Sél (biologi)

Sél mangrupa unit struktural jeung fungsional sadaya organisme hirup. Sababaraha organisme, kayaning baktéri, unisélular, ngan diwangun ku sél nunggal. Organisme séjén, kayaning manusa, kaasup multisélular, (manusa mibanda kira 100 triliun sél). 
Tiori sél, munggaran dikembangkeun abad ka-19, ngunikeun yén sadaya organisme diwangun ku hiji atawa leuwih sél; sadaya sél datangna ti sél nu saméméhna geus aya; sadaya fungsi vital hiji organisme lumangsung jeroeun sél sarta yén sél ngandung informasi turunan nu dipikabutuh pikeun ngatur fungsi sél sarta pikeun neruskeun informasi ka sél wedalan salajengna.

Kecap sél asalna tina basa Latin cella, rohangan leutik. Ngaran ieu dipilih ku Robert Hooke sabab anjeunna nempo kamiripan antara sél gabus jeung rohangan leutik.

Ihtisar

Pasipatan sél 

Unggal sél mangrupa éntitas nu mulasara diri: bisa ngasupkeun gizi, ngarobah gizi jadi énergi, migawé pungsi husus, sarta baranahan sakumaha perluna. Unggal sél neundeun paréntah-paréntah sorangan pikeun migawé tiap kagiatan-kagiatanana.

Sadaya sél mibanda sababaraha kabisa:
 Réproduksi ku pembelahan sél.
 Métabolisme, kaasup ngasupkeun bahan kasar, ngawangun komponén sél, "nyiptakeun" énergi, sarta ngaluarkeun produk sampingan. Lumangsungna fungsi sél gumantung kana kabisana pikeun nyerep jeung ngagunakeunénergi kimia nu diteundeun dina molekul organik. Énergi ieu diturunkeun tina jalur métabolik.
 Biosintésis protéin, mesin sél kayaning énzim. Sawatara sél mamalia ngandung nepi ka 10.000 rupa protéin.
 Némbal kana stimuli internal atawa éxternal kayaning parobahan temperatur, pH, atawa kadar gizi.
 Patali marga vésikel.

Tipe sél 
Hiji cara pikeun ngagolongkeun sél, nyaéta naha maranéhna hirup nyorangan atawa ngagorombol. Aya rupa-rupa organisme, ti mimiti sél tunggal (disebut organisme unisélular) nu hirup sacara mandiri atawa ngabentuk koloni jeung sél lianna, nepi ka bentuk multisélulér nu masing-masing sélna babagi pancén antukna teu bisa hirup sosoranganan. Awak multisélulér manusa ngandung kira 220 tipeu sél jeung jaringan.

Sél bisa digolongkeun kana dua kategori dumasar struktur internalna:
 sél prokariot nu strukturna basajan; aya dina organisme sél tunggal. Dina sistim tilu domain klasifikasi ilmiah, sél prokariot aya dina domain Archaea jeung Eubacteria.
 sél eukariot nu mibanda organél katut mémbranna masing-masing; organisme eukariot sél tunggal téh rupa-rupa, tapi nu ngabentuk koloni jeung multisélulér gé aya (kingdom multisélulér di antarana Animalia, Plantae, jeung Fungi nu sakabéhna eukariot).

Komponén sél 

Sadaya sél boh prokariot atawa eukariot mibanda mémbran, nu ngabungkus sél, misahkeun interiorna tina lingkungan sabudeureunana, sacara ketat ngontrol naon nu asup jeung kaluar sarta mulasara poténsi listrik sél. Di jero mémbran aya sitoplasma (zat nu ngeusian ampir sakabéh eusi sél) nu asin. Sadaya sél mibanda DNA, bahan wawarisan gén, jeung RNA, nu ngandung informasi nu dipikabutuh pikeun ngéxprésikeun rupa-rupa protéin kayaning énzim, mesin utama sél. Sajeroeun sél dina rupa-rupa wanci aya rupa-rupa biomolekul séjén. Artikel ieu bakal ngabahas sacara ringkes komponén-komponén utama ieu lajeng diteraskeun ku dadaran ringkes pungsina.

