Control mechanisms

genes that are always needed and are constantly transcribed

In transcription, the DNA sequence of a gene is transcribed (copied out) to make an RNA molecule.

Transcriptional Posttranscriptional translational posttranslational

transcriptional control regulates which genes are transcribed (DNA to mRNA) or controls the rate of transcription

Posttranscriptional controls mRNA undergoing changes in the nucleus before translation, introns are removed and exons are spliced together

 controls how often and how rapidly mRNA transcripts will be translated into proteins  affects the length of time it takes to activate mRNA and the speed of the enzymes which destroy the mRNA

posttranslational  before proteins become functional they must pass through the cell membrane, a number of control mechanisms affect the rate at which a protein becomes active

 a cluster of genes under the control of one promoter and one operator

found in prokaryotic cells only

The lac Operon  regulates the production of β-galactosidase and other proteins involved in the metabolism of lactose  consists of a cluster of three genes controlled by one promoter and one operator  the lac1 repressor protein binds to the operator when lactose levels are low, therefore blocking RNA polymerase from transcribing the gene  high levels of lactose induce the operon because lactose binds to the lac1 repressor protein, changing its shape, and thus preventing it from being able to bind to the lac operon.  in this case, lactose is referred to as an inducer (It binds to a repressor protein to cause transcription)

 regulates the production of the amino acid tryptophan  consists of a cluster of five genes controlled by one promoter and one operator  when tryptophan levels are low, the trp repressor is not attached to the operator (its shape will not allow it to bind), so transcription of the gene occurs  when tryptophan levels are high, the tryptophan binds to the trp repressor protein, changing its shape, and the complex then binds to the operator, therefore blocking transcription (repressing the operon)  in this case, tryptophan is referred to as a corepressor (It binds to a repressor molecule to activate the repressor molecule and block transcription)

 regulates the production of the amino acid tryptophan  consists of a cluster of five genes controlled by one promoter and one operator  when tryptophan levels are low, the trp repressor is not attached to the operator (its shape will not allow it to bind), so transcription of the gene occurs  when tryptophan levels are high, the tryptophan binds to the trp repressor protein, changing its shape, and the complex then binds to the operator, therefore blocking transcription (repressing the operon)  in this case, tryptophan is referred to as a corepressor (It binds to a repressor molecule to activate the repressor molecule and block transcription)

LAC Z, LAC Y, LAC A

controlling transcriptin/translation ex Lac and trp operons

molecule that binds to the repressor to change its shape

signal molecule that triggers expression of operons genes

B-galactosidase

yes

the LAC1 protein is bound to the operator, preventing RNA polymerase from transcribing the gene

Lactose binds to the LAC1 repressor protein and changes its shape causing it to fall off allowing transcription to occur

amino acid used by bacteria to make proteins

1) allows transcription to occur 2) inactivates the repressor so it wont bind to operator and block production of tryptophan 3) allows RNA polymerase to transcribe genes