transcription

Copying a DNA sequence into messenger RNA (mRNA). The first step of gene expression — reading the genome.

process

1. initiation: RNA polymerase binds to the promoter region of a gene, transcription factors assist binding
2. elongation: RNA polymerase unwinds DNA and synthesizes mRNA in the 5’ to 3’ direction, using the template (antisense) strand
3. termination: RNA polymerase reaches a terminator sequence, releases the mRNA transcript

eukaryotic processing

• 5’ capping: modified guanine cap added, protects mRNA and aids ribosome binding
• splicing: introns (non-coding regions) removed, exons joined. Alternative splicing produces multiple proteins from one gene
• 3’ polyadenylation: poly-A tail added, stabilizes mRNA and aids nuclear export

regulation

• transcription factors: proteins that activate or repress gene expression
• enhancers and silencers: distant DNA elements modulating transcription rate
• epigenetics: DNA methylation and histone modification alter accessibility without changing sequence

connections

Produces the mRNA template for translation (protein synthesis). Gene expression during mitosis and meiosis depends on transcription. The central dogma: DNA → (transcription) → RNA → (translation) → protein. polymerization of nucleotides by RNA polymerase is the physical mechanism.