Введение
Транспортировка веществ через мембрану
Mediated transport refers to transport mediated by a membrane transport protein. Substances in the human body may be hydrophobic, electrophilic, contain a positively or negatively charge, or have another property. As such there are times when those substances may not be able to pass over the cell membrane using protein independent movement. The cell membrane is imbedded with many membrane transport proteins that allow such molecules to travel in and out of the cell. There are three types of mediated transporters: uniport, symport, and antiport. Things that can be transported are nutrients, ions, glucose, etc, all depending on the needs of the cell. One example of a uniport mediated transport protein is GLUT1. GLUT1 is a transmembrane protein, which means it spans the entire width of the cell membrane, connecting the extracellular and intracellular region. It is a uniport system because it specifically transports glucose in only one direction, down its concentration gradient across the cell membrane. Another example of a uniporter mediated transport protein is microsomal triglyceride transfer protein (MTTP) who is responsible for catalyzing the assembly of the triglyceride rich lipoproteins as well mediating their release from the lumen of the endoplasmic reticulum. What is distinguishable about this specific transfer protein is that it requires the protein PRAP1 to bind to the lipoprotein to facilitate the transport of said lipoprotein. MTTP only recognizes the PRAP1 lipoprotein complex and only then will it catalyze the transport reaction. In a way, the PRAP1 protein acts as a signal for MTTP. The importance of such interactions implies that mediated transport is not only dependent on transmembrane proteins but can also require the presence of additional non transmembrane proteins. For instance, studies show that in the absence of a fully functional PRAP1 protein, MTTP fails to transport specific lipoproteins across the endoplasmic reticulum membrane. An example of a symporter mediated transport protein is SGLT1, a sodium/glucose co transporter protein that is mainly found in the intestinal tract. The SGLT1 protein is a symporter system because it passes both glucose and sodium in the same direction, from the lumen of the intestine to inside the intestinal cells. An example of an antiporter mediated transport protein is the sodium calcium antiporter, a transport protein involved in keeping the cytoplasmic concentration of calcium ions in the cells, low. This transport protein is an antiporter system because it transports three sodium ions across the plasma membrane in exchange for a calcium ion, which is transported in the opposite direction. Types of Mediated TransportersUniporter (I)Symporter (II)Antiporter (III)Allows transportation of one solute at a timeTransports solute and countertransported solute at the same time and in the same directionTransports the solute in one direction while the countertransported solute is moved the opposite direction in or out of the cell
Mechanism of transport. A molecule will bind to a transporter protein, altering its shape. The change of shape or other added substances such as ATP will, in turn, cause the transport protein to alter its shape and release the molecule onto the other side of the cell membrane.
Опосредованная транспортировка относится к транспортировке, осуществляемой с помощью мембранного транспортного белка. Вещества в организме человека могут быть гидрофобными, электрофильными, содержать положительный или отрицательный заряд или обладать другими свойствами. В связи с этим, в некоторых случаях эти вещества не могут проходить через клеточную мембрану без участия белка. Клеточная мембрана содержит множество мембранных транспортных белков, которые обеспечивают перемещение таких молекул внутрь и из клетки. Существует три типа опосредованных транспортеров: унипортер, симпортер и антипортер. Транспортируемыми веществами являются питательные вещества, ионы, глюкоза и т.д., в зависимости от потребностей клетки. Одним из примеров унипортера является GLUT1. GLUT1 – трансмембранный белок, то есть он пронизывает всю ширину клеточной мембраны, соединяя внеклеточное и внутриклеточное пространства. Это унипортерная система, поскольку она специфически транспортирует глюкозу только в одном направлении, по градиенту концентрации через клеточную мембрану. Другим примером унипортерного транспортного белка является микросомальный триглицеридопереносчик (MTTP), который отвечает за катализ сборки липопротеинов, богатых триглицеридами, а также за их высвобождение из просвета эндоплазматической сети. Особенностью этого белка является то, что для облегчения транспорта липопротеина требуется связывание белка PRAP1 с липопротеином. MTTP распознает только комплекс PRAP1-липопротеин и только тогда катализирует транспортную реакцию. В некотором смысле, белок PRAP1 действует как сигнал для MTTP. Важность таких взаимодействий указывает на то, что опосредованная транспортировка зависит не только от трансмембранных белков, но также может требовать присутствия дополнительных немембранных белков. Например, исследования показывают, что при отсутствии полностью функционального белка PRAP1, MTTP не может транспортировать специфические липопротеины через мембрану эндоплазматической сети. Примером симпортерного транспортного белка является SGLT1, натрий/глюкозный котранспортер, который в основном находится в кишечном тракте. Белок SGLT1 является симпортерной системой, поскольку он пропускает глюкозу и натрий в одном направлении, из просвета кишечника внутрь клеток кишечника. Примером антипортерного транспортного белка является натрий-кальциевый антипортер, транспортный белок, участвующий в поддержании низкой цитоплазматической концентрации ионов кальция в клетках. Этот транспортный белок является антипортерной системой, поскольку он транспортирует три иона натрия через плазматическую мембрану в обмен на ион кальция, который транспортируется в противоположном направлении.
