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A. Klebsiella spKlebsiella sp scientific classification: Kingdom: Bacteria Phylum: Proteobacteria Class: Gamma proteobacteria Order: Enterobacteriales Family: Enterobacteriaceae Genus: Klebsiella Species: - Klebsiella pneumoniaKlebsiella oxytoca,, Klebsiella ozaena, Klebsiella rhinoscleromatis

 Morphology and properties of the bacteria Klebsiella spBacteria are gram (-), short rod-shaped, has a size of 0.5 to 1.5 x 1.2 ТЕ. This bacterium has a capsule, but does not form spores. Klebsiella unable to move because they do not have flagella but capable of fermenting carbohydrates to form acids and gases.Klebsiella species show mucoid growth, a large polysaccharide capsule and not motile. They usually give a positive test result for lysine decarboxylase and citrate. Klebsiella Voges-Proskauer reaction gives a positiveCulture nature or culture of Klebsiella sp on EMB and Mac Conkey medium to red colonies. Then on solid media grew mucoid colonies (24 hours). Easily cultured in simple media (bouillon order) with a colony of gray and white glossy surfaces.
 Antigen typeKlebsiella has the structure of the antigen. Members of the genus Klebsiella usually reveal two types of antigens on their cell surface, namely:ТЗ O antigen is the outer portion of the cell wall lipopolysaccharide and polysaccharide composed of repeating units. Some of the O-specific polysaccharide containing a unique sugar. O antigen is resistant to heat and alcohol and is usually detected by bacterial agglutination. Antibodies against the O antigen is IgM.ТЗ K antigen is the outermost part of the O antigens in some, but not in the Enterobacteriaceae. Some of the K antigen is a polysaccharide and the other protein.
Klebsiella pneumoniae enzymeKlebsiella bacteria have urease enzyme and the enzyme citrate permiase. Klebsiella enzyme is also capable of producing ESBL (Extended Spectrum Beta lactamase) which can paralyze the action of various types of antibiotics. This leads to resistant bacteria and difficult disabled.Resistance to antibiotics in the following manner:(1) Drug inactivation by degradation or modification enzymes such as beta and vamino lactamaces glycoside transferases,(2) Change target drug
 (3) The emergence of a bypass pathway that is not inhibited by the drug(4) Reduced membrane permeability for drug
 (5) Drug efflux from cells.

CHAPTER IIISI

Lower respiratory tract infection remains a major problem in the health field, both in developing countries and that has been developed. SEAMIC Health Statistics data from 2001 influenza and pneumonia is the leading cause of death in Indonesia number 6, number 9 in Brunei, Malaysia's number 7, number 3 in Singapore, the number 6 in Thailand and number 3 in Vietnam. 1999 WHO report states that the cause of death due to infectious diseases in the world is an acute respiratory tract infection including pneumonia and influenza. The incidence of pneumonia community in America is 12 cases per 1000 people per year and is the leading cause of death due to infection in adults in the country. The death rate from pneumonia in the United States is 10%.In the United States by any cause invasive pneumonia found only 50%. Cause of pneumonia is difficult to find and may take several days to get results, whereas pneumonia can cause death if not treated immediately, then the initial treatment of pneumonia are given antibiotics empirically.Household Survey of Health Department of Health in 2001, lower respiratory tract infection disease ranks second as a cause of death in Indonesia. In the SMF in 2001 Friendship Dr Lung infection is also the main pulmonary disease, 58% among ambulatory patients are cases of infection and 11.6% of cases nontuberkulosis, in patients hospitalized cases of infection 58.8% and 14.6% of cases nontuberkulosis . In Dr H. Adam Malik Medan 53.8% and 28.6% of cases of infection including an infection nontuberkulosis. In hospitals Dr. Surabaya Soetomo the data obtained about 180 community pneumonia with mortality rates between 20-35%. Pneumonia ranks fourth community and the ten most illnesses are treated per year.




