DNA Replication and Biotechnology

Vocabulary practice flashcards covering cellular DNA replication mechanics, replication enzymes, polymerase chain reaction (PCR), and gel electrophoresis.

DNA Replication

The biological process of producing new strands of DNA with base sequences identical to existing strands, occurring prior to cell division during the S phase of the cell cycle.

Semiconservative Replication

The mechanism of DNA replication in which each newly created double-stranded DNA molecule consists of one conserved parental strand and one newly synthesized strand.

Meselson-Stahl Experiment

The scientific experiment that experimentally proved that DNA replicates via a semiconservative mechanism rather than a conservative or dispersive model.

Origins of Replication

Specific nucleotide sites where DNA replication initiates; prokaryotes contain a single origin, whereas eukaryotic chromosomes have multiple origins.

Replication Bubble

An unwound opening in eukaryotic DNA formed when replication proceeds bidirectionally away from an origin of replication, bounded by two replication forks.

Replication Fork

The Y-shaped active region where double-stranded parental DNA is unwound and separated into single template strands for replication.

Replisome

The large multiprotein complex consisting of various enzymes and functional units that coordinate and carry out DNA replication at the replication fork.

DNA Polymerase III

The primary enzyme responsible for synthesizing new DNA strands by catalyzing the covalent addition of nucleotides in a $5' \rightarrow 3'$ direction.

Deoxynucleoside Triphosphates (dNTPs)

Free nucleotides containing three phosphate groups; DNA polymerase cleaves off two phosphates (pyrophosphate) to release the energy needed to form phosphodiester bonds.

RNA Primer

A short sequence of RNA synthesized by primase that binds to the template strand to provide a free $3'$ hydroxyl end required for DNA polymerase to initiate strand synthesis.

Leading Strand

The new DNA strand that is synthesized continuously toward the replication fork in the $5' \rightarrow 3'$ direction.

Lagging Strand

The new DNA strand that is synthesized discontinuously away from the replication fork in short segments called Okazaki fragments.

Okazaki Fragments

Short stretches of newly synthesized DNA formed discontinuously on the lagging strand during DNA replication.

Helicase

An enzyme that unzips and unwinds the DNA double helix at the replication fork by breaking hydrogen bonds between complementary base pairs.

DNA Primase

An enzyme that synthesizes short RNA primers onto single-stranded DNA templates to provide starting attachment points for DNA polymerase.

DNA Polymerase I

An enzyme that removes RNA primers from the lagging strand and replaces them with DNA nucleotides, also participating in proofreading.

DNA Ligase

An enzyme that catalyzes the formation of phosphodiester bonds to join adjacent Okazaki fragments and seal nicks in the sugar-phosphate backbone.

DNA Gyrase

An enzyme that helps unwind double-stranded DNA by relieving structural strain and supercoiling ahead of the replication fork.

Single-Strand Binding (SSB) Proteins

Proteins that attach to separated single DNA strands to stabilize them and prevent them from prematurely re-annealing.

DNA Proofreading

The self-correcting enzymatic mechanism in which DNA polymerases identify mismatched base pairs immediately after addition and excise them using $3' \rightarrow 5'$ exonuclease activity.

Polymerase Chain Reaction (PCR)

An in vitro laboratory technique used to rapidly amplify large quantities of a specific DNA sequence from a minute starting sample through repetitive cycles of temperature change.

Thermal Cycler

An automated laboratory instrument programmed to rapidly cycle through precise temperature fluctuations required for the denaturation, annealing, and elongation phases of PCR.

Melting / Denaturation (PCR)

The initial step of a PCR cycle where DNA is heated to approximately $95^\top\text{C}$ for $1\text{ min}$ to separate the double helix into single strands by breaking hydrogen bonds between base pairs.

Annealing (PCR)

The second step of a PCR cycle where the temperature is lowered to approximately $55^\top\text{C}$ for $1\text{ min}$ to allow short DNA primers to bind to the $3'$ ends of the target sequence.

Elongation (PCR)

The third step of a PCR cycle where the temperature is raised to approximately $72^\top\text{C}$ for $2\text{ min}$, enabling heat-tolerant DNA polymerase (Taq) to synthesize new complementary strands.

Taq Polymerase

A heat-tolerant DNA polymerase commonly derived from Thermus aquaticus used in PCR because it withstands the high temperatures required for double-strand denaturation.

Gel Electrophoresis

A laboratory technique used to separate and isolate fragments of DNA or proteins according to size and mass by driving them through an agarose gel using an applied electric field.

Restriction Enzymes

Enzymes that recognize specific nucleotide sequences and cut double-stranded DNA at precise locations to generate fragments of varying sizes.

Short Tandem Repeats (STRs)

Non-coding DNA regions containing repetitive core sequences (such as AGAT) where the repeat counts differ significantly among individuals, serving as the basis for DNA profiling.

DNA Profiling

The comparative analysis of individual-specific DNA banding patterns generated via PCR and gel electrophoresis, routinely applied in forensic investigations and paternity testing.