MCB 150 Lecture Notes - Lecture 28: Peptide, Lac Repressor, Repressor
7 Dec 2017
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Transcription of lacz gene to make one copy of 1 protein energy is from triphosphate group. Translation of lacz gene 3 atp per aa 1000aa = 3000 atp. That"s ~6,000 atp equivalents for 1 copy of this 1,000 aa protein! In bacteria, translation is ~20 aa/sec. , so to make a 1,000 aa protein would take. 6,000 atp used up in 50 seconds gives an average cost of 120 atp per second! Expressing all genes all the time would be too expensive Turn off genes it doesn"t need!! E. g. , e. coli can use many different sugars (glucose, lactose, arabinose, maltose, etc. ) as food source. Collection of enzymes suites of enzymes not needed unless the food source is available. Different suites of enzymes needed to utilize each of those sugars. Doesn"t make sense to make genes for metabolizing lactose if there"s no lactose available to the cell. Many genes are turned on and off as the needs of the cell change regulation:
