BIO 150 Metabolism and Cell DivisionCELL REPRODUCTION(Cell Division)

Cellular Organization of the Genetic MaterialGenome-the entire organisms hereditary information.A genome can consist of a single DNA molecule (common in prokaryotic cells) or a number of DNA molecules (common in eukaryotic cells)DNA molecules in a cell are packaged into chromosomes

Every eukaryotic species has a characteristic number of chromosomes in each cell nucleusSomatic cells (non-reproductive cells) have two sets of chromosomesGametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells

Distribution of Chromosomes During Eukaryotic Cell DivisionIn preparation for cell division, DNA is replicated and the chromosomes condenseEach duplicated chromosome has two sister chromatids (joined copies of the original chromosome), which separate during cell divisionThe centromere is the narrow waist of the duplicated chromosome, where the two chromatids are most closely attached

During cell division, the two sister chromatids of each duplicated chromosome separate and move into two nuclei

Figure 12.5-3ChromosomesChromosomal DNA moleculesCentromereChromosome armChromosome duplication (including DNA replication) and condensationSister chromatidsSeparation of sister chromatids into two chromosomes123

Eukaryotic cell (somatic cells) division consists ofMitosis, the division of the genetic material in the nucleusCytokinesis, the division of the cytoplasmGametes are produced by a variation of cell division called meiosis

Mitosis Single cell splits into two identical daughter cells, each with an exact copy of the original parent cell.Most of the cell in human body is having this type of reproduction. E.g: stomach cells & skin cells do not live very long and constantly have to be replaced with new cells by mitosis.

Meiosis Meiosis yields non-identical daughter cells that have only one set of chromosomes, half as many as the parent cellDuring fertilization in animal, the gamete cell from female called an egg, combines with a gamete cell from the male organisms called a sperm to form new cell.The daughter cell have a unique gene assortment coming from the combination from both of the parent cell.Further cell reproduction occurs by mitosis.

Phases of the Cell CycleThe cell cycle consists ofInterphase (cell growth and copying of chromosomes in preparation for cell division)- 90% of the cycle- G1 phase (first gap)S phase (synthesis)G3 phase (second gap)Mitotic (M) phase (mitosis and cytokinesis)-shortest part of cell cycle-less than 1h

Interphase The cell grows during all three phases, but chromosomes are duplicated only during the S phase.During interphase the cell is not dividing.The cell gets nutrients from its surrounding, grows by producing proteins and cytoplasmic organelles, duplicates its chromosomes and prepares for cell division.

Figure 12.6INTERPHASEG1G2S (DNA synthesis)MITOTIC (M) PHASECytokinesisMitosisthe cell acquires or synthesizes the materials needed for cell division. When the cell grows to right size and receives necessary signal its entering to the S phase

involve DNA synthesis or DNA replication.the cell completes its growth before leaving the interphase.

Mitotic cell divisionConsists of mitosis and cytokinesis.Mitosis nuclear division Cytokinesis cytoplasmic divisionThe entire process takes about an hour and followed by interphase of the daughter cells.It is a continuous process and no breaks between one stage and the next.

The Mitotic Spindle: A Closer LookThe mitotic spindle- structure made of microtubules, controls chromosome movement during mitosisIn animal cells, assembly of spindle microtubules begins in the centrosome, the microtubule organizing center

The centrosome replicates during interphase, forming two centrosomes that migrate to opposite ends of the cell during prophase and prometaphaseAn aster (a radial array of short microtubules) extends from each centrosomeThe spindle includes the centrosomes, the spindle microtubules, and the asters

During prometaphase, some spindle microtubules attach to the kinetochores of chromosomes and begin to move the chromosomes Kinetochores are protein complexes associated with centromeresAt metaphase, the chromosomes are all lined up at the metaphase plate, an imaginary structure at the midway point between the spindles two poles

Figure 12.8Sister chromatidsAsterCentrosomeMetaphase plate (imaginary)Kineto- choresOverlapping nonkinetochore microtubulesKinetochore microtubulesMicrotubulesChromosomesCentrosome0.5 m1 m

In anaphase, sister chromatids separate and move along the kinetochore microtubules toward opposite ends of the cellThe microtubules shorten by depolymerizing at their kinetochore ends

Figure 12.9Chromosome movementMicrotubuleMotor proteinChromosomeKinetochoreTubulin subunitsKinetochoreMarkSpindle poleEXPERIMENTRESULTSCONCLUSION

Nonkinetochore microtubules from opposite poles overlap and push against each other, elongating the cellIn telophase, genetically identical daughter nuclei form at opposite ends of the cellCytokinesis begins during anaphase or telophase and the spindle eventually disassembles 2011 Pearson Education, Inc.

