4. Pembelahan Sel ok

8/2/2019 4. Pembelahan Sel ok

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PEMBELAHAN SEL

Sri Mumpuni WW. M.Si


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Introductory Concepts

Chromatin, Chromosomes

Chromatin is a mass of uncoiled DNA and

associated proteins calledhistones.

When cell division begins, DNA coils

around the proteins forming visible

structures calledchromosomes.


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Below: Human chromosomes (female)


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Haploid, Diploid

Diploid cells (2N) have two complete setsof chromosomes. The body cells of

animals are diploid.

Haploid cells have one complete set of

chromosomes. In animals, gametes (sperm

and eggs) are haploid.


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Homologous Chromosomes

Diploid organisms have two copies of each

chromosome (except the sex chromosomes). Eachpair of chromosomes ishomologous. For

example, the two #7 chromosomes are

homologous. The homologue to the #3

chromosome would be the other #3 chromosome.

Genes

A small segment of DNA that contains theinformation necessary to construct a protein or

part of a protein (polypeptide) is called a

gene. Genes are the unit of inheritance.


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Types of Cell Division

A cell divides by pinching into two. Each

of two daughter cells produced contains

genetic material inherited from theoriginal (parent) cell.


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Why Divide?

Single-celled organisms divide to reproduce.

Cell division in multicellular organisms enablesthe organism to grow larger while the cellsremain small.

Organisms with many cells can have cellswhich are specialized for different functionsand tasks. For example, red blood cells arespecialized for carrying oxygen but neurons(nervous tissue) are specialized for conductingsignals from one cell to another.

Some cells of multicellular organisms mustdivide to produce sex cells (gametes).


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Mitosis

Mitosis produces two daughter cells that are

identical to the parent cell. If the parent cellis haploid (N), then the daughter cells willbe haploid. If the parent cell is diploid, the

daughter cells will also be diploid.N N

2N 2N

This type of cell division allowsmulticellular organisms to grow and repairdamaged tissue.


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Meiosis

Meiosis produces daughter cells that have one half

the number ofchromosomes as the parent cell.2N N

Meiosis enables organisms to reproducesexually.

Gametes (sperm and eggs) are haploid.

Meiosis is necessary in sexually-reproducing

organisms because the fusion of two gametes

(fertilization) doubles the number of

chromosomes. Meiosis involves two divisions producing a total

of four daughter cells.
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/shared%20files/glossary.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/shared%20files/glossary.htm


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Chromosome Structure and Replication

Achromatidis a single DNA molecule.

Double-stranded chromosomes have twochromatids; normally, each one is identical to the

other. The point where the two chromatids areattached is called thecentromere.

Chromosome Doubling vs DNA Synthesis

Splitting chromosomes into two will double theirnumber because each chromatid is identical.


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DNA replication occurs when a single-strandedchromosome produces a second chromatid.

DNA replicates during the S period ofinterphase.

Chromosomes double when they split at the end of

metaphase.


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Summary of Mitosis

prophase - coil

metaphase - align

anaphase - separate

telophase - uncoil
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htm


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Overview of the Cell Cycle

Interphase (G1 and G2)

Chromosomes are not visible because they

are uncoiled


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Prophase

The chromosomes coil.

The nuclear membrane disintegrates.The spindle apparatus forms.


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Metaphase

The chromosomes become aligned.


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Anaphase

The chromatids separate (The number of

chromosomes doubles).


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When the chromosomes split at

anaphase, the chromosome number is

doubled. For example, the number of

chromosomes and chromatids during

each phase in a human cell is:

Phase # Chromosomes # Chromatids

Prophase 46 92

Metaphase 46 92

Anaphase 92 92

Telophase 92 92


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Telophase

The nuclear membrane reappears.

The chromosomes uncoil.The spindle apparatus breaks down.

The cell divides into two.


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Plants form a spindle apparatus as animals do

but plants lack centrioles.

Instead of furrowing, vesicles derived from

the Golgi apparatus fuse at the equator to

form acell plate. The vesicles contain

materials necessary to construct a cell wallbetween the cells.


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G Interphase


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G1 Interphase

The chromosomes have one chromatid.

G2 Interphase

The chromosomes have two chromatids.


