AS AQA BIO Unit 1: Starch and carbohydrates

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Preview of AS AQA BIO Unit 1: Starch and carbohydrates

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Starch
Starch is made of amylase and amylo-pectin. Starch is formed by the linking of many Alpha-glucose
molecules through condensation. It is therefore a polysaccharide. To test for starch, you add iodine
solution to it. If it turns black, starch is present.
Amylase
Amylase is a long chain of alpha-glucose molecules, linked by glycosidic bonds. They coil into a spiral
which is held in place by h bonds.
Amylo-pectin
Amylo-pectin is also a polymer of alpha-glucose, except the molecules are branched. Glycogon is
similar to amylo-pectin in structure; it is the storage poly-saccharide in animals.
How is starch digested?
The glucose used in respiration comes from the carbohydrates that we eat. Starch is too large to be
absorbed in the intestine, therefore is must be digested, first to maltose, then to glucose. Amylase
and maltase are used in the breaking down of starch. Maltose is a disaccharide.
Disaccharides that need to be learned
Alpha glucose + Alpha glucose = Maltose
Alpha glucose + Fructose = Sucrose
Alpha glucose + Galactose = Lactose
Reducing sugars
When reducing sugars are heated with Benedict's solution, a brick-red precipitate is formed. This is
because Cu(II) is reduced to Cu(I). This is because they have an aldehyde group.

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