DNA Replication and Fluorescent Tagging Machinery

Vocabulary practice flashcards covering the core mechanisms of DNA replication, bacterial replisome components, RNA vs. DNA polymerases, translational fusion protein engineering (mCherry-DnaN), and replication coordination.

Anti-parallel DNA

The structural property of double-stranded DNA where if one strand is oriented in the $5' \rightarrow 3'$ direction, the complementary strand must run in the $3' \rightarrow 5'$ direction.

Directionality of Polymerisation

The biochemical rule stating that polymerisation of both DNA and RNA always proceeds in the $5' \rightarrow 3'$ direction.

Primer

A short sequence (typically RNA or DNA) providing the free $3'\text{-OH}$ group required by DNA polymerase to initiate strand synthesis.

DNA Polymerase

An enzyme responsible for replication ($\text{DNA} \rightarrow \text{DNA}$) that synthesizes DNA in a $5' \rightarrow 3'$ direction, requires a template to copy, and strictly requires a $3'\text{-OH}$ group provided by a primer to initiate polymerisation.

RNA Polymerase

An enzyme responsible for transcription ($\text{DNA} \rightarrow \text{RNA}$) that synthesizes RNA in a $5' \rightarrow 3'$ direction and requires a template to copy, but does not require a $3'\text{-OH}$ group or primer to initiate synthesis.

oriC

The chromosomal origin of replication; the specific site on the chromosome where DNA replication is initiated.

DnaA

The origin-binding protein that recognizes and binds to $oriC$ to initiate the opening and unwinding of the DNA duplex.

DnaB

The replicative helicase enzyme recruited to the replication origin to unwind double-stranded DNA.

DnaC

The helicase loader protein that loads the DnaB helicase onto the DNA at the replication origin.

Single-Stranded Binding Proteins (SSBs)

Proteins that bind to and protect exposed single-stranded DNA from degradation or re-annealing once the duplex has been unwound.

DnaG (Primase)

The primase enzyme that synthesizes short RNA segments called primers, providing DNA polymerase with a starting place ($3'\text{-OH}$ group) to initiate DNA synthesis.

DNA Polymerase III Holoenzyme

The primary bacterial replicative polymerase complex that synthesizes new leading and lagging DNA strands in the $5' \rightarrow 3'$ direction using dNTP substrates during elongation.

$\beta$ Clamp

A ring-shaped sliding clamp that holds DNA polymerase III attached to the template strand during elongation.

DNA Replication Initiation and Elongation Pathway

The sequential four-step assembly process consisting of: (1) origin binding by DnaA at $oriC$, (2) helicase recruitment and loading by DnaB and DnaC, (3) primer synthesis by DnaG primase, and (4) elongation by DNA polymerase III and the $\beta$ clamp on the leading and lagging strands.

DNA Polymerase I

The enzyme responsible for removing RNA primers and filling in the resulting gaps with DNA during the processing of the lagging strand.

DNA Ligase

The enzyme that covalently joins adjacent ends (nicks) of newly synthesized DNA on the lagging strand.

Translational Fusion Product (Fusion Protein)

A single chimeric protein generated by joining the coding sequences of two distinct proteins (e.g., a fluorescent marker and a replication subunit) into a single continuous reading frame translated as one functional polypeptide.

mCherry

A functional red fluorescent protein used experimentally as Domain 1 of a fusion construct to allow visual tracking of cellular machinery.

dnaN

The gene encoding the $\beta$ clamp subunit of DNA polymerase; used as Domain 2 in a fusion protein to direct fluorescent signals directly to the replisome.

mCherry-DnaN Fusion Protein

A bifunctional reporter protein combining red fluorescent protein (Domain 1) and the DNA polymerase $\beta$ clamp subunit (Domain 2), allowing researchers to visualize where the replisome machinery is localized in the cell.

Flexible Linker

An optional peptide sequence engineered between two domains (such as mCherry and DnaN) of a fusion protein to provide sufficient physical spacing so that each domain folds and functions properly.

Translational Fusion mRNA Architecture

An mRNA transcript design for producing a single fusion protein, featuring a single RBS, a single start codon at the beginning, no stop codon between Domain 1 and Domain 2 (allowing continuous translation), and a final stop codon at the end of Domain 2.

Mall-YFP

A fluorescent fusion protein composed of Mall (a protein that binds near $oriC$) and Yellow Fluorescent Protein (YFP), used to mark the approximate location of the origin of replication inside the cell.

Replisome and Origin Spatiotemporal Coordination

The cell cycle dynamic demonstrating that the origin ($oriC$, tracked by Mall-YFP) is positioned earlier in the cell cycle before the replisome machinery (tracked by mCherry-DnaN) is fully localized.

Coordination of Replication

The biological requirement that DNA replication must be precisely synchronized with chromosome partitioning and cell division.

In Vitro Applications of DNA Polymerase

Biotechnological uses of DNA polymerase in the laboratory outside of living cells, specifically including DNA sequencing and Polymerase Chain Reaction (PCR).