DNA Structure and Replication

These vocabulary flashcards cover the key historical experiments, chemical structures, enzymes, and mechanisms involved in DNA structure and replication in both prokaryotes and eukaryotes.

Griffith (1928) Transformation

The observation where live Bacterial Strain A and dead Bacterial Strain B resulted in live Bacterial Strain A with a new genotype/phenotype.

Avery, McCloud & McCarty (1944)

A variation of Griffith's experiment which demonstrated that when DNA is destroyed, no live S strain is recovered and the mouse lives, identifying DNA as the transforming molecule.

Hershey & Chase (1952)

An experiment using T2 phage and ${32}P$ to label DNA and ${35}S$ to label protein, proving that DNA is the genetic material because radioactivity was recovered in the bacteria only when DNA was labeled.

Deoxyribonucleotide

A nucleotide structure consisting of a Phosphate, a Deoxyribose sugar, and a Nitrogenous Base.

Phosphodiester Bonds

Chemical bonds formed between adjacent nucleotides at the $5'$ Phosphate and the $3'$ hydroxyl via a condensation reaction.

Anti-parallel

The structural orientation of the two chains in a DNA double helix, where the strands run in opposite directions.

Purines

A group of nitrogenous bases with a double-ring structure, specifically Adenine (A) and Guanine (G).

Pyrimidines

A group of nitrogenous bases with a single-ring structure, specifically Cytosine (C) and Thymine (T).

Chargaff's Rules

Fundamental rules stating that the total amount of Pyrimidines equals Purines ($T+C = A+G$) and specifically that $T = A$ and $C = G$.

Complementary Base Pairing Bonds

Specific hydrogen bonding where $G$ and $C$ are held together by three hydrogen bonds, and $A$ and $T$ are held together by two hydrogen bonds.

Semi-conservative replication

A mode of DNA replication where each daughter molecule contains one parent strand and one newly synthesized strand.

DNA Helicase

The enzyme responsible for separating the two DNA strands by breaking hydrogen bonds during replication.

Single-strand binding protein (SSB)

Proteins that stabilize and maintain the single strands of DNA after they have been separated by helicase.

DNA Gyrase

A DNA topoisomerase that relieves the tension and positive supercoiling caused by the unwinding of the DNA helix.

Primase

An enzyme that synthesizes short RNA oligonucleotides (primers) which are copied from DNA to provide a $3'$ end for synthesis.

DNA Polymerase III

The major DNA replication enzyme in prokaryotes that elongates RNA primers with new DNA in the $5' \rightarrow 3'$ direction.

DNA Polymerase I

An enzyme that removes RNA primers at the $5'$ end of neighboring fragments via $5' \rightarrow 3'$ exonuclease activity and fills the resulting gaps with DNA.

DNA Ligase

An enzyme that seals gaps and connects adjacent DNA fragments (such as Okazaki fragments) by facilitating phosphodiester bond formation.

Replisome

The complex of all proteins and enzymes involved in replication, including the Pol III Holoenzyme, DnaB, and Primase.

$\beta$ clamp

A protein that helps stabilize DNA Polymerase III on the DNA strand during elongation.

Leading Strand

The DNA strand that is synthesized continuously in the same direction as the replication fork movement ($5' \rightarrow 3'$).

Lagging Strand

The DNA strand that is replicated discontinuously in the opposite direction of the replication fork opening, forming Okazaki fragments.

Okazaki fragments

Short, discontinuous segments of DNA synthesized on the lagging strand during DNA replication.

Primosome

A multimolecular structure in E. coli containing primase and six other proteins.

Rolling circle replication

A specialized replication process used by plasmids where a nuclease cuts a phosphodiester bond and nucleotides are added to the $3'-OH$ end, displacing the other strand.

Telomerase

An enzyme that carries a template RNA to lengthen the $3'$ overhang of eukaryotic chromosomes, preventing the shortening of coding regions during replication.

Eukaryotic DNA Polymerases

The five polymerases identified in eukaryotes: $\alpha$, $\beta$, $\gamma$, $\delta$, and $\epsilon$.