Campbell Biology – Chapter 16: The Molecular Basis of Inheritance

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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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47 Terms

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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.

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Double Helix

The two-stranded, right-handed helical structure of DNA proposed by Watson and Crick in 1953.

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DNA Replication

The process of copying DNA before cell division, producing two identical DNA molecules from one parent molecule.

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Transformation (Griffith)

Heritable change in genotype/phenotype due to assimilation of foreign DNA by a cell.

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Bacteriophage (Phage)

A virus that infects bacteria; key tool in molecular genetics (e.g., Hershey-Chase experiment).

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Hershey-Chase Experiment

1952 study showing that DNA, not protein, enters bacteria during phage infection—proving DNA is the genetic material.

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Chargaff’s Rules

In any DNA sample, A = T and G = C; base composition varies between species.

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X-ray Crystallography

Technique used by Rosalind Franklin to photograph DNA, revealing its helical structure.

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Antiparallel

Orientation of DNA strands running in opposite 5′ → 3′ directions.

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Nucleotide

DNA monomer composed of a nitrogenous base, deoxyribose sugar, and phosphate group.

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Purine

Double-ring nitrogenous base (adenine or guanine) in nucleic acids.

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Pyrimidine

Single-ring nitrogenous base (cytosine or thymine in DNA; uracil in RNA).

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Semiconservative Model

DNA replication mechanism in which each daughter molecule contains one parental strand and one new strand (verified by Meselson-Stahl).

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Replication Origin

Specific DNA sequence where replication begins, forming a replication bubble.

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Replication Fork

Y-shaped region at each end of a replication bubble where new DNA strands elongate.

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Helicase

Enzyme that unwinds the DNA double helix at replication forks.

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Single-Strand Binding Protein (SSB)

Protein that stabilizes and protects unwound single DNA strands during replication.

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Topoisomerase

Enzyme that relieves overwinding (torsional strain) ahead of replication forks by cutting, swiveling, and rejoining DNA.

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Primase

RNA polymerase that synthesizes short RNA primers needed to start DNA synthesis.

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RNA Primer

Short stretch of RNA providing a 3′-OH end for DNA polymerase to add nucleotides.

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DNA Polymerase III

Main bacterial enzyme that extends new DNA strands by adding nucleotides to the 3′ end.

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DNA Polymerase I

Enzyme that removes RNA primers and replaces them with DNA nucleotides.

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Sliding Clamp

Protein ring that holds DNA polymerase to the DNA template during strand elongation.

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Leading Strand

DNA strand synthesized continuously toward the replication fork (5′ → 3′ direction).

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Lagging Strand

DNA strand synthesized discontinuously away from the fork as Okazaki fragments.

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Okazaki Fragment

Short segment of DNA produced on the lagging strand and later joined together.

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DNA Ligase

Enzyme that seals nicks between Okazaki fragments and joins 3′ ends of DNA segments.

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Nucleoside Triphosphate (dNTP)

Activated nucleotide substrate for DNA synthesis; releases pyrophosphate when added.

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Proofreading

DNA polymerase activity that corrects mispaired nucleotides during replication.

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Mismatch Repair

Post-replication process where enzymes correct incorrectly paired bases missed by proofreading.

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Nucleotide Excision Repair

Repair mechanism in which a nuclease removes damaged DNA segments, DNA polymerase fills the gap, and ligase seals it.

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Mutation

Permanent change in DNA sequence; raw material for evolution.

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Telomere

Non-coding, repetitive nucleotide sequence at eukaryotic chromosome ends that protects genes from erosion.

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Telomerase

Enzyme that extends telomeres in germ cells (and many cancer cells), counteracting shortening.

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Chromatin

DNA-protein complex forming eukaryotic chromosomes; exists as euchromatin or heterochromatin.

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Histone

Positively charged protein that binds DNA; core of nucleosomes aiding DNA packing.

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Nucleosome

“Bead” of DNA wrapped around an octamer of histone proteins; basic unit of chromatin.

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Euchromatin

Loosely packed chromatin accessible for transcription during interphase.

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Heterochromatin

Highly condensed chromatin (e.g., centromeres, telomeres) generally transcriptionally inactive.

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30-nm Fiber

Coiled nucleosome filament forming a thicker chromatin fiber during packing.

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Looped Domain

300-nm chromatin loop attached to a protein scaffold inside the nucleus.

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Metaphase Chromosome

Most condensed form of chromatin (≈1,400 nm wide) visible during cell division.

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Nucleoid

Region in a bacterium where the supercoiled circular chromosome resides.

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Supercoiling

Over- or under-winding of DNA helix, compacting bacterial chromosomes.

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Meselson-Stahl Experiment

1958 study that confirmed semiconservative DNA replication using 15N and 14N isotopes.

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Avery–McCarty–MacLeod Experiment

1944 work identifying DNA as Griffith’s transforming principle.

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Watson-Crick Base Pairing

Specific hydrogen-bond pairing: A with T (2 bonds) and G with C (3 bonds), ensuring uniform helix width.