1. the cell cycle & reproduction

8/13/2019 1. the Cell Cycle & Reproduction

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THE CELL CYCLE &REPRODUCTION

Janice V. Ng, MScNatSci2Dept. of Biology, CAS, UP Manila

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LECTURE CONTENT

Introduction to the Cell CycleCell Division

Mitosis: division of somatic cells

Meiosis: division of gametes

ReproductionAsexual: simple cell division

Sexual: fertilization to growth & development

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Omnis cellula e cellula

All cells from cells

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Cell Cycle

Interphase

G1 phase S phase G2 phase

M-phase

Mitosis Meiosis

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INTERPHASE

G1: Period of growth before DNA is replicatedS Phase: DNA replicationG2 Phase: Cell prepares for cell division

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DUPLICATING THE GENETICINFORMATION

An organisms biological information is found in the sequence ofnucleotides in the DNA molecule

Theres about ~2m of DNA per nucleus per cell

Condensation DNA-protein complex

DNA + Histones Chromatin

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Chromosomes arecharacterized by:a. Lengthb. Position of the centromerec. Banding patterns

telomere

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Apoptosis check point

Restriction point

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CELL CYCLE

Mitosis(somatic cells)

ProphaseMetaphaseAnaphaseTelophase

Meiosis (sex

cells)Meiosis IMeiosis II

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Transition mediated byCyclin-dependent kinase(Cdk)Cyclin

Cdk+Cyclin (e.g. MPF)


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MITOSIS

Division of somatic cells (non reproductive cells) ineukaryotesA single cell divides into two identical daughter cells

(cellular reproduction)Maintenance of chromosome ploidy levelPloidy refers to the number of pairs or set of chromosomesin cells

Haploid one copy of each chromosome; designated as n

Diploid two copies (=pair) of each chromosome, designated as 2n

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h h


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Each species has acharacteristic

number ofchromosomes

2n = 46n = 23 (22 pairs of homologousnon sex chromosomes and1 pair of sex chromosomes)

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2n = 46n = 23

(22 pairs of homologous nonsex chromosomes and

1 pair of sex chromosomes[either XX or XY])

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Diploid organisms receive one chromosome from female parent (= maternal) and onechromosome from male parent (= paternal )

A matched pair of maternal and paternal chromosomes are called homologues

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Mitosis is essential for growth and developmentof all body cells excluding sex cells.

Karyokinesis = nuclear division; Cytokinesis = cytoplasmic division

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MITOSIS - WHITEFISH

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MITOSIS ONION ROOT TIP

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MEIOSIS

Maintain normal number of chromosomesProduction of gametes

Gonads (animal)

Sporangia (plants)Gamete formation

Gametogenesis spermatogenesis, oogenesisMicro- or Megasporogenesis (Spore Formation)

Last from several days to upto 40-50 years (in humanfemale)

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MEIOSIS

Meiosis I ( PI, MI, AI, TI) Reductional divisionMeiosis II (PII, MII, AII, TII) Equational division

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PROPHASE I

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DIFFERENT CELL TYPES, DIFFERENT LENGTH OF CELLCYCLE:

1) Rapid cell division , continuous throughout life:- epithelial cells of mucosal layer of stomach,

intestines, body cavities- epithelial cells of stratum germinativum of skin- hematopoetic stem cells

- spermatogonia

2) Do not divide- mature nerve tissues- mature muscle tissues- mature red blood cells

3) Divide when induced-liver cells in mature liver-lymphocytes

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MITOSIS VS. MEIOSIS

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MITOSIS VS MEIOSIS

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Meiosis I Mitosis

Prophase I Prophase

Pairing of chromosomes No pairing

Metaphase I MetaphaseHomologous chromosomes at Duplicated chromosomes at

Metaphase plate metaphase plate

Anaphase I AnaphaseHomologous chromosomes separate Sister chromatids separate, becoming

Daughter chromosomes

Telophase I Telophase

Daughter cells are haploid Daughter cells are diploid

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Meiosis II Mitosis

Prophase II Prophase

No pairing of chromosomes No pairingMetaphase II Metaphase

Haploid # of chromosomes at metaphase Diploid # of duplicatedchromosomes at plate metaphase plate