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1. late Prophase/ea

rlyMetaphase

2. Metaphase

3. Telophase

4. early Telophase

5. early Telophase

6. Metaphase

7. Prophase

8. Anaphase

9. late


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1. late Anaphase

2. Telophase

3. late

Anaphase4. Prophase

5. Telophase

6. Prophase


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Life Cycles Meiosis functions to reduce the number of

chromosomes to one half. Each daughter

cell that is produced will have one half as

many chromosomes as the parent cell.

Meiosis is part of the sexual process

because gametes (sperm, eggs) have one

half the chromosomes as diploid (2N)individuals.
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20102/Bio%20102%20lectures/Animal%20Reproduction/animal.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/Bio%20102/Bio%20102%20lectures/Animal%20Reproduction/animal.htm


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In animals, meiosis occurs only when

gametes (sperm, eggs) are formed.


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In plants, gametes are not produced directly.

Instead meiosis produces spores and then

mitosis produces gametes. Although plants

have an additional step, meiosis eventually

results in the production of haploid gametes.


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Phases of Meiosis

There are two divisions in meiosis; the firstdivision is meiosis 1 and the second is meiosis 2.

The phases have the same names as those of

mitosis. A number indicates the division number

(1st or 2nd):

meiosis 1: prophase 1, metaphase 1,

anaphase 1, and telophase 1

meiosis 2: prophase 2, metaphase 2, anaphase 2,and telophase 2

In the first meiotic division, the number of cells is

doubled but the number of chromosomes is not.

This results in 1/2 as many chromosomes per cell.


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The second meiotic division is like mitosis; the

number of chromosomes does not get reduced.

The diagram below shows that the chromosome

alignment pattern during metaphase ofmitosis

results in the chromosomes splitting (doubling).

Prophase, anaphase and telophase are not shown.

Below: The alignment pattern during metaphase I of


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Below: The alignment pattern during metaphase I ofmeiosis results in pairs separating; there is nodoubling.

Below: Metaphase 1 and metaphase 2 of meiosis


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Phases of Meiosis

Prophase I

The events that occur during prophase of mitosis

also occur during prophase I of meiosis. The

chromosomes coil up, the nuclear membrane begins

to disintegrate, and the centrosomes begin moving

apart.

Synapsis (joining) of homologous


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Synapsis (joining) of homologous

chromosomes producestetrads (also called

bivalents).

The two chromosomes may exchange

fragments by a process calledcrossing over.


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When the chromosomes partially separate in lateprophase, the areas where crossing over occurredremain attached and are referred to as Chiasmata

(sing. chiasma). They hold the chromosomestogether until they separate during anaphase.

Crossing over between homologous chromosomesis likely to occur at several different points,

resulting in chromosomes that are mixtures of theoriginal two chromosomes.

One kinetochore forms on each chromosomeinstead of on each chromatid as in mitosis.

The spindle fibers attach to the chromosomes andbegin to move them to the center of the cell asthey do in mitosis.
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htm


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Independent Alignment of HomologousChromosomes

During Prophase I when the paternal andmaternal homologues line-up on theequatorial plane there is fifty percent chanceof either being distributed to either daughtercell. Therefore, at each meiosis division thereis a "shuffling" of the paternal and maternalchromosomes.

Amount of variability = 2n where n = haploid

chromosome number.Therefore in humans 223 = 8.4 X 106 geneticallydifferent gametes.


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Metaphase I


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Metaphase I

Bivalents (tetrads) become aligned in the

center of the cell and are attached to spindle

fibers.

Th h li ill d b l i


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The chromosome alignment illustrated below isfrom a cell with a diploid chromosome numberof 8.

Independent assortment refers to the random


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Independent assortment refers to the randomarrangement of pairs of chromosomes. Thediagram below shows four possible arrangementsof chromosomes during metaphase 1 from anindividual that has 6 total chromosomes. Supposethat the pink chromosomes are those that theindividual inherited from its mother and the bluecolored ones were inherited from its father. For

each chromosome pair, the chromosome that is onthe left (maternal or paternal) is determinedrandomly. As can be seen, there are severalalignment possibilities.


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Anaphase I

Anaphase I begins when homologouschromosomes separate.

T l h I
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htm


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Telophase I

The nuclear envelope reforms and nucleoli

reappear. This stage is absent in some species.

Interkinesis
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Cells/cells.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Cells/cells.htm


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Interkinesis

Interkinesis is similar to interphase except

DNA synthesis does not occur.

The events that occur during meiosis II are

similar to mitosis.

