Application of genetic and biochemical methods has allowed determination of the energy source required for chemotaxis. On one hand it seems logical that ATP would be the direct source of the mechanical energy required for swimming since most energy transductions in higher cells appear to use ATP. On the other hand, the flagella originate in the cell membrane, and a substantial proton gradient exists across the inner membrane under most growth conditions. Therefore the direct source of energy could also derive from the membrane potential.

ATP and the proton motive force across the inner membrane are normally interconvertible by means of the membrane-bound ATPase (Fig. 1). The membrane potential generates ATP and, conversely, ATP can be used to generate a membrane potential. Therefore, blocking formation of either ATP or the membrane potential could have an effect on the other. Arsenate permits decoupling to determine what actually drives the motor of the flagella. It blocks ATP formation both by glycolysis and by ATPase, but does not directly affect the membrane potential. Cells treated with arsenate are found to be motile, but they do not swim up gradients of attractants. This shows that ATP is not required for motility, but probably is involved with the process of modulating run duration.

Fig1. A schematic of the inner membrane of a cell showing that electron flow down the electron transport chain leads to export of protons and ultimate transfer of electrons to oxygen. Reentry of protons to the cell through the ATPase generates ATP. Conversely, ATP can be hydrolyzed by ATPase to pump protons out of the cell.

Next, to investigate the role of the membrane potential, cells can be grown anaerobically. This blocks the usual means of generation of the membrane potential because the electron transfer chain becomes inactive owing to the lack of a terminal electron acceptor. Then, to prevent energy from ATP from being used to create a membrane potential, an ATPase-negative mutant can be used. Anaerobically grown ATPase mutants are found not to be motile, leading to the conclusion that the motors that drive the flagella are run by the cell’s membrane potential. Other experiments show that cells swim when transmembrane pH gradient or membrane potentials are generated artificially.

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مع وصول الزيارة ذروتها.. العتبة العباسية المقدسة تستنفر ملاكاتها لخدمة زائري مرقدي الإمامين العسكريين (عليهما السلام)

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قسم حفظ النظام يشارك في تأمين زيارة الإمام الحسن العسكري (عليه السلام) بمدينة سامراء

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دون آثار جانبية.. زيت عشبة طبيعية قد يعالج القلق

"ليكانيماب".. علاج الزهايمر يطرح رسميا في السوق الألمانية

متى يجب تنظيف الأسنان في الصباح.. قبل أم بعد الإفطار؟

ارتفاع الوفيات.. منظمة الصحة تدق جرس الإنذار بشأن الكوليرا

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الآخبار التكنلوجية

أكبر مشروع طاقة رياح في نصف الكرة الجنوبي يحقق إنجازين جديدين

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ضوء إدارة المحرك: أسئلة مهمة لفهم عمله ومعانيه

"واتساب" يطلق خاصية جديدة لكتابة الرسائل بالذكاء الاصطناعي

المزيد

مواضيع ذات صلة

Chemotaxis: Methylation and Adaptation

The Mechanism of Chemotaxis

How Cells Swim

Fundamental Properties of Chemotaxis

Assaying Chemotaxis

Lambda Phage Assembly: Formation of the Tail

Lambda Phage Assembly: Packaging the DNA and Formation of the cos Ends

Lambda Phage Assembly: The Head Assembly Sequence and Host Proteins

Lambda Phage Assembly: The Geometry of Capsids

Determining Details of Local Ribosomal Structure

Experiments with in vitro Ribosome Assembly

The Global Structure of Ribosomes