Voldemort_7

*Pengertian :
Metabolisme berasal dari kata metabole (yunani) yg artinya berubah.

Metabolisme adalah keseluruhan proses kimiawi dalam tubuh organisme yang melibatkan energi dan enzim, diawali dgn substrat awal dan diakhiri produk akhir.

Metabolism (chemistry), inclusive term for the chemical reactions by which the cells of an organism transform energy, maintain their identity, and reproduce. All life forms—from single-celled algae to mammals—are dependent on many hundreds of simultaneous and precisely regulated metabolic reactions to support them from conception through growth and maturity to the final stages of death. Each of these reactions is triggered, controlled, and terminated by specific cell enzymes or catalysts, and each reaction is coordinated with the numerous other reactions throughout the organism.
Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

*Tujuan :
Metabolisme bertujuan u8ntuk mengahsilkan energi, yg berguna bagti aktivitas kehidupan, baik tingkat seluler (pembelahan sel, transpor molekul ke luar dan ke dalam sel) maupun tingkat individu (membaca, menulis, berjalan, berlari, dsb)

Metabolisme terbagi 2, yaitu katabolisme dan anabolisme.



*Pengertian Enzim : enzim berasal dari kata in + zyme (sesuatu di dlm ragi)

Enzim→suatu protein yang berupa molekul besar, bertindak sebagai biokatalisator yang dapat meningkatkan kecepatan reaksi kimia tapi tidak berubah dalam reaksi kimia tersebut.

*Karakteristik enzim (sifat2 enzim) :
- Merupakan senyawa protein
- Bekerja pada substrat tertentu saja (cth : e.ptialin : merubah amilum→maltosa)
- Bersifat katalis (mempercepat reaksi kimia)
- Hanya diperlukan dalam jumlah sedikit (apabila terlalu banyak dapat merusak)
- Dapat bekerja secara bolak-balik (reversible)
- Dipengaruhi oleh faktor2 tertentu (suhu, pH, activator, inhibitor/penghambat, konsentrasi enzim, dan konsentrasi substrat)
- Enzim tdk berubah pd akhir reaksi (tdk terurai)

Komponen enzim :
Enzim tersusun dari komponen protein (apoenzim) dan komponen nonprotein (gugus prostetik).
- Apoenzim biasanya bersifat termolabil/tdk tahan lama
- Gugus prostetik dapat berupa ion-ion anorganik/kofaktor, gugus protein, dan koenzim.

Cara kerja enzim :
Enzim mengakatalis reaksi dengan meningkatkan kecepatan reaksi. Enzim meningkatkan kecepatan reaksi dengan cara menurunkan energi aktivasi.
Ada 2 macam kerja enzim :
1. Teori gembok dan anak kunci (lock and key theory)
Enzim dan substrat bergabung membentuk kompleks seperti kunci yang masuk ke dalam gembok. Substrat akan bereaksi, maka kompleks akan lepas, melepaskan produk dan membebaskan enzim.
2. Teori kecocokan yang terinduksi (induced fit theory)
Sisi aktif enzim dapat berubah (fleksibel) sesuai dengan bentuk substrat.

Tahapan Respirasi Aerob :
1. Glikolisis = rangkaian reaksi perubahan molekul glukosa menjadi asam piruvat.
2. Dekarboksilasi Oksidatif = reaksi oksidasi asam piruvat hasil glikolisis.
3. Siklus krebs = reaksi tahap ke-3 respirasi aerob, menghasilkan 6 NADH, 2 FADH2, 2 ATP, 4 CO2, serta membentuk kembali asam oksaloaselat.

During the Krebs cycle, the acetyl coenzyme A molecules are processed. As this complex pathway progresses, six molecules of NADH are formed. Additional carbon dioxide is created, and this process releases energy that is used to build two molecules of ATP from a pool of ADP and phosphate groups in the mitochondria. Hydrogens and electrons then are transferred to a molecule of flavin adenine dinucleotide (FAD++)to form FADH2, a molecule like NADH that temporarily stores hydrogen and electrons for later use. By the end of the Krebs cycle, most of the usable energy from the original glucose molecule has been transferred to ten molecules of NADH (two from glycolysis, two from the transition stage, and six from the Krebs cycle); two molecules of FADH2; and four molecules of ATP, two of which were formed in glycolysis.



Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

4. Transpor elektron = tahapan reaksi dr respirasi aerob ketika elektron dari siklus krebs dialirkan berturut-turut pada enzim dan kofaktor membran mitokondria, aliran elektron menyebabkan terjadinya sintesis ATP.

Fotosintesis
- Pengertian : fotosintesis berasal dari kata fotos (cahaya) dan sintesis (membuat bahan kimia, memasak)
Fotosintesis = peristiwa penggunaan energi cahaya untuk memebentuk senyawa dasar karbohidrat dari karbon dioksida dan air
- Tempat berlangsung : fotosintesis terjadi di dlm kloroplas. Kloroplas merupakan organel plastida yang mengandung pigmen hijau daun (klorofil) pada protein integral membran tilakoid.

Perbedaan respirasi aerob-anaerob:



Fotosintesis terjadi dalam 2 tahap, yaitu reaksi terang dan reaksi gelap.