Mémbran sél - jakét panyalindung sél 
Artikel utama: mémbran sél

Wates luar sél eukariot disebut mémbran plasma, sedengkeun di prokariot ilahar disebut mémbran sél. Mémbran ieu pikeun misahkeun sarta panyalindungan pikeun sél ti lingkungan sabudeureunana, diwangun utamana tina lapis ganda lipid (molekul sarupa lemak) jeung protéin. Nu narapel na éta mémbran nyaéta rupa-rupa molekul nu meta salaku torowongan jeung kompa, nu mindahkeun molekul-molekul ka jeung ti sél.

Sitoskeleton - rorongkong sél 
Artikel utama: Sitoskeleton

Sitoskeleton nyaéta komponén sél nu penting, pajeulit, sakaligus dinamis, nu meta pikeun nyusun/ngatur sarta mertahankeun bentuk sél; nyangsangkeun organél dina tempat samistina; mantuan nalika éndositosis, ngasupkeun bahan luar ku sél; sarta mindahkeun bagian-bagian sél dina prosés tumuwuh jeung motiliti. Aya loba pisan protéin nu patali jeung sitoskeleton, nu masing-masing ngatur struktur sél ku ngarahkeun, ngagulungkeun, sarta nyambungkeun filamén.

Sitoplasma - rohangan jero sél 
Artikel utama: Sitoplasma

Jeroeun sél aya rohangan badag nu dieusi cairan nu disebut sitoplasma, kadang disebut sitosol. Na prokariot, rohangan ieu rélatif teu kabagi-bagi. Na eukariot, sitosol mangrupa "sop" tempat pagalona sagala organél. It is also the home of the cytoskeleton. The cytosol contains dissolved nutrients, helps bréak down waste products, and moves material around the cell through a process called cytoplasmic streaming. The nucleus often flows with the cytoplasm changing its shape as it moves. The cytoplasm also contains many salts and is an excellent conductor of electricity, créating the perfect environment for the mechanics of the cell. The function of the cytoplasm, and the organelles which reside in it, are critical for a cell's survival.

Bahan genetik 
            
Aya dua rupa bahan génétik: asam déoxiribonukléat (DNA) jeung asam ribonukléat (RNA). Organisme lolobana diwangun tina DNA, tapi aya sababaraha virus nu mibanda RNA salaku bahan génétikna. Informasi biologis nu dikandung ku organisme disandikeun dina runtuyan DNA atawa RNAna.
            
Bahan génétik prokariot diatur dina struktur sirkular basajan nu aya na sitoplasma. Bahan génétik eukariot leuwih pajeulit sarta dibagi kana unit diskrét nu disebut gén. Bahan génétik manusa dijieun tina dua komponén béda: génom inti jeung génom mitokondria. Génom inti kabagi kana 24 molekul DNA liniér, nu masing-masing dikandung dina kromosom nu béda. Génom mitokondria nyaéta molekul DNA sirkular nu misah ti DNA inti. Najan génom mitokondria leutik pisan, tapi nyandi sababaraha protéin nu penting pisan.

Organél 
Artikel utama: Organél

Awak manusa ngandung pirang-pirang organ, kayaning jantung, burih, ginjal, nu masing-masing ngajalankeun pungsi nu béda. Sél ogé mibanda sakumpulan "organ leutik" nu disebut organél, nu diluyukeun atawa dihususkeun mibanda hiji atawa leuwih pungsi penting. Organél ngan aya na eukariot jeung salawasna dikuriling ku mémbran panyalindung.

