Dinding Sel

• FUNCTION of the wall:

– Memberi bentuk, – Untuk proteksi sel,– Membatasi pertumbuhan, – Sebagai barrier, – lokasi adhesins, – contributes to motility...

Dinding Sel tumbuhan

• Tebal, kuat kaku; pelindung sel• Bertautan antara sel 1 dg sel lain plasmodesmata• Sel muda ddg sel tipis lunak = ddg sel

primerdinamis• Sel dewasa ddg sel tebal, kuat, kaku = ddg sel

sekunder• Ssn molekuler tdr atas molekul protein & polisakarida

pd tumb tinggi : serabut = selulosa, matrix ddg sel berupa glikoprotein & 2 jns polisakarida yi. Hemiselulosa & pektin

• Selain selulosa, hemiselulosa, pektin & glikoprotein, ddg sel tumb jg mengandung lignin, kitin & suberin

In the absence of a cell wall, plant cells adopt a spherical shape

Ddg sel primer & sekunder

Komponen penyusun ddg sel primer

• Polisakarida :– Selulose– Matrix polisakarida (hemiselulose, pektin)

• Protein :– Protein struktural : arabinogalaktan, ekstensin– Enzimatik : ekspansin, pektin methylesterase

• Ddg sel fungi & bakteri berbeda dg ddg sel tumb tinggi

• Pd fungi struktur ddg sel berlapis2 tgt tk kedewasaan fungi, & tdpt kitin & β glukan yg membedakan ddg sel fungi dg ddg sel tumb tk tinggi.

Ddg sel bakteri

• Ddg sel bakteri semi kaku krn mengandung peptidoglikan

• Pd bakteri Gr + kandungan peptidoglikan 40-90% & sbg ciri khas tdpt asam teikoat 20-50% berat kering ddg sel.

• Pd bakteri Gr – kandungan peptidoglikan 1%

• Note:

– Protoplast: sel bakteri / fungi yg sensitive sec osmotik akibat hilangnya ddg sel. Membran sitoplasma tetap kokoh.

– Spheroplast: Sel bakteri yg sec osmotik sensitive akibat hilangnya sebagian ddg sel.

– L-form: n [Lister Institute, London, where it was first isolated] (1948) : suatu varian bakteri dg btk L dibwh kondisi stress & tidak mempunyai ddg sel.

By electron microcopy…

Peptidoglycan (murein) umum pd bakteri Gram positif & Gram negatif.

• peptidoglycan memiliki 2 komponen– glycan

• N-acetylglucosamines & N-acetylmuramic acids dihubungkan oleh -1,4 glycosidic bonds

– peptide• tetrapeptide (in its mature form) dg dua btk D- & dua

btk L• Variasi ikatan peptida

Susunan…

Organization…

What we need to examine about composition

• Components:– N-acetylglucosamine– N-acetylmuramic acid– D and L amino acids– Dicarboxylic acids

• Linkages: -1,4 glycoside and peptide linkages

dicarboxylic acids:

• oxalic acid............HOOC-COOH

• maleic acid..........HOOC-CH2-COOH

• succinic acid........HOOC-CH2-CH2-COOH

• glutaric acid.........HOOC-CH2-CH2-CH2-COOH

• adipic acid...........HOOC-CH2-CH2-CH2-CH2-COOH

• pimelic acid.........HOOC-CH2-CH2-CH2-CH2-CH2-COOH

Dua diamino acids (satu diantaranya adalah dicarboxylic)

Susunan…

Susunan…

The big picture of the gram positive WALL

What else needs to be known about G+ and G- “WALLS”?

• Gram POSITIVE– teichoic acids

– phosphodiesters of substituted polyalcohols

What else needs to be known about G+ and G- “WALLS”?

• Gram POSITIVE– teichoic acids

– phosphodiesters of substituted polyalcohols

Some bacteria have specialized surface proteins, e. g., the M-protein of Streptococcae spp.

• The coiled-coil dimeric nature of M protein and its relationship to the bacterial cell surface is shown. The N-terminal region of the M protein, distal to the cell surface, varies among different M types, thereby providing the molecular basis of the Lancefield method of serotyping group A streptococci.

The big picture of the gram negative ENVELOPE

What else needs to be known about G+ and G- “WALLS”?

• Gram NEGATIVE have LPS: LipoPolySacchrides

…“wall” …“envelope” …???• A cell is a “discrete

mass… surrounded by a membrane…”

• Typically (except for the Mycoplasma and a few other variants), there is a wall or membrane “distal” to the cell surface.

• What is between the cell membrane and these outer structures?

What is the periplasm?

“A space between the cytoplasmic membrane and peptidoglycan layer (gram positives) and the outer envelope (gram negatives).”

• Function?

• A repository for proteins that:

– Bind sugars, amino acids, vitamins, and minerals;

– Degrade large, impermeable macromolecules (this group includes nucleases, proteases, phosphatases);

– Detoxify noxious components (e. g., lactams [using beta-lactamases].)

OK for the “overview”…

• There are Gram positive and Gram negative “walls” and “envelopes.”

• What variations exist?

• The previous question is effectively answered by examining the Archea.

• Interestingly, the Archea have variations in both cytoplasmic membrane and cell wall structure that substantiates the distinction between “Bacteria” and “Archea”

Some Archea have proteinaceous surfaces…

Called an S-layer

No Archea have an authentic murein

But some have a “pseudomurein”…

Archea juga berbeda pd cytoplasmic membranes…