Biology · Chemistry

Biomolecules and Enzymes

1,432 Questions

This topic focuses on biomolecules, specifically proteins, enzymes, and amino acids. It includes questions on enzyme structures, protein folding, and catalysis. These concepts are crucial for medical and biology competitive exams.

Enzyme catalysisProtein structuresAmino acid synthesisPolypeptide chainsBiomolecule properties

Biomolecules and Enzymes Questions

Multiple choice

Which type of covalent bonds link the amino acids in a protein?

  1. Peptide bonds

  2. Hydrogen bonds

  3. Ionic bonds

  4. Glycosidic bonds
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A peptide bond is a chemical bond formed between two molecules when the carboxyl group of one molecule reacts with the amino group of the other molecule, releasing a molecule of water (H2O).

Multiple choice

What is the similarity between enzymes and hormones?

  1. They are similar with respect to their chemical composition.

  2. They are similar with respect to their molecular weight.

  3. They are similar with respect to the way they participate in a reaction.

  4. They are both effective in low concentration.
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

They are both effective in low concentration.

Multiple choice

Which of the following is/are examples of iron-sulphur proteins?

  1. Rubredoxin
  2. Methane monooxygenase
  3. Rieske proteins
  4. Aconitase

  1. Only 1 and 2

  2. Only 1, 2 and 3

  3. Only 1, 3 and 4

  4. Only 2 and 3

  5. Only 2, 3 and 4
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Yes, all are correct. Rubredoxin is a small iron-sulphur protein found in various sulphur-metabolising bacteria. Rieske proteins are iron-sulphur protein components of cytochrome bc1 complexes and cytochrome b6f complexes, which were first discovered and isolated by John S. Rieske and co-workers in 1964. Aconitase is an iron-sulphur protein that catalyses the interconversion of citrate and isocitrate

Multiple choice

In a β-adrenergic receptor signal-transduction pathway, to prevent the continuous activation of G-protein

  1. the intrinsic GTPase activity of the G-protein is enough

  2. the ability of the protein’s subunits to form heterotrimer is enough

  3. the phosphorylation of serine and threonine residues is enough

  4. both the intrinsic GTPase activity and dissociation of the ligand is necessary

  5. the binding of B-arrestin is enough
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

In the first step, the intrinsic GTPase activity of the G-protein inactivates the stimulatory G-alpha subunit of the enzyme by forcing it to bind with GDP. After GTP hydrolysis, the phosphate is released and the G-alpha subunit reassociates with the G-beta, gama to form the heterotrimeric protein. Now, the inactivated G-protein no more activates adenylate cyclase and stops cyclic AMP formation, but this will not terminate the continuous activation of G-protein unless the ligand is permanently removed from the receptor. Therefore, the next important step is the resetting of the hormone-bound activated receptor. This is achieved by two processes. The first step marks the removal of hormone, and the receptor goes back to the inactivated state. The next step involves the phosphorylation of the serine and threonine residues in the carboxyl-terminal of the hormone-receptor complex. The final step includes the binding of B-arrestin to the phosphorylated receptor. This finally reduces the G-protein-activating ability of the receptor completely. Thus, the continuous activation of the G-protein is prevented by the phosphorylation and binding of B-arrestin that desensitize the receptor after continuous exposure to epinephrine hormone.

Multiple choice

Which of the following statements is not true for the cell-surface protein kinases- linked receptors?

  1. Ligand binding stimulates the receptors.

  2. Kinases are part of the receptors or associated with the plasma membrane.

  3. All protein kinases linked receptors have intrinsic enzymatic activity.

  4. Animal cells contain two types of kinases.

  5. The activity of the kinases is opposed by the activity of phosphatases.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

This statement for the protein kinases-linked receptors is incorrect because the tyrosine kinases-linked receptors lack intrinsic catalytic activity. However, the binding of the ligand prompts the formation of a dimeric receptor, which then interacts with the cytosolic enzymes.

Multiple choice

Proteins which help other proteins to fold properly are called

  1. chaperones

  2. actins

  3. porins

  4. synthases
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Proteins which help other proteins to fold properly are called chaperones. Chaperones are proteins that assist the covalent folding or unfolding and the assembly or disassembly of other macromolecular structures.

Multiple choice

Not all proteins have a

  1. primary structure

  2. secondary structure

  3. tertiary structure

  4. quarternary structure
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

All proteins do not have a quarternary structure. Quaternary structure is the arrangement of multiple folded proteins or coiling protein molecules in a multi-subunit complex.

Multiple choice

A tripeptide contains

  1. 3 amino acids

  2. 4 amino acids

  3. 6 amino acids

  4. 2 amino acids
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

A tripeptide is a peptide consisting of three amino acids joined by peptide bonds.

Multiple choice

Which of the following is a set of essential amino acids?

  1. Alanine, aspartic acid, proline, serine

  2. Lysine, leucine, methionine, tryptophan

  3. Proline, methionine, serine, tryptophan

  4. Alanine, lysine, methionine, serine

  5. Aspartic acid, leucine, proline, tryptophan
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Lysine, leucine, methionine, tryptophan: All are essential amino acids.