proliferasi sel
TRANSCRIPT
PROLIFERASI SEL
Dr. Rhandyka Rafli, Sp.OnkRad
• Pertambahan jumlah sel karena pertumbuhan dan pembelahan
• Stimulasi • Fisiologis : Growth hormon, endometrium pada siklus
mens• Patologis : trauma, kematian sel
Signaling proliferasi sel• Stimulasi Growth factor ikatan reseptor sinyal sel
target transkripsi gen mitosis/meiosis
• Model signalling• Autocrine signaling • Paracrine signalling• Endocrine signaling
Tujuan sel membelah
• Homeostasis• Pertumbuhan Mitosis (pembelahan somatic)• Differensiasi
• Berkembang biak Meiosis (pembelahan gamet)
Homeostasis pertumbuhan sel
• Positif : pertumbuhan/regenerasi• Stabil : kematian = pertumbuan• Negatif : degenerasi
Aktivitas proliferasi sel• continuously dividing tissues (labile tissues)high proliferation
epithelia : mucosal lining, hemopoetik
• Quiescent (stable tissues) low proliferationmesenkim : hepar, otot, vascular
• Nondividing (permanent tissues)(≠ siklus sel, ≠mitosis) tulang, jantung, saraf
Siklus Sel• G0 (siklus arrest)• G1 presintetik
• G1/S Checkpoint • S sintetik• G2 premitotik
• G2/M Checkpoint • M mitosis
G1 → (G: Gap1)• Segera setelah cytogenesis.• Metabolisme tinggi : transportation, synthesis, lysis reactions, organelle
production, RNA synthesis dan fungsi jaringan paling tinggi• It is the longest stage. Cells that lose their ability to divide continue with
their functions and life activities (e.g., muscle and nerve cells still function at this stage).
S → (S: Synthesis)• DNA is duplicated and the number of chromatins doubles (→ replication).• The most intense protein synthesis is performed at this stage.• The order of centromere duplication is observed.
G2 → (G: Gap2)• Sintesis enzim pembelahan• The number of organelles increases.• DNA synthesis finishes, but RNA synthesis continues.• Centrosome synthesis finishes, and these centrosomes start moving towards
opposite poles.
G0 phase• Cells have a natural mechanism that protects them during difficult developmental• conditions. Under these conditions, the cells transiently stop their cellular
activities.• This phase is called the G0 phase. In the G0 phase, some genes in the DNA are
covered• with various proteins; i.e., the DNA is programmed.
Mitosis• Interphase
• Prophase
• Metaphase
• Anaphase
• Telophase
Interphase• Interesting things happen!1. Cell preparing to divide2. Genetic material doubles
Prophase• Chromosome pair up!1. Chromosomes thicken and shorten
-become visible-2 chromatids joined by a centromere
2. Centrioles move to the opposite sides of the nucleus3. Nucleolus disappears4. Nuclear membrane disintegrate
Metaphase• Chromosomes meet in the middle!1. Chromosomes arrange at equator of cell2. Become attached to spindle fibres by centromeres3. Homologous chromosomes do not associate
Anaphase• Chromosomes get pulled apart1. Spindle fibres contract pulling chromatids to the
opposite poles of the cell
Telophase• Now there are two!1. Chromosomes uncoil2. Spindle fibres disintegrate3. Centrioles replicate4. Nucleur membrane forms5. Cell divides
Meiosis• 4 daughter cells produced• Each daughter cell has half the chromosomes of the
parent• 2 sets of cell division involved
Term • Homologous chromosome Chromosome with the similar size, shape and the position of their
centromeres.• Synapsis Condition of chromosome pairing• Bivalent Structure of homologous pair• Tetrad Homologous chromosome that have 4 chromatids• Sister chromatid Chromatid from same homologous chromosome • Chiasma Point at which crossing over occur
Bivalent
Stages of meiosis IReduction division• It reduces the number of chromosome from 46 (2n) to 23
(n).• The cell divide has homologous pair of chromosome. • One homolog comes from mother (maternal) and one from
father (paternal). • When meiosis begins, DNA of each homologous replicates,
forming two chromatids joined at two centromeres.
Prophase I
1. Duplicated chromosomes condense and become visible.2. Pairing up of homologous chromosomes forming bivalent. This process is called
synapsis.3. Synapsis cause the homologous chromosomes closely associated.4. Both homologous chromosomes interwine at chiasma and this process is known as
crossing over.5. Crossing over causes exchange the genetic material (DNA) between paternal and
maternal chromosomes.
6. Crossing over produces new combination of genes.7. The genetic recombination from this process greatly enhance the genetic variation. 8. Spindle fibers are form. 9. Nuclear envelope breaks down.
Metaphase I1. Homologous chromosomes line up
at the equator of the cell.
2. Form double rows of homologous chromosomes.
3. Unipolar spindle attachment to single kinetochore at each homologue.
Anaphase I
• Homologous chromosomes separate and move to opposite poles of the cell.
• Sister chromatids remain attached at their centromeres.
Telophase I1. One of each pair of
homologous chromosomes is at each pole.
2. Cytokinesis occur.
3. The nuclear envelope reforms and the nucleoli reappear.
Stages in meiosis II• Equational division• Same like mitosis.• Produce 4 daughter cells with haploid
(n) number of chromosomes.
Prophase II• The chromosomes are again
condensed and visible, become short and thick.
• Nucleolus and membrane nucleus dissapear.
• Centriole move to opposite poles.
• DNA does not replicate again.
Metaphase II• Chromosomes line up at the equator of
the cell.
Anaphase II• Centomere separation occurs.• Chromatids moves to opposite poles.
Telophase II• Nuclei formed at opposite poles of each
cell.• Chromosomes gradually elongate to form
chromatin fibers.• Cytokinesis occurs.• Four haploid cells are produced.
Importance of meiosis
• For sexual reproduction.• Maintains the chromosome numbers constant from
generation to generation.• Assures a different genetic make up for the next
generation as a result of crossing over and new combination of genes.
Comparison between mitosis and meiosis
Mitosis Meiosis
Dividing cells can be diploid or haploid
Dividing cells are diploid
Occurs in somatic cell in all parts of the body
Only in sexual reproduction cell, gamete cell
DNA replicates once during the S phase of interphase, and nucleus divides once.
DNA replicates once during S phase of interphase but there are two successive nuclear division.
Chromosomes do not associate during prophase.
Homologous chromosomes associated to form bivalen during prophase I.
Chiasma are never formed and crossing over never occurs.
Chiasma form and crossing over occurs during prophase I.
Mitosis Meiosis Chromosomes form a single row at the equator of the cell during metaphase.
Chromosomes form two rows at the equator of the cell during metaphase I.
Chromatids move to opposite poles during anaphase.
Chromosomes move to opposite poles during anaphase I.
Daughter cells have the same number of chromosomes as the parent cell.
Daughter cells have only half the number of chromosomes found in the parent cell.
In the absence of mutation, daughter cells are genetically identical to parental cell.
Daughter cells are genetically different from parental cell.
2 daughter cells are formed. 4 daughter cells are formed. In male human, 4 sperm cells are formed. In female human, one ovum and 3 polar bodies are formed.