Cell Biology PDF

by smooth ER itself. The protein moleculeS l, -: r,-: r-.----:r€ are mostly synthesized and insertedintomembraneattheler.elof roug:-Ei. -r- ::.,::'--:... of glycosylatioryshortchains of sugars, called oligosaccharides, are adde.1:l :': :--- ,=. - - :L'oterns and lipidsatthe levelof Colgi apparatus....

by smooth ER itself. The protein moleculeS l, -: r,-: r-.----:r€ are mostly synthesized and insertedintomembraneattheler.elof roug:-Ei. -r- ::.,::'--:... of glycosylatioryshortchains of sugars, called oligosaccharides, are adde.1:l :': :--- ,=. - - :L'oterns and lipidsatthe levelof Colgi apparatus. For exarrrple, the forrnation of p-a.::-:. -r';:-.:'rrr'.€, calied membrane biogenesis, involves the folior.r.ing organelles, all formrng tire.,-- -:: --..i endomembrane system: Rough ER 6. --+ Sn-Looth ER --+ Golgi apparatus - Se.:..,-- :-, - esicie -+ Plasma membrane. Proteilsr,r-hicharesurthesizedtr thecel,alith,er,:;-:e ease.1 rntooutermediumofthecell,are calied secretory proteins. Exal'Lp1es oi secreton proter-r,i rr-Lclr-ide mucus, digestive enzymes and hormones (e.g., insulin). These proteins are sr-nthesized L.r rougl-r ER..' : - Differences in rough endoplasmic reticulum (RER) ancl smooth endoplasmic reticulum (SER) 1. It contains fla ttened sacs called cisternae. 2. Ribosomes are attached to the outer surface of its 1. It is mainl-,, formed of vesicles 2. Tt does not coniain rihtrsr,mes. and tuirules membrane. 3. Itis specialized to synthesize proteins. 4. It is abundant in exocrine pancreatic cells and 3. 4. antibodies secreting plasma cells. ;: #;:r".*:s.*.i, It is speciaiized to svnthcsize iipids and steroids. trt is abundant in liver and the testicular ce1ls (e.9., i-elrdig ceils) sr"11ti11:sizing s teroid hormoires. :i*,A. Nature and occurrence. Ribosomes are dense, spherical and grannular particles which occur freely in the matrix (cytosot) or remain attached to the endoplasmic reticulurn (RER). Chemically, the major constituents of ribosomes are the ribonucleic acid (RNA) and proteins. Lipids are not present in ribosomes. Ribosomes are not bounded by a membrane. They are present both in prokaryotic and eukaryotic cells (except mammalian RBC). Function. Ribosomes play an important part in the synthesis of proteins (Figure 32)..]..,,ft4"e;'-eri:,ri*rBi:Ggij*- i* :. ;, t, -:; *",, -* ",.,:{:i:Ei *j}r.* +i*;fi i mesaenger RNA trans or maturir'!g tace discharE*d ve$ici€ 1t \ljg riborcme small subunit cisterna large subunit qd \., endoplawric membrane j':'r " er, s # 11 \eg cis forming face Proteins/'.:-.r : - --'- I,.---::fREF. vesicles iusing wilh cis tace Golgiapparatr-rs. Nature and occurrence. - -- 1r apparatus (Box 9) consists of a set of membrale-bounded, fluid-fi1led vesicles, vacuoles and f-1attene. :LSternae (closed sacs)" Cisternae are usuallr. stacked together (placed 34 I