Cell growth and differentiation

Posted on February 25, 2009

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Siklus sel
Stimulator : IAA, sitokinin, GA
nutrient (sukrosa)

Inhibitor : ABA

Why is cell division important?
Life cycle of a living organism: birth, growth and death…

Individual cells have a life cycle too!

25 million cell divisions occur in your body EVERY SECOND!!!
Diseases such as cancer: when cell division goes wild… (half million deaths/year!)
Pentingnya pembelahan sel
Meningkatkan kemampuan tumbuh jaringan / organ

Informasi yang menentukan diferensiasi terjadi pada siklus pembelahan sel

Arah pembelahan sel menentukan posisi dan fungsi sel hasil pembelahan
Pembelahan sel
Pembelahan sel: Proses dimana satu sel membelah menjadi dua.
Meliputi 2 bagian :
* pembelahan nucleus
Cell Cycle
Mulai dari saat pembelahan sel ke pembelahan sel berikutnya
Ada dua fase:
M phase : fase mitosis
Interphase : replikasi
kromosom
Most of the time (90%),
the cell is in interphase
(non-dividing stage)
Interphase
Interphase is the metabolically active stage.
Three phases:
G1 (gap 1)
S (synthesis)
G2 (gap 2)

Interphase stages
Persiapan pembelahan sel terjadi selama interphase (Interphase is not part of mitosis)

G1 phase: (First Gap) period of intense biological activity:
1. cell is actively growing,
2. organelles enlarge and divide,
3. protein synthesized,
4. respiration, etc.

S phase: (Synthesis) DNA is duplicated
Interphase stages
G2 phase: (Second Gap) Sintesis protein meningkat, persiapan pembelahan sel mencapai tahap akhir

Akhir G2 phase merupakan awal
pembelahan sel (mitosis)

Chromosomes?
CHROMO = Colored; SOMA = Bodies
Carry the genetic information (DNA): all the genes of an organism…
Genes: basic units of heredity, contain information for making one RNA and usually one protein
Approx. 30,000 genes/human or plant
Chromosomes
Condensed DNA and proteins (chromatin) coiled up together.
S phase: replikasi DNA
Pada saat S phase terjadi duplikasi DNA (dapat diukur dg aplikasi bahan radioaktif 32P atau 3H-thymidine)

DNA is replicated by the enzyme………………………….

MITOSIS
Mitosis is the process of nuclear division
Consists of four stages:
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase

Phases of Mitosis:
1. Prophase
Chromatin (DNA + proteins) mulai mengalami kondensasi dan menebal, membentuk chromosomes.
membrane nukleus dannucleolus menghilang.
Chromosomes bebas
didalam sitoplasma.
1. Prophase
Spindle starts to form
Spindle: a framework of microtubules thatpulls the chromosomes from the center ofthe cells to the poles.
(microtubules – fibers thatact like muscles)

2. Metaphase
Chromosomes line up on the cell’s equator
Each centromere is attached to a spindle fiber (microtubule)
Cell has two poles
At end of metaphase,centromeres divide

3. Anaphase
Sister chromatids are pulled to opposite ends of the cell – by contraction of the spindle fibers
Each chromatid is now considered one chromosome
Genetic material divided in 2 identical sets
4. Telophase
Nuclear membrane re-forms (2)
Chromatids unwind and lengthen: become indistinct (chromatin)
Two distinct nuclei are evident
Nucleolus reappears
Cell plate begins to appear
CYTOKINESIS
Cytoplasm division that separates two daughter nuclei into two cells
Cytokinesis begins in late anaphase, is completed by late telophase
Phragmoplast: vessicles, microtubules, and ER accumulates across center of dividing cell (Golgi)
Cell plate: forms in the middle of cell, becomes the cell wall separating two cells
Cytokinesis: Plants vs. animals
In animals, cell cleavage
In plants, cell plate forms, new cell wall
Kontrol siklus sel
Cyclin & cyclin-dependent kinase (CDKs)

Cyclin & cyclin-dependent kinase (CDKs)

Transisi G1 to S : tergantung pd bermacam gen
ekspresi gen tsb perlu faktor transkripsi E2F
Aktivitas E2P diatur oleh protein Rb
(retinoblastoma protein)
Pembelahan pada sel-sel yang telah dewasa : * natural * tanggapan terhadap stimulus lingkungan

Arah pembelahan sel
Is determined during late interphase

Microtubules di dalam sitoplasma
Become concentrated into a ring called the preprophase band

Arah dan simetri pembelahan sel penting dalam penentuan bentuk sel

If the planes of division of cells are parallel to the plane of the first division

A single file of cells will be produced

If the planes of division vary randomly
Asymmetrical cell division occurs
Mekanisme dan kontrol pembentangan sel
Meristem akar : 30 – 100 x lipat
Arah pembentangan berpengaruh pada bentuk organ dan arah pertumbuhan
Pada umumnya (tidak selalu) pembentangan sel terjadi setelah pembelahan sel
* pada umbi kentang : pembelahan dan pembentangan
terjadi bersamaan
Proses pembentangan sel :
* penyerapan air dan berbagai larutan yg lain
* vakuola bergabung membentuk central vacuole
* arah pembentangan dipengaruhi oleh orientasi
mikrofibril pada dinding sel

Hormon dan pemanjangan sel
Auksin
Konsentrasi optimum berbeda pada organ yang berbeda
Induksi plastisitas dinding sel

Giberelin

Loosening of cell wall

Posted in: BIOLOGI