DNA Replication and Transcription in Prokaryotes

INITIATION

The first step in DNA replication where the process begins.

ELONGATION

The stage in DNA replication where new DNA strands are synthesized.

TERMINATION

The final step in DNA replication where the process is completed.

Ori-C

The origin/start of replication in bacterial DNA.

DnaA

A protein that initiates DNA replication.

DnaB

Helicase that unzips DNA during replication.

DnaC

Helicase loader that assists DnaB.

Dna gyrase

An enzyme that releases pressure on DNA, functioning as a topoisomerase.

SSB

Single-strand binding protein that prevents reannealing of DNA strands.

DnaG

Primase that adds RNA primers to the DNA strands.

Dna Pol III

The main DNA polymerase that synthesizes new DNA by adding nucleotides from the 5' to 3' end.

Dna Pol I & II

DNA polymerases involved in DNA repair.

Rnase H

An enzyme that removes RNA primers from the newly synthesized DNA.

DNA ligase

An enzyme that ligates pieces of DNA together.

Tus

A protein that forms a complex with the ter site to stop DNA replication.

Bidirectional replication

A type of DNA replication where two replication forks move in opposite directions.

Semiconservative replication

A method of DNA replication where each new DNA molecule consists of one old strand and one new strand.

DnaA-ATP complexes

: Complexes that bind to 9-bp repeats in oriC to initiate DNA replication.

Replication bubble

A structure that forms after initiation of replication, containing two replication forks.

Leading strand

The strand of DNA that is synthesized continuously during replication.

Lagging strand

The strand of DNA that is synthesized discontinuously during replication.

Catenane link

A structure formed when replisomes meet and fall apart at the end of replication.

End-replication problem

The issue that arises in linear chromosomes where the lagging strand cannot be fully replicated.

Telomere

The end of a linear chromosome that protects it from deterioration.

Telomerase

An enzyme that extends the 3' end of a chromosome to allow primase to add a primer.

Genotype

The genetic constitution of an individual organism

Phenotype

The set of observable characteristics of an individual resulting from the interaction of its genotype with the environment.

Nucleoid

The region in a prokaryotic cell where the genetic material is located.

Cell receptors

Proteins that can detect necessary extracellular molecules (ligands).

Cistron

A DNA segment that codes for a single polypeptide.

Operon

A polycistronic unit of gene expression that includes multiple genes under the control of a single promoter.

Regulon

A collection of operons and genes with a unified biochemical purpose under control of a regulatory protein/regulator.

Monocistronic

A type of mRNA that codes for a single protein.

Polycistronic

A type of mRNA that codes for multiple proteins.

Transcription

The process of synthesizing RNA from a DNA template.

Translation

The process of synthesizing proteins from mRNA.

Promoter

A sequence of DNA where RNA polymerase binds to initiate transcription.

Sigma factor

A protein that binds to specific promoters to assist RNA polymerase in initiating transcription.

Template strand

The strand of DNA that RNA polymerase uses to synthesize mRNA.

Coding strand

The DNA strand that has the same sequence as the mRNA (except for thymine being replaced by uracil).

Transcription bubble

The region where the DNA strands are unwound and RNA synthesis occurs.

Rho-independent termination

A type of transcription termination that occurs without the aid of the rho protein.

Rho-dependent termination

A type of transcription termination that requires the rho protein to dissociate RNA polymerase from the DNA.

Downstream

Nucleotides after a specific site in DNA.

Upstream

Nucleotides before a specific site in DNA.

Protein synthesis from mRNA

The process by which proteins are synthesized from messenger RNA.

Reading frame

Each codon after the start is translated in a systematic fashion until a stop codon.

Codon

3 ribonucleotides that correspond to 1 amino acid.

Stop codons

3 different codons that signal the ribosome to stop translation.

Start codon

The codon that initiates translation.

Ribosome

The molecular machine that synthesizes proteins by reading mRNA.

30S subunit

The ribosomal subunit that binds the Shine-Dalgarno sequence during initiation of translation.

Polycistronic mRNA

An mRNA that encodes multiple proteins and forms a polyribosome structure.

Transfer RNAs (tRNAs)

Molecules that bind codons via an anticodon and add the corresponding amino acid to the polypeptide chain.

Release factor

A protein that recognizes the stop codon and facilitates the termination of translation.

RNA Polymerases

Three types of RNA polymerases (RNA Pol I, II & III) involved in transcription.

5' cap

A modified guanine nucleotide added to the 5' end of mRNA, signaling for exportation.

3' poly-A tail

A string of adenine nucleotides added to the 3' end of mRNA, providing degradation protection.

Pre-mRNA

The initial transcript that contains both exons and introns.

Exons

Segments of pre-mRNA that encode for functional polypeptides.

Introns

Segments of pre-mRNA that do not encode for functional polypeptides.

RNA splicing

The process of removing introns from pre-mRNA.

Alternative splicing

A process where some introns are kept and some exons are removed.

Kozak sequence

A sequence found in most eukaryotic transcripts that includes the start codon.

Shine-Dalgarno sequence

A ribosomal binding site in bacterial mRNA that helps initiate translation.