Klebsiella pneumoniae was first discovered by Carl Friedlander. Carl Friedlander is a pathological and microbiological findings from Germany, which helps the bacteria that causes pneumonia in 1882. Carl Friedlander is the person who first identified the bacterium Klebsiella pneumoniae from the lungs of people who died of pneumonia. Because of his services, Klebsiella pneumoniae are often called the bakery Friedlander.Klebsiella pneumoniae is a Gram negative rod-shaped (bacillus). Klebsiella pneumonia bacteria classified as unable to perform the movement (non motile). Based on their need for oxygen, Klebsiella pneumoniae is an aerobic facultative bacteria. Klebsiella pneumoniae can ferment lactose. In the test with indole, Klebsiella pneumoniae will show negative results. Klebsiella pneumoniae can reduce nitrate. Klebsiella pneumoniae is found in the mouth, skin, and sal gut, but the natural habitat of Klebsiella pneumoniae is on the ground.Klebsiella pneumoniae can cause pneumonia. Pneumonia is an acute infection of the lung tissue (alveoli). Pneumonia caused by Klebsiella pneumoniae pneumonia can be community or community acquired pnuemonia. Community or community acquired pneumonia is pneumococcal pnuemonia in getting from the community. The new strain of Klebsiella pneumoniae can cause pneumonia or hospitality nosomikal acquired pneumonia, which means the disease is in peumonia get when patients are in hospitals or health centers. Klebsiella pneumonia generally attacks people with weak immune system, such as alcoholics, people with diabetes and those with chronic lung disease.
A. Pathogenicity of bacteria Klebsiella pneumoniaeThrough the upper respiratory tract bacteria into the lung tissue, tissue destruction occurs, forming the purulent and necrotic lung parenchyma, there was a lung abscess, bronchiectasis, bacteria enter the bloodstream, septicemia, liver abscess.- The capsules have the ability to defend the organism against phagocytosis and killing by normal serum- A capsulated strain is more virulent than encapsulated strains (in animals)- There are no toxins in addition to endotoxin that contributes to opportunistic infectionsKlebsiella pneumoniae strains that produce enterotoxins exist (has been isolated from patients with tropical sprue) is similar to the ST toxin (heat resistant) and LT (heat-labile enterotoxin) of E. coli, the ability to produce toxin is mediated by the Klebsiella pneumoniae plasmid. Cause pneumonia can infect other places besides the respiratory tract.These bacteria often lead to urinary tract due to nosocomial infection, meningitis, and pneumonia in patients with diabetes mellitus or alcohol addicts. Symptoms of pneumonia caused by bacteria in the form of acute symptoms of fever, malaise (lethargy), and a dry cough and the cough becomes productive and produce bloody sputum and purulent (pus). If the disease continues to happen abscess of lung tissue necrosis, and vibrosis bronchiectasi lungs.
2. Mode of transmission of the bacteria Klebsiella pnemoniaeKlebsiella pneumoniae causes lung disease gives the appearance of swelling of the lungs so that the left and right lobe of the lung are not the same; fever (chills), cough (bronchitis), thickening of the mucosal wall, and bloody sputum.Modes of transmission (infection) of Klebsiella pneumoniae in hospitalized patients can be through three ways, namely:A. Or oropharyngeal aspiration of gastric fluid containing colonies of pathogenic bacteria.2. Hematogenous spread of bacteria into the lungs3. Airborne transmission by aerosols or droplets containing microbes.3. Clinical symptomsThe symptoms of Klebsiella pneumoniae-infected person is breathing fast and shortness of breath, because suddenly inflamed lung. Frequency limit of fast breathing is breathing 50 times per minute or more in children aged 2 months to less than 1 year, and 40 times per minute or more in children aged 1 year to less than 5 years. Serious pneumonia characterized by coughing or (accompanied) difficulty breathing, shortness of breath or withdrawal of the chest wall into the bottom of (severe chest indrawing) in children aged 2 months to less than 5 years. In this age group is also known as very severe pneumonia, with symptoms of cough, difficulty breathing accompanied by symptoms of central cyanosis and can not drink. Meanwhile, for children under 2 months, severe pneumonia characterized by a frequency of 60 times per minute or more or (accompanied) strong withdrawal on the chest wall into the bottom of, cough, changes in sputum characteristics, body temperature over 38 ТК C. Other symptoms, ie when the physical examination found bronchial breath sounds, and leukocyte bronkhi more than 10,000 or less than 4500/uL.In elderly patients or patients with a low immune response, symptoms of atypical pneumonia, which is a non-respiratory symptoms such as dizziness, worsening of pre-existing illness and fainting. Increased respiratory rate is usually rapid and rare fever.
4. TreatmentSeveral types of Klebsiella pneumonia can be treated with antibiotics, especially antibiotics containing beta-lactam ring.Examples of such antibiotics are ampicillin, carbenicillin, amoxiciline, etc.. From the survey results revealed that Klebsiella pneumonia had a sensitivity of 98.4% for meropenem, 98.2% for imipenem, 92.5% for chloramphenicol, 80% to ciprofloxacin, and 2% to ampicillin. New strains and Klebsiella pneumoniae resistant to different types of antibiotics and is still doing research to find the right drug to inhibit the activity or even kill the bacteria.


