DNA Structure, Replication, and Recombination

Comprehensive vocabulary flashcards covering DNA structure, historical experiments (Griffith, Avery, Hershey-Chase, Watson-Crick), replication mechanisms, and recombination processes based on the lecture notes.

Nuclein

Phosphorus-rich, weakly acidic material extracted from the nuclei of white blood cells by F. Meischer in 1869.

Phosphodiester bonds

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

Transformation

The ability of a substance to change the genetic characteristics of an organism, as demonstrated by F. Griffith's 1928 experiments with Streptococcus pneumoniae.

Transforming principle

The substance responsible for transforming nonvirulent R cells into virulent S cells; identified as DNA by Avery, MacLeod, and McCarty in 1944.

Bacteriophages

Viruses that infect bacteria, consisting of roughly equal parts protein and DNA, used by Hershey and Chase to confirm DNA as the genetic material.

Purine

A nitrogenous base with a two-ring structure ($1-9$ position numbering); examples include adenine (A) and guanine (G).

Pyrimidine

A nitrogenous base with a one-ring structure ($1-6$ position numbering); examples include cytosine (C), thymine (T), and uracil (U).

5' end and 3' end

The chemically distinct ends of a DNA polymer, designated by the presence of either a free $5'$ carbon or a free $3'$ carbon atom.

Chargaff's rules

The observation that the ratio of A to T is $1:1$ and the ratio of G to C is $1:1$ in the DNA of most organisms.

B-form DNA

The standard double helix structure which forms a right-handed helix and has a smooth backbone.

Z-form DNA

A DNA variant that forms a left-handed helix and possesses an irregular backbone.

Semiconservative replication

The Watson-Crick model of replication where the two strands of the parental double helix separate, each serving as a template for a new complementary strand.

Conservative replication

A hypothetical model where the parental double helix remains intact and the daughter helix is composed of two entirely new strands.

Dispersive replication

A hypothetical model where both strands of the daughter helices contain a mixture of parental and newly synthesized DNA.

DNA polymerase III

The enzyme in E. coli that catalyzes the formation of new phosphodiester bonds during the elongation stage of DNA replication.

Initiation

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

DNA Helicase

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

Single-strand binding proteins (SSBs)

Proteins that bind to the unwound DNA strands to keep the helix open during replication.

Primase

An enzyme that synthesizes short RNA primers that are complementary and antiparallel to the DNA template strands.

Leading strand

The DNA strand that undergoes continuous synthesis in the $5'$ to $3'$ direction toward the replication fork.

Lagging strand

The DNA strand that undergoes discontinuous synthesis in the form of short segments called Okazaki fragments.

Okazaki fragment

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

DNA polymerase I

The enzyme that replaces RNA primers with DNA sequences during the elongation process.

DNA ligase

The enzyme that covalently joins successive Okazaki fragments together and seals nicks in the sugar-phosphate backbone.

DNA topoisomerase

An enzyme that relaxes supercoils created by unwinding DNA by cutting and re-sealing the sugar-phosphate backbone.

Gene conversion

The physical change of one allele in a heterozygote to the other, often occurring via mismatch repair in a heteroduplex region.

DNA Polymerase II

An enzyme involved in DNA repair and the synthesis of new DNA strands during DNA replication, particularly in the replication of damaged DNA in prokaryotes. It plays a secondary role in DNA replication compared to DNA polymerase III.