Organel Sel Sel Unit dari struktur dan fungsi

Organel Sel

Sel : = Unit dari struktur dan fungsi organisme = Unit terkecil dari kehidupan Sel Jaringan Organisme

Jenis sel, ada 2 yaitu: 1. Sel prokariota (Pro : ‘sebelum’) + (karyon : kernel/nukleus) Sel yang “tidak mempunyai nukleus” materi genetik ada pada daerah nukleoid 2. Sel eukariota (Eu: “sebenarnya”) + (karyon) Sel yang mempunyai inti sebenarnya, dibungkus oleh selubung/membran

Struktur sel a b Diagram: a. Sel bakteri, umumnya Ukuran: 1 – 10 um c Paling kecil: mikoplasma (0, 1 – 1 um) b. Sel tumbuhan c. Sel hewan Ukuran sel hewan & tumbhn: 10 – 100 um

Komposisi dari sel eukarita: 1. Sistem endomembran 2. Sitoplasma 3. Organel (dibentuk oleh sistem membran di dalam sel): - Nucleus/inti - Reticulum Endoplasma (RE) - Badan Golgi - Mitochondria, in plants: chloroplast - Lysosome - Peroxisome 4. Sitoskeleton

Contoh: Sel epitel pada saluran reproduksi pria

1. Plasma membran -Berfungsi sbg pembatas yang selektif permeabel antara lingkungan yang hidup dan yang mati - Banyak proses biokimia penting terjadi di permukaan membran plasma. Mis: metabolisme lipid - Komposisi kimia membran plasma sel prokariota berbeda dengan sel eukariota - Lipid dan protein merupakan bahan penyusun utama membran, juga sering ditemukan karbohidrat - Penyusunan molekul-molekul tsb dlm plasma membran, disebut dgn model mozaik fluida ( lipid bilayer dengan protein tersisip diantaranya, diperkenalkan oleh Singer & Nicolson, 1972)

Membran plasma sel eukariota

Permukaan dinding sel pada bakteri

2. Sitoplasma - terdiri dari medium semicair yg disebut sitosol, di dalamnya terletak organel - Sitosol, volumenya lebih 50% dari volume sel, merupakan tempat untuk sintesis dan degradasi protein 3. Organel a. Nukleus/inti sel - Organel paling besar/menyolok (rata 2 diameter 5 um) - tempat untuk sintesis DNA dan RNA

- Membran inti terdiri atas : * membran dalam, yg berisi protein spesifik yg mengikat kromatin dan lamina inti. Lamina inti merupakan filamen yang memperkuat struktur inti * membran luar, yang berlanjut/berhubungan dengan membran organel lain yaitu reticulum endoplasma Masing-masing merupakan lipid bilayer. Pada membran inti terdapat pori-pori, tempat keluar masuk molekul.

-Di dalam inti terdapat DNA yang diorganisasikan bersama protein histon, membentuk kromatin. - Ketika sel siap membelah, kromatin memadat membentuk kromosom; membran inti terurai A B A. Structur kromosom B. Kromosom dilihat dengan mikroskop elektron C. Berbagai jenis bentuk kromosom C

Nucleolus: Structure in the nucleus where ribosomal RNA (r. RNA) is transcribed and ribosomal subunits are assambled - r. RNA : specific RNA molecules that form part of the structure of a ribosome and participate in the synthesis of proteins. Often distinguished by their sedimentation coefficient: 28 S r. RNA or 5 S r. RNA

b. Endoplasmic Reticulum -Constitutes more than half of total membrane of an average animal cell -Is organized into a netlike labyrinth of branching tubules and flattened sacs extending throughout the cytosol ER network in mammalian cell

ER is divided into two subcompartment: a. the rough endoplasmic reticulum (RER) has ribosomes bound to its cytosolic surface RER is the starting point of the biosynthetic pathway: the site of synthesis protein, carbohydrate chains and phospholipids

c. Ribosome • is small granulle (+ 25 nm), • found in eukaryotic, prokaryotic and plant cell; located in the surface of mitochondria or chloroplast, but mainly in the surface of endoplasmic reticulum, • doesn’t have cell membrane • produced in nucleolus • composed by ribosomal RNA and ribosomal protein that associates with m. RNA • catalyzed of protein synthesis

Ribosome and its function in protein synthesis

b. the smooth endoplasmic reticulum (SER) lacks assosiated ribosomes -extensively developed in a number of the cell types -Function, i. e: * Synthesis of steroids hormones * Detoxifications in the liver of a wide variety of organic compounds

d. Golgi complex -has characteristic morphology consisting primary of flattened, disliked and membranous cisternae - Receives lipids and protein from ER and dispatches them to a variety of destination -is divided into several function distinct compartment, from the cis or entry face closest to the ER, to the trans or exit face at the opposite end

The cis face composed of an interconnected network, refers as, cis Golgi Network (CGN). The function is as a sorting station that distinguishes between protein to be shipped back to the ER and those that are allowed to proceed to the next Golgi station The trans face containing a distinct network of tubules and vesicles, called trans Golgi Network (TGN), is sorting station for diifferent types of vesicle heading either to plasma membrane or to various intracellular destinations

e. Mitochondria - The organelle that be able to utilize the oxygen for the energy extraction.

The structure of mitochondria - contains two membranes: * outer mitochondrial membrane * inner mitochondrial membrane -There is two aqueous compartment: * Matrix, within the interior * Intermembrane space, between OMM and IMM

Role of mitochondria produce ATP 5 respiration enzyme complexes complex I (NADH oxydoreductase : Ubiquinone) complex II (suksinat oxydoreductase : ubiquinone) complex III (ubiquinol oxydoreductase : sitokrom c) complex IV (Cytocrome c oxydase) complex V (ATPsynthase).

Mitochondrial DNA Chromosome No. 25 Genome circular double stranded DNA Maternal inherited Mito DNA : 16. 569 bp Nuclear DNA : 3 x 109 bp

f. Lysosome -is an animal cell’s digestive organelles -Contains approximately 50 different hydrolytic enzymes produced in the ERE and targeted to these organelles -Enzymes have their optimal activity at an acid p. H (= acid hydrolase), and can hydrolize every type of macro molecules

Lysosome range in size, from large size (over 1 um) to very small (25 -50 nm in diameter)

Three pathways to degradation in lysosome

Phagocytosis: Process by which particulate material (particle or microorganism) is endocytosed (“eaten”) by a cell Endocytosis: Uptake of material into a cell by an invagination of plasma membrane and its internalization in a membrane-bounded vesicle Autophagy: Digestion of worn-out organelles by the cell’s own lysosomes

g. Peroxisome (microbody) - found in all eukaryotic cell - The site of synthesis and degradation of hydrogen peroxide (H 2 O 2), a highly reactive and toxic oxiding agents -Is mayor site of oxigen utilization, like mitochondria - Contains oxidatives enzymes, such as catalase and urate oxidase

Peroxisome contain one or more enzymes that use molecular oxygen to remove hydrogen atoms from specific organic substrates in an oxidative reaction that produces hydrogen peroxide (H 2 O 2) RH 2 + O 2 R + H 2 O 2 Catalase utilizes the H 2 O 2 generated by other enzymes in the organelle, to oxidize a variaty of other substrates 2 H 2 O 2 + R’ H 2 R’ + 2 H 2 O

References Alberts et al. , 2002. Molecular Biology of the Cell. 4 ed. Karp G. 2005. Cell and Molecular Biology. 4 ed.

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