5. Laboratory DiagnosisOn laboratory examinations are an increasing number of leukocyte, usually more than 10.000/ТЕl sometimes reach 30.000/ТЕl, and the type of leukocyte count and left shift are an increase in LED. To determine the etiologic diagnosis required examination of sputum, blood culture and serology.
CHAPTER IIICLOSING
Conclusion:
 Klebsiella pneumoniae is a Gram negative rod-shaped (bacillus). Klebsiella pneumoniae bacteria are classified as unable to perform the movement (non motile). Based on their need for oxygen, Klebsiella pneumoniae is an aerobic facultative bacteria. These bacteria can ferment lactose. In the test with indole, Klebsiella pneumoniae would have a negative but it can reduce nitrate.Klebsiella pneumoniae can cause pneumonia. Pneumonia itself is the process of acute infection of the lung tissue (alveoli). Klebsiella pneumoniae causes lung disease gives the appearance of swelling of the lungs so that the left and right lobe of the lung are not the same; fever (chills), cough (bronchitis), thickening of the mucosal wall, and bloody sputum.In the laboratory tests can be carried out a survey Aanthal Leukocytes and LED, and can do the examination of sputum, blood culture, and serology.

ALKALIMETRI

A. Standard solution of Primary

            Primary standard solution is a solution made of materials that the concentration of the solution can be directly determined from the weight of the dissolved material is very pure.
A. A standard substance should qualify as below:

          a.zat be easily obtained, easily purified, easy to dry (preferably at a temperature of 100-120oC)

        b.zat must have the equivalent of high, so weighing aberration can be ignored.
c. substances must be readily soluble in the conditions in which it was in use.

   d. substances should be tested against the impurity substances with qualitative tests or other tests of sensitivity in the know (the total amount of impurity substances, generally should not exceed 0.01 to 0.02%)
e. reaction with the standard solution must be stoichiometric and practically instant \. Tutrasi aberration can be ignored, or easily in tetapakan closely with experiment.
f. substances should be no change in the air during the weighing, these conditions imply that the substance should not be hygroscopic, was also in the oxidation by air or carbon dioxide is influenced by the NII. These standards must be on guard so that its composition does not change during penyimpana.


            Primary standard solution standard solution whose concentration is obtained by weighing.
2. Examples of compounds that can be used for primary standards are:

    a. Arsenic trioxide (As2O3) is used to make sodium arsenit NaASO2 used to standardize a solution of sodium periodat NaIO4, I2 iodine solution, and cerium (IV) sulphate Ce (SO4) 2.

    b. Bensoat acid is used to standardize a solution of ethanolic sodium, isopropanol, or DMF.

    c. Potassium bromate KBrO3 to standardize a sodium thiosulfate solution Na2S2O3.

    d. Potassium hydrogen phtalat (KHP) was used to standardize a solution of perchloric acid and acetic acid.

    e. Sodium Carbonate is used to standardize a solution of H2SO4, HCl and HNO3.

     f. Sodium chloride (NaCl) to standardize a solution of AgNO3

    g. Sulfanilik acid (4-aminobenzene sulfonic acid) is used to standardize a solution of sodium nitrite.

