Bagaimanakah tahapan Siklus Krebs atau Siklus Asam Sitrat?
Updated: November 16, 2024
Summary
The Krebs Cycle, named after scientist Hans Krebs, is the third stage of aerobic respiration. It involves a series of reactions where acetyl-CoA and oxaloacetate combine to form citrate. Through various transformations and enzyme-catalyzed steps, different carbon compounds are produced leading to the generation of NADH, FADH2, and ATP. This cycle is crucial for extracting energy from carbohydrates and plays a key role in the overall cellular respiration process.
Pengenalan Siklus Krebs
Siklus Krebs merupakan tahap ketiga dalam proses respirasi aerob setelah proses dekarboksilasi oksidatif. Dinamakan sebagai siklus Krebs sebagai penghargaan kepada ilmuwan Hans Krebs dari Jerman.
Tahap Pertama: Asetil-Koa dan Oksaloasetat
Penjelasan mengenai tahap pertama siklus Krebs di mana asetil-koa dan oksaloasetat mengalami kondensasi untuk membentuk senyawa berkarbon 6 yang dikenal sebagai sitrat atau asam sitrat.
Tahap Kedua: Isositrat
Proses perubahan sutra menjadi isositrat yang masih memiliki 6 karbon dengan reaksi isomerisasi. Pada tahap ini terjadi pelepasan dan penambahan molekul air.
Tahap Ketiga: Alfa Ketoglutarat
Isositrat diubah menjadi Alfa ketoglutarat yang memiliki 5 atom karbon. Proses dekarboksilasi atau pengurangan karbon terjadi serta pelepasan elektron.
Tahap Keempat: Suksinil Koenzim A
Alfa ketoglutarat diubah menjadi suksinil koenzim a yang memiliki 4 atom karbon. Pada tahap ini terjadi karbon baru dan reduksi NAD+.
Tahap Kelima: Suksinat
Suksinil koenzim a diubah menjadi suksinat yang tetap memiliki 4 atom karbon. Pada tahap ini terjadi fosfatan organik dan pembentukan energi ATP atau GTP.
Tahap Keenam: Kumarat
Suksinat diubah menjadi kumarat dan terjadi pelepasan elektron yang ditangkap oleh FADH2. Enzim suksinat dehidrogenase berperan dalam tahap ini.
Tahap Ketujuh: Malat
Kumarat diubah menjadi malat dengan bantuan enzim fumarase. Pada tahap ini terjadi penambahan air. Enzim malat dehidrogenase berperan dalam konversi malat menjadi oksaloasetat.
Pembentukan Kembali Oksaloasetat
Tahap terakhir di mana malat diubah kembali menjadi oksaloasetat. Proses ini juga melibatkan pembentukan NADH +. Dalam satu siklus Krebs menghasilkan 3 NADH, 1 FADH2, dan 1 ATP.
FAQ
Q: Who was Hans Krebs and why is the citric acid cycle named after him?
A: Hans Krebs was a German scientist. The citric acid cycle is named after him as a tribute to his contributions in discovering the cycle.
Q: What is the citric acid cycle?
A: The citric acid cycle is the third stage of aerobic respiration, where acetyl-CoA and oxaloacetate undergo a condensation reaction to form citrate or citric acid, leading to the production of energy.
Q: Describe the first step of the citric acid cycle.
A: In the first step, acetyl-CoA and oxaloacetate condense to form citrate. This process involves the conversion of a 6-carbon compound into citrate or citric acid.
Q: What is the role of isocitrate in the citric acid cycle?
A: Isocitrate is formed from citrate through an isomerization reaction. It still contains 6 carbons and undergoes further reactions in the cycle.
Q: Explain the significance of the conversion of alpha-ketoglutarate to succinyl-CoA.
A: The conversion of alpha-ketoglutarate to succinyl-CoA involves decarboxylation and electron release, leading to the generation of energy intermediates like ATP or GTP.
Q: What occurs during the conversion of succinate to fumarate in the citric acid cycle?
A: During this step, succinate is converted to fumarate while electrons are released and captured by FADH2. The enzyme succinate dehydrogenase plays a key role in this process.
Q: How is malate formed from fumarate in the citric acid cycle?
A: Malate is formed from fumarate with the help of the enzyme fumarase. Water is added during this conversion.
Q: What is the final step in the citric acid cycle?
A: The final step involves the conversion of malate back to oxaloacetate, leading to the generation of NADH+.
Q: How many NADH, FADH2, and ATP are produced in one cycle of the citric acid cycle?
A: In one cycle, the citric acid cycle produces 3 NADH, 1 FADH2, and 1 ATP which are essential for further energy production.
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