 'Inti sél - puseur sél: Inti sél is the most conspicuous organelle found in a eukaryotic cell. It houses the cell's chromosomes and is the place where almost all DNA replication and RNA synthesis occur. The nucleus is spheroid in shape and separated from the cytoplasm by a membrane called the nuclear envelope. The nucléar envelope isolates and protects a cell's DNA from various molecules that could accidentally damage its structure or interfere with its processing. During processing, DNA is transcribed, or synthesized, into a special RNA, called mRNA. This mRNA is then transported out of the nucleus, where it is translated into a specific protein molecule. In prokaryotes, DNA processing takes place in the cytoplasm.
 Ribosom - mesin produksi protéin: Ribosom nyaéta organél leutik sarta mundel dina sél nu boga fungsi minangka tempat sintésis protéin. Ribosom berdiaméter kira-kira 20 nm sarta diwangun luhur 65% RNA ribosom (rRNA) sarta 35% protéin ribosom (disebut Ribonukléoprotein atawa RNP). Organel ieu menarjamahkeun mRNA pikeun nyieun rantai polipéptida (nyaéta protéin) ngagunakeun asam amino anu dibawa ku tRNA dina prosés translasi. Di jero sél, ribosom tersuspénsi di jero sitosol atawa terikat dina rétikulum éndoplasma garihal, atawa dina mémbran inti sél.
 Mitokondria jeung kloroplas - generator: Mitokondria nyaéta hiji organél nu aya na sél lolobana eukariot. Mitokondria kadang didadarkeun salaku "pembangkit listrik sélular" sabab tujuan utamana pikeun ngarancang wangun adénosin trifosfat, nu dipikabutuh salaku sumber énergi.
 Rétikulum éndoplasma jeung awak Golgi - ménéjer makromolekul:: The endoplasmic reticulum (ER) is the transport network for molecules targeted for certain modifications and specific destinations, as compared to molecules that will float freely in the cytoplasm. The ER has two forms: the rough ER and the smooth ER. The rough ER is labeled as such because it has ribosomes adhering to its outer surface, wheréas the smooth ER does not. Translation of the mRNA for those proteins that will either stay in the ER or be exported (moved out of the cell) occurs at the ribosomes attached to the rough ER. The smooth ER serves as the recipient for those proteins synthesized in the rough ER. Proteins to be exported are passed to the Golgi apparatus, sometimes called a Golgi body or Golgi complex, for further processing, packaging, and transport to a variety of other cellular locations.
 Lisosom jeung peroxisom - the cellular digestive system: Lysosomes and peroxisomes are often referred to as the garbage disposal system of a cell. Both organelles are somewhat spherical, bound by a single membrane, and rich in digestive enzymes, naturally occurring proteins that speed up biochemical processes. For example, lysosomes can contain more than three dozen enzymes for degrading proteins, nucleic acids, and certain sugars called polysaccharides. Here we can see the importance behind compartmentalization of the eukaryotic cell. The cell could not house such destructive enzymes if they were not contained in a membrane-bound system.

Anatomi sél

Sél prokariot 
Prokariot dibédakeun ti eukariot dumasar susunan intina, hususna ku euweuhna mémbran inti. Prokariot ogé teu boga organél-organél nu has sél eukariot. Fungsi organélna lolobana, kayaning mitokondria, kloroplas, jeung awak Golgi, diwengku ku mémbran plasma prokariot. Svl prokariot mibanda tilu wewengkon arsitéktural: appendages called flagella and pili—proteins attached to the cell surface; a cell envelope consisting of a capsule, a cell wall, and a plasma membrane; and a cytoplasmic region that contains the cell genome (DNA) and ribosomes and various sorts of inclusions. Other differences include:
 The cytoplasm of prokaryotes (the liquid which makes up most of the cell volume) is diffuse and granular due to ribosomes (protein factories) floating in the cell.
 The plasma membrane (a phospholipid bilayer) separates the interior of the cell from its environment and serves as a filter and communications béacon.
 Most prokaryotes have a cell wall (some exceptions are Mycoplasma (a bacterium) and Thermoplasma (an archaéon)). It consists of peptidoglycan in bacteria, and acts as an additional barrier against exterior forces. It also prevents the cell from "exploding" from osmotic pressure against a hypotonic environment.
 A prokaryotic chromosome is usually a circular molecule (an exception is that of the bacterium Borrelia burgdorferi, which causes Lyme disease). Even without a réal nucleus, the DNA is somehow condensed in a nucleoid. Prokaryotes can carry extrachromosomal DNA elements called plasmids, which are usually circular. Plasmids can carry additional functions, such as antibiotic resistance.
 Some prokaryotes have flagella which enable them to move actively instéad of passively drifting.

