SIKLUS SEL Made Pharmawati

Kontinuitas kehidupan Didasarkan atas reproduksi sel atau pembelahan sel Figure 12.1

100 µm (a) Reproduction. An amoeba, a single-celled eukaryote, is dividing into two cells. Each new cell will be an individual organism (LM).

Organisme multiseluler tergantung pada pembelahan sel untuk: Perkembangan (dari sel yang terfertilisasi) Pertumbuhan Repair 20 µm 200 µm (b) Growth and development. This micrograph shows a sand dollar embryo shortly after the fertilized egg divided, forming two cells (LM). (c) Tissue renewal. These dividing bone marrow cells (arrow) will give rise to new blood cells (LM). Figure 12.2 B, C

Semua organisme kompleks berasal dari a single fertilized egg. Melalui pembelahan sel, jumlah sel meningkat Sel kemudian terspesialisasi dan berubah menjadi fungsinya masing2

Tipe pembelahan sel Mitosis: Growth, development & repair Asexual reproduction (yields identical cells) Occurs in somatic (body) cells Meiosis: Sexual reproduction (yields different cells) Occurs in specific reproductive cells So far, I’ve been talking about mitosis only What? Somatic (body) cells Why? Growth & development, repair lost or injured cells Allows many organisms to reproduce asexually But there is a 2nd type of cell division - meiosis that occurs only in select cells within certain tissue at particular phases of an organism’s lifetime. meiosis is involved with organisms that undergo SEXUAL REPRODUCTION --means of reducing number of chromosomes in sperm or egg so when combined through fertilization, the original number is restored -- reduction of genetic state from diploidy to haploidy necessary --occurs in reproductive organs in humans -- ovary & testis -- produces haploid cells called gametes (sperm, egg) --completed with fertilization of male gamete & female gamete to produce diploid zygote

Pembelahan sel menghasilkan sel anak yang secara genetik identik Phases of Mitosis 1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase Pembelahan sel menghasilkan sel anak yang secara genetik identik Sel harus menduplikasikan material genetiknya Before they divide, ensuring that each daughter cell receives an exact copy of the genetic material, DNA

Distribution of Chromosomes During Cell Division Pada persiapan cell division, DNA bereplikasi dan kromosom memadat Tiap chromosome yang terduplikasi memiliki dua sister chromatids, yang berpisah selama cell division Sentromer merupakan daerah ceking dari chromosome yang terduplikasi, diaman dua chromatids terikat dengan dekat

Figure 12.1 prophase 1X metahase Anaphase Telophase Cytokinesis

Cell division results in genetically identical daughter cells Sel menduplikasikan material genetik sebelum membelah, utk memastikan bahwa tiap sel anak menerima copy DNA dengan tepat A cell’s endowment of DNA (its genetic information) is called its genome Molekul DNA dalam sel ter-pack menjadi kromosom

Setiap spesies eukariot memiliki sejumlah tertentu kromosom pada nukleus Sel somatik (nonreproductive) memiliki 2 set kromosom Gamet (reproductive cells: sperm and eggs) memiliki jumlah kromosom setengah jumlah kromosom sel somatik Kromosom eukaryotik terdiri dari kromatin, sebuah komplex DNA dan protein yang memampat selama pembelahan sel

Fig. 19.1, p. 345: cartoon (left), EM (right) Chromatin = helix wrapped around protein -- giving bead-like structure These proteins are called ‘histones’ Nucleosome = DNA + histone complex Chromatin = a string of these beads (thread-like) Chromosome = looped and compacted chromatin

0.5 µm Chromosome duplication (including DNA synthesis) Centromere Separation of sister chromatids Sister chromatids Centromeres A eukaryotic cell has multiple chromosomes, one of which is represented here. Before duplication, each chromosome has a single DNA molecule. Once duplicated, a chromosome consists of two sister chromatids connected at the centromere. Each chromatid contains a copy of the DNA molecule. Mechanical processes separate the sister chromatids into two chromosomes and distribute them to two daughter cells. Figure 12.4

Pembelahan sel pada eukariot terdiri dari: Mitosis, the division of the nucleus Cytokinesis, the division of the cytoplasm Gamet diproduksi dalam pembelahan sel yang disebut meiosis Meiosis menghasilkan sel anak yang tidak identik dengan induk yaitu hanya memiliki 1 set kromosom

Pada pembelahan sel, fase mitosis bergantian dengan interfase Pada tahun 1882, ahli anatomi Jerman Walther Flemming mengembangkan pewarna untuk mengamati kromosom selama mitosis dan sitokinesis Bagi Flemming, terlihat sel tumbuh membesar Sekarang dapat diketahui banyak peristiwa kritis terjadi selama tahapan siklus sel

Fase-fase dalam siklus sel Siklus sel terdiri dari Fase mitosis Interphase INTERPHASE G1 S (DNA synthesis) G2 Cytokinesis Mitosis MITOTIC (M) PHASE Figure 12.5 Interphase G1 phase S phase G2 phase The mitotic phase mitosis cytokinesis

Phases of the Cell Cycle Siklus sel terdiri dari Mitotic (M) phase (mitosis and cytokinesis) Interphase (cell growth and copying of chromosomes in preparation for cell division) Interphase (terdiri dari sekitar 90% dari siklus sel) yang dapat dibagi dalam sub fase: G1 phase (“first gap”) S phase (“synthesis”) G2 phase (“second gap”)

