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Ch.26 Nucleic Acids and Protein Synthesis
Chapter 26, Problem 26.8

Write the complementary sequence of bases for each DNA strand shown next.


a. 5′T-A-T-A-C-T-G 3′

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1
Identify the direction of the given DNA strand, which is 5' to 3'.
Recall that DNA strands are complementary and antiparallel, meaning the complementary strand will run in the opposite direction, 3' to 5'.
Use the base pairing rules for DNA: Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G).
Write the complementary bases for each base in the given strand: T pairs with A, A pairs with T, C pairs with G, and G pairs with C.
Construct the complementary strand by writing the complementary bases in the 3' to 5' direction.

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Key Concepts

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

DNA Structure

DNA is composed of two strands forming a double helix, with each strand made up of nucleotides. Each nucleotide contains a phosphate group, a sugar, and a nitrogenous base. The four types of nitrogenous bases are adenine (A), thymine (T), cytosine (C), and guanine (G). The specific pairing of these bases (A with T and C with G) is crucial for the stability and replication of DNA.
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Complementary Base Pairing

Complementary base pairing refers to the specific pairing of nitrogenous bases in DNA. Adenine pairs with thymine (A-T), and cytosine pairs with guanine (C-G). This pairing is essential for the accurate replication of DNA, as each base on one strand dictates the corresponding base on the complementary strand, ensuring genetic information is preserved during cell division.
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5' and 3' Ends of DNA Strands

DNA strands have directionality, indicated by the 5' (five-prime) and 3' (three-prime) ends. The 5' end has a phosphate group attached, while the 3' end has a hydroxyl group. When determining complementary sequences, it is important to maintain this directionality, as the complementary strand must be synthesized in the opposite direction, from 3' to 5' relative to the original strand.
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