As2O3, bensoat acid, KBrO3, KHP, Na2CO3, NaCl, and acid sulfanilik above is the primary standard so this compound is weighed by a certain weight and then dissolved in distilled water to obtain a certain volume of primary standard solution.

    Secondary standard solution is a solution whose concentration is obtained by titrating with a solution of primary standard. NaOH can not be used for the primary standard because NaOH is hygroscopic and therefore it should be titrated NaOH with KHP advance that can be used as a primary standard. So also with H2SO4 and HCl can not be used as a primary standard, to make the secondary standard solution can be titrated with a solution of primary standard NaCO3.
B. Secondary standard solution

         while the secondary solution is a solution made from materials that the concentration of the solution can not be directly determined. To determine the concentration of this solution must be standardized prior to the primary standard solution.

         Examples of kinds of kinds of secondary standard solutions that can be used in the titration alkalimetri:

A. NaOH solution to titrate Strong - Strong Bases

 example:

                    - Strong acids: HCl

                    - Weak Bases: NH4OH

    The reaction equation:

    NH4OH + HCl → NH4Cl + H2O
2. NH4OH solution in the titration of strong acid - Weak base

    example:

                    - Strong acids: HCl

                    - Weak Bases: NH4OH

    The reaction equation:

    NH4OH + HCl → NH4Cl + H2O
3. NaOH solution in the titration of Weak Acid - Strong Bases

  example:

                    - Weak acid: CH3COOH

                    - A strong base: NaOH

    The reaction equation:

    CH3COOH + NaOH + H2O → NaCH3COO

    Ionic reactions:

    H + + OH-→ H2O


            Preparation of Secondary NaOH solution can be done by weighing a number of crystalline NaOH and then diluted with a precise volume. To standardize the NaOH solution can be used a standardized solution H2C2O4 first as a primary standard substance and add pp indicators. The achievement of the equivalence point is marked with a violet color change young.
The reaction between NaOH and H2C2O4 are as follows:
2NaOH (aq) + H2C2O4 (aq) → Na2C2O4 (aq) + H2O (l)

            Please note that a solution of known concentration is called the titrant. Titrant is added little by little (from the buret) in titrat (titrated solution) until the color changes and titrat good indicator is usually a solution of titrant. When the color change indicator, the titration is stopped. When the indicator changes color and is called the titration end point and the expected end of the titration end point equal to the equivalence point titration. The farther end point titration equivalence point titration, the greater the error and, therefore, the selection of indicators is very important that the indicator changes color at the equivalence point is reached. At the equivalence point is reached pH 7 (neutral).
C. Indicator

            Various indicators have different ionization constants, and consequently they show color at different pH range (Keenan, 2002).

            Fenolphtalein classified as very weak acid in a state that is not ionized indicator is colorless. If the ionized alkaline environment fenolphtalein will give more color and light as the anion (Day, 1981).

            Methyl orange is salt Na from an acidic sulphonic where in a solution of many ionized, and the environment alkali anion gives the yellow color, whereas under acidic methyl orange is a weak base and take the ions H +, there is a change in the structure and gives the red color of the ions(Day, 1981).

