Cell Biology - DNA Replication and Repair

Vocabulary flashcards covering key concepts, enzymes, structural components, and mechanisms in DNA replication and DNA repair.

Semiconservative Replication

A mechanism of DNA replication in which each parent strand acts as a template for synthesis of a complementary daughter strand, resulting in two dsDNA molecules that each contain one original parental strand and one newly synthesized daughter strand.

Origin of Replication (ORI)

A specific nucleotide sequence where DNA replication is initiated and initiator proteins separate double-stranded DNA into single-stranded DNA.

Replication Bubble

The shape formed by the separation of double-stranded DNA into two single-stranded DNA strands during the initiation of DNA replication.

Replication Fork

The Y-shaped junction formed at the site of DNA synthesis where replication machinery moves along DNA to open up the double helix.

Replisome

A large complex of proteins that forms at a replication fork to replicate both strands of single-stranded DNA simultaneously.

Single-Stranded Binding Proteins (SSBs)

Proteins that bind single-stranded DNA during replication to prevent the separated strands from coming back together to form double-stranded DNA.

DNA Helicase

A ring-shaped ATPase protein that loads onto single-stranded DNA through its central channel to unwind double-stranded DNA into single-stranded DNA at the replication fork.

Primase

An enzyme that synthesizes a short RNA primer (approximately 10 RNA nucleotides long) using a DNA template to provide a starting point for DNA polymerase.

Leading Strand

The single-stranded DNA template deflected away from helicase that runs in the 5' to 3' direction, allowing continuous DNA synthesis toward the replication fork.

Lagging Strand

The single-stranded DNA template that runs through helicase in the 3' to 5' direction, resulting in discontinuous DNA synthesis in the direction opposite to replication fork movement.

Supercoil

A segment of DNA twisted around itself produced by the unwinding action of DNA helicase during replication.

Topoisomerase

An enzyme that relieves tension in supercoiled DNA by cleaving phosphodiester bonds, allowing the DNA to unwind, and reforming the phosphodiester bonds.

Clamp Loader

A protein complex in the replisome that loads sliding clamps onto single-stranded DNA during DNA replication.

Sliding Clamp

A ring-shaped protein complex that binds single-stranded DNA and holds DNA polymerase III onto the strand to prevent it from leaving the DNA prematurely.

DNA Polymerase III

The primary enzyme responsible for polymerizing new complementary DNA in the 5' to 3' direction during replication, using deoxynucleoside triphosphate precursors and proofreading errors.

Okazaki Fragments

Short, discontinuous segments of newly synthesized daughter DNA produced on the lagging strand template during DNA replication.

DNA Polymerase I

An enzyme that removes RNA primers using its exonuclease activity, fills in the resulting gaps with complementary DNA nucleotides, and proofreads the sequence.

DNA Ligase

An enzyme that joins adjacent DNA fragments by creating covalent phosphodiester bonds to seal nicks in the sugar-phosphate backbone.

Telomere

A repetitive non-coding nucleotide sequence located at the end of linear eukaryotic chromosomes that prevents chromosome shortening after DNA replication.

Telomerase

A specialized RNA-containing reverse transcriptase polymerase that extends telomere repeats at the 3' end of the lagging strand template using its internal RNA template.

Endogenous DNA Damage

DNA damage caused by internal cellular factors or processes, such as replication errors, molecular collisions, depurination, and deamination.

Depurination

An endogenous chemical reaction, often caused by thermal collisions with water molecules, that removes adenine or guanine purine bases from DNA without breaking the phosphodiester backbone.

Deamination

An endogenous chemical reaction in which a cytosine base loses an amino group upon reacting with water, converting it into a uracil base.

Exogenous DNA Damage

DNA damage caused by agents outside the cell, such as ultraviolet (UV) radiation or chemical mutagens.

Thymine Dimer

An exogenous DNA lesion produced by ultraviolet (UV) radiation, forming covalent cross-links between adjacent thymine bases on the same DNA strand.

DNA Mismatch Repair System

A repair mechanism that corrects mispaired bases escaped from polymerase proofreading by identifying the newly synthesized daughter strand and replacing the erroneous sequence.

Non-Homologous End Joining (NHEJ)

An emergency double-strand break repair mechanism active in interphase that cleaves overhangs and rejoins broken DNA ends without a homologous template, often incurring nucleotide loss at the repair site.

Homologous Recombination (HR)

An accurate double-strand break repair mechanism occurring after DNA replication that uses an undamaged sister chromatid sequence as a template to restore the original sequence without loss of nucleotides.

Sister Chromatids

Two identical linear DNA molecules joined together following eukaryotic DNA replication that remain paired until cell division.

Rad51

A protein that binds single-stranded DNA during homologous recombination and searches the sister chromatid for complementary sequences to guide accurate repair.