DNA Structure and Replication

Vocabulary flashcards covering key terms related to DNA structure and replication.

Nucleic Acid

A polymer of nucleotides; DNA or RNA.

Nucleotide

The monomer of nucleic acids, consisting of a deoxyribose sugar, a phosphate group, and a nitrogenous base.

Deoxyribose

Five-carbon sugar lacking a 2′-hydroxyl group; the sugar component of DNA nucleotides.

Ribose

Five-carbon sugar containing a 2′-hydroxyl group; found in RNA nucleotides.

Nitrogenous Base

Nitrogen-containing ring structure in a nucleotide; adenine, thymine, guanine, or cytosine in DNA.

Purine

Double-ring nitrogenous base category; includes adenine (A) and guanine (G).

Pyrimidine

Single-ring nitrogenous base category; includes cytosine (C) and thymine (T).

Phosphodiester Bond

Covalent linkage connecting the 3′-OH of one nucleotide to the 5′-phosphate of the next.

Sugar-Phosphate Backbone

Repeating chain of deoxyribose sugars and phosphates forming the exterior of a DNA strand.

5′ End

The beginning of a nucleic acid strand with a free phosphate attached to the 5′ carbon.

3′ End

The terminus of a nucleic acid strand with a free hydroxyl on the 3′ carbon.

Antiparallel

Describes DNA strands running in opposite 5′→3′ directions within the double helix.

Complementary Base Pairing

Specific hydrogen bonding in DNA where A pairs with T and C pairs with G.

Hydrogen Bond

Weak interaction that holds complementary nitrogenous bases together in DNA.

Double Helix

The twisted-ladder, two-strand 3-D structure of DNA elucidated by Watson and Crick.

Semiconservative Replication

DNA replication model in which each daughter molecule contains one parental strand and one newly synthesized strand.

Origin of Replication

Specific DNA sequence where replication begins.

Replication Fork

Y-shaped region where parental strands separate and new strands are synthesized.

DNA Polymerase

Enzyme that adds nucleotides to a growing DNA strand in the 5′→3′ direction and proofreads for errors.

Helicase

Enzyme that unwinds the DNA double helix by breaking hydrogen bonds between bases.

Gyrase

Bacterial topoisomerase that relieves supercoiling ahead of the replication fork.

Topoisomerase

Class of enzymes that alter DNA supercoiling to reduce torsional strain.

Ligase

Enzyme that seals nicks in the sugar-phosphate backbone, joining DNA fragments.

Leading Strand

DNA strand synthesized continuously toward the replication fork.

Lagging Strand

DNA strand synthesized discontinuously away from the fork in short fragments.

Nucleoside Triphosphate

Free nucleotide with three phosphates that provides both the building block and energy for DNA synthesis.

Mutation

Permanent change in DNA sequence that escapes repair.

Proofreading

DNA polymerase function that excises and corrects misincorporated bases to ensure high fidelity.