologous chromosomes.DiploteneDissolution of the synaptonemal complex.Recombined chromosomes of the tetrad separate fromeach other except at the sites of crossovers. These X-shapedstructures, are called chiasmata.Diakinesisterminalisation of chiasmata.Chromosomes are fully condensed.Meiotic spindle is assembled to prepare the homologouschromosomes for separation.By the end of diakinesis, the nucleolus and nuclear envelopedisappear.Prepared by –Dr. Anurag mittal
6CH 10 – CELL CYCLE & CELL DIVISIONhttps://biologyaipmt.com/Metaphase I: The bivalent chromosomes align on the equatorial plate.The microtubules from the opposite poles of the spindle attach to the pair of homologouschromosomes.Anaphase I: The homologous chromosomes separate, while sister chromatids remain associated at theircentromeres.Telophase I The nuclear membrane and nucleolus reappear.cytokinesis follows telophase I. Although in many cases the chromosomes do undergo some dispersion, they do not reach theextremely extended state of the interphase nucleus. The stage between the two meiotic divisionsis called interkinesis and is generally short lived. Interkinesis is followed by prophase II, a much simpler prophase than prophase I.Meiosis II Meiosis II resembles a normal mitosis.Prophase II:Meiosis II is initiated immediately after cytokinesis.The nuclear membrane disappears by the end of prophase II.The chromosomes again become compact.Metaphase II:At this stage the chromosomes align at the equator and the microtubules from opposite poles ofthe spindle get attached to the kinetochores of sister chromatids.Anaphase II:splitting of the centromere of each chromosome.Chromosomes move toward opposite poles of the cell.Telophase II:the two groups of chromosomes once again get enclosed by a nuclear envelope.cytokinesis follows resulting in the formation of four haploid daughter cells).SIGNIFICANCE OF MEIOSIS(1) by meiosis conservation of specific chromosome number of each species is achieved acrossgenerations in sexually reproducing organisms.(2) It also increases the genetic variability in the population of organisms from one generation to thenext. Variations are very important for the process of evolution.Prepared by –Dr. Anurag mittal
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.)
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.
1 Cell Cycle and Mitosis THE CELL CYCLE The cell cycle, or cell-division cycle, is the series of events that take place in a eukaryotic cell between its formation and the moment it replicates itself. These events can be divided in two main parts: interphase (
The cell cycle includes all of the events in the life of an individual cell, from cell division to the period when a cell is not dividing while it carries out it’s regular functions. We can thus divide the cell cycle into: A. Interphase: Period of cell cycle when cell is not dividing 1. G1 Phase: Cellular organelles begin to duplicate. 2.
Apr 12, 2012 · Concept 12.3: The cell cycle is regulated by a molecular control system In each experiment, cultured mammalian cells at two different phases of the cell cycle were induced to fuse. The frequency of cell division – Varies with the type of cell 1 These cell cycle differences – Result from regulation at the molecular level
Fig. 1. Overview of the eukaryotic cell cycle. During cell division, cells pass through a series of stages collectively referred to as the cell cycle. To ensure that healthy cells are produced after each round of cell division, the cell cycle consists of three major checkpoints with distinct functions: G1, G2, and Spindle (M) checkpoints.
Part 6: Modeling the cell cycle in a normal cell Part 7: Modeling the cell cycle in a cancer cell Living Environment Major Understandings: Gene mutations in a cell can result in uncontrolled cell division, called cancer. Exposure of cells to certain chemicals and radiation increases mutations and thus increases the chance of cancer.
American Revolution in Europe working to negotiate assistance from France, Spain, and the Netherlands. Foreign Assistance French ultimately provided critical military and financial assistance Spain and the Netherlands provided primarily financial assistance to the American cause. A comparison of the resources held by the British and by the colonies: The population of the thirteen colonies .