Cell Cycle Final

7/29/2019 Cell Cycle Final

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Ciclo celular

M. C. Eloy Gasca Prez

Propedutico de ingreso

Maestra en Qumica Bioorgnica


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Cell Division

All cells are derived from pre-existing cells

New cells are produced for growth and to replace damaged or old cells

Differs in prokaryotes (bacteria) and eukaryotes (protists, fungi,plants, & animals)


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Keeping Cells Identical

The instructions for making cell parts

are encoded in the DNA, so each newcell must get a complete set of the

DNA molecules


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DNA Replication

DNA must be copied or

replicated before cell

division

Each new cell will then

have an identical copy of

the DNA

Original DNAstrand

Two new,

identical DNA

strands


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Identical Daughter Cells

Parent Cell

Twoidentical

daughter

cells


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Chromosomes


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Prokaryotic Chromosome

The DNA of prokaryotes

(bacteria) is one, circular

chromosome attached to the

inside of the cell membrane


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Eukaryotic Chromosomes

All eukaryotic cells store genetic information in chromosomes

Most eukaryotes have between 10 and 50 chromosomes in their

body cells

Human body cells have 46 chromosomes or 23 identical pairs


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Eukaryotic Chromosomes

Each chromosome is composed of a single, tightly coiled DNA

molecule

Chromosomes cant be seen when cells arent dividing and are

called chromatin


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Compacting DNA into Chromosomes

DNA is tightly coiled

around proteins

called histones


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Chromosomes in Dividing Cells

Duplicated chromosomes are

called chromatids & are held

together by the centromere

Called Sister Chromatids


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Karyotype

A picture of the chromosomesfrom a human cell arranged inpairs by size

First 22 pairs are calledautosomes

Last pair are the sexchromosomes

XX female or XY male


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Boy or Girl?

Y - Chromosome

X - Chromosome

The Y Chromosome Decides


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Cell Reproduction


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Types of Cell Reproduction

Asexual reproduction involves a single cell dividing tomake 2 new, identical daughter cells

Mitosis & binary fission are examples of asexualreproduction

Sexual reproduction involves two cells (egg & sperm)joining to make a new cell (zygote) that is NOTidentical to the original cells

Meiosis is an example


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Cell Division in Prokaryotes


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Cell Division in Prokaryotes

Prokaryotes such as

bacteria divide into 2identical cells by the

process of binary fission

Single chromosome

makes a copy of itself

Cell wall forms between

the chromosomes

dividing the cell

Parent cell

2 identical daughter cells

Chromosome

doubles

Cell splits


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Prokaryotic Cell Undergoing

Binary Fission


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Animation of Binary Fission


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The Cell Cycle


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Five Phases of the Cell Cycle

G1 - primary growth phase

S synthesis; DNA replicated

G2 - secondary growth phasecollectively these 3 stages are called interphase

M - mitosis

C - cytokinesis


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Cell Cycle


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Interphase - G1 Stage

1st growth stage after cell division

Cells mature by making more cytoplasm & organelles

Cell carries on its normal metabolic activities


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Interphase S Stage

Synthesis stage

DNA is copied or replicated

Twoidentical

copies of

DNA

Original DNA


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Interphase G2 Stage

2nd Growth Stage

Occurs after DNA has been copied

All cell structures needed for division are made (e.g. centrioles)

Both organelles & proteins are synthesized


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Whats Happening in Interphase?

What the cell looks like

Animal Cell

Whats occurring


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Sketch the Cell Cycle

Daughter

Cells

DNA Copied

Cells

Mature

Cells prepare for Division

Cell Divides into Identical cells


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Mitosis


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Mitosis

Division of the nucleus

Also called karyokinesis

Only occurs in eukaryotes

Has four stages

Doesnt occur in some cellssuch as brain cells


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Four Mitotic Stages

Prophase

Metaphase

Anaphase

Telophase


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Early Prophase

Chromatin in nucleus condenses to form visible chromosomes

Mitotic spindle forms from fibers in cytoskeleton or centrioles(animal)

Chromosomes

Nucleolus Cytoplasm

Nuclear Membrane


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Late Prophase

Nuclear membrane & nucleolus are broken down

Chromosomes continue condensing & are clearly visible

Spindle fibers called kinetochores attach to the centromere

of each chromosome

Spindle finishes forming between the poles of the cell


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Late Prophase

Nucleus & Nucleolus have disintegrated

Chromosomes


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Spindle Fiber attached

to Chromosome

Kinetochore Fiber

Chromosome


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Review of Prophase


Whats happening


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Spindle Fibers

The mitotic spindle form from the microtubules in plantsand centrioles in animal cells