Mitosis is conventionally divided into five phasesProphasePrometaphaseMetaphaseAnaphaseTelophaseCytokinesis overlaps the latter stages of mitosis

ProphaseIn prophase, the cell begins the process of division. Chromatin condense into discrete chromosomes. Nucleoli disappear.Duplicated chromosomes appear as sister chromatid joined at centromeres by cohesins.Mitotic spindle begin to form.Centrosomes move away from each other by lengthening microtubules between them.

PrometaphaseNuclear envelope fragmentsMicrotubules invade nuclear area.Chromosome more condense.Each chromatids have kinetochores.Non kinetochores microtubules interacting with those from opposite pole.

MetaphaseMetaphase is where the chromosomes are lined up on the metaphase plate or equator of the cell.Centrosomes at opposite ends. Kinetochores of sister chromatids attached to kinetochore microtubules from opposite poles.

AnaphaseIn anaphase, the sister chromatid divide.Kinetochores microtubules shorten moving the chromosomes toward opposite ends.Non kinetochores microtubules lengthen-cell elongatesAt the end of anaphase, two ends of cell have equivalent chromosomes.

TelophaseTwo daughter nuclei form in the cellNuclear envelop arise from the fragments.Nucleoli reappear, chromosome less condenseSpindle microtubules depolymerized.Division of one nuclei into two genetically identical nuclei is complete.

CytokinesisOnce the cell has completed the four stages of mitosis, the cell now separates its cytoplasm and forms two new daughter cells.After cytokinesis is completed, two new daughter are formed which are identical to the parent cell.At this point cell division is complete.In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrowIn plant cells, a cell plate forms during cytokinesis

Figure 12.10(a) Cleavage of an animal cell (SEM)(b) Cell plate formation in a plant cell (TEM)Cleavage furrowContractile ring of microfilamentsDaughter cellsVesicles forming cell plateWall of parent cellCell plateNew cell wallDaughter cells100 m1 m

Triploid (3n)Tetraploid (4n)Haploid (n)Diploid (2n)

Figure 12.11Chromatin condensingNucleusNucleolusChromosomesCell plate10 mProphasePrometaphaseMetaphaseAnaphaseTelophase12345

The essential principle underlying mitosisDaughter cells receive precisely the same number and types of chromosomes as the original parent cellThe chromosomes of parent cell replicate before the cell divide so it contain twice its normal number of chromosomes.The arrangement of the chromosomes on the metaphase plate ensures the chromosomes are equally divided.

The importance of MitosisCells which go through the process of mitosis divide to produce two new cellsThis allows an organism to:GrowProduce new cell through asexual reproductionRegenerate (repair) damaged tissues or body partsReplace malfunctioning cellsReplace dead cells

Recall Chap 1 & 2Sum up the amount of energy in the form of ATP from a single glucose molecule that go through glycolysis, formation of acetyl coA, Krebs cycle and ETC.Draw labeled diagram and describe the induced-fit model of enzyme-substrate interactions.

Overview: Variations on a ThemeLiving organisms are distinguished by their ability to reproduce their own kindGenetics is the scientific study of heredity and variationHeredity is the transmission of traits from one generation to the nextVariation is demonstrated by the differences in appearance that offspring show from parents and siblings

Figure 13.1

Offspring acquire genes from parents by inheriting chromosomesIn a literal sense, children do not inherit particular physical traits from their parentsIt is genes that are actually inherited

Inheritance of GenesGenes are the units of heredity, and are made up of segments of DNAGenes are passed to the next generation via reproductive cells called gametes (sperm and eggs) Each gene has a specific location called a locus on a certain chromosomeMost DNA is packaged into chromosomes

Comparison of Asexual and Sexual Reproduction In asexual reproduction, a single individual passes genes to its offspring without the fusion of gametesA clone is a group of genetically identical individuals from the same parentIn sexual reproduction, two parents give rise to offspring that have unique combinations of genes inherited from the two parents

