DNA Transcription

Prokaryotic Initiation

1. RNA polymerase binds to a promoter region (-10 and -35 sites)

2. No need for transcription factors—RNA polymerase recognizes promoter directly

3. DNA unwinds and RNA synthesis begins at the +1 site

Prokaryotic Elongation

RNA polymerase reads the DNA template and adds RNA nucleotides (A, U, C, G) to build the RNA strand

Prokaryotic Termination

1. Transcription stops when RNA polymerase hits a terminator sequence

2. Can be Rho-dependent (extrinsic) or Rho-independent (intrinsic)

Key Features of Prokaryotic Transcription

1. Occurs in the cytoplasm

2. No RNA processing required

3. Polycistronic: one mRNA encodes multiple proteins

Eukaryotic Initiation

1. RNA polymerase II binds to DNA only with the help of transcription factors

2. Attaches to TATA box in the promoter region

Eukaryotic Elongation

1. RNA polymerase II adds RNA nucleotides to form pre-mRNA

2. DNA rewinds behind the enzyme

Eukaryotic Termination

A specific sequence signals the end and RNA polymerase releases the RNA strand

Eukaryotic RNA Processing

1. 5’ cap is added (protects RNA and assists with ribosome binding)

2. Poly-A tail is added to the 3’ end to stabilize RNA

3. Splicing removes introns (non-coding regions) and joins exons (coding regions)

Key Features of Eukaryotic Transcription

1. Occurs in the nucleus

2. mRNA must be processed and exported to the cytoplasm for translation

3. Monocistronic: one mRNA codes for one protein