DNA Replication and Bacterial Binary Fission

Vocabulary practice flashcards covering fundamental concepts of DNA replication, replication enzymes, nucleotide anatomy, fork dynamics, and bacterial binary fission.

Gene

A specific DNA sequence that produces a functional RNA or contributes to a protein product, responsible for a single inherited characteristic or phenotype of an organism.

DNA Replication

The biological process in which the original double-stranded DNA of a mother cell is duplicated into two identical copies prior to cell division.

Meselson-Stahl Experiment

The landmark experiment demonstrating that DNA replication is semiconservative, ruling out conservative and dispersive replication models based on density gradient centrifugation results.

Semiconservative Replication

The mechanism of DNA duplication where each parent strand remains intact and acts as a template, producing two daughter molecules that each consist of one original strand and one newly synthesized strand.

Complementary Base Pairing

The precise pairing rule where adenine (A) pairs exclusively with thymine (T) via $2$ hydrogen bonds, and guanine (G) pairs with cytosine (C) via $3$ hydrogen bonds.

DNA Gyrase

A DNA topoisomerase that relieves supercoiling ahead of the replication fork by introducing a double-stranded break, rotating the two halves relative to each other at the expense of cellular energy, and resealing the cut ends.

DNA Helicase

An ATP-powered enzyme that moves along template DNA ahead of the replication fork to separate the double helix by disrupting hydrogen bonds between complementary base pairs without cleaving the backbone.

Single Strand Binding Protein (SSB)

A specialized protein that binds tightly to separated single-stranded DNA to prevent the two parental strands from reannealing back together during replication.

DNA Polymerase III (Pol III)

The primary enzyme complex responsible for synthesizing new DNA strands by lining up matching nucleotides against the template strand and rejecting mismatched base pairs.

Sliding Clamp ($\beta$ clamp)

A ring-shaped protein structure (composed of $2$ subunits with $3$ domains each in bacteria such as Streptococcus pyogenes) that encircles DNA and tethers DNA polymerase to its template.

Processivity

The ability of DNA polymerase to continuously add many nucleotides along the DNA template per binding event without prematurely disengaging, facilitated by the sliding clamp.

Deoxyribose

The five-carbon pentose sugar component of DNA nucleotides, numbered with prime marks ($1'$ to $5'$), attaching to a nitrogenous base at the $1'$ carbon and a phosphate group at the $5'$ carbon.

Antiparallel Strands

The opposing directional arrangement of the two complementary strands in a DNA double helix, where one strand runs in the $5' \rightarrow 3'$ direction and the other runs in the $3' \rightarrow 5'$ direction.

Direction of DNA Synthesis

The universal rule of strand elongation stating that new DNA always begins at the $5'$ end and grows toward the $3'$ end, because incoming nucleotides can only attach to the free $3'\text{-OH}$ group.

Replication Fork

The Y-shaped active region of DNA duplication that includes unwound single-stranded DNA stabilized by SSBs, DNA helicase, DNA gyrase, and two active DNA polymerase III complexes.

Leading Strand

The newly synthesized DNA strand formed continuously in the $5' \rightarrow 3'$ direction toward the advancing replication fork, initiated by a single starting primer.

Lagging Strand

The newly synthesized DNA strand built discontinuously in the $5' \rightarrow 3'$ direction away from the replication fork, producing a series of short segments separated by gaps.

Okazaki Fragments

The short segments of newly synthesized DNA formed discontinuously along the lagging strand template during DNA replication.

RNA Primase

An enzyme that synthesizes short complementary RNA primers on single-stranded template DNA to supply the free $3'\text{-OH}$ ends required for DNA polymerase to elongate a strand.

DNA Polymerase I (Pol I)

The enzyme responsible for processing lagging strand Okazaki fragments by removing RNA primers and replacing them with deoxyribonucleotides to fill the gaps.

DNA Ligase

The enzyme that seals remaining nicks in the sugar-phosphate backbone by catalyzing phosphodiester bond formation between adjacent Okazaki fragments.

Primosome

A multiprotein complex consisting of DNA helicase and DNA primase located ahead of the replication fork to synthesize primers for strand elongation.

Origin of Replication

The specific nucleotide sequence on a chromosome where DNA replication initiates and proceeds bidirectionally.

Binary Fission

The asexual process of bacterial cell division wherein a cell duplicates its single chromosome, forms a transverse septum across its center, and divides into two separate daughter cells.

Replicon Model

The mechanism describing bacterial chromosome segregation, in which replicated origin regions transiently bind to specific sites on the cell membrane so that membrane growth directs daughter chromosomes into opposite ends.