Mediated transport refers to transport mediated by a membrane transport protein. Substances in the human body may be hydrophobic, electrophilic, contain a positively or negatively charge, or have another property. As such there are times when those substances may not be able to pass over the cell membrane using protein independent movement. The cell membrane is imbedded with many membrane transport proteins that allow such molecules to travel in and out of the cell. There are three types of mediated transporters: uniport, symport, and antiport. Things that can be transported are nutrients, ions, glucose, etc, all depending on the needs of the cell. One example of a uniport mediated transport protein is GLUT1. GLUT1 is a transmembrane protein, which means it spans the entire width of the cell membrane, connecting the extracellular and intracellular region. It is a uniport system because it specifically transports glucose in only one direction, down its concentration gradient across the cell membrane. Another example of a uniporter mediated transport protein is microsomal triglyceride transfer protein (MTTP) who is responsible for catalyzing the assembly of the triglyceride rich lipoproteins as well mediating their release from the lumen of the endoplasmic reticulum. What is distinguishable about this specific transfer protein is that it requires the protein PRAP1 to bind to the lipoprotein to facilitate the transport of said lipoprotein. MTTP only recognizes the PRAP1 lipoprotein complex and only then will it catalyze the transport reaction. In a way, the PRAP1 protein acts as a signal for MTTP. The importance of such interactions implies that mediated transport is not only dependent on transmembrane proteins but can also require the presence of additional non transmembrane proteins. For instance, studies show that in the absence of a fully functional PRAP1 protein, MTTP fails to transport specific lipoproteins across the endoplasmic reticulum membrane. An example of a symporter mediated transport protein is SGLT1, a sodium/glucose co transporter protein that is mainly found in the intestinal tract. The SGLT1 protein is a symporter system because it passes both glucose and sodium in the same direction, from the lumen of the intestine to inside the intestinal cells. An example of an antiporter mediated transport protein is the sodium calcium antiporter, a transport protein involved in keeping the cytoplasmic concentration of calcium ions in the cells, low. This transport protein is an antiporter system because it transports three sodium ions across the plasma membrane in exchange for a calcium ion, which is transported in the opposite direction. Types of Mediated TransportersUniporter (I)Symporter (II)Antiporter (III)Allows transportation of one solute at a timeTransports solute and countertransported solute at the same time and in the same directionTransports the solute in one direction while the countertransported solute is moved the opposite direction in or out of the cell
Mechanism of transport. A molecule will bind to a transporter protein, altering its shape. The change of shape or other added substances such as ATP will, in turn, cause the transport protein to alter its shape and release the molecule onto the other side of the cell membrane.
Типы опосредованных транспортеров:
Унипортер (I) – позволяет транспортировать один растворенный компонент за один раз.
Симпортер (II) – транспортирует растворенный компонент и контр-транспортируемый компонент одновременно и в одном направлении.
Антипортер (III) – транспортирует растворенный компонент в одном направлении, в то время как контр-транспортируемый компонент перемещается в противоположном направлении внутрь или наружу клетки.
Mediated transport refers to transport mediated by a membrane transport protein. Substances in the human body may be hydrophobic, electrophilic, contain a positively or negatively charge, or have another property. As such there are times when those substances may not be able to pass over the cell membrane using protein independent movement. The cell membrane is imbedded with many membrane transport proteins that allow such molecules to travel in and out of the cell. There are three types of mediated transporters: uniport, symport, and antiport. Things that can be transported are nutrients, ions, glucose, etc, all depending on the needs of the cell. One example of a uniport mediated transport protein is GLUT1. GLUT1 is a transmembrane protein, which means it spans the entire width of the cell membrane, connecting the extracellular and intracellular region. It is a uniport system because it specifically transports glucose in only one direction, down its concentration gradient across the cell membrane. Another example of a uniporter mediated transport protein is microsomal triglyceride transfer protein (MTTP) who is responsible for catalyzing the assembly of the triglyceride rich lipoproteins as well mediating their release from the lumen of the endoplasmic reticulum. What is distinguishable about this specific transfer protein is that it requires the protein PRAP1 to bind to the lipoprotein to facilitate the transport of said lipoprotein. MTTP only recognizes the PRAP1 lipoprotein complex and only then will it catalyze the transport reaction. In a way, the PRAP1 protein acts as a signal for MTTP. The importance of such interactions implies that mediated transport is not only dependent on transmembrane proteins but can also require the presence of additional non transmembrane proteins. For instance, studies show that in the absence of a fully functional PRAP1 protein, MTTP fails to transport specific lipoproteins across the endoplasmic reticulum membrane. An example of a symporter mediated transport protein is SGLT1, a sodium/glucose co transporter protein that is mainly found in the intestinal tract. The SGLT1 protein is a symporter system because it passes both glucose and sodium in the same direction, from the lumen of the intestine to inside the intestinal cells. An example of an antiporter mediated transport protein is the sodium calcium antiporter, a transport protein involved in keeping the cytoplasmic concentration of calcium ions in the cells, low. This transport protein is an antiporter system because it transports three sodium ions across the plasma membrane in exchange for a calcium ion, which is transported in the opposite direction. Types of Mediated TransportersUniporter (I)Symporter (II)Antiporter (III)Allows transportation of one solute at a timeTransports solute and countertransported solute at the same time and in the same directionTransports the solute in one direction while the countertransported solute is moved the opposite direction in or out of the cell
Mechanism of transport. A molecule will bind to a transporter protein, altering its shape. The change of shape or other added substances such as ATP will, in turn, cause the transport protein to alter its shape and release the molecule onto the other side of the cell membrane.