            An indicator can change color at certain pH regions, for example:Metal orange: red pH 3.1 - pH 4.4 yellow
Bromtimol blue: yellow pH 6.0 - pH 7.6 bluePhenolphthalein: Clear pH 6.0 - pH 9.6 red
Ways of making alkalimetri indicators for examination:
A. phenolphthalein
a. Weigh as much as 1 gram phenolphthalein.
b. Dissolve in 250 ml of alcohol (ethanol)
c. Mix together, make the solution to 500 ml by adding distilled water.
2. Methyl orange
a. Weigh as much as 1 gram of methyl orange.
b. Dissolve in 500 ml 95% alcohol.
c. Mix together, make a 1 liter by adding distilled water.
3. Brom thymol blue
a. Brom thymol Blue weigh as much as 0.1 gram
b. Dissolved in 1.5 ml of 0.1 M NaOH solution
c. Dilute with water to a volume of 100 ml

Urungkan pengeditan

Kamus

kompleksomtri

PORTOFOLIO KOMPLEKSOMETRI

MAGNESIUM SULFAT DALAM AIR SADAH

A.    PENDAHULUAN

1.      Latar belakang

               Air merupakan sumber alam yang sangat di butuhkan oleh mahkluk hidup. Sekitar 70% permukaan bumi diselimuti oleh air. Oleh karena itu, air dapat dikatakan sebagai bagian yang essensial dari sistem kehidupan . Air mempunyai kemampuan yang besar untuk melarutkan bermacam-macam zat, baik yang berupa gas, cairan, maupun padatan. Adanya bahan-bahan yang tidak bermanfaat akan dapat mengakibatkan penurunan kualitas air. Penurunan kualitas air ini diakibatkan oleh adanya zat pencemar, baik berupa komponen organik maupun anorganik.

Akibat yang disebabkan oleh beberapa zat anorganik yaitu salah satunya adalah kesadahan, Air sadah tidak begitu berbahaya untuk diminum, namun dapat menyebabkan beberapa masalah. Air sadah dapat menyebabkan pengendapan mineral, yang menyumbat saluran pipa dan keran. Air sadah juga menyebabkan pemborosan sabun di rumah tangga, dan air sadah yang bercampur sabun dapat membentuk gumpalan scum yang sukar dihilangkan. Dalam industri, kesadahan air yang digunakan diawasi dengan ketat untuk mencegah kerugian. Untuk menghilangkan kesadahan biasanya digunakan berbagai zat kimia, ataupun dengan menggunakan resin penukar ion.

Ion Mg ²⁺  dalam jumlah kecil dapat membantu pertumbuhan tulang, sedangkan dalam jumlah besar akan menyebabkan rasa mual. Permenkes RI nomor 416/ MENKES/PER /IX/1990 telah menetapkan standar air minum untuk jumlah kadar Mg²⁺ dalam air yaitu sebesar 30-50 mg/L. Kesadahan digolongkan menjadi 2 jenis berdasarkan jenis anion yang iikat oleh kation Ca²⁺atau Mg²⁺ .

2.      Rumusan Masalah

Apakah kesadahan sebagai Mg²+ dalam air memenuhi syarat kualitas air minum?

B.     METODE PENELITIAN

1.                                 Dasar Teori

                  Air Sadah adalah Air yang mengandung ion Ca²⁺ dan atau ion Mg²⁺. Kesadahan air adalah kandungan mineral-mineral tertentu di dalam air, umumnya ion kalsium (Ca) dan magnesium (Mg) dalam bentuk garam karbonat. Air sadah atau air keras adalah air yang memiliki kadar mineral yang tinggi. Selain ion kalsium dan magnesium, penyebab kesadahan juga bisa merupakan ion logam lain maupun garam-garam bikarbonat dan sulfat.

            Senyawa kompleks dapat didefinisikan sebagai senyawa yang terbentuk antara dua senyawa kimia  dengan mekanisme donor aseptor elektron atau senyawa asam basa menurut Lewis. Setiap atom atau ion non logam, baik bebas atau terikat pada molekul yang netral atau berbentuk ion, dapat bertindak sebagai donor asalkan dapat memberikan pasangan elektron. Sedangkan sebagai akseptor yaitu dapat menerima atau bersama-sama mengikat pasangan elektron tersebut dan biasanya adalah atom logam atau atom yang netral.

