Molecules of life: Practice Questions

Which of the following classes of biomolecules serves as the primary and immediate source of energy for most living cells?

A student performed several food tests on a liquid extract from a bean seed and recorded the following results:
(1) Benedict's test: The mixture remained blue after boiling.
(2) Iodine test: The mixture turned blue-black.
(3) Grease spot test: No permanent translucent spot was observed on the filter paper.

Which of the following molecules are present in the extract based on these observations?

The primary structure of a small, soluble globular protein dictates its functional three-dimensional shape. This shape is critically dependent on the hydrophobic effect, which drives the burial of non-polar amino acid side chains away from the surrounding aqueous environment, forming a stable core.

Suppose a mutation occurs in the gene encoding this protein, resulting in the substitution of an internal, non-polar amino acid (Leucine) with a highly polar, charged amino acid (Glutamate) at a position crucial for core stability.

What is the MOST severe and immediate consequence of this substitution on the protein's overall structure and function?

A student is provided with an unknown solution and performs a series of biochemical tests. The observations are recorded below:

1. Biuret test: The solution turns purple.
2. Iodine test: The solution remains yellow-brown.
3. Benedict's test: After heating, the solution remains blue.

A second sample of the same unknown solution is first boiled with dilute hydrochloric acid, then neutralized with sodium hydrogencarbonate. When the Benedict's test is repeated on this treated sample, a brick-red precipitate is formed. Which of the following combinations of biomolecules was present in the original solution?

An unknown organic molecule consists of carbon, hydrogen, and oxygen, where the ratio of hydrogen atoms to oxygen atoms is significantly higher than \(2:1\). Which of the following descriptions about this molecule are correct?

(1) It releases more energy than an equal mass of glycogen when completely oxidized.
(2) It can be detected by the presence of a permanent translucent spot on filter paper.
(3) It is the primary component of the middle lamella in plant tissues.
(4) Its building blocks are linked by peptide bonds.

Triglycerides are a major class of lipids that function primarily as energy storage molecules in the body. What are the two types of smaller molecules that combine chemically to form a single triglyceride molecule?

Explain why nitrogen is an essential element for both the transmission of genetic information and the catalysis of metabolic reactions in a cell.

Magnesium ions (\(Mg^{2+}\)) are crucial for various cellular processes. Explain their role as a cofactor for enzymes, specifically detailing how they facilitate the activity of ATPases or DNA polymerase during nucleic acid metabolism or energy transfer.

Biochemical tests are fundamental tools used in biology to identify various molecules found in living tissues.

(a) If a food sample contains starch, state the color change that will be observed when iodine solution is added to it. (1 mark)

(b) In the Benedict's test for reducing sugars, what is an essential procedure that must be performed after mixing the sample with the reagent to observe a result? (1 mark)

(c) Which class of biomolecules is specifically identified using the grease spot test? (1 mark)

(d) State the basic building blocks of the biomolecule class identified in part (c). (1 mark)

Biomolecules and inorganic ions are fundamental to the maintenance of life, each serving specific structural and functional roles. Provide detailed explanations for the following:

(a) Magnesium (\(Mg^{2+}\)) and Iron (\(Fe^{2+}\)) are essential inorganic ions. For each ion, name one specific complex biomolecule it is incorporated into and explain the functional consequence for an organism if that specific ion is deficient. (2 marks)

(b) Phospholipids and triglycerides are two types of lipids with different structures. Describe one structural difference between them and explain how this difference relates to their distinct biological functions in a cell. (3 marks)

(c) Proteins are polymers of amino acids. Explain how the chemical properties of R-groups and the formation of hydrogen bonds contribute to the specific three-dimensional shape of a functional protein. (2 marks)