Prophase II

M t h II
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Mitosis/mitosis.htm


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Metaphase II

Anaphase II

Telophase II


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Telophase II

Daughter Cells


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Variation

Sexual reproduction promotes variationbecause each gamete (sperm or egg)contains a mixture of genes from two

different parents. Crossing-over andIndependent assortment

promote variation. During prophase of

meiosis, crossing-over results inchromosomes that have some genes fromone parent and some genes from the otherparent.


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Individuals contain two sets of each chromosome

but gametes contain only one set. For each

homologous pair of chromosomes, one

chromosome will be randomly selected for each

gamete formed (independent assortment).

Variation is necessary for natural selection. Recall

that natural selection favors individuals withcharacteristics that are best adapted to their

environments. Variation is therefore necessary for

species to become adapted to their environment

and it enables them to change when theenvironment changes.
http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Natural%20Selection/natural.htmhttp://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20101/Bio%20101%20Lectures/Natural%20Selection/natural.htm


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Gametogenesis

Gametogenesis is the formation of gametes.

The formation of eggs isoogenesis and the

formation of sperm isspermatogenesis. In animals, gametes are formed by meiosis.


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Spermatogenesis

Spermatogenesis occurs inseminiferoustubules in testes.


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The cell that undergoes meiosis is aprimary


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e ce t at u de goes e os s s a p ima y

spermatocyte. The first meiotic division

produces twosecondary spermatocytes and

the second division produces spermatids,which mature to form sperm.

Meiosis I, Meiosis II, and the maturation

process each take approximately 16 days(48 days total).


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Males do not run out of sperm because

mitosis precedes each meiosis. The diagram

above shows that a spermatogonium divides

by mitosis to produce a primary

spermatocytes and a spermatogonium.

Human males produce approximately1000

sperm per second (30 billion/year).

Each ejaculation should contain 200 - 300

million sperm.


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Oogenesis

Oogenesis occurs in the ovary.

Each of the divisions in humans is unequal.During the first meiotic division, a largesecondary oocyte and a small polar body areproduced. The secondary oocyte will divideto produce an egg and a polar body. Thefirst polar body may divide to produce two

more polar bodies. Although the polar bodies are very small

and nonfunctional, they contain a full set ofchromosomes.


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The photograph below shows a cross section of a


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p g prabbit ovary X 40. The primary oocyte iscontained within a structure called a follicle. Asthe follicle enlarges, it produces hormones. Duringovulation, the follicleruptures and, in humans, releases the secondaryoocyte

Meiosis in human females begins before


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Meiosis in human females begins before

person is born but stops in prophase I and

does not resume until after puberty. Each month, approximately 1000 primary

oocytes will to mature but most will die.

Ovulation occurs approximately once every28 days. Females ovulate approximately

400 times during their lifetime.

Secondary oocytes are released at ovulation.The second meiotic division resumes after

penetration by sperm.

In humans, secondary oocytes are


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In humans, secondary oocytes are

fertilized. Eggs are produced only after

fertilization of a secondary oocyte.

In the diagram above, the first polar body producedafter the first meiotic division did not divide again.

OR

This polar body may or may not divide a second time.


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Women are born with all of the primary

oocytes that they will ever have (2 million).

At puberty, there are approximately 400,000

left.

Some chromosomal abnormalities

associated with maternal age may be due tothe long time they remain paired during

prophase I.


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NB The ovum contains all th cytoplasmthat will be used by the zygote to begin

development. The sperm only donatesits nucleus, that is the paternal set ofchromosomes to the union.


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Selain di dalam inti sel, DNA juga bisa


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Selain di dalam inti sel, DNA juga bisa

ditemukan di dalam mitokondria, yaitu bagian

dari sel yang menghasilkan energi. Berkatmitokondria, kita bisa bernapas dan sel bisamemperbaiki diri. Tanpa mitokondria, selakan mati.

DNA mitokondria hanya diturunkan dari ibu.

Keunikan pola pewarisan DNA mitokondria

menyebabkan DNA ini dapat digunakan

sebagai penanda untuk mengidentifikasi

hubungan kekerabatan secara maternal/garisibu.


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Kasih ibu sepanjang jalan dan kiniperkembangan ilmu pengetahuan telah

mendapat bukti-bukti yangmendukungnya.

Berkembang diantara para pakar biologi


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Berkembang diantara para pakar biologi bahwa pada organisme multiselular,dipercayai entitas utama ini bukanlah inti sel

seperti yang dipercayai sebelumnya namuntidak lain adalah maternal mitochondrion yaitu mitokondria yang kini diketahuidiwarisi secara maternal.

