The question asks about the number of essential amino acids required by humans. Amino acids are the building blocks of proteins. Essential amino acids are those that the human body cannot synthesize on its own and must obtain from the diet.
Therefore, the correct number of essential amino acids is 9.
Correct Option: D) 9
This question asks about the definition of the primary structure of a protein. Understanding the four levels of protein structure (primary, secondary, tertiary, and quaternary) is crucial for answering this question correctly.
Correct Option: A) Sequence of amino acids in the polypeptide chain
The primary structure of a protein is defined as the specific linear order or sequence in which amino acids are linked together to form a polypeptide chain. This sequence dictates all subsequent levels of protein folding and ultimately its function.
The question asks to identify the structural level of proteins to which \(\alpha\)-helix and \(\beta\)-pleated sheet belong. This requires understanding the four levels of protein structure: primary, secondary, tertiary, and quaternary.
Correct Option: C) Secondary structure — \(\alpha\)-helix and \(\beta\)-pleated sheet are the most common types of secondary structures in proteins, formed by hydrogen bonding within the polypeptide backbone.
The question asks to identify the amino acid that contains a sulfur-containing side chain capable of forming disulfide bonds. This requires knowledge of the chemical structures and properties of common amino acids, specifically their side chains (R-groups).
Cysteine is the only amino acid among the options that has a thiol group (-\(SH\)) in its side chain. Specifically, its side chain is \(-\text{CH}_2\text{SH}\). The hydrogen atom in the thiol group is relatively acidic and can be removed during an oxidation reaction, allowing two cysteine residues to form a disulfide bond (\(-\text{S-S}-\)) with the loss of two protons and two electrons. These disulfide bonds play a crucial role in stabilizing the tertiary and quaternary structures of proteins.
The question asks about the chemical nature of enzymes. To answer this, recall the basic biochemical composition of enzymes and other major biological macromolecules.
D) Proteins — Enzymes are primarily protein molecules. Their catalytic activity is due to their unique three-dimensional structure, which forms an active site where substrates bind and reactions occur.
The question asks to identify the scientist who coined the term 'enzyme' and the year it was introduced. This is a factual recall question related to the history of biochemistry.
The term 'enzyme' was coined by German physiologist Wilhelm Kühne in 1877. He derived the word from the Greek "enzymos" (meaning "in leaven" or "in yeast") to describe the non-living chemical agents responsible for fermentation, distinguishing them from the living organisms (like yeast) that produced them.
B) Wilhelm Kühne in 1877 is the correct answer. Wilhelm Kühne was the first to use the term "enzyme" in 1877 to describe these biological catalysts.