Question

How is glucose moved across the cell membrane against a concentration gradient? I did not get good notes on this during biochem today. I think it is to involve sodium-glucose transporter sorta thing? Thank you for your help, (I know this is bio related, but it is for biochem and at my uni it is more of a chem based class than bio)

Answer 1

Ans: Cell membrane composed of a specific structure which allow movement if ions across membrane and a special ability of semipermeability. This ability allow some molecules to pass the membrane while block the ithers. Membrane consist of phospholipid chains having phosphate head which is hydrophilic and lipd tails which are hydrophobic and these and arranged in bilayers with tails in between. These allow small ,non polar molecules to pass easily while block large and polar molecules .also these have trnasmembrane proteins embedded in between bilayer.

Glucose is transported across membrane in following ways:

1. Facilitated diffusion: This allow movement of ions in the case when they are blocked by bilayer. Trans membrane proteins then allow movement of ions in such cases. These proteins make a transport channel for glucose and allow it to pass interior although not using energy from cell but concentration gradient. For example GLUT4 channels.
2. Active transport: This is the mechanism where the molecule is moving against it's concentration gradient so needs energy. Example of this is a sodium potassium pump. Here energy is gained from ATP of cell by ATPase enzyme which hydrolizes and transport ions. This is also used to transport glucose across membrane during glucose starvation in body.
3. Secondary active transport: In this mechanism glucose is moved either with or against concentration gradient. In this energy is not got from the ATP molecules of the cell but sodium glucose symporter is used instead. Energy of sodium to move across membrane is used to move glucose as well. 1glucose molecule is moved with 2 sodium molecules across the membrane. In this case of SGLT2 transporter sodium which is major extracellular action and tend to move interior of cell along its concentration gradient takes 1glucose molecule along with then.