Structure of Proteins: Primary and Secondary Levels
The word structure means different things at different levels of organisation in a protein. This quiz focuses on the first two of those levels.
- Primary structure — the amino acid sequence, read from the N-terminal amino acid to the C-terminal amino acid.
- Secondary structure — the local folded forms of the protein thread, including the helix (like a revolving staircase) and other folded arrangements.
A protein thread is not an extended rigid rod throughout, and in proteins only right-handed helices are observed. Work through the fifteen questions below to check how firmly you have grasped this terminology before moving on to tertiary and quaternary structure.
Q1. In the study of proteins, the primary structure refers to:
The primary structure of a protein is its amino acid sequence, as stated for an enzyme like any other protein.
Q2. The first amino acid of a polypeptide chain is called the:
The first amino acid is called the N-terminal amino acid; the last one is the C-terminal amino acid.
Q3. The last amino acid of a polypeptide chain is known as the:
The lesson states clearly that the last amino acid is called the C-terminal amino acid.
Q4. A protein thread, according to the lesson, does not exist throughout as:
The text states that a protein thread does not exist throughout as an extended rigid rod; it is folded.
Q5. The helix form of the protein thread is compared to:
The lesson compares the helix to a revolving staircase.
Q6. Regarding the helix in proteins, the lesson notes that:
In proteins, only right handed helices are observed.
Q7. Which statement about the helix in a protein is correct?
The lesson states that only some portions of the protein thread are arranged in the form of a helix.
Q8. Regions of the protein thread folded into forms other than the helix are said to belong to the:
Other regions folded into other forms are described as the secondary structure.
Q9. The secondary structure of a protein refers to:
Secondary structure covers the helix and the other folded forms adopted by regions of the thread.
Q10. The word structure, when applied to a protein, is best understood as:
Structure refers to the spatial arrangement of constituent parts at a defined level of organisation, which is why several levels exist.
Q11. The amino acid sequence of a protein is read directionally from:
The sequence is read directionally, beginning with the N-terminal amino acid and ending with the C-terminal amino acid.
Q12. An enzyme, like any protein, has a primary structure. This means the enzyme has:
The lesson states that an enzyme like any protein has a primary structure, i.e., the amino acid sequence of the protein.
Q13. Which of the following is NOT part of the secondary structure as described in the lesson?
The arrangement of separate subunits with respect to each other is the quaternary structure, not the secondary structure.
Q14. A learner claims that a protein thread is a straight, stiff rod from one end to the other. This claim is incorrect because:
The thread is not an extended rigid rod; some portions form a helix and other regions fold into other forms.
Q15. Which pair correctly matches the level of protein structure with its description?
Primary structure is the amino acid sequence, while secondary structure covers the helix and the other folded forms of the thread.