Polar fibers extend from one pole of the cell to the opposite

pole

Kinetochore fibers extend from the pole to the centromereof the chromosome to which they attach

Asters are short fibers radiating from centrioles

Sk t h Th S i dl


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Sketch The Spindle


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Metaphase

Chromosomes, attached to the kinetochore fibers,

move to the center of the cell

Chromosomes are now lined up at the equator

Pole of

the Cell

Equator of Cell


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Metaphase

Chromosomes lined

at the Equator

Asters at the

poles

Spindle Fibers


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Metaphase

Aster

Chromosomes at Equator


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Review of Metaphase


Whats occurring


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Anaphase

Occurs rapidly

Sister chromatids arepulled apart to opposite

poles of the cell by

kinetochore fibers

A h


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Anaphase

Sister Chromatids

being separated


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Anaphase Review

What the cell

looks like

Whats

occurring


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Telophase

Sister chromatids at opposite poles

Spindle disassembles

Nuclear envelope forms around each set of sisterchromatids

Nucleolus reappears

CYTOKINESIS occurs

Chromosomes reappear as chromatin


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Comparison of Anaphase & Telophase


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Cytokinesis

Means division of the cytoplasm

Division of cell into two, identical halves calleddaughter cells

In plant cells, cell plate forms at the equator to dividecell

In animal cells, cleavage furrow forms to split cell


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Cytokinesis

Cleavage furrow in animal cellCell plate in animal cell


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Mitotic Stages


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Daughter Cells of Mitosis

Have the same number of chromosomes as each otherand as the parent cell from which they were formed

Identical to each other, but smaller than parent cell

Must grow in size to become mature cells (G1 ofInterphase)


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Identical Daughter Cells

Chromosome number the same, but cells smaller than parent cell

What is the

2n or diploid

number?

2


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Review of

Mitosis


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Draw & Learn these Stages


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Draw & Learn these Stages

Name the Mitotic Stages:


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Interphase

Prophase

Metaphase

Anaphase

Telophase

Name the Mitotic Stages:

Name this?

Name this?

Eukaryotic Cell Division


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Eukaryotic Cell Division

Used for growth and repair

Produce two new cells identical to theoriginal cell

Cells are diploid (2n)

Chromosomes duringMetaphase of mitosis

Prophase Metaphase Anaphase TelophaseCytokinesis


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Mitosis Animation

Name each stage as you see it occur?

Mi i i O i R Ti


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Mitosis in Onion Root Tips

Do you see any stages of mitosis?


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Test Yourselfover Mitosis


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Mitosis Quiz


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Mitosis Quiz

N th St f Mit i


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Name the Stages of Mitosis:

Interphase

Early prophase

Mid-ProphaseLate

Prophase

Metaphase

Late

Anaphase

Early Anaphase

Early

Telophase,

Begincytokinesis

Late telophase,

Advanced

cytokinesis


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Identify the Stages

Early, Middle, & Late Prophase

Late ProphaseMetaphase Anaphase

Late Anaphase TelophaseTelophase &

Cytokinesis

?

? ? ?

? ? ?

L t th F Mit ti


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Locate the Four Mitotic

Stages in Plants

Metaphase

Prophase

Anaphase

Telophase

U t ll d Mit i


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Uncontrolled Mitosis

If mitosis is not controlled,

unlimited cell division occurs

causing cancerous tumors

Oncogenes are special

proteins that increase the

chance that a normal cell

develops into a tumor cell

Cancer cells


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MeiosisFormation of Gametes

(Eggs & Sperm)


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Facts About Meiosis

Preceded by interphase which includes chromosome replication

Two meiotic divisions --- Meiosis I and Meiosis II

Called Reduction- division

Original cell is diploid (2n)

Four daughter cells produced that are monoploid (1n)


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Facts About Meiosis

Daughter cells contain half the number of

chromosomes as the original cell

Produces gametes (eggs & sperm)

Occurs in the testes in males (Spermatogenesis)

Occurs in the ovaries in females (Oogenesis)


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Start with 46 double stranded chromosomes (2n)

After 1 division - 23 double stranded chromosomes (n)

After 2nd division - 23 single stranded chromosomes (n)

Occurs in our germ cells that produce gametes

More Meiosis Facts


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Why Do we Need Meiosis?

