5.Continuity of Life

8/3/2019 5.Continuity of Life

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Continuity of Life:

Cellular Reproduction


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Continuity of Life:

Cellular

Reproduction


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All living things reproduce

Reproduction is

Asexual reproduction

Sexual reproduction


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Chapter 11 6

Binary Fission

DNA replicated

Membrane added


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Chapter 11 7

Binary Fission 2

constriction

fission


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Protozoa:

New individuals


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Yeasts:Asexual Reproduction by Mitosis

Budding Nucleus divides by

mitosis

Bud forms on cell Nucleus moves into

bud

Bud separates


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Hydra:Asexual Reproduction by Mitosis


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Advantage

Can make off spring fast

Dont need partner

Disadvantage :

Species cannot change and adapt

One disease can wipe the completepopulation


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Advantage

Variation in population

Individual will be different

Foundation of evolution Species adapt to changes in environment

If egg and sperm have same amount of

chromosomes as the other body cells thenthe baby will have to many chromosomes---so meiosis is the way


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The two types of cell division playimportant role in the cell cycle

Mitotic cell division

Meiotic cell division


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Mitotic cell division in eukaryotic cells1. produces cells needed for growth, development,

and maintenance and repair2. produce the cells that make up the body of an

embryo .3. Mitotic cell divisions continue to allow the embryo

to grow, eventually, into an adult.

4. Mitotic is a continuous processEx: In the adult, mitotic cell divisions maintaintissues such as skin that are made of cells with shortlife spans

Mitotic division


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Mitotic

celldivision

Mitoticcelldivision&

differ-entiation

Functions of Mitosis

Tissues

Organs

Fertilized egg(zygote) Multicell stage


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Activity of genetic information before themitotic cell division

Before cell division begins, the DNA double helix ineach chromosome replicates.

The two newly made double helices remain

associated with each other. When cell division begins, the duplicate

chromosomes condense and become visible.. At this

stage, each duplicated chromosome contains two

identical DNA double helices. Each DNA double helixis contained within a sister chromatid.


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Interphase : Thechromosomes (blue)are in the thin,extended state and

appear as a mass inthe center of the cell.The microtubules(red) extend outwardfrom the nucleus toall parts of the cell.

Metaphase: Thechromosomes havemoved along thespindlemicrotubules to theequator of the cell.

Late prophase:Chromosomes (blue)have condensed andattached tomicrotubules of spindle

fibers (red).Microtubules havereorganized to formthe spindle;chromosomes, now

condensed, are clearlyvisible.

Phases of Mitosis, 1


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Chapter 11 20

Separation of Sister Chromatids

In metaphase, sister chromatidsare held together at centromere

At end of metaphase, centromere

releases sister chromatids

In anaphase, they move toopposite poles


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Anaphase: Sisterchromatids haveseparated, andone set of

chromosomesmoves along thespindlemicrotubule toeach pole of the

cell.

Telophase: Thechromosomeshave gathered intotwo clusters, one

at the site of eachfuture nucleus.

Next interphase:Chromosomes arerelaxing again intotheir extended

state. Spindle fibersare disappearing,and themicrotubules of the2 daughter cellsrearrange into theinterphase pattern.

Phases of Mitosis, 2


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Mitosis:Prophase - Metaphase

Kinetochoresalign at cellsequator

Nucleolusdisappears;Nuclear envelopebreaks down

Microtubulesattach tokinetochores

Chromosomescondense andshorten

Centrioles begin

to move apart;Spindle forms

Duplicatedchromosomesremain elongated

Centrioles havealso been

duplicated

LateInterphase

EarlyProphase

LateProphase

Metaphase


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(a) Late interphase: The chromosomes

have been duplicated but remain elongatedand relaxed within the nucleus. Thecentrioles have also been duplicated.

(b) Early prophase: The chromosomescondense, shortening and thickening. Thecentrioles begin to move apart, and thespindle microtubules begin to form

between them.


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(c) Late prophase: The nucleolusdisappears; the nuclear envelope breaksdown, and the spindle microtubules attach

to the kinetochore of each sister chromatid(red spot).

(d) Metaphase: Interactions between the

kinetochores and the microtubules havelined up the chromosomes at the cellsequator


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MitosisAnaphase - Cytokinesis

Free spindlefibers pushpoles apart

Chromatidsbecomeindependent

chromosomes

One set of

chromosomes;Begin unwinding

Nuclearenvelope re-

forms

Cytoplasmdivided alongequator

Each daughtergets 1 nucleus& half of

cytoplasm

Spindledisappears;Nucleolus

reappears

Anaphase Telophase CytokinesisNext

Interphase


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(e) Anaphase: Chromatids separate at the centromere,

becoming independent chromosomes that move toward the

opposite poles of the cell. The free spindle microtubules slide

past one another, pushing the poles farther apart.

(f) Telophase: One complete set of chromosomes reaches

each pole. The chromosomes relax into their extended state,

the spindle microtubules begin to disappear, and the nuclear

envelopes begin to re-form.

(g) Cytokinesis: At the end of telophase, the cytoplasm isdivided along the equator of the parent cell, with each

daughter cell receiving one nucleus and about half theoriginal cytoplasm.


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(h) Interphase of daughter cells: Thedaughter cells enter interphase. The spindlemicrotubules disappear, the nuclear

envelope re-forms, the chromosomes finishextending, and the nucleolus reappears.

