Biological molecules: Practice Questions

Which of the following describes the molecular difference between \(\alpha\)-glucose and \(\beta\)-glucose, and correctly identifies a polysaccharide formed from \(\beta\)-glucose?

A specific triglyceride is formed from one glycerol molecule and three molecules of the same fatty acid. If the fatty acid has the chemical formula \(C_{17}H_{33}COOH\), what is the correct molecular formula for the resulting triglyceride?

A researcher is studying a polypeptide consisting of 40 amino acids. During the formation of the specific tertiary structure of this protein, several different types of bonds are formed between R-groups. If the researcher successfully inhibits only the formation of disulfide bridges, which of the following amino acid properties would most likely be responsible for the loss of structural stability?

Which reagent is used in the biochemical test to identify the presence of starch?

A researcher is studying the formation of a phospholipid. Which of the following correctly describes the components and the bonds formed during the synthesis of one phospholipid molecule?

Name the chemical reagent used in the emulsion test to detect the presence of lipids in a sample, and state what positive result is observed.

Describe one structural difference between a triglyceride and a phospholipid, and explain how this difference affects the molecule's interaction with water.

Explain how the chemical structure of \(\beta\)-glucose leads to the specific arrangement of molecules in a cellulose fiber, and describe one structural feature of this fiber that contributes to its high tensile strength in plant cell walls.

A student carries out an investigation to identify the biological molecules present in a food sample.

(a) Name the reagent used to test for the presence of starch.

(b) State the colour change observed when this reagent reacts positively with starch.

Starch and cellulose are both plant polysaccharides composed of glucose monomers. Despite this similarity, their chemical structures and functions in plant cells are distinct.

(a) Compare the chemical structures of starch and cellulose. Your answer should include reference to the specific glucose isomers involved and the types of glycosidic bonds formed. (4 marks)

(b) Explain how the specific arrangement of molecules in a cellulose cell wall provides strength to the plant cell. (2 marks)

(c) A student tests a sample of starch using the iodine/potassium iodide solution and observes a blue-black color. They then boil a separate sample of the same starch with dilute hydrochloric acid, neutralize it, and perform a Benedict's test. Describe the expected result and explain why this occurs in terms of chemical bonds. (2 marks)