DNA Mitokondria (mtDNA) diturunkan darisatu generasi ke generasi berikutnya tanpadipengaruhi atau dihalang-halangi oleh

mekanisme seksual. sementara DNA inti (nDNA) tidak lain dari

campuran antara DNA ibu dan ayah.

Mitokondria sebagai entitas utama dalam suatu sel


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gadalah pengertian yang dapat dibandingkandengan Revolusi Copernicus, organel intra sellular

tidak lagi mengorbit di sekeliling Nukleus, tapijustru semua mengorbit disekeliling dan melayanikepentingan mitokondria maternal.

Mitokondria berkuasa atas hidup dan matinya

sebuah sel karena ia memiliki kontrol atas programmed cell death ini mengapa sel manusiamendedikasikan lebih dari 100 gen inti untukmelayani mtDNA yang hanya mengkode 13 protein

saja. 13 protein yang memiliki kontrol total atasproses produksi energi mitokondria yangmensuplai energi untuk sel hingga pada gilirannyamemegang kunci atas hidup dan matinya sebuahsel, atau bahkan keseluruhan organisme tersebut.


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sebagai kesimpulan mitokondria diangkatsebagai entitas master karena memiliki

kualitas yang tidak dimiliki yang lainyaitu :

garis keturunan tidak terputus dari

generasi sel ke generasi berikutnya kontrol atas produksi energi

mengatur kematian sel

Mungkin mata kita adalah milik ayah, kulit


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g y ,kita milik ibu, hidung kita milik nenek, danpostur kita milik kakek, semua yang tampak

pada diri kita adalah hasil kontribusi banyakgenerasi kedua orang tua kita,

namun energi yang menggerakkan kehidupankita sehari-hari di produksi oleh satu saja,

yaitu warisan dari ibu kita. Buatlah ia kecewa dan tersakiti hatinya,

bukan tidak mungkin Allah berkehendak maka kutukannya akan

mengalir menuju setiap mitokondriakita dan BUMM ! menjadi batu, kaku,tanpa energi, seperti robot yang dilepas

baterainya.

dibalik setiap pemimpin yang sukses


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dibalik setiap pemimpin yang suksesdisitu ada istri dan ibu yang setia dan berbakat, dibalik setiap prestasi dangerak langkah sehari-hari tersembunyididalam tubuh berkah cinta ibu kita, warisan cintanya menjadi energi

penggerak. Ibu, ibu, ibu dan barulahayah,

betapa banyak kita mendengar berita bahwa keikhlasan, ridha dan maaf dari

seorang ibu telah membebaskananaknya dari sakaratul maut yangberkepanjangan.


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Jadi kawan ini adalah kisah cinta abadiseorang ibu pada anaknya tidak terputusmeski ribuan generasi berlalu, Allah jadikanenergi cinta itu bagian utama dari hidup kita,hormatilah maka surga ganjarannya,

khianatilah maka jangan terkejut bila hidupdan mati kita berada pada ridha ibu,demikianlah Allah menempatkan posisi ibudiantara kehidupan dimuka bumi ini

berbanggalah dan berbahagialah ataskehormatan yang Allah berikan pada Ibu !

Pada saat remaja androgen diperlukan untuk


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Pada saat remaja androgen diperlukan untukpertumbuhan, psikologi dan pengaruhseksual.

Androgen mempengaruhi pertumbuhanmemanjang dan maturasi otot tulang

Pertumbuhan juga diperantarai oleh kerja

anabolik dari androgen khususnyapeningkatan sintesa protein, kebanyakanpada otot.

Pada perilaku, androgen mempengaruhiagresiffitas dan libido. Terakhir, androgenmenggiatkan perkembangan karakteristikseks primer dan sekunder.

Selama pubertas estrogen bekerja serupa


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Selama pubertas estrogen bekerja serupadengan androgen. Menstimulasipertumbuhan linier dan maturasi otottulang, tetapi kurang aktifdalammenginduksi sistesa protein otot.

Menyebabkan perubahan perilaku dan

perkembangan karakteristik sek primer dansekunder.

Karakteristik seks primer termasuk genitalia

internal dan eksternal, sedangkan sexsekunder yaitu perkembangan mamae poladeposisi lemak tubuh.


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TERIMA KASIH

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