      Titrasi kompleksometri adalah titrasi berdasarkan pembentukan senyawa kompleks antara kation dengan zat pembentuk kompleks. Salah satu zat pembentuk kompleks yang banyak digunakan dalam titrasi kompleksometri adalah garam dinatrium etilendiamina tetraasetat (dinatrium EDTA). Titrasi kompleksometri juga dikenal sebagai reaksi yang meliputi reaksi pembentukan ion-ion kompleks ataupun pembentukan molekul netral yang terdisosiasi dalam larutan. Persyaratan mendasar terbentuknya kompleks demikian adalah tingkat kelarutan tinggi. reaksi dapat dinyatakan oleh persamaan :

M(H₂O)_n + L = M(H₂O)_(n-1) L + H₂O

                             Erichrome Black T (EBT) adalah indikator kompleksometri yang merupakan bagian dari titrasi pengompleksian contohnya proses determinasi kesadahan air. Di dalamnya bentuk protonated Eriochrome Black T berwarna biru. Lalu berubah menjadi merah ketika ketika membentuk komplek dengan kalsium, magnesium atau logam lain. Nama lain dari Eriochrome Black T adalah solochrome Black T atau EBT.

                        Indikator EBT berwarna biru langit dalam larutan tetapi membentuk kompleks merah anggur (Mg – EBT)²⁺ (aq):

Mg ²⁺ (aq) + EBT (aq) –> (Mg – EBT)²⁺ (aq)

                        semua ion sadah telah terkompleksikan dengan H2Y^2-  dan membentuk kompleks berwarna biru:  

(Mg – EBT)²⁺ (aq) + H2Y^2- (aq) –> MgY(aq)  + 2H⁺ (aq) + EBT(aq)

2.                              Cara kerja

A.    Standarisasi

1.      Memipet 10,0 ml larutan standar primer ZnSO₄. 7H₂O dan masukan ke dalam erlemeyer.

2.      Menambahkan 2 ml buffer PH 10.

3.      Menambah 3 tetes indikator EBT.

4.      Titrasi dengan larutan Na₂EDTA dari warna merah anggur hingga warna biru.

B.     Cara kerja sampel

1.      Memipet 10,o ml larutan sampel dan masukan ke dalam erlemeyer.

2.      Menambahkan 2 ml buffer PH 10.

3.      Menambahkan 3 tetes indikator EBT.

4.      Menitrasi dengan larutan Na₂EDTA standar dari berwarna merah anggur hingga warna biru.

C.       KESIMPULAN

1.      Hal-hal penting yang perlu di perhatikan

a.       Titrasi Na2EDTA menggunakan indikator EBT dan penyangga dengan pH 10. Tujuan awalnya untuk memelihara agar pH tetap yang disebabkan ketika ion hidrogen lepas pada proses titrasi yang dapat menyebabkan terjadinya perubahan pH dalam titrasi kompleksiometri. Kedua mencegah terbentunya endapan logam hidroksida, dengan demikian,penyangga itu dapat bertindak sebagai zat pembentuk kompleks tambahan

2.      Manfaat percobaan bagi masyarakat

1.      Mengetahui kadar Mg ²⁺ dalam air sumur.

2.      Membantu memberi informasi kepada masyarakat mengenai air bersih.

D.      Daftar Pustaka

1.      DR.Ir.G.Alaerts&Ir.Sri Srimestri Santika,MSc,1984.METODA PENELITIAN AIR.Usaha Nasional:Surabaya

2.http://wahyusyah.multiply.com/journal/item/40/ANALISIS_KESADAHAN_AIR?&show_interstitial=1&u=%2Fjournal%2Fitem ( Diunduh tanggal 13 April 2012)

3. http://belajarsejarahfun.blogspot.com/2011/01/laporan-kimia-b2-analisis-kesadahan-air.html (Diunduh tanggal 14 april 2012)

Translasi (biomolekuler)

Translasi

            Translasi adalah proses penerjemahan kode genetik oleh tRNA ke dalam urutan asam amino yang menyusun suatu polipeptida atau protein.

