Organel Sel

 

Sel :

= Unit dari struktur dan fungsi organisme

= Unit terkecil dari kehidupan

Sel

Jaringan

Organ

Organisme

 

Jenis sel, ada 2 yaitu:

1. Sel prokariota(Pro  : „sebelum‟) + (karyon : kernel/nukleus)Sel yang “tidak mempunyai nukleus”  materigenetik ada pada daerah nukleoid

2. Sel eukariota(Eu : “sebenarnya”) + (karyon )Sel yang mempunyai inti sebenarnya, dibungkusoleh selubung/membran

 

Struktur sel

a b

c

Diagram:

a. Sel bakteri, umumnya

Ukuran: 1 – 10 um

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 permeabelantara lingkungan yang hidup dan yang mati

- Banyak proses biokimia penting terjadi di permukaanmembran plasma. Mis: metabolisme lipid

- Komposisi kimia membran plasma sel prokariotaberbeda dengan sel eukariota

- Lipid dan protein merupakan bahan penyusun utamamembran, juga sering ditemukan karbohidrat

- Penyusunan molekul-molekul tsb dlm plasma membran,disebut dgn model mozaik fluida ( lipid bilayerdengan protein tersisip diantaranya, diperkenalkanoleh 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 (rata2 diameter 5 um)

- tempat untuk sintesis DNA dan RNA

 

- Membran inti terdiri atas :

* membran dalam, yg berisi protein spesifik yg mengikatkromatin dan lamina inti. Lamina inti merupakan filamen

 yang memperkuat struktur inti

* membran luar, yang berlanjut/berhubungan denganmembran organel lain yaitu reticulum endoplasma

Masing-masing merupakan lipid bilayer. Pada membraninti terdapat pori-pori, tempat keluar masuk molekul.

 

 A B C

A. Structur kromosom

B. Kromosom dilihat dengan mikroskop elektron

C. Berbagai jenis bentuk kromosom

-Di dalam inti terdapat DNA yang diorganisasikan bersamaprotein histon, membentuk kromatin.

- Ketika sel siap membelah, kromatin memadat membentukkromosom; membran inti terurai

 

Nucleolus:

Structure in the nucleus where ribosomal RNA

(rRNA) is transcribed and ribosomal subunits are

assambled

- rRNA : 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: 28S rRNA or 5S rRNA

 

b. Endoplasmic Reticulum

-Constitutes more than half of total membrane of anaverage animal cell

-Is organized into a netlike labyrinth of branchingtubules and flattened sacs extending throughout thecytosol

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 andphospholipids

 

•  is small granulle (+ 25 nm),•  found in eukaryotic, prokaryotic and plant cell;

located in the surface of mitochondria orchloroplast, but mainly in the surface ofendoplasmic reticulum,

•  doesn’t have cell membrane •  produced in nucleolus•  composed by ribosomal RNA and ribosomal protein

that associates with mRNA•  catalyzed of protein synthesis

c. Ribosome

 

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 oforganic compounds

 

d. Golgi complex

-has characteristic morphology consisting primary offlattened, disliked and membranous cisternae

- Receives lipids and proteinfrom ER and dispatches themto a variety of destination

-is divided into severalfunction distinctcompartment, from the cis  orentry face closest to the ER,to the trans  or exit face atthe opposite end

 

The cis face composed of an interconnected network,refers as, cis  Golgi Network (CGN). The function is as asorting station that distinguishes between protein to beshipped back to the ER and those that are allowed toproceed to the next Golgi station

The trans face containing a distinct network of tubules andvesicles, called trans Golgi Network (TGN), is sortingstation for diifferent types of vesicle heading either toplasma membrane or to various intracellular destinations

 

e. Mitochondria

- The organelle that be able to utilize the oxygen forthe 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

 

 

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).

Role of mitochondria

 

Mitochondrial DNA

Chromosome No. 25

Genome circular doublestranded 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 pH (= acid

hydrolase), and can hydrolize

every type of macro

molecules

 

Lysosome range in size,from large size (over 1um) to very small (25-50nm 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 hydrogenperoxide (H2O2), a highly reactive and toxic oxidingagents

-Is mayor site of oxigenutilization, likemitochondria

- Contains oxidativesenzymes, such as catalaseand 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 (H2O2)

RH2  + O2  R + H2O2

Catalase utilizes the H2O2 generated by other enzymes in

the organelle, to oxidize a variaty of other substrates

2 H2O2 + R’ H2 R’ + 2 H2O

 

References

Alberts et al., 2002. Molecular Biology of the Cell.

4 ed.

Karp G. 2005. Cell and Molecular Biology. 4 ed.

 

Thanks you