Structure, Replication, and Recombination of Genes

Flashcards covering DNA molecular structure, historical experiments identifying DNA as genetic material, the mechanism of DNA replication, and the molecular stages of recombination.

Nuclein

A phosphorus-rich, weakly acidic material extracted by F. Meischer in 1869 from the nuclei of human white blood cells, later identified as DNA.

Transformation

The ability of a substance to change the genetic characteristics of an organism, first observed by F. Griffith in 1928 with Streptococcus pneumoniae.

Nucleotide

A subunit of DNA consisting of a deoxyribose sugar connected to a phosphate group and one of four nitrogenous bases.

Phosphodiester bonds

Covalent bonds that join adjacent nucleotides by connecting the $3'$ carbon of one nucleotide to the $5'$ carbon of the next.

Purines

Nitrogenous bases with a two-ring structure, which include adenine (A) and guanine (G).

Pyrimidines

Nitrogenous bases with a one-ring structure, which include cytosine (C), thymine (T), and uracil (U).

Antiparallel

The structural arrangement of the two strands in a DNA double helix, where the strands have opposite $5'$ to $3'$ orientations.

B-form DNA

The common form of DNA that characterizes a right-handed helix with a smooth backbone.

Z-form DNA

A DNA variant that forms a left-handed helix with an irregular backbone, often associated with high concentrations of $GC$ pairs.

Chargaff's Rules

Observation that in DNA from any organism, the ratio of A to T is $1:1$ and G to C is $1:1$, and the total amount of purines equals the total amount of pyrimidines.

Semiconservative Replication

The model of DNA replication where each strand of the double helix acts as a template for a new strand, resulting in two daughter helices each containing one parental and one new strand.

DNA Polymerase (pol)

An enzyme that catalyzes the formation of new phosphodiester bonds and adds nucleotides to the $3' \text{-OH}$ of the growing new strand.

Initiation

The first stage of DNA replication where proteins open the double helix and prepare it for complementary base pairing.

DNA Helicase

An enzyme that unwinds the DNA double helix during the initiation of replication.

Primase

An enzyme that synthesizes RNA primers that are complementary and antiparallel to the template strand.

Leading strand

The newly synthesized DNA strand that undergoes continuous synthesis in the direction of the replication fork.

Lagging strand

The newly synthesized DNA strand that undergoes discontinuous synthesis in small segments in the direction opposite the replication fork.

Okazaki fragment

Short DNA segments synthesized on the lagging strand during DNA replication.

DNA topoisomerase

An enzyme that relaxes supercoils by cutting the sugar-phosphate backbone and resealing it after the strands have unwound.

Spo11

A conserved protein that initiates homologous recombination by breaking the phosphodiester bonds of both strands of one chromatid.

Resection

A process in recombination where exonucleases degrade the $5'$ ends of broken strands to create $3'$ single-stranded tails.

Heteroduplex

A region of DNA where one strand is maternal and the other is paternal; these regions occur at sites of genetic exchange and may contain base mismatches.

Gene conversion

The physical change of one allele in a heterozygote to the other, caused by the mismatch repair of heteroduplex regions.

Site-specific recombination

A process that promotes the breakage and rejoining of DNA molecules at particular sequences, catalyzed by a single protein called recombinase.