Механизм транспорта. Молекула связывается с транспортным белком, изменяя его форму. Изменение формы или добавление других веществ, таких как АТФ, в свою очередь, заставляет транспортный белок изменить свою форму и высвободить молекулу на другую сторону клеточной мембраны.
Mediated transport refers to transport mediated by a membrane transport protein. Substances in the human body may be hydrophobic, electrophilic, contain a positively or negatively charge, or have another property. As such there are times when those substances may not be able to pass over the cell membrane using protein independent movement. The cell membrane is imbedded with many membrane transport proteins that allow such molecules to travel in and out of the cell. There are three types of mediated transporters: uniport, symport, and antiport. Things that can be transported are nutrients, ions, glucose, etc, all depending on the needs of the cell. One example of a uniport mediated transport protein is GLUT1. GLUT1 is a transmembrane protein, which means it spans the entire width of the cell membrane, connecting the extracellular and intracellular region. It is a uniport system because it specifically transports glucose in only one direction, down its concentration gradient across the cell membrane. Another example of a uniporter mediated transport protein is microsomal triglyceride transfer protein (MTTP) who is responsible for catalyzing the assembly of the triglyceride rich lipoproteins as well mediating their release from the lumen of the endoplasmic reticulum. What is distinguishable about this specific transfer protein is that it requires the protein PRAP1 to bind to the lipoprotein to facilitate the transport of said lipoprotein. MTTP only recognizes the PRAP1 lipoprotein complex and only then will it catalyze the transport reaction. In a way, the PRAP1 protein acts as a signal for MTTP. The importance of such interactions implies that mediated transport is not only dependent on transmembrane proteins but can also require the presence of additional non transmembrane proteins. For instance, studies show that in the absence of a fully functional PRAP1 protein, MTTP fails to transport specific lipoproteins across the endoplasmic reticulum membrane. An example of a symporter mediated transport protein is SGLT1, a sodium/glucose co transporter protein that is mainly found in the intestinal tract. The SGLT1 protein is a symporter system because it passes both glucose and sodium in the same direction, from the lumen of the intestine to inside the intestinal cells. An example of an antiporter mediated transport protein is the sodium calcium antiporter, a transport protein involved in keeping the cytoplasmic concentration of calcium ions in the cells, low. This transport protein is an antiporter system because it transports three sodium ions across the plasma membrane in exchange for a calcium ion, which is transported in the opposite direction. Types of Mediated TransportersUniporter (I)Symporter (II)Antiporter (III)Allows transportation of one solute at a timeTransports solute and countertransported solute at the same time and in the same directionTransports the solute in one direction while the countertransported solute is moved the opposite direction in or out of the cell
Mechanism of transport. A molecule will bind to a transporter protein, altering its shape. The change of shape or other added substances such as ATP will, in turn, cause the transport protein to alter its shape and release the molecule onto the other side of the cell membrane.
Мутации в транспортных белках
Важность опосредованных транспортных белков становится очевидной при наличии мутаций, делающих эти белки нефункциональными. Наглядным примером служат мутации в гене Archain 1, кодирующем транспортные белки COPI и COPII. Основная функция этих белков – обеспечивать перенос молекул из эндоплазматической сети в аппарат Гольджи и обратно. Мутированный ген ARCN1 приводит к образованию аномального COPI, который не способен транспортировать коллаген I типа, что вызывает его секрецию. Поскольку коллаген I типа является основным компонентом соединительной ткани, подобные мутации становятся причиной множества тяжелых скелетных заболеваний, таких как несовершенный остеогенез и краниолентикулярный синдактильный дисплазия. Различные проявления этих заболеваний характеризуются видимой физической дисплазией. Этот пример подчеркивает важность транспортных белков не только для переноса определенных молекул через мембрану, но и для нормального развития организма.