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A set of key vocabulary flashcards covering major terms and concepts from Campbell Biology Chapter 16 on the molecular basis of inheritance.
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DNA (Deoxyribonucleic Acid)
The hereditary material in all cells, consisting of a double-stranded helix of nucleotides that encodes genetic information.
Double Helix
The two-stranded, right-handed helical structure of DNA proposed by Watson and Crick in 1953.
DNA Replication
The process of copying DNA before cell division, producing two identical DNA molecules from one parent molecule.
Transformation (Griffith)
Heritable change in genotype/phenotype due to assimilation of foreign DNA by a cell.
Bacteriophage (Phage)
A virus that infects bacteria; key tool in molecular genetics (e.g., Hershey-Chase experiment).
Hershey-Chase Experiment
1952 study showing that DNA, not protein, enters bacteria during phage infection—proving DNA is the genetic material.
Chargaff’s Rules
In any DNA sample, A = T and G = C; base composition varies between species.
X-ray Crystallography
Technique used by Rosalind Franklin to photograph DNA, revealing its helical structure.
Antiparallel
Orientation of DNA strands running in opposite 5′ → 3′ directions.
Nucleotide
DNA monomer composed of a nitrogenous base, deoxyribose sugar, and phosphate group.
Purine
Double-ring nitrogenous base (adenine or guanine) in nucleic acids.
Pyrimidine
Single-ring nitrogenous base (cytosine or thymine in DNA; uracil in RNA).
Semiconservative Model
DNA replication mechanism in which each daughter molecule contains one parental strand and one new strand (verified by Meselson-Stahl).
Replication Origin
Specific DNA sequence where replication begins, forming a replication bubble.
Replication Fork
Y-shaped region at each end of a replication bubble where new DNA strands elongate.
Helicase
Enzyme that unwinds the DNA double helix at replication forks.
Single-Strand Binding Protein (SSB)
Protein that stabilizes and protects unwound single DNA strands during replication.
Topoisomerase
Enzyme that relieves overwinding (torsional strain) ahead of replication forks by cutting, swiveling, and rejoining DNA.
Primase
RNA polymerase that synthesizes short RNA primers needed to start DNA synthesis.
RNA Primer
Short stretch of RNA providing a 3′-OH end for DNA polymerase to add nucleotides.
DNA Polymerase III
Main bacterial enzyme that extends new DNA strands by adding nucleotides to the 3′ end.
DNA Polymerase I
Enzyme that removes RNA primers and replaces them with DNA nucleotides.
Sliding Clamp
Protein ring that holds DNA polymerase to the DNA template during strand elongation.
Leading Strand
DNA strand synthesized continuously toward the replication fork (5′ → 3′ direction).
Lagging Strand
DNA strand synthesized discontinuously away from the fork as Okazaki fragments.
Okazaki Fragment
Short segment of DNA produced on the lagging strand and later joined together.
DNA Ligase
Enzyme that seals nicks between Okazaki fragments and joins 3′ ends of DNA segments.
Nucleoside Triphosphate (dNTP)
Activated nucleotide substrate for DNA synthesis; releases pyrophosphate when added.
Proofreading
DNA polymerase activity that corrects mispaired nucleotides during replication.
Mismatch Repair
Post-replication process where enzymes correct incorrectly paired bases missed by proofreading.
Nucleotide Excision Repair
Repair mechanism in which a nuclease removes damaged DNA segments, DNA polymerase fills the gap, and ligase seals it.
Mutation
Permanent change in DNA sequence; raw material for evolution.
Telomere
Non-coding, repetitive nucleotide sequence at eukaryotic chromosome ends that protects genes from erosion.
Telomerase
Enzyme that extends telomeres in germ cells (and many cancer cells), counteracting shortening.
Chromatin
DNA-protein complex forming eukaryotic chromosomes; exists as euchromatin or heterochromatin.
Histone
Positively charged protein that binds DNA; core of nucleosomes aiding DNA packing.
Nucleosome
“Bead” of DNA wrapped around an octamer of histone proteins; basic unit of chromatin.
Euchromatin
Loosely packed chromatin accessible for transcription during interphase.
Heterochromatin
Highly condensed chromatin (e.g., centromeres, telomeres) generally transcriptionally inactive.
30-nm Fiber
Coiled nucleosome filament forming a thicker chromatin fiber during packing.
Looped Domain
300-nm chromatin loop attached to a protein scaffold inside the nucleus.
Metaphase Chromosome
Most condensed form of chromatin (≈1,400 nm wide) visible during cell division.
Nucleoid
Region in a bacterium where the supercoiled circular chromosome resides.
Supercoiling
Over- or under-winding of DNA helix, compacting bacterial chromosomes.
Meselson-Stahl Experiment
1958 study that confirmed semiconservative DNA replication using 15N and 14N isotopes.
Avery–McCarty–MacLeod Experiment
1944 work identifying DNA as Griffith’s transforming principle.
Watson-Crick Base Pairing
Specific hydrogen-bond pairing: A with T (2 bonds) and G with C (3 bonds), ensuring uniform helix width.