Figure 13.2(a) Hydra(b) RedwoodsBudParent0.5 mm

Sets of Chromosomes in Human CellsHuman somatic cells (any cell other than a gamete) have 23 pairs of chromosomesThe two chromosomes in each pair are called homologous chromosomes, or homologs.Chromosomes in a homologous pair are the same length and shape and carry genes controlling the same inherited characters

The sex chromosomes, which determine the sex of the individual, are called X and YHuman females have a homologous pair of X chromosomes (XX)Human males have one X and one Y chromosomeThe remaining 22 pairs of chromosomes are called autosomes

Each pair of homologous chromosomes includes one chromosome from each parentThe 46 chromosomes in a human somatic cell are two sets of 23: one from the mother and one from the fatherA diploid cell (2n) has two sets of chromosomesFor humans, the diploid number is 46 (2n = 46)

A gamete cell (sperm or egg) contains a single set of chromosomes, and is haploid (n)For humans, the haploid number is 23 (n = 23) consists of 22 autosomes and a single sex chromosomeIn an unfertilized egg (ovum), the sex chromosome is XIn a sperm cell, the sex chromosome may be either X or Y

Fertilization and meiosis alternate in sexual life cycles

A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism

Meiosis reduces the number of chromosome sets from diploid to haploidLike mitosis, meiosis is preceded by the replication of chromosomesMeiosis takes place in two sets of cell divisions, called meiosis I and meiosis IIThe two cell divisions result in four daughter cells, rather than the two daughter cells in mitosisEach daughter cell has only half as many chromosomes as the parent cell

The Stages of MeiosisAfter chromosomes duplicate, two divisions followMeiosis I (reductional division): homologs pair up and separate, resulting in two haploid daughter cells with replicated chromosomesMeiosis II (equational division) sister chromatids separateThe result is four haploid daughter cells with unreplicated chromosomes

Figure 13.7-3Pair of homologous chromosomes in diploid parent cellDuplicated pair of homologous chromosomesChromosomes duplicateSister chromatidsDiploid cell with duplicated chromosomesHomologous chromosomes separateHaploid cells with duplicated chromosomesSister chromatids separateHaploid cells with unduplicated chromosomesInterphaseMeiosis IMeiosis II

Meiosis I involves:Synapsis homologous chromosomes pair up. Chiasmata form (crossing over of non-sister chromatids).In Metaphase I, homologous pairs line up at metaphase plate.In Anaphase I, sister chromatids do NOT separate.Overall, separation of homologous pairs of chromosomes, rather than sister chromatids of individual chromosome.

Meiosis I is preceded by interphase, when the chromosomes are duplicated to form sister chromatidsThe sister chromatids are genetically identical and joined at the centromereThe single centrosome replicates, forming two centrosomes

Division in meiosis I occurs in four phasesProphase IMetaphase IAnaphase ITelophase I and cytokinesis

Figure 13.8aProphase IMetaphase IAnaphase ITelophase I and CytokinesisCentrosome (with centriole pair)Sister chromatidsChiasmataSpindleHomologous chromosomesFragments of nuclear envelopeDuplicated homologous chromosomes (red and blue) pair and exchange segments; 2n 6 in this example.Centromere (with kinetochore)Metaphase plateMicrotubule attached to kinetochoreChromosomes line up by homologous pairs.Sister chromatids remain attachedHomologous chromosomes separateEach pair of homologous chromosomes separates.Cleavage furrowTwo haploid cells form; each chromosome still consists of two sister chromatids.

Prophase IChromosomes begin to condense, homologs loosely paired.Paired homologs undergo synapsis: the homologs physically connected by synaptonemal complex.Crossing over: genetic rearrangement between non-sister chromatid-exchange of DNA segments.

4. Each pair of chromosomes forms a tetrad, a group of four chromatidsEach tetrad usually has one or more chiasmata, X-shaped regions where crossing over occurred

Centrosome movement, spindle formation, nuclear envelop breakdown.

Late prophase: microtubules attach to kinetochores at the centromere of the two homologs.