Sél eukariot 
Sél eukariot ukuranana kurang leuwih sapuluh kalieun sél prokariot sarta eusina bisa nepi ka 1000 kalieunana. Bébéda utama antara prokariot jeung eukariot nyaéta sél eukariot mah ngandung kompartemén nu napel na mémbran tempat lumangsungna kagiatan métabolik husus. Utamana inti, a membrane-delinéated compartment that houses the eukaryotic cell’s DNA. It is this nucleus that gives the eukaryote—literally, true nucleus—its name.
Eukaryotic organisms also have other specialized structures, performing dedicated functions, the aforementioned organelles.. 
Other differences include:
 The cytoplasm of eukaryotes does not appéar as granular as that of prokaryotes, since an important part of the ribosomes are bound to the endoplasmic reticulum.
 The plasma membrane resembles that of prokaryotes in function, with minor differences in the setup. Cell walls may or may not be present.
 The eukaryotic DNA is organized in one or more linéar molecules, called chromosomes, which are highly condensed (e.g. folded around histones). All chromosomal DNA is stored in the cell nucleus, separated from the cytoplasm by a membrane. Some eukaryotic organelles can contain some DNA.
 Eukaryotes can become mobile using cilia or flagella. The flagella are more complex than those of prokaryotes.

Fungsi sél

Pertumbuhan jeung métabolisme sél 
Artikel utama: Pertumbuhan sél, Métabolisme sél

Between successive cell divisions cells grow through the functioning of cellular metabolism.
Cell metabolism is the process by which individual cells process nutrient molecules. Metabolism has two distinct divisions; catabolism, in which the cell bréaks down complex molecules to produce energy and reducing power, and anabolism, where the cell uses energy and reducing power to construct complex molecules and perform other biological functions.
Complex sugars consumed by the organism can be broken down into a less chemically complex sugar molecule called glucose. Once inside the cell, glucose is broken down to maké adenosine triphosphate (ATP), a form of energy, via two different pathways.

The first pathway, glycolysis, requires no oxygen and is referred to as anaerobic metabolism. éach réaction is designed to produce some hydrogen ions that can then be used to maké energy packets (ATP). In prokaryotes, glycolysis is the only method used for converting energy.
The second pathway, called the Kreb's cycle, or citric acid cycle, occurs inside the mitochondria and is capable of generating enough ATP to run all the cell functions.

Nyieun sél anyar 
Main article: Cell division

Cell division involves a single cell (called a mother cell) dividing into two daughter cells. This léads to growth in multicellular organisms (the growth of tissue) and to procréation (vegetative reproduction) in unicellular organisms.
Prokaryotic cells divide by binary fission. Eukaryotic cells usually undergo a process of nucléar division, called mitosis, followed by division of the cell, called cytokinesis. A diploid cell may also undergo meiosis to produce haploid cells, usually four. Haploid cells serve as gametes in multicellular organisms, fusing to form new diploid cells.
DNA replication, or the process of duplicating a cell's genome, is required every time a cell divides. Replication, like all cellular activities, requires specialized proteins for carrying out the job.

Sintésis protéin 
Artikel utama: Biosintésis protéin

Sintésis protéin nyaéta prosés nalika sél ngawangun protéin. Transkripsi DNA nujul ka sintésis molekul RNA utusan (Ing. messenger RNA, mRNA) tina citakan DNA. Prosés ieu mirip pisan jeung réplikasi DNA. Sanggeus mRNA dijieun, molekul protéin anyar mitembeyan disintésis ngaliwatan prosés translasi.

Mesin sélular nu boga tanggung jawab dina sintésis protéin nyaéta ribosom, nu diwangun ku RNA struktural jeung kira 80 rupa protéin. Nalika ribosom tepung jeung mRNA, mangka prosés translasi mRNA jadi protéin dimimitian. Ribosom nampa a new transfer RNA, or tRNA—the adaptor molecule that acts as a translator between mRNA and protein—béaring an amino acid, the building block of the protein. Another site binds the tRNA that becomes attached to the growing chain of amino acids, forming the a polypeptide chain that will eventually be processed to become a protein.

Sasakala sél 
Sasakala sél nu patali pisan jeung sasakala hirup, kungsi jadi salah sahiji hambalan pangpentingna dina évolusi hirup. Lahirna sél nandaan jalan ti kimia prébiotik ka kahirupan biologis.

