Describe: gene expression b.stev

GENE EXPRESSION components to be outlined in the description: RNA polymerase Transcription Initiation Transcription Termination mRNA translation

RNA polymerase

Transcription Initiation

Transcription Termination

mRNA translation

RNA polymerase: - enzyme attaches to promoter sequence & then pries apart the DNA strands for transcription - moves along the strand during the process and completes the base-pairing along the template (Campbell N. A, Reece J. B, 2005)

regulatory gene structural genes promoter TRANSCRIPTION FACTOR OPERON direction of transcription when the REPRESSOR PROTEIN binds to the OPERATOR it prevents transcription operator RNA polymerase

Transcription INITIATION: - for the process to occur the RNA polymerase must then encounter the codons to make the mRNA transcript ; located after the operator - RNA polymerase attaches to promoter sequence - IF: the regulatory gene has been activated to make a repressor protein that attaches to the operator ; transcritpion CAN NOT occur - repressor protein: blocks RNA poly in it’s process from commencement to interaction with the next set of codons that instruct structure OR function - IF: not activated transcription shall occur (Pommerville J.C, 2004)

when the REPRESSOR PROTEIN binds to the OPERATOR it prevents transcription regulatory gene operator structural genes promoter TRANSCRIPTION FACTOR OPERON RNA polymerase direction of transcription

Transcription TERMINATION: - transcription occurs until defined codons that signal cessation are read by the DNA poly - called : STOP codons [UGA/ UAA/ UAG] - process stops and the mRNA transcript breaks away to float freely in the cytoplasm , until, it encounters a ribosome: translates to protein - RNA poly detaches from the DNA transcript (Campbell N. A, Reece J. B, 2005)

A P E large ribosome mRNA transcript small ribosome bind site: upstream to the start codon is a specific sequence that the small ribosome recognises and binds to, so follows the large ribosome that attaches above this 5’ 3’ RIBOSOME bind sites E: exit site P: peptidyl-tRNA site A: aminoacyl-tRNA site direction of translation

direction of translation tRNA – transfers amino acids in sequence to make a protein 3’ 5’ tRNA moves along through the A& then the P bind site(s) then exits from the E site after attachment of the amino acid to the polypeptide chain = a protein P A E amino acid set of codons : attach to their match in the mRNA mRNA transcript TRANSLATION

direction of translation 3’ 5’ A E mRNA transcript TRANSLATION tRNA polypeptide - when complete the STOP codon does not match any tRNA - the polypeptide breaks away & is thus a complete protein

Bibliography Campbell N. A, Reece J. B. (2005). Biology (7th ed.) . San Francisco: Benjamin Cummings Pommerville J.C. (2004). Alcamo’s – Fundamentals of Microbiology (7 th ed.). Massachusetts: Jones and Bartlett.