evelync12
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i don't understand the co-transport mechanism for glucose and sodium :/

Glucose moves in with sodium (into epithelial cell);
Via (carrier / channel) protein / symport;
5 max
Sodium removed (from epithelial cell) by active transport / sodium- potassium pump;
Into blood;
Maintaining low concentration of sodium (in epithelial cell) / maintaining sodium concentration gradient (between lumen and epithelial cell);
Glucose moves into blood; By (facilitated) diffusion;

pls explain
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bsharp984
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Co-transport is a type of transport across cell membrane and it requires transport proteins embedded in the membrane of the cell. The best way to explain how this process works is to exemplify it. Good example is the absorption of glucose by epithelial cells in the gut.

In the gut, glucose is co-transported with sodium ions. There are three transport proteins involved in the whole process of absorption of glucose. One of these is a pump that sits in the membrane adjacent to the capillary (on the other side from the gut lumen) and actively transports sodium ions out of the cell using ATP. This creates a concentration gradient for sodium ions (Na+) to be able to diffuse from the lumen into the cell.

Second transport protein involved is Na+/glucose pump that pumps sodium with glucose into the cell. Since there is concentration gradient for sodium ions, they will bind to the pump with glucose and be diffused into the cell taking glucose with them. This allows transport of glucose into the cell (even against its concentration gradient) and creates concentration gradient for glucose between the inside of the cell and the capillary. Therefore glucose can be moved by facilitated diffusion using the third transport protein out of the cell and into the capillary.

Co-transport can occur also with different molecules and in different locations but the principle is basically the same. A molecule is essentially transported against its concentration gradient when its driven with an ion which can diffuse down its concentration gradient through a specific transport protein. This is allowed by active pumping of that ion out of the cell. (If I was to teach this to a student, I would use mainly diagrams to explain this process to allow him/her to be able to visualize it.)
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evelync12
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(Original post by bsharp984)
Co-transport is a type of transport across cell membrane and it requires transport proteins embedded in the membrane of the cell. The best way to explain how this process works is to exemplify it. Good example is the absorption of glucose by epithelial cells in the gut.

In the gut, glucose is co-transported with sodium ions. There are three transport proteins involved in the whole process of absorption of glucose. One of these is a pump that sits in the membrane adjacent to the capillary (on the other side from the gut lumen) and actively transports sodium ions out of the cell using ATP. This creates a concentration gradient for sodium ions (Na+) to be able to diffuse from the lumen into the cell.

Second transport protein involved is Na+/glucose pump that pumps sodium with glucose into the cell. Since there is concentration gradient for sodium ions, they will bind to the pump with glucose and be diffused into the cell taking glucose with them. This allows transport of glucose into the cell (even against its concentration gradient) and creates concentration gradient for glucose between the inside of the cell and the capillary. Therefore glucose can be moved by facilitated diffusion using the third transport protein out of the cell and into the capillary.

Co-transport can occur also with different molecules and in different locations but the principle is basically the same. A molecule is essentially transported against its concentration gradient when its driven with an ion which can diffuse down its concentration gradient through a specific transport protein. This is allowed by active pumping of that ion out of the cell. (If I was to teach this to a student, I would use mainly diagrams to explain this process to allow him/her to be able to visualize it.)
thank you this made me understand now
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bsharp984
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Glad I could help!
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