Nucleic Acid Structure, DNA Replication, and Repair

Vocabulary practice cards covering DNA and RNA structures, classic historical replication experiments, replication mechanics, end-replication problem solutions, and DNA repair pathways.

DNA Polymerase I Proofreading

The immediate checking of base pair sizes and correction of mismatched nucleotides performed by DNA polymerase I during replication.

Mismatch Repair

A post-replication DNA repair mechanism that detects and fixes base mismatches that escaped proofreading, utilizing methyl groups on the original DNA strand to distinguish it from the new strand.

Basic DNA Repair Strategy

A common multi-step pathway used by many DNA-repair processes consisting of removing damaged DNA, synthesizing replacement DNA with DNA polymerase, and sealing the backbone nick with ligase.

Sequencing-by-Synthesis

A DNA sequencing method that reads sequence information by detecting which specific fluorescent nucleotide is incorporated next during synthesis.

Griffith's Experiment

A late 1920s study on Streptococcus pneumoniae demonstrating that mixing heat-killed deadly smooth (S) bacteria with live non-deadly rough (R) bacteria transformed R into S, establishing that a chemical can transfer heritable traits.

Avery, MacLeod, and McCarty Experiment

An experiment that identified DNA as the transforming chemical by systematically destroying cellular biomolecules and demonstrating that transformation fails only when DNA is degraded.

Hershey-Chase Experiment

An experiment showing that viral genetic material is nucleic acid (DNA or RNA) rather than protein by demonstrating that viral phosphorus (DNA) enters host cells while viral sulfur (protein) remains outside.

DNA Double Helix Discovery

The 1953 determination of the 3D double-helical structure of DNA achieved by Watson, Crick, Wilkins, and Franklin using X-ray diffraction data and model building.

Antiparallel Strands

The structural arrangement of double-stranded DNA where two complementary strands run in opposite directional orientations ($5' \rightarrow 3'$ relative to $3' \rightarrow 5'$).

Semi-Conservative Replication Model

The mechanism of DNA replication in which the two strands of a parent DNA molecule separate, with each original strand acting as a template to form a new complementary daughter strand.

Meselson-Stahl Experiment

A late 1950s experiment that confirmed semi-conservative DNA replication by tracking heavy isotopic nitrogen ($^{15}\text{N}$) in DNA across generations, revealing a hybrid density band followed by a growing light band.

Okazaki Fragments

Short segments of newly synthesized DNA produced on the lagging strand because DNA polymerase can only extend strands in the $5' \rightarrow 3'$ direction.

Replication Origins

Specific DNA sequence locations where replication initiates; prokaryotic chromosomes typically feature one origin, while eukaryotic chromosomes utilize many.

DNA Helicase

An enzyme that unwinds and separates the parental double-stranded DNA into single strands ahead of the replication fork.

Primase

An RNA polymerase enzyme that synthesizes a short RNA primer to provide a free $3'$ end for DNA polymerase to begin synthesis.

DNA Polymerase III

The main replication enzyme that covalently attaches complementary nucleotides to the $3'$ end of an RNA primer during daughter strand elongation.

Telomerase

An enzyme that addresses the end-replication problem of linear chromosomes by maintaining telomere lengths; its activity extends replicative lifespan in somatic cells and is frequently reactivated in cancer cells.

DNA (Deoxyribonucleic Acid)

The double-stranded nucleic acid containing deoxyribose sugar and bases adenine, thymine, guanine, and cytosine ($\text{A}$, $\text{T}$, $\text{G}$, $\text{C}$) that stores cellular genetic material and remains inside the nucleus.

RNA (Ribonucleic Acid)

A typically single-stranded nucleic acid containing ribose sugar and bases adenine, uracil, guanine, and cytosine ($\text{A}$, $\text{U}$, $\text{G}$, $\text{C}$) that primarily functions in protein synthesis and can exit the nucleus.