Protein Synthesis- Transcription DNA-->RNA

Expression of Gene or Protein Synthesis I. Transcription A. Initiation B. Elongation C. Termination D. RNA processing

A. Initiation-There is a region prior to beginning of a gene that the RNA polymerase attaches to, called the promoter region. The promoter region determines which side of the gene will be transcribed. A promoter region tells the RNA polymerase where a gene starts

Down from the promoter region a sequence TAC means "Start transcribing here"

B. RNA polymerase unwinds the DNA and base pairs RNA nuclelotides to the DNA gene. A-->U and G-->C in eukaryotes at a rate approximately 60 RNA nucleotides/minute. The RNA molecule will peel off of the DNA gene and DNA molecule will reform. The average mRNA is 8000 base pairs long. A gene can be simultaneously transcribed by a number of RNA polymerases.

mRNA is 8000 base pairs long. A gene can be simultaneously transcribed by a number of RNA polymerases.

C. Termination- Once the termination site is reached, the RNA molecule will be released. These are the stop codons.

D. RNA processing- 1. 5' cap with a modified guanine nucleotide is added. 2. At the 3' end adenine nucleotides are added (poly-A-tail). -These modifications prevent the mRNA from being degraded -Signal the ribosome where to attach.

3. The average immature RNA is 8000 nucleotides long but the mature mRNA is 1200 nucleotides long. There are noncoding regions (introns) that are removed in eukaryotic cells. The remaining regions (exons) are joined together to form the cistron. A particle called a spliceosome removes the introns. Spliceosomes are composed of smaller particles called snRNP (made of proteins and snRNA). The spliceosome will splice the intron at a specific RNA sequence.

form the mRNA gene. A particle called a spliceosome removes the introns.

This mRNA has been processed and is called mature mRNA and is ready to go to the cytoplasm for translation