Chapter 14: DNA Structure and Replication

Vocabulary flashcards covering the chemical structure of DNA, historical discoveries, replication mechanics, and enzymatic DNA repair pathways from Chapter 14.

Pyrimidines

A class of single-ring nitrogenous bases found in nucleic acids, consisting of cytosine (C), thymine (T) in DNA, and uracil (U) in RNA.

Purines

A class of double-ring nitrogenous bases found in nucleic acids, consisting of adenine (A) and guanine (G).

Nucleoside

A structural subunit of nucleic acids consisting of a nitrogenous base covalently linked to a pentose sugar (ribose or deoxyribose) via a glycosidic bond, lacking phosphate groups.

Chargaff's Rule

A rule established by Erwin Chargaff (1950) stating that in DNA, purines always equal pyrimidines ($A + G = T + C$), where the amount of adenine equals thymine ($A = T$) and guanine equals cytosine ($G = C$).

Double Helix

The molecular structure of DNA proposed by Watson and Crick (1953), characterized as a right-handed, double-stranded spiral of uniform diameter with a sugar-phosphate backbone and bases facing inward.

Antiparallel

The opposite directional orientation of the two strands in a DNA duplex, where one strand runs from the $5'$ end to the $3'$ end and the complementary strand runs from the $3'$ end to the $5'$ end.

$5'$ End and $3'$ End

The chemical designations for the termini of a nucleic acid strand, where the $5'$ end terminates with a phosphate group ($\text{OPO}_3^{-}$) and the $3'$ end terminates with a free hydroxyl group ($\text{OH}^{-}$).

Complementary Base Pairing

The specific hydrogen bonding between nitrogenous base pairs within the DNA helix, specifically two hydrogen bonds between adenine and thymine (A-T) and three hydrogen bonds between guanine and cytosine (G-C).

Kornberg Requirements for DNA Synthesis

The three components demonstrated by Arthur Kornberg as necessary and sufficient to synthesize DNA: substrates (deoxyribonucleoside triphosphates), an enzyme (DNA polymerase), and a DNA template.

Semiconservative Replication

The mechanism of DNA duplication demonstrated by Meselson and Stahl (1957), in which parental strands separate to serve as templates for new complementary strands, yielding daughter duplexes composed of one original and one newly synthesized strand.

DNA Polymerase

The replication enzyme that synthesizes a new DNA strand by covalently attaching complementary deoxynucleotides to the free $3'$ hydroxyl end of an existing chain, releasing pyrophosphate.

Primase

An enzyme that binds to the single-stranded DNA template and synthesizes a short RNA primer to initiate synthesis by DNA polymerase.

RNA Primer

A short sequence of RNA synthesized by primase that provides the initial $3'$ hydroxyl group required by DNA polymerase to begin polymerization, which is subsequently degraded and replaced with DNA.

Leading Strand

The newly replicated strand of DNA that is synthesized continuously in the $5' \rightarrow 3'$ direction toward the unwinding replication fork.

Lagging Strand

The newly replicated DNA strand synthesized discontinuously in the $5' \rightarrow 3'$ direction away from the replication fork, producing separate segments known as Okazaki fragments.

Okazaki Fragments

Short discontinuous stretches of DNA synthesized on the lagging strand during DNA replication, which require individual RNA primers.

Telomeres

Repetitive, non-coding sequences situated at the ends of eukaryotic linear chromosomes that require specialized replication machinery to prevent progressive chromosome shortening.

Telomerase

A ribonucleoprotein enzyme carrying an integral RNA template that elongates the $3'$ overhang of eukaryotic chromosome ends, allowing the lagging strand replication machinery to complete replication.

Proofreading

An immediate error-correcting activity carried out by DNA polymerase during replication, where improperly paired nucleotides are recognized, cleaved, and replaced from the growing $3'$ end.

Mismatch Repair

A post-replication surveillance mechanism that scans newly synthesized DNA strands to detect, excise, and replace mismatched base pairs that escaped initial proofreading by DNA polymerase.