Question

Which of the following is the true reason for the alpha-helix structure of proteins?
(a) The hydrogen bonds between a carbonyl group of one amino acid and the amino group of another
(b) The hydrogen bonds between variable groups
(c) The interactions between hydrophobic and hydrophilic variable groups
(d) The interactions between the positively and negatively charged variable groups
(e) All of the above

Answer 1

Hint: Proteins are large, complex molecules that play several important roles in the human body. They are essential for the structure, function, and regulation of the body's tissues and organs, and they do the majority of their work in cells.

Complete answer:
Proteins are made up of hundreds or thousands of smaller units known as amino acids that are linked in long chains. A protein is made up of 20 different types of amino acids that can be combined in various ways. The amino acid sequence determines the three-dimensional structure and function of each protein. Combinations of three DNA building blocks (nucleotides), determined by the sequence of genes.
A right-handed helix with a repeat length of 3.6 amino acid residues per helical turn makes up the helix, a common structural motif in proteins. Hydrogen bonds between amide hydrogen of one amino acid and a carbonyl oxygen four amino acids away stabilize the helix.
A hydrogen bond between the hydrogen atom attached to the electronegative nitrogen atom of a peptide linkage and the electronegative carbonyl oxygen atom of the fourth amino acid present on the amino-terminal side of that peptide bond stabilizes the alpha-helical structure of the protein. This results in all peptide bonds (except those near the helix's ends) being occupied in such a stabilizing hydrogen bonding.

Thus, the answer is option A: The hydrogen bonds between a carbonyl group of one amino acid and the amino group of another.

Note: Each protein has a distinct shape. These interactions may be disrupted if the temperature or pH of a protein's environment is changed, or if it is exposed to chemicals, causing the protein to lose its three-dimensional structure and revert to an unstructured string of amino acids. A protein is said to be denatured when it loses its higher-order structure but not its primary sequence.