Overview of Carbohydrate Metabolism


Carbohydrates or sugars contain a number of chiral carbons so have many possible stereoisomers.

All of the sugars in the body are found cyclized, as pyranose or furanose rings.

Glucose forms a pyranose ring when the electron rich oxygen on carbon #5 is attracted to the delta positively charged aldehyde carbon (carbon #1).

When glucose forms a ring the original aldehyde carbon becomes chiral and is labeled the anomeric carbon, usually designated with a *.

The hydroxyl group attached to the new chiral carbon has a 50% chance of being above the plane of the ring or beta and a 50% chance of being below the plane of the ring or alpha.

In a disaccharide, two monosaccharides attached by a glycosidic bond, will contain two anomeric carbons from the original two monosaccharides.

If one of these anomeric carbons is not attached to anything, i.e. another sugar, a phosphate group etc, the sugar is said to be “a reducing sugar”. This means the free oxygen attached to the anomeric carbon is capable of reducing a metal.


Glucose Transport:

When you consume sugars it causes your blood sugar level to rise, this signals the pancreas to release a hormone called insulin.

The insulin binds to most cells and allows them to transport and use the sugar in your blood as a fuel.

There are three cell types (organs) in your body that can immediately, without waiting for insulin to be released (Insulin Insensitive), use blood sugar: brain, red blood cells and liver.

All of your other cells must wait for insulin to be released before they can utilize the glucose in your blood.


Pathways of the Carbohydrate System:

It is important that you know the names of the pathways and what each pathway does.

Overviews of Glucose Metabolism in Selected Tissues:

None of this material will be on Exam 3.

Notice how simple red blood cells are with relatively few pathways as compared to the liver.

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