Prosesing RNA

            Bila dibandingkan dengan transkripsi, translasi merupakan proses yang lebih rumit karena melibatkan fungsi berbagai makromolekul. Oleh karena kebanyakan di antara makromolekul ini terdapat dalam jumlah besar di dalam sel, maka sistem translasi menjadi bagian utama mesin metabolisme pada tiap sel. Makromolekul yang harus berperan dalam proses translasi tersebut meliputi:

1. Lebih dari 50 polipeptida serta 3 hingga 5 molekul RNA di dalam tiap ribosom

2. Sekurang-kurangnya 20 macam enzim aminoasil-tRNA sintetase yang akan mengaktifkan asam amino

3. Empat puluh hingga 60 molekul tRNA yang berbeda

4. Sedikitnya 9 protein terlarut yang terlibat dalam inisiasi, elongasi, dan terminasi

polipeptida.

            Translasi, atau pada hakekatnya sintesis protein, berlangsung di dalam ribosom, suatu struktur organel yang banyak terdapat di dalam sitoplasma. Ribosom terdiri atas dua subunit, besar dan kecil, yang akan menyatu selama inisiasi translasi dan terpisah ketika translasi telah selesai. Translasi menjadi tiga tahap (sama seperti pada transkripsi) yaitu inisiasi, elongasi, dan terminasi. Semua tahapan ini memerlukan faktor-faktor protein yang membantu mRNA, tRNA, dan ribosom selama proses translasi. Inisiasi dan elongasi rantai polipeptida juga membutuhkan sejumlah energi. Energi ini disediakan oleh GTP (guanosin triphosphat), suatu molekul yang mirip dengan ATP.

1.  Inisiasi

            Tahap inisiasi terjadi karena adanya tiga komponen yaitu mRNA, sebuah tRNA yang memuat asam amino pertama dari polipeptida, dan dua sub unit ribosom.

            Sebuah molekul mRNA akan terikat pada permukaan ribosom yang kedua subunitnya telah bergabung. Pengikatan ini terjadi karena pada mRNA prokariot terdapat urutan basa tertentu yang disebut sebagai tempat pengikatan ribosom (ribosom binding site) atau urutan Shine-Dalgarno. Sementara itu, pada eukariot pengikatan ribosom dilakukan oleh ujung 5’ mRNA. Selanjutnya, berbagai aminoasil-tRNA akan berdatangan satu demi satu ke kompleks ribosom-mRNA ini dengan urutan sesuai dengan antikodon dan asam amino yang dibawanya. Urutan ini ditentukan oleh urutan triplet kodon pada mRNA. Ikatan peptida terbentuk di antara asam-asam amino yang terangkai menjadi rantai polipeptida di tapak P ribosom.

            Penggabungan asam-asam amino terjadi karena gugus amino pada asam amino yang baru masuk berikatan dengan gugus karboksil pada asam amino yang terdapat pada rantai polipeptida yang sedang diperpanjang. mRNA yang keluar dari nukleus menuju sitoplasma didatangi oleh ribosom, kemudian mRNA masuk ke dalam “celah” ribosom. Ketika mRNA masuk ke ribosom, ribosom “membaca” kodon yang masuk. Pembacaan dilakukan untuk setiap 3 urutan basa hingga selesai seluruhnya. Sebagai catatan ribosom yang datang untuk mebaca kodon biasanya tidak hanya satu, melainkan beberapa ribosom yang dikenal sebagai polisom membentuk rangkaian mirip tusuk satu, di mana tusuknya adalah “mRNA” dan daging adalah “ribosomnya”.

            Padaumumnya sebuah mRNA akan ditranslasi secara serempak oleh beberapa ribosom yang satu sama lain berjarak sekitar 90 basa di sepanjang molekul mRNA. Kompleks translasi yang terdiri atas sebuah mRNA dan beberapa ribosom ini dinamakan poliribosom atau polisom. Besarnya polisom sangat bervariasi dan berkorelasi dengan ukuran polipeptida yang akan disintesis. Sebagai contoh, rantai hemoglobin yang tersusun dari sekitar 150 asam amino disintesis oleh polisom yang terdiri atas lima buah ribosom (pentaribosom).

