About sucrose and cell membrane.?

Question

I wonder to know why maltose can pass through the selectively permeable cell membrane but not sucrose. Although they are both disaccharides, having the same molecular fomular of C12H22O11

no..... they have the same chemical formula.... shouldn't they have the same size???????????????????????

Answer 1

Maltose and sucrose have to pass through specific carrier or symport proteins. If a cell lacks a sucrose transporter, it will not pass sucrose across the membrane.

Answer 2

They don't have the same formula actually. Sucrose has eleven carbons, maltose has twelve. Sucrose is made of fructose, a five-carbon monosaccharide, and glucose, a six-carbon monosaccharide, where maltose is made of two glucoses. Lactose, which is made of Glucose and Galactose, and MAltose however, each have the same formula, but are different because the shape of the molecule s are different. The one difference between them is that one has a Glucose and the other a galactose. The one difference between a glucose and a galactose is that in galactose there is an OH group bonded to a carbon on the inside of the ring. Because there is a hydroxide group on the inside of the galactose ring, which is very polar, it pulls at other molecules in the ring. In glucose, the OH group is on the outside, so it doesn't pull the other molecules as much since it's farther away. This makes the shapes of Lactose and Maltose different, which means the transmembrane proteins they need to go through to get into the membrane proteins must be different to accomodate different shapes. Remember that proteins are VERY specific as to what molecules they affect. So a selectively permeable membrane that will allow maltose will not allow lactose nor sucrose.

Answer 3

it depends on the shape and size of the molecules. smaller molecules, easier to pass through the membrane.