Question

Complete the base sequence in a complementary DNA segment if a portion of the parent strand has each of the following base sequences: a. \(-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\mathrm{A}-\) b. \(-\mathrm{G}-\mathrm{G}-\mathrm{G}-\mathrm{G}-\mathrm{G}-\mathrm{G}-\) c. \(-\mathrm{A}-\mathrm{G}-\mathrm{T}-\mathrm{C}-\mathrm{C}-\mathrm{A}-\mathrm{G}-\mathrm{G}-\mathrm{T}-\) d. \(-\mathrm{C}-\mathrm{T}-\mathrm{G}-\mathrm{T}-\mathrm{A}-\mathrm{T}-\mathrm{A}-\mathrm{C}-\mathrm{G}-\mathrm{T}-\mathrm{T}-\mathrm{A}-\)

Short answer

Complementary sequences are: a) -T-T-T-T-T-T-, b) -C-C-C-C-C-C-, c) -T-C-A-G-G-T-C-C-A-, d) -G-A-C-A-T-A-T-G-C-A-A-T-

Step-by-step solution

Understand DNA Base Pairing Rules

In DNA, adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C). Use these pairing rules to determine the complementary sequence.

Complementary Sequence for Part a

Given: -A-A-A-A-A-A- According to the pairing rules, each adenine (A) pairs with a thymine (T). Therefore, the complementary sequence is: -T-T-T-T-T-T-

Complementary Sequence for Part b

Given: -G-G-G-G-G-G- According to the pairing rules, each guanine (G) pairs with a cytosine (C). Therefore, the complementary sequence is: -C-C-C-C-C-C-

Complementary Sequence for Part c

Given: -A-G-T-C-C-A-G-G-T- According to the pairing rules, the complementary sequence is: -T-C-A-G-G-T-C-C-A-

Complementary Sequence for Part d

Given: -C-T-G-T-A-T-A-C-G-T-T-A- According to the pairing rules, the complementary sequence is: -G-A-C-A-T-A-T-G-C-A-A-T-

Key concepts

complementary DNA sequences

DNA is a remarkable molecule that carries the genetic information of all living organisms. The structure of DNA is made up of two long strands that coil around each other to form a double helix. Each strand consists of units called nucleotides. These strands are complementary, meaning that each nucleotide on one strand pairs with a corresponding nucleotide on the other strand, following specific pairing rules.
Complementary DNA sequences are crucial in the process of DNA replication and repair. When DNA replicates, each original strand serves as a template for a new complementary strand. This ensures that the genetic information is accurately passed on.
Understanding how to determine complementary sequences is straightforward. According to the base pairing rules:

• Adenine (A) always pairs with Thymine (T)
• Guanine (G) always pairs with Cytosine (C)

For example, if you have a DNA strand with the sequence -A-G-T-C-, the complementary strand would be -T-C-A-G-.

nucleotide base pairs

Nucleotide base pairs are the building blocks of DNA. Each nucleotide consists of three components:

• A phosphate group
• A sugar molecule (deoxyribose in DNA)
• A nitrogenous base

There are four types of nitrogenous bases in DNA: adenine (A), thymine (T), guanine (G), and cytosine (C). The bases pair specifically, with A pairing with T, and G pairing with C. These specific pairs are known as complementary base pairs.
The pairs are held together by hydrogen bonds, which are strong enough to hold the strands together but weak enough to allow them to separate during DNA replication. This precise pairing mechanism enables DNA to store genetic code efficiently and helps in error-checking and repair mechanisms within cells.
When looking at parts (a) and (b) of the exercise:

• -A-A-A...- pairs with -T-T-T...-
• -G-G-G...- pairs with -C-C-C...-

This follows the rule that A pairs with T and G pairs with C.

DNA replication

DNA replication is the process by which a DNA molecule makes a copy of itself. This is essential for cell division and for passing on genetic information from one generation to the next. The replication process ensures that each new cell has an exact copy of the DNA.
The process of DNA replication can be broken down into several steps:

• Initiation: The DNA double helix unwinds, and the two strands separate to form a replication fork.
• Elongation: Each original strand serves as a template for a new complementary strand. DNA polymerase, an enzyme, adds new nucleotide bases to the growing strand, ensuring that A pairs with T and G pairs with C.
• Termination: Once the entire molecule has been replicated, the replication process ends, resulting in two identical DNA molecules.

In parts (c) and (d) of the exercise:

• The sequence -A-G-T-C-C-A-G-G-T- would pair with -T-C-A-G-G-T-C-C-A-
• The sequence -C-T-G-T-A-T-A-C-G-T-T-A- would pair with -G-A-C-A-T-A-T-G-C-A-A-T-

This complementary pairing is crucial for the fidelity of DNA replication, ensuring that all genetic information is accurately copied.