Monday
April 21, 2014

Homework Help: carbon+sugar=starch

Posted by DrJeff on Saturday, August 27, 2005 at 9:40am.

Why are you saying that carbon is needed to make starch? Actually only sugar (glucose) is needed along with an enzyme to catalyze the linkage of multiple glucose units in a dehydration (loss of water) reaction.

Glucose + Glucose ----> maltose + H2O

maltose is disaccharide.

maltose + glucose ----> maltotriose + H2O

maltotriose is a trisaccharide (has three sugars hooked together)

This keeps going on and on with four sugars, five sugars, six sugars... until there are hundreds of glucose units hooked together. Then one has starch.




Im confused! heres the exact question the teacher asked.

Describe how sugars combine to form starch. Carbon seems to be an essential componet of sugar and sugars combine to form starch. How does that happen? You may use illustrations to answer this question. Do not go into great detail. A brief summary of the process will suffice.

Do you think you can help? thanks


The formula for glucose is C6H12O6.

The carbon is a component of the glucose molecule. Carbon, per se, is not used to form starch. Actually, one could argue that hydrogen and oxygen and are essential components too. The formula for maltose is C12H22O11. As explained previously, two glucose units are combined to form

C6H12O6 + C6H12O6 ----> C12H22O11 + H2O

C12H22O11 = maltose.

If you add up all the carbons, hydrogens, and oxygens on both sides of the reaction above, they will total 12 carbons, 24 hydrogens, and 12 oxygens.

Now, if another glucose is combined with maltose, maltotriose is obtained.

C12H22O11 + C6H12O6 ----> C18H32O16 + H2O

Do a Google search on the phrase "Three common sugars share the same molecular formula" and click on the first link. Look at the section on polysaccharides.

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