Cytokinesis has almost separated the two

daughter cells


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Meiosis


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Meiosis I

Homologouschromosomes pairand cross over

Homologouschromosomes exchangeDNA & align on equator

Homologouschromosomes move toopposite poles

Prophase I Metaphase I Anaphase I Telophase I


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Title:

In meiotic cell division (meiosis and cytokinesis),

the homologous chromosomes of a diploid cell areseparated, producing four haploid daughter cells.

Each daughter cell contains one member of each

pair of parental homologous chromosomes.

In these diagrams, two pairs of homologouschromosomes are shown, large and small. Theyellow chromosomes are from one parent (forexample, the father), and the violet chromosomesare from the other parent..


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(a) Prophase I. Duplicated chromosomescondense. Homologous chromosomes pair

up and chiasmata occur as chromatids ofhomologues exchange parts. The nuclearenvelope disintegrates, and spindle

microtubules form (b) Metaphase I. Paired homologous

chromosomes line up along the equator of

the cell. One homologue of each pair faceseach pole of the cell and attaches to spindlemicrotubules via its kinetochore (red).


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(c) Anaphase I. Homologues separate, onemember of each pair going to each pole of the cell.Sister chromatids do not separate.

(d) Telophase I. Spindle microtubules disappear.

Two clusters of chromosomes have formed, eachcontaining one member of each pair ofhomologues. The daughter nuclei are thereforehaploid.

Cytokinesis commonly occurs at this stage. Thereis little or no interphase between meiosis I andmeiosis II.


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Meiosis II

Prophase II Metaphase IIAnaphase IITelophase IIFourHaploidCells

Similar to Mitosis


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(e) Prophase II: If chromosomes have relaxed

after telophase I, they recondense. Spindlemicrotubules re-form and attach to thesister chromatids.

(f) Metaphase II: Chromosomes line up alongthe equator, with sister chromatids of each

chromosome attached to spindlemicrotubules that lead to opposite poles.


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(g) Anaphase II: Chromatids separate intoindependent daughter chromosomes, one former

chromatid moving toward each pole.

(h) Telophase II: Chromosomes finish moving toopposite poles. Nuclear envelopes re-form, and

the chromosomes become extended again

(i) Four haploid cells. Cytokinesis results in four

haploid cells, each containing one member ofeach pair of homologous chromosomes (shownhere in condensed state).


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Meiosis vs Mitosis:


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Meiosis vs. Mitosis:Comparison of Stages

Si il i i b i i d


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Similarities between meiosis andmitosis:

1. Both are a type of cell division

2. Both have no new gene combinationswhen each new cell splits

3. Each new cell has the same number ofchromosomes

4. Both are involved in DNA replication

5. Both have inter, pro, meta, ana, andtelophases


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Differences between Meiosis andMitosis

1.Mitosis occurs in somatic cells andmeiosis occurs in reproductive cells

2. Dividing cells in mitosis can be either

diploid or haploid but in meiosis, thedividing cells can only be diploid

3.In mitosis, two daughter cells are formed

but in meiosis, four daughter cells areformed


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4.Mitosis helps in growth and in bodyrepairs but meiosis helps in sexualreproduction ;) and regulation of the

number of chromosomes5.In mitosis, cytokinesis occurs only once,but in meiosis, cytokinesis may take place

once or twice (depending on the type ofcell)

Th E k ti


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G0: nondividing

interphase

The EukaryoticCell Cycle

S:Synthesis ofDNA;chromosom

esduplicated

G1: Growth

G2: Growth


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The eukaryotic cell cycle consists of twomajor phases, interphase and mitotic celldivision. Each is divided into subphases.

Inter phase :G1 PhaseS Phase

G2 Phase


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Enzymes Drive the Cell Cycle

The cell cycle is driven by proteins calledCyclin-dependent kinases, or Cdks

Kinases are enzymes that phosphorylate(add a phosphate group to) otherproteins, stimulating or inhibiting theiractivity

Cdks are active only when they bind toother proteins called cyclins


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Enzymes Drive the Cell Cycle

Activated Cdks promote a variety of cellcycle events Synthesis and activation of proteins

required for DNA synthesis

Chromosome condensation Nuclear membrane breakdown

Spindle formation

Attachment of chromosomes to spindle

Sister chromatid separation andmovement


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Ch k i t C t l C ll C l


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Checkpoints Control Cell Cycle

Although Cdks drive the cell cycle,

multiple checkpoints ensure that The cell successfully completes DNA

synthesis during interphase Proper chromosome movements occur

during mitotic cell division

There are three major checkpoints inthe eukaryotic cell cycle, each

regulated by protein complexes1. G1 to S:2. G2 to mitosis3. Metaphase to anaphase


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Chapter 11 55


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G1 to S: Ensures that the cells DNA is suitablefor replication

p53 protein expressed when DNA is

damaged Inhibits replication

Stimulates synthesis of DNA repair

enzymes Triggers cell death (apoptosis) if damage

cant be repaired


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G2 to mitosis: Ensures that DNA has beencompletely and accurately replicated

p53 protein expression leads to decrease insynthesis and activity of an enzyme thatfacilitates chromosome condensation

chromosomes remain extended andaccessible to DNA repair enzymes, whichfix DNA before cell enters mitosis


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Metaphase to anaphase: Ensuresthat the chromosomes are aligned

properly at the metaphase plate a variety of proteins prevent

separation of the sister chromatids if

there are defects in chromosomealignment or spindle function


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5.Continuity of Life

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