Anaphase II AnaphaseSister chromatids separate, becoming Sister chromatids separate, becoming

daughter chromosomes daughter chromosomes

Telophase I Telophase

4 haploid daughter cells Daughter cells are diploid

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MODES OF REPRODUCTION

AsexualMost primitive

Uniparental

Mitosis

Does not involve exchange of genetic material between 2 organisms,hence, offspring is an exact replica of the parent, called clone

Advantageous when organisms are well adapted to constantenvironment

Fission, Budding, Fragmentation

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ASEXUAL REPRODUCTION

FissionSplitting of parent cell into daughter cells

Amoeba E. coli Giardia lamblia

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BuddingA small replica of the parent grows out of the parent (buds out)

Bud cells proliferate to form a cylindrical structure new animal

If bud remains in parent colony

Yeast Ginger

Hydra

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FragmentationA portion of the parent separates and develops into a like organism

Body part is lost and then regenerate into new organism

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Flatworm

Lichen

Sea star


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MODES OF REPRODUCTION

SexualBiparental

Meiosis and fertilization

Basic pattern is similar in all sexual animalsProcess for production of individual involving exchange of geneticmaterial between organisms, hence, offsprings are variants of theparents

More variation greater likelihood for survival in changingenvironment

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SEXUAL REPRODUCTION

Types of Meiosis (based on meiotic product)Gametic Meiosis direct products of meiosis are gametes (Animals)

Sporic Meiosis direct products of meiosis are spores (Plants andsome algae)Zygotic Meiosis Zygote does not develop into adult but directlyundergoes meiosis to produce haploid cells that develop intohaploid adults (Some fungi and algae)

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SEXUAL REPRODUCTION

Types of Fertilization (based on whatstructures are directly involved in thefusion event)

Syngamy both gametes physically fuse to

produce zygoteIsogamy

Anisogamy

Oogamy

Conjugation protoplast or genetic materialfrom one of the gametes is transferred to theother gamete where the fusion event takesplace

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SEXUAL REPRODUCTION

Types of Fertilization (based on site of fertilization)

External Fertilization

Eggs shed by female and

fertilized by male in theenvironment

Occurs in moist habitat

Many eggs involved

Internal Fertilization

Sperm are deposited in the

female reproductive tract; eggand sperm unite within

Copulatory organ, accessoryorgan

Few egg/s involved

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SPECIAL TYPES OF REPRODUCTION

HermaphroditismBoth male and female reproductive organs are found in asingle organism

MonoeciousSequential hermaphrodites: sex reversal during itslifetime

Protandrous:Clownfish

Protogynous:Wrasse

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SPECIAL TYPES OF REPRODUCTION

PolyembryonyProduction of two or more individuals from onefertilized egg by separation of the cells in early stage of

development

Wasps eggs

Armadillo

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You began life as a single cell, butthere are now more cells in yourbody than stars in the Milky Way

Just in the past second,millions of your cellshave divided in two

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The movement of the

chromosomes in a dividing cell isso precise that only one erroroccurs in 100,000 cell divisions

Each sperm or egg produced inyour reproductive organs carriesone of over 8 million possiblecombinations of parentalchromosomes

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ASEXUAL REPRODUCTION -ADVANTAGES

Produce large number ofoffsprings faster populationgrowth

Less energy required

Advantageous in a stable, favorableenvironment because itreproduces a successful genotypeprecisely.

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SEXUAL REPRODUCTION -ADVANTAGES

Sexual reproduction increases variability in the population important during times of environmental change.

Production of more novel genotypes

In crowded habitats, selection is intense and diversityprevents extinction.

Longer life span

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FERTILIZATION

Acrosomal Reaction in Sperm cell

Cortical Reaction in Egg cell

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Acrosomal ReactionAcrosome: organellecontaining hyaluronidaseenzyme that breaks the

outer membrane of anovum

Sperm has proteins on itstip which attach to specialreceptor sites on egg.

Specificity preventsfertilization by anotherspecies

FERTILIZATION

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FERTILIZATION

Cortical reactionCortical granules:secretory vesiclescontaining calcium

Fertilization triggersfusion of plasmamembrane forming afertilizationmembrane

Functions to preventpolyspermy (multiplefertilization)

1. the cell cycle & reproduction

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