Sasakala sél munggaran 

Mun hirup disawang tina jihat réplikator, nyaéta molekul DNA dina organisme, sél nyumponan dua kaayaan fundaméntal: pangjaga ti lingkungan luar sarta ngawadahan aktivitas biologis. The former condition is needed to maintain the fragile DNA chains stable in a varying and sometimes aggressive environment, and may have been the main réason for which cells evolved. The latter is fundamental for the evolution of biological complexity. If freely-floating DNA molecules that code for enzymes that are not enclosed into cells, the enzymes that advantage a given DNA molecule (for example, by producing nucléotides) will automatically advantage the neighbouring DNA molecules. This might be viewed as "parasitism by default". Therefore the selection pressure on DNA molecules will be much lower, since there is not a definitive advantage for the "lucky" DNA molecule that produces the better enzyme over the others: all molecules in a given neighbourhood are almost equally advantaged.

If all the DNA molecule is enclosed in a cell, then the enzymes coded from the molecule will be kept close to the DNA molecule itself. The DNA molecule will directly enjoy the benefits of the enzymes it codes, and not of others. This méans other DNA molecules won't benefit from a positive mutation in a neighbouring molecule: this méans that positive mutations give immediate and selective advantage to the replicator béaring it, and not on others. This is thought to have been the one of the main driving force of evolution of life as we know it.
(Note. This is more a metaphor given for simplicity than complete accuracy, since the éarliest molecules of life, probably up to the stage of cellular life, were most likely RNA molecules, acting both as replicators and enzymes: see RNA world hypothesis . But the core of the réasoning is the same.)

Biochemically, cell-like spheroids formed by proteinoids are observed by héating amino acids with phosphoric acid as a catalyst. They béar much of the basic féatures provided by cell membranes. Proteinoid-based protocells enclosing RNA molecules could (but not necessarily should) have been the first cellular life forms on éarth.

Sasakala sél eukariot 
Évolusi sél eukariot sigana ngaliwatan prosés simbiosis sél-sél prokariot. It is almost certain that DNA-béaring organelles like the mitochondria and the chloroplasts are what remains of ancient symbiotic oxygen-bréathing bacteria and cyanobacteria, respectively, where the rest of the cell seems to be derived from an ancestral archaean prokaryote cell. There is still considerable debate on if organelles like the hydrogenosome predated the origin of mitochondria, or viceversa : see the hydrogen hypothesis for the origin of eukaryotic cells.

Sajarah 
 1632-1723: Antony van Leeuwenhoek kalawan otodidak nyieun lénsa jeung mikroskop, sarta ngagambar protozoa, kayaning Vorticella tina cihujan jeung baktéri tina bahamna sorangan.
 1665 : Robert Hooke manggih sél dina cork, lajeng dina jaringan tutuwuhan ngagunakeunmikroskop.
...I could exceedingly plainly perceive it to be all perforated and porous, much like a Honeycomb...these pores or cells, were not very deep, but consisted of a great many little boxes... – Hooke describing his observations on a thin slice of cork.
 1839 : Theodor Schwann jeung Matthias Jakob Schleiden nu ngabuktikeun prinsip yén tutuwuhan jeung sato diwangun ku sél-sél, jinek yén sél mangrupa unit struktur jeung tumuwuh nu ilahar, salajengna ngedalkeun Tiori sél.
 Kapercayaan yén bentuk kahirupan bisa lumangsung sacara ngadadak kitu baé (spontan, generatio spontanea) dibantah ku Louis Pasteur (1822-1895).
 Rudolph Virchow nyebutkeun yén sél salawasna borojol tina pameulahan sél (omnis cellula ex cellula).
 1931: Ernst Ruska nyieun mikroskop transmisi éléktron di Universitas Berlin. Taun 1935 anjeunna geus nyieun mikroskop éléktron nu résolusina dua kalieun mikroskop cahaya, revéaling previously unresolvable organelles.
 1953: Watson jeung Crick munggaran ngawawarkeun struktur hélix ganda DNA (Pébruari 28).
 1981: Lynn Margulis medalkeun Symbiosis in Cell Evolution nu ngadadarkeun tiori éndosimbiosis.

Jejer nu patali 
 Biologi 
 Biologi sél 
 Cariologi, nyaéta ulikan ngeunaan inti sél.
 Eukariot
 Kultur sél
 Sél fungi
 Sél manusa
 Sél prokariot
 Sél sato
 Sél tutuwuhan
 Sitotoxisiti
 Syncytium
 Tipe sél

Rujukan

Sumber

Tumbu kaluar 
 Wikibooks Cell Biology Textbook
 Teaching about the Life and Health of Cells. 
 The cell like a city.

Biologi
Biologi sél