            Dengan demikian, proses pembacaan kodon dapat berlangsung secara berurutan. Ketika kodon I terbaca ribosom (misal kodonnya AUG), tRNA yang membawa antikodon UAC dan asam amino metionin datang. tRNA masuk ke celah ribosom. Ribosom di sini berfungsi untuk memudahkan perlekatan yang spesifik antara antikodon tRNA dengan kodon mRNA selama sintesis protein. Sub unit ribosom dibangun oleh protein-protein dan molekul-molekul RNA ribosomal.

2.  Elongasi

            Pada tahap elongasi dari translasi, asam amino-asam amino ditambahkan satu per satu pada asam amino pertama (metionin). Ribosom terus bergeser agar mRNA lebih masuk, guna membaca kodon II. Misalnya kodon II UCA, yang segera diterjemahkan oleh tRNA berarti kodon AGU sambil membawa asam amino serine. Di dalam ribosom, metionin yang pertama kali masuk dirangkaikan dengan serine membentuk dipeptida.

            Ribosom terus bergeser, membaca kodon III. Misalkan kodon III GAG, segera diterjemahkan oleh antikodon CUC sambil membawa asam amino glisin. tRNA tersebut masuk ke ribosom. Asam amino glisin dirangkaikan dengan dipeptida yang telah terbentuk sehingga membentuk tripeptida. Demikian seterusnya proses pembacaan kode genetika itu berlangsung di dalam ribobom, yang diterjemahkan ke dalam bentuk asam amino guna dirangkai menjadi polipeptida.

            Kodon mRNA pada ribosom membentuk ikatan hidrogen dengan antikodon molekul tRNA yang baru masuk yang membawa asam amino yang tepat. Molekul mRNA yang telah melepaskan asam amino akan kembali ke sitoplasma untuk mengulangi kembali pengangkutan asam amino. Molekul rRNA dari sub unit ribosom besar berfungsi sebagai enzim, yaitu mengkatalisis pembentukan ikatan peptida yang menggabungkan polipeptida yang memanjang ke asam amino yang baru tiba. Pemanjangan atau elongasi rantai polipeptida akan terus berlangsung hingga suatu tripet kodon yang menyandi terminasi memasuki tapak A.

            Sebelum suatu rantai polipeptida selesai disintesis terlebih dahulu terjadi deformilisasi pada f-metionin menjadi metionin. Terminasi ditandai oleh terlepasnya mRNA, tRNA di tapak P, dan rantai polipeptida dari ribosom. Selain itu, kedua subunit ribosom pun memisah. Pada terminasi diperlukan aktivitas dua protein yang berperan sebagai faktor pelepas atau releasing factors, yaitu RF-1 dan RF-2.

3.  Terminasi

            Tahap akhir translasi adalah terminasi. Elongasi berlanjut hingga kodon stop mencapai ribosom. Triplet basa kodon stop adalah UAA, UAG, dan UGA. Kodon stop tidak mengkode suatu asam amino melainkan bertindak sinyal untuk menghentikan translasi. Polipeptida yang dibentuk kemudian “diproses” menjadi protein.

Proses translasi

Perbedaan translasi pada Prokariot dan Eukariot.

            Pada prokariot translasi seringkali dimulai sebelum transkripsi berakhir. Hal ini dimungkinkan terjadi karena tidak adanya dinding nukleus yang memisahkan antara transkripsi dan translasi. Dengan berlangsungnya kedua proses tersebut secara bersamaan, ekspresi gen menjadi sangat cepat dan mekanisme nyala-padam (turn onturn off) ekspresi gen, seperti yang akan dijelaskan nanti, juga menjadi sangat efisien. Namun, tidak demikian halnya pada eukariot. Transkripsi terjadi di dalam nukleus, sedangkan translasi terjadi di sitoplasma (ribosom).

DAFTAR PUSTAKA

http://www.biomol.edublogs.org/files/2010/02/BAB-IV-TRANSLASI.pdf

http://desybio.wordpress.com/tag/2-translasi/