Mitosis terdiri dari 5 phases Prophase Prometaphase G2 OF INTERPHASE PROPHASE PROMETAPHASE Centrosomes (with centriole pairs) Chromatin (duplicated) Early mitotic spindle Aster Centromere Fragments of nuclear envelope Kinetochore Nucleolus Nuclear envelope Plasma membrane Chromosome, consisting of two sister chromatids Kinetochore microtubule Figure 12.6 Nonkinetochore microtubules

Metaphase Anaphase Telophase Figure 12.6 Metaphase plate Centrosome at one spindle pole Daughter chromosomes METAPHASE ANAPHASE TELOPHASE AND CYTOKINESIS Spindle Metaphase plate Nucleolus forming Cleavage furrow Nuclear envelope forming Figure 12.6

Spindle muncul dari sentromer The mitotic spindle mikrotubul yang mengontrol pergerakan kromosom selama mitosis Spindle muncul dari sentromer spindle microtubules asters

Perakitan spindle microtubules dimulai dari sentrosom - microtubule organizing center Sentrosom bereplikasi membentuk dua sentrosom yang bermigrasi ke kutub yang berlawanan, dan spindle microtubules tumbuh dari sentrosom Aster (a radial array of short microtubules) muncul dari tiap sentrosom

The Spindle Spindle memiliki struktur seperti web terbuat dari microtubule . Sangat penting pada mitosis karena mengatur kromosom untuk berada pada posisi yang benar Mitotic center Click the return button to return to the prophase slide. Or the house button to return to the main menu. The purpose of the spindle is to organise the chromosomes during mitosis. It is a cradle of microtubule fibres which cause constriction around the centre of the cell, causing the cytoplasm to split. A cell at metaphase a spindle Microtubule

Some spindle microtubules Berikatan dengan kinetochores chromosomes Centrosome Aster Sister chromatids Metaphase Plate Kinetochores Overlapping nonkinetochore microtubules Kinetochores microtubules Chromosomes Microtubules 0.5 µm 1 µm Figure 12.7

Chromosomes attached to spindle during nuclear division

Two kinds of microtubules Kinetochore microtubules : berikatan dengan kinetochores chromosomes dan menggerakkan kromosom ke daerah metafase Nonkinetochores: overlap satu sama lain tetapi tidak berikatan dengan chromosome 1 µm

Pada anafase, sister chromatid berpisah Dan bergerak sepanjang kinetochore microtubules menuju arah berlawanan ujung sel Spindle pole Kinetochore Figure 12.8

Initiation of Anaphase

The microtubules shorten by depolymerizing at their kinetochore ends Nonkinetechore microtubules from opposite poles Overlap and push against each other, elongating the cell In telophase Genetically identical daughter nuclei form at opposite ends of the cell

Cytokinesis is the splitting of cytoplasm Division of the cytoplasm Mitosis is the splitting of the nucleus. Cytokinesis is the splitting of cytoplasm It usually begins during ANAPHASE

Pada sel hewan Cytokinesis terjadi oleh proses yang disebut cleavage, membentuk sebuah a cleavage furrow Cleavage furrow Contractile ring of microfilaments Daughter cells 100 µm (a) Cleavage of an animal cell (SEM)

Pada sel tumbuhan, selama cytokinesis Terbentuk plat sel (cell plate) Daughter cells 1 µm Vesicles forming cell plate Wall of patent cell Cell plate New cell wall (b) Cell plate formation in a plant cell (SEM) Figure 12.9 B

Mitosis in a plant cell Nucleus Chromatine condensing Chromosome 1 Prophase. The chromatin is condensing. The nucleolus is beginning to disappear. Although not yet visible in the micrograph, the mitotic spindle is staring to from. Prometaphase. We now see discrete chromosomes; each consists of two identical sister chromatids. Later in prometaphase, the nuclear envelop will fragment. Metaphase. The spindle is complete, and the chromosomes, attached to microtubules at their kinetochores, are all at the metaphase plate. Anaphase. The chromatids of each chromosome have separated, and the daughter chromosomes are moving to the ends of cell as their kinetochore microtubles shorten. Telophase. Daughter nuclei are forming. Meanwhile, cytokinesis has started: The cell plate, which will divided the cytoplasm in two, is growing toward the perimeter of the parent cell. 2 3 4 5 Nucleus Nucleolus Chromosome Chromatine condensing Figure 12.10

Purpose of Interphase – to duplicate cell contents; 90% of the cell’s growth cycle Purpose of Mitosis – to divide the genetic material into exact two halves Purpose of Cytokinesis – to divide all other contents (except nucleus) into two cells

Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission In binary fission – The bacterial chromosome replicates – The two daughter chromosomes actively move apart

Chromosome replication begins. Soon thereafter, LE 12-11_1 Cell wall Origin of replication Plasma membrane E. coli cell Bacterial chromosome Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. Two copies of origin

Chromosome replication begins. Soon thereafter, LE 12-11_2 Cell wall Origin of replication Plasma membrane E. coli cell Bacterial chromosome Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. Two copies of origin Origin Origin Replication continues. One copy of the origin is now at each end of the cell.

Chromosome replication begins. Soon thereafter, LE 12-11_3 Cell wall Origin of replication Plasma membrane E. coli cell Bacterial chromosome Chromosome replication begins. Soon thereafter, one copy of the origin moves rapidly toward the other end of the cell. Two copies of origin Origin Origin Replication continues. One copy of the origin is now at each end of the cell. Replication finishes. The plasma membrane grows inward, and new cell wall is deposited. Two daughter cells result.

A comparison of mitosis and meiosis

A comparison of mitosis and meiosis: summary