Genetics Part 1: DNA Structure and Replication

Vocabulary flashcards covering key terms, historical experiments, chemical structures, and enzymatic mechanisms in DNA structure and replication.

Bacteriophages (Phages)

Viruses that infect bacteria, consisting of genetic material enclosed in a protective protein coat, which are widely used in molecular genetics research.

Hershey-Chase Experiment

A landmark $1952$ study by Alfred Hershey and Martha Chase using radioactive sulfur ($^{35}\text{S}$) to label phage protein and radioactive phosphorus ($^{32}\text{P}$) to label phage DNA, proving that DNA is the genetic material of the T2 phage.

Chargaff's Rules

Two rules formulated by Erwin Chargaff in $1950$ stating that: 1) DNA base composition varies between species, and 2) in any species, the percentages of Adenine (A) and Thymine (T) bases are equal, and the percentages of Guanine (G) and Cytosine (C) bases are equal.

X-Ray Crystallography of DNA

A technique used by Maurice Wilkins and Rosalind Franklin to produce diffraction images of DNA, which allowed James Watson to deduce its helical shape, width, and base spacing.

DNA Nucleotide

The monomer of DNA consisting of a deoxyribose sugar, a phosphate group attached to the $5'$ carbon, and one of four nitrogenous bases (Adenine, Thymine, Guanine, or Cytosine) attached to the $1'$ carbon.

DNA Double Helix Dimensions

The physical dimensions of the DNA double helix: a uniform diameter of $2\text{ nm}$, nitrogenous bases spaced $0.34\text{ nm}$ apart, and one complete helical turn every $10\text{ base pairs}$ ($3.4\text{ nm}$).

Antiparallel

The arrangement in a DNA double helix where the two sugar-phosphate backbones run in opposite directions relative to their $5'$ and $3'$ ends.

Purine-Pyrimidine Base Pairing

The structural base-pairing rule in DNA where a double-ring purine always pairs with a single-ring pyrimidine, producing a constant width of $2\text{ nm}$ consistent with X-ray diffraction data.

Base Pair Hydrogen Bonding

The specific bonding that holds DNA strands together: Adenine (A) forms two hydrogen bonds with Thymine (T), while Guanine (G) forms three hydrogen bonds with Cytosine (C).

Template Strand DNA Replication

The copying mechanism where the parental DNA double helix unwinds and each separated strand serves as a template to build a complementary daughter strand.

DNA Polymerase

An enzyme involved in DNA replication that synthesizes new DNA strands and proofreads newly added nucleotides, immediately replacing incorrect ones.

Mismatch Repair

A cellular mechanism in which specific enzymes identify, remove, and replace incorrectly paired nucleotides that were missed during DNA polymerase proofreading.

Nucleotide Excision Repair

A DNA repair mechanism where a nuclease cuts out damaged stretches of DNA, DNA polymerase fills in the missing nucleotides, and DNA ligase seals the new backbone.

Nuclease

An enzyme that cuts out damaged or mismatched segments of DNA during nucleotide excision repair.

Telomeres

Special non-coding nucleotide sequences consisting of multiple repetitions of a short sequence (such as TTAGGG in humans) at the ends of linear eukaryotic chromosomes, which postpone the shortening of essential genes.

Telomerase

An enzyme that catalyzes the lengthening of telomeres in germ cells to prevent the loss of essential genes across generations.