Back to Basics - Food Molecules Quiz

Answer: Monosaccarides

All three (glucose, fructose and galactose) contain 6 oxygen atoms, 6 carbon atoms and 12 hydrogen atoms. However, all are arranged differently and have different shapes.
All three are soluble in water.

Answer: Condensation reaction

In a condensation reaction, water is removed and a peptide bond forms between the amino group of one amino acid and the carboxyl group of another.
It is the order of amino acids which determines the structure and function of the protein.
Carbohydrates and triglycerides also arise from the joining of molecules via condensation reactions.

Answer: At least one C=C double bond

If a fat/lipid contains at least on C=C double bond, it is classified as an unsaturated fat, and will usually be liquid at room temperature.
Triglyceride molecules consist of one molecule of glycerol bonded to three fatty acids by ester bonds. Each fatty acid contains an "R" group which is a hydrocarbon chain which determines whether the fat is saturated or unsaturated.

Answer: Protein

Biuret's solution typically consists of equal amounts of sample and sodium hydroxide with 5 drops of copper sulphate solution.

When testing for a fat the emulsion test is carried out. The sample is dissolved in ethanol and if the solution becomes cloudy when added to water a fat is present.

Benedict's test will show a brick red precipitate in the presence of a reducing sugar (glucose, fructose, galactose, maltose or lactose).
Iodine is used to test for the presence of starch which turns the iodine black/blue.

Answer: Protein

Endopeptidase is one of the three main enzymes which catalyse the breakdown of proteins into amino acids. Endopeptidase is produced in the stomach and the pancreas and breaks long chain polypeptides into shorter chains.

The clue is in the name endoPEPTIDase as it is peptide bonds which join amino acids together.

Answer: Fatty acids and glycerol

Fats are churned and heated in the stomach, emulsified by bile secreted by the gall bladder and then broken down by lipase secreted by the pancreas.

After forming chylomicrons they diffuse into a lacteal and are transported to the subclavian vein.

Answer: Fats

It is well known that respiration typically involves the oxidation of glucose, however when glucose is in short supply triglyceride molecules can be broken down. These yield about three times more energy than glucose.

Answer: Cellulose

Glycogen and starch are both made from alpha-glucose molecules.
The difference between alpha and beta-glucose molecules is small but significant. The -H and -OH groups in a beta-glucose molecule swap positions relative to in an alpha-glucose molecule.

Answer: Loss of one fatty acid and gain of one inorganic phosphate group

Although the "phosphate head" of a phospholipid is water soluble (hydrophilic) the "fatty acid tail" is insoluble (hydrophobic) and so the phospholipid bilayer provides a barrier to polar, water soluble molecules.

Although water molecules are polar, they are small enough to slip between phospholipids and so enter the cell.

Answer: Hydrogen bonds

Disulphide bridges, ionic bonds and Van der Waals' forces also keep the enzyme in its shape.

The reason enzyme shape is so important is because each enzyme has a complimentary shape to a particular substrate.

Hydrogen bonds are also the bonds between water molecules and are what keep two strands of DNA together.