بسم الله الرحمن الرحيم
دورة كربس هى المرحلة الثانية من دورة تسبقها لتحليل الجلوكوز وتسمى بـ Glycolysis والتى تبدا بسكر جلوكوز وتنتهى بحمض البيروفيك والذى منه نبدا دورة كربس
ومن المعروف ان دورة Glycolysis تتم لاهوائيا اى لا نحتاج لوجود الاكسجين فيها وتتم فى السيتوبلازم الخاص بالخليه
ولا تتم فى
الميتوكندريا (بيوت الطاقة والتى يوجد بها اكسجين وتتم فيها دورة كربس)
بينما دورة كربس تحتاج للاكسجين وتتم فى الميتوكندريا
وتعتبر Glycolysis هى مصدر الطاقة الاوليه لمعظم الكائنات الحية
فى دورة Glycolysis يتم استهلاك 2 جزئATP
وينتج فى نهايتها هذه الدورة
4 جزيئات من ATP
بالاضافة الى 2من NADH2
وبما ان جزيئ الواحد منNADH2
يساوى 3 ATP ان ينتج لنا حوالى 10 جزيئات من ATP وبطرح الاتنين ATPتم استهلاكهم فى اول الدورة نجد لدينا 8 جزيئات ATP طاقة صافى تم الحصول عليها من خلال دورة Glycolysis اللاهوائية
خطوات الدورة
Glucose 6-phosphate is formed when the 6th carbon on the glucose molecule is phosphorylated by an ATP molecule.
Glucose 6-phosphate is converted into a 5-carbon ring isomer, fructose 6-phosphate.
. Fructose 6-phosphate is phosphorylated by another ATP to form fructose 1, 6-diphosphate.
Fructose 1, 6-diphosphate is processed by an enzyme into two glyceraldehyde 3-phosphate molecules.
Two molecules of glyceraldehyde 3-phosphate are oxidized, losing hydrogen atoms and gaining phosphate groups to form 1, 3-diphosphoglycerate. Two molecules of NAD+ are converted into NADH2+ in the process.
Two 1,3-diphosphoglycerate molecules phosphorylate ADP (adenine diphosphate) to yield two molecules of 3-phosphoglycerate and two ATPs are produced.
The phosphate groups on 3-phosphoglycerate move to the 2nd carbon, forming 2-phosphoglycerate.
The two 2-phosphoglycerate molecules are dehydrated and forms two high-energy phosphoenolpyruvate molecules.
The two phospoenolpyruvate phosphorylates two ADPs and produces two more ATPs and two molecules of pyruvate
نلاحظ اننا بدانا بجزئ سكر الجلوكوز (به 6 ذرات كربون)
وانتهينابـ 2 جزئ بيروفيك (به 3 ذرات كربون لكل جزئ)+8جزيئات طاقةATP
وناخد من هنا بيروفيك الذى يدخل الى الميتوكندريا ونبدا دوره كربس وتسمى ايضا دورة التنفس الهوائى لوجود اكسجين بها Aerobic Respiration
1. Prior to entering the Krebs Cycle, pyruvate must be converted into acetyl CoA (pronounced: acetyl coenzyme A). This is achieved by removing a CO2 molecule from pyruvate and then removing an electron to reduce an NAD+ into NADH. An enzyme called coenzyme A is combined with the remaining acetyl to make acetyl CoA which is then fed into the Krebs Cycle. The steps in the Krebs Cycle are summarized below:
2. Citrate is formed when the acetyl group from acetyl CoA combines with oxaloacetate from the previous Krebs cycle..
3. Citrate is converted into its isomer isocitrate..
4. Isocitrate is oxidized to form the 5-carbon α-ketoglutarate. This step releases one molecule of CO2 and reduces NAD+ to NADH2+.
5. The α-ketoglutarate is oxidized to succinyl CoA, yielding CO2 and NADH2+.
6. Succinyl CoA releases coenzyme A and phosphorylates ADP into ATP.
7. Succinate is oxidized to fumarate, converting FAD to FADH2.
8. Fumarate is hydrolized to form malate.
9. Malate is oxidized to oxaloacetate, reducing NAD+ to NADH2+.
We are now back at the beginning of the Krebs Cycle. Because glycolysis produces two pyruvate molecules from one glucose, each glucose is processes through the kreb cycle twice. For each molecule of glucose, six NADH2+, two FADH2, and two ATP.
دورة كربس
المشاركة الأصلية كتبت بواسطة nona
اقتباس