Metaphase IIn metaphase I, tetrads line up at the metaphase plate, with one chromosome facing each poleMicrotubules from one pole are attached to the kinetochore of one chromosome of each tetradMicrotubules from the other pole are attached to the kinetochore of the other chromosome

Anaphase IIn anaphase I, pairs of homologous chromosomes separateOne chromosome moves toward each pole, guided by the spindle apparatusSister chromatids remain attached at the centromere and move as one unit toward the pole

Telophase I and CytokinesisIn the beginning of telophase I, each half of the cell has a haploid set of chromosomes; each chromosome still consists of two sister chromatidsCytokinesis usually occurs simultaneously, forming two haploid daughter cellsChromosome decondense, nuclear envelopes form

In animal cells, a cleavage furrow forms; in plant cells, a cell plate formsNo chromosome replication occurs between the end of meiosis I and the beginning of meiosis II because the chromosomes are already replicated

Division in meiosis II also occurs in four phasesProphase IIMetaphase IIAnaphase IITelophase II and cytokinesisMeiosis II is very similar to mitosis

Figure 13.8bProphase IIMetaphase IIAnaphase IITelophase II and CytokinesisSister chromatids separateHaploid daughter cells formingDuring another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing unduplicated chromosomes.

Prophase IIIn prophase II, a spindle apparatus formsIn late prophase II, chromosomes (each still composed of two chromatids) move toward the metaphase plate

Metaphase IIIn metaphase II, the sister chromatids are arranged at the metaphase plateBecause of crossing over in meiosis I, the two sister chromatids of each chromosome are no longer genetically identicalThe kinetochores of sister chromatids attach to microtubules extending from opposite poles

Anaphase IIIn anaphase II, the sister chromatids separateThe sister chromatids of each chromosome now move as two newly individual chromosomes toward opposite poles

Telophase II and CytokinesisIn telophase II, the chromosomes arrive at opposite polesNuclei form, and the chromosomes begin decondensingCytokinesis separates the cytoplasmAt the end of meiosis, there are four daughter cells, each with a haploid set of unreplicated chromosomesEach daughter cell is genetically distinct from the others and from the parent cell

A Comparison of Mitosis and MeiosisMitosis conserves the number of chromosome sets, producing cells that are genetically identical to the parent cellMeiosis reduces the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell

Figure 13.9aProphaseDuplicated chromosomeMITOSISChromosome duplicationParent cell2n 6MetaphaseAnaphase Telophase2n2nDaughter cells of mitosisMEIOSISMEIOSIS IMEIOSIS IIProphase IMetaphase IAnaphase ITelophase IHaploid n 3ChiasmaChromosome duplicationHomologous chromosome pairDaughter cells of meiosis IDaughter cells of meiosis IInnnn

Three events are unique to meiosis, and all three occur in meiosis lSynapsis and crossing over in prophase I: Homologous chromosomes physically connect and exchange genetic informationAt the metaphase plate, there are paired homologous chromosomes (tetrads), instead of individual replicated chromosomesAt anaphase I, it is homologous chromosomes, instead of sister chromatids, that separate

FIN

Verily, after each difficulty, there are relief- Al-InsyirahAthirahs UiTM Pahang 14

*****Figure 12.5 Chromosome duplication and distribution during cell division.***Figure 12.6 The cell cycle.*For the Cell Biology Video Spindle Formation During Mitosis, go to Animation and Video Files.

***Figure 12.8 The mitotic spindle at metaphase.*For the Cell Biology Video Microtubules in Anaphase, go to Animation and Video Files.

*Figure 12.9 Inquiry: At which end do kinetochore microtubules shorten during anaphase?*For the Cell Biology Video Microtubules in Cell Division, go to Animation and Video Files.

*For the Cell Biology Video Myosin and Cytokinesis, go to Animation and Video Files.*Figure 12.10 Cytokinesis in animal and plant cells.*Figure 12.11 Mitosis in a plant cell.**Figure 13.1 What accounts for family resemblance?****Figure 13.2 Asexual reproduction in two multicellular organisms.*******Figure 13.7 Overview of meiosis: how meiosis reduces chromosome number.**For the Cell Biology Video Meiosis I in Sperm Formation, go to Animation and Video Files.**Figure 13.8 Exploring: Meiosis in an Animal Cell********Figure 13.8 Exploring: Meiosis in an Animal Cell******Figure 13.9 A comparison of mitosis and meiosis in diploid cells.*