It is the fundamental basis of sexual reproduction

Two haploid (1n) gametes are brought together throughfertilization to form a diploid (2n) zygote

F tili ti P tti it ll t th


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FertilizationPutting it all together

1n =3

2n = 6

Replication of Chromosomes


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p

Replication is the processof duplicating achromosome

Occurs prior to division

Replicated copies arecalled sister chromatids

Held together atcentromere

Occurs in

Interphase

A Replicated Chromosome


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p

Homologs

(same genes,different alleles)

Sister

Chromatids(same genes,same alleles)

Gene X

Homologs separate in meiosis I and therefore

different alleles separate.

Meiosis Forms Haploid Gametes


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Meiosis Forms Haploid Gametes

Meiosis must reduce the chromosome number by half

Fertilization then restores the 2n number

from mom from dad child

meiosis reduces

genetic content

too

much!

The right

number!


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Meiosis: Two Part Cell Division

Homologs

separate

Sister

chromatids

separate

Diploid

Meiosis

I

Meiosis

II

DiploidHaploid


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Meiosis I: Reduction Division

NucleusSpindle

fibersNuclear

envelopeEarly Prophase I

(Chromosome

number doubled)Late

Prophase I Metaphase I Anaphase I Telophase I

(diploid)

Prophase I


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Prophase I

Early prophase

Homologs pair.Crossing over occurs.

Late prophase

Chromosomes condense.

Spindle forms.

Nuclear envelope fragments.


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Tetrads Form in Prophase I

Homologous chromosomes

(each with sister chromatids)Join to form aTETRAD

Called Synapsis

Crossing-Over


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Homologous

chromosomes in atetrad cross over each

other

Pieces of

chromosomes or genesare exchanged

Produces Genetic

recombination in the

offspring

Homologous Chromosomes


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Homologous Chromosomes

During Crossing-Over


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Crossing-over multiplies the already huge number of different

gamete types produced by independent assortment

Crossing-Over


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Metaphase I

Homologous pairs of

chromosomes align along

the equator of the cell


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Anaphase I

Homologs separate and move

to opposite poles.

Sister chromatids remain

attached at their centromeres.

T l h I


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Telophase I

Nuclear envelopes reassemble.

Spindle disappears.

Cytokinesis divides cell into two.

Meiosis II


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Meiosis II

Only one homolog of each chromosomeis present in the cell.

Meiosis II produces gametes with one copy of each chromosome andthus one copy of each gene.

Sister chromatids carry

identical geneticinformation.

Gene X

M i i II R d i Ch N b


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Meiosis II: Reducing Chromosome Number

Prophase IIMetaphase II

Anaphase II

Telophase II

4 Identical haploid

cells

P h II


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Prophase II

Nuclear envelope fragments.

Spindle forms.

M t h II


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Metaphase II

Chromosomes align

along equator of cell.

A h II


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Anaphase II

Sister chromatids separate and

move to opposite poles.

Equator

Pole

T l h II


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Telophase II

Nuclear envelope assembles.

Chromosomes decondense.

Spindle disappears.

Cytokinesis divides cell into two.

R lt f M i i


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Results of Meiosis

Gametes (egg & sperm) form

Four haploid cells with one copy of

each chromosome

One allele of each gene

Different combinations of alleles for

different genes along the chromosome


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Gametogenesis

Oogenesisor

Spermatogenesis

Spermatogenesis


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p g

Occurs in the testes

Two divisions produce 4

spermatids

Spermatids mature into sperm

Men produce about

250,000,000 sperm per day

S t i i th T t


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Spermatogenesis in the Testes

Spermatid


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Oogenesis


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Oogenesis

Occurs in the ovaries

Two divisions produce 3 polar bodies that die and 1 egg

Polar bodies die because of unequal division of cytoplasm

Immature egg called oocyte

Starting at puberty, one oocyte matures into an ovum (egg)

every 28 days

Oogenesis in the Ovaries


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Oogenesis in the Ovaries

Oogenesis


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g

Oogonium

(diploid)

Mitosis

Primary

oocyte

(diploid)

Meiosis I

Secondaryoocyte

(haploid)

Meiosis II

(if fertilization

occurs)

First polar body

may divide

(haploid)Polar

bodies

die

Ovum (egg)

Second

polar body

(haploid)

a

A

X

X

a

X

A X

a

X

a

X

Mature

egg

A

X

A

X


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Comparing

Mitosis and Meiosis

Comparison of Divisions


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Mitosis Meiosis

Number ofdivisions

1 2

Number of

daughter cells2 4

Geneticallyidentical?

Yes No

Chromosome # Same as parent Half of parent

Where Somatic cells Germ cells

When Throughout life At sexual maturity

Growth and Sexual

Documents

Cell Cycle Final