Gene Expression

Gene Expression

The process of converting genetic information (DNA) into functional products, primarily proteins.

Central Dogma

Describes the flow of genetic information: DNA → RNA → Protein.

Reverse Transcriptase

An enzyme that synthesizes DNA from an RNA template.

Transcription

The process of converting DNA into RNA by RNA polymerase.

RNA Polymerase (RNAP)

The enzyme complex that synthesizes RNA from DNA.

Holoenzyme

The complete form of RNA polymerase, including core enzyme and initiation factors like sigma in bacteria.

Sigma Factor

A subunit of bacterial RNAP that directs it to specific promoters by binding -10 and -35 sequences.

Gene Promoter

A DNA sequence where RNAP binds to initiate transcription.

-10 Box (Pribnow Box)

A conserved DNA sequence recognized by sigma factor, found about 10 bases upstream of start site.

-35 Box

A conserved DNA sequence in bacterial promoters found ~35 bases upstream from start site.

Initiation

Stage where RNAP binds promoter and begins RNA synthesis.

Open Complex (OC)

Unwound DNA region at promoter where transcription begins.

Elongation

RNAP synthesizes RNA by adding nucleotides to the growing chain.

Termination

The end of transcription; RNA is released.

Intrinsic Termination

Also called Rho-independent; involves hairpin loop and U-rich region.

Rho-dependent Termination

Requires Rho protein binding to RNA and causing RNAP to release.

NusA

Protein that aids in forming hairpin structures during intrinsic termination.

Rho

ATP-dependent helicase that terminates transcription by displacing RNAP.

Translation

Process where ribosomes convert mRNA into protein.

Codon

A three-nucleotide sequence on mRNA that codes for a specific amino acid.

tRNA

Transfer RNA; carries amino acids to the ribosome.

tRNA Synthetase

Enzyme that attaches amino acids to tRNA.

rRNA

Ribosomal RNA; structural and catalytic components of ribosomes.

Ribosome

A complex of rRNA and proteins that synthesizes proteins.

A Site

Ribosome site where aminoacyl-tRNA enters.

P Site

Ribosome site where the growing peptide is held.

E Site

Ribosome site where discharged tRNA exits.

Translation Initiation Region (TIR)

Region on mRNA where translation begins.

Shine-Dalgarno Sequence

Ribosomal binding site in bacterial mRNA.

Initiation Factors (IFs)

Proteins that assist in the formation of the translation initiation complex.

Elongation Factors (EF-Tu, EF-G)

Proteins that assist with tRNA delivery and ribosome translocation.

Peptidyl Transferase

Catalyzes peptide bond formation; part of 23S rRNA in LSU.

Translocation

Ribosome shifts to the next codon on mRNA.

Release Factors (RF1, RF2, RF3)

Terminate translation by releasing the polypeptide.

Ribosome Recycling Factor (RRF)

Disassembles ribosome after translation termination.