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Ch.11 Nucleic Acids Big Molecules with a Big Role
Frost - General, Organic and Biological Chemistry 4th Edition
Frost4th EditionGeneral, Organic and Biological ChemistryISBN: 9780134988696Not the one you use?Change textbook
Chapter 7, Problem 15

Describe the orientation of antiparallel strands in DNA. Use the terms 3' and 5' in your description.

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DNA is composed of two strands that form a double helix structure.
Each strand of DNA has a directionality, which is determined by the orientation of the sugar-phosphate backbone.
The ends of each DNA strand are referred to as 3' (three prime) and 5' (five prime), based on the carbon numbers in the sugar molecule of the nucleotide.
In an antiparallel arrangement, one strand runs in the 5' to 3' direction, while the complementary strand runs in the 3' to 5' direction.
This antiparallel orientation is crucial for the complementary base pairing and the overall stability of the DNA double helix.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Antiparallel Strands

In DNA, the two strands run in opposite directions, a configuration known as antiparallel. This means that one strand runs from the 5' end to the 3' end, while the complementary strand runs from the 3' end to the 5' end. This orientation is crucial for the base pairing and the overall stability of the DNA double helix.
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5' and 3' Ends

The terms 5' (five prime) and 3' (three prime) refer to the carbon numbers in the DNA's sugar backbone. The 5' end has a phosphate group attached to the fifth carbon of the sugar, while the 3' end has a hydroxyl group attached to the third carbon. This directional notation is essential for understanding DNA replication and transcription processes.
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Base Pairing

Base pairing refers to the specific hydrogen bonding between nitrogenous bases in DNA, where adenine pairs with thymine (A-T) and cytosine pairs with guanine (C-G). This pairing occurs between the antiparallel strands, allowing for the complementary nature of the DNA structure. The orientation of the strands is vital for accurate base pairing and the integrity of genetic information.
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