Digestion of Carbohydrates Flashcards
What are carbohydrates made from?
They are polymers. The monomers that they’re made from are monosaccharides ( glucose, fructose and galactose )
What kind of sugar is glucose and explain why.
A hexose sugar. Because there are six carbon atoms per molecule.
Draw the structure of an alpha glucose molecule
( the molecule should be a cyclo molecule with the H’s on the two side carbons facing up with the OH’s facing Dow .
How are the monosaccharides joined together?
Via a condensation reaction with another monosaccharide. Just like with polypeptide formation except the bond being made is a glycosidic bond. The H from the right hand side of the molecule breaks off and bonds with the OH from the left side of another molecule leaving only an oxygen atom.
How are polysaccharides and disaccharides digested by the intestinal epithelium cells?
A hydrolysis reaction occurs where a molecule of water breaks the glycosidic bond reducing a poly/disaccharide into a monosaccharide which is small enough to be absorbed by the epithelial cells.
Name the three main disaccharides and the two monomers that form them.
Maltose = glucose + glucose Sucrose = glucose + fructose Lactose = glucose + galactose
What are the enzymes that hydrolyse the main disaccharides
Maltose = Maltase Sucrose = Sucrase Lactose = Lactase
What is lactose intolerance?
Lactose is broken down by the enzyme lactase. If you don’t produce enough lactase the lactose won’t get broken down. This undigested lactose is fermented by bacteria me can cause stomach cramps, excessive flatulence and diarrhoea. The lactose can change the water potential in your intestines cause water to diffuse by osmosis into your intestines.
Describe what the Benedicts test is and what it is used for.
The benedicts test is used for detecting the presence of reducing sugars. Reducing sugars include all monosaccharides and some disaccharides. You start by adding benedicts reagent to a sample and gently heat it using a water bath at about 60 degrees. If a reducing sugar is present then a brick red precipitate will form.
Give an example of a non reducing sugar and explain how you would a. Know if it is non reducing and b. Carry out the benedicts test.
Sucrose. Heat another sample to 60 degrees in a water bath with Benedicts reagent. If it stays blue then you have a non reducing sugar. This time boil a new sample ( the non reducing sugar sample ) with hydrochloric acid then neutralise with am weak alkaline like sodium hydrogencarbonate. Add the benedicts reagent and the solution should produce a brick red precipitate.
Explain why you add hydrochloric acid to test for non reducing sugars in the benedicts test.
Hydrochloride acid will break down the glycosidic bonds in the disaccharide turning it into two monosaccharides which are reducing sugars.
What two polysaccharides is starch made from?
Amylopectin and amylose
How is starch digested?
First the starch is broken down into maltose by amylase. Amylase is produced by salivary glands and the pancreas. Maltose is then hydrolysed by the enzyme maltase into alpha glucose molecules.
Describe the iodine test for starch.
Add iodine solution ( or a solution containing iodide ions ) to the sample you are testing. If the sample turns dark blue, black then starch is present. If it remains brown then there is no starch present.