A. Reaksi terang (reaksi yang bergantung pada cahaya)
Merupakan tahap awal fotosintesis. Dlm reaksi terang, terjadi 3 proses yang berlangsung di dalam kloroplas, khususnya di membran tilakoid :
- Pigmen fotosintesis menyerap energi cahaya dan melepaskan elektron yang akan masuk ke sistem transpor elektron.
- Molekul air pecah, ATP dan NADPH terbentuk, dan oksigen dilepaskan.
- Pigmen fotosintesis yang, melepaskan elektron menerima kembali elektron sebagai gantinya.
Photosynthesis relies on flows of energy and electrons initiated by light energy. Electrons are minute particles that travel in a specific orbit around the nuclei of atoms and carry a small electrical charge. Light energy causes the electrons in chlorophyll and other light-trapping pigments to boost up and out of their orbit; the electrons instantly fall back into place, releasing resonance energy, or vibrating energy, as they go, all in millionths of a second. Chlorophyll and the other pigments are clustered next to one another in the photosystems, and the vibrating energy passes rapidly from one chlorophyll or pigment molecule to the next, like the transfer of energy in billiard balls.
Light contains many colors, each with a defined range of wavelengths measured in nanometers, or billionths of a meter. Certain red and blue wavelengths of light are the most effective in photosynthesis because they have exactly the right amount of energy to energize, or excite, chlorophyll electrons and boost them out of their orbits to a higher energy level. Other pigments, called accessory pigments, enhance the light-absorption capacity of the leaf by capturing a broader spectrum of blue and red wavelengths, along with yellow and orange wavelengths. None of the photosynthetic pigments absorb green light; as a result, green wavelengths are reflected, which is why plants appear green.
Photosynthesis begins when light strikes Photosystem I pigments and excites their electrons. The energy passes rapidly from molecule to molecule until it reaches a special chlorophyll molecule called P700, so named because it absorbs light in the red region of the spectrum at wavelengths of 700 nanometers.
Until this point, only energy has moved from molecule to molecule; now electrons themselves transfer between molecules. P700 uses the energy of the excited electrons to boost its own electrons to an energy level that enables an adjoining electron acceptor molecule to capture them. The electrons are then passed down a chain of carrier molecules, called an electron transport chain. The electrons are passed from one carrier molecule to another in a downhill direction, like individuals in a bucket brigade passing water from the top of a hill to the bottom. Each electron carrier is at a lower energy level than the one before it, and the result is that electrons release energy as they move down the chain. At the end of the electron transport chain lies the molecule nicotine adenine dinucleotide (NADP+). Using the energy released by the flow of electrons, two electrons from the electron transport chain combine with a hydrogen ion and NADP+ to form NADPH.
When P700 transfers its electrons to the electron acceptor, it becomes deficient in electrons. Before it can function again, it must be replenished with new electrons. Photosystem II accomplishes this task. As in Photosystem I, light energy activates electrons of the Photosystem II pigments. These pigments transfer the energy of their excited electrons to a special Photosystem II chlorophyll molecule, P680, that absorbs light best in the red region at 680 nanometers. Just as in Photosystem I, energy is transferred among pigment molecules and is then directed to the P680 chlorophyll, where the energy is used to transfer electrons from P680 to its adjoining electron acceptor molecule.
From the Photosystem II electron acceptor, the electrons are passed through a different electron transport chain. As they pass along the cascade of electron carrier molecules, the electrons give up some of their energy to fuel the production of ATP, formed by the addition of one phosphorus atom to adenosine diphosphate (ADP). Eventually, the electron transport carrier molecules deliver the Photosystem II electrons to Photosystem I, which uses them to maintain the flow of electrons to P700, thus restoring its function.
P680 in Photosystem II is now electron deficient because it has donated electrons to P700 in Photosystem I. P680 electrons are replenished by the water that has been absorbed by the plant roots and transported to the chloroplasts in the leaves. The movement of electrons in Photosystems I and II and the action of an enzyme split the water into oxygen, hydrogen ions, and electrons. The electrons from water flow to Photosystem II, replacing the electrons lost by P680. Some of the hydrogen ions may be used to produce NADPH at the end of the electron transport chain, and the oxygen from the water diffuses out of the chloroplast and is released into the atmosphere through pores in the leaf.
The transfer of electrons in a step-by-step fashion in Photosystems I and II releases energy and heat slowly, thus protecting the chloroplast and cell from a harmful temperature increase. It also provides time for the plant to form NADPH and ATP. In the words of American biochemist and Nobel laureate Albert Szent-Gyorgyi, “What drives life is thus a little electric current, set up by the sunshine.”
Microsoft ® Encarta ® 2006. © 1993-2005 Microsoft Corporation. All rights reserved.

B. Reaksi gelap (reaksi yang tidak bergantung secara langsung pada cahaya)
Disebut juga siklus Calvin-Benson. Reaksi ini berlangsung dalam gelap dan hanya dapat berlangsung jika ada ATP dan NADPH yang dihasilkan dari reaksi terang. Tahapan reaksi gelap :
- Karbon dioksida diikat oleh RuBP (Ribulosa Bifosfat yang terdiri dari 5 atom karbon) menjadi senyawa 6 karbon yang labil. Senyawa 6 karbon kemudian dipecah menjadi 2 fosfogliserat (PGA).
- Masing-masing PGA menerima gugus fosfat dari ATP dan menerima hidrogen serta elektron dari NADPH. Reaksi ini menghasilkan PGAL (fosfogliseraldehida)
- Tiap 6 molekul CO2 yang diikat akan dihasilkan 12 PGAL
- Dr 12 PGAL, 10 molekul kembali ke tahap awal menjadi RuBP, dan seterusnya RuBP akan mengikat CO2 yang baru.
- 2 PGAL lainnya akan berkondensasi menjadi glukosa 6 fosfat.

Perbedaan fotosintesis dengan Kemosintesis :


oleh : Inertia Indi H.