Strands in the stem of stem-loop RNA structures are parallel.
True
False
The correct answer and explanation is :
False.
In a stem-loop RNA structure, the strands in the stem are antiparallel, not parallel. This means that the two strands run in opposite directions in terms of their 5′ to 3′ polarity.
Explanation:
- Structure of a Stem-Loop:
A stem-loop (or hairpin) is a common secondary structure in RNA molecules. It consists of a double-stranded stem formed by complementary base pairing and a single-stranded loop that connects the two ends of the stem. - Antiparallel Orientation:
- RNA, like DNA, has a directional backbone composed of ribose sugars and phosphate groups. The strands are oriented from 5′ (phosphate end) to 3′ (hydroxyl end).
- In the stem of a stem-loop, complementary base pairing occurs through Watson-Crick interactions (A-U and G-C in RNA).
- For base pairing to happen effectively, one strand must be in the 5′ to 3′ direction, while the complementary strand must run in the 3′ to 5′ direction.
- Comparison with DNA:
- Similar to the antiparallel nature of double-stranded DNA, the RNA stem in a stem-loop adopts the same principle to maintain stable base pairing.
- If the strands were parallel (both running 5′ to 3′ in the same direction), proper hydrogen bonding between bases would not occur, leading to an unstable structure.
- Functional Importance:
Stem-loop structures are crucial for RNA stability, regulation of gene expression, and interactions with proteins. Their antiparallel nature ensures strong and stable base pairing, which is necessary for these biological roles.
Thus, the correct answer is False because the strands in the stem of a stem-loop RNA structure are antiparallel, not parallel.