Bacterial Keys to Success • Respond quickly to environmental changes – Simultaneous transcription and translation • Avoid wasteful activities by using biochemical and genetic controls – Feedback inhibition of key enzymes – DNA binding proteins to control transcription • Exchange genes with other organisms to improve adaptation to environment – Conjugation; exchange of plasmids and chromosomal DNA 1
22
Embed
Bacterial Keys to Success Respond quickly to environmental changes –Simultaneous transcription and translation Avoid wasteful activities by using biochemical.
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Bacterial Keys to Success• Respond quickly to environmental changes
– Simultaneous transcription and translation
• Avoid wasteful activities by using biochemical and genetic controls– Feedback inhibition of key enzymes– DNA binding proteins to control transcription
• Exchange genes with other organisms to improve adaptation to environment– Conjugation; exchange of plasmids and chromosomal
DNA
1
Using DNA is expensive to the cell• Model: protein of 50,000 daltons
– Approximately 500 amino acids, so 500 codons• 500 codons is 1500 RNA bases
• Transcription– Every base added (NTP to NMP) spends 2 phosphates, so
equivalent of 2 ATP– 1500 bases/mRNA = 3000 ATP
• Translation– 1 ATP to move ribosome, 1 to charge tRNA /codon– 2 ATP/ codon = 2 * 500 = 1000 ATP for every single
• Operon codes for enzymes that make a needed amino acid (for example); genes are “on”.– Repressor protein is NOT attached to DNA– Transcription of genes for enzymes needed to make
amino acid is occurring.• The change: amino acid is now available in the
culture medium. Enzymes normally needed for making it are no longer needed.– Amino acid, now abundant in cell, binds to repressor protein
which changes shape, causing it to BIND to operator region of DNA. Transcription is stopped.
• This is also Negative regulation (protein + DNA = off).
14Repression picture
Transcription by RNA polymerase prevented.
15Regulation can be fine tuned
The more of the amino acid present in the cell, the more repressor-amino acid complex is formed; the more likely that transcription will be prevented.
Induction
• Genes normally off are turned on– Example of negative regulation
• Presence of inducer allows gene expression– Inducer binds to repressor which comes off DNA
16
17Structure of the Lac operonKEY:P O are the promoter and operator regions. lac Z is the gene for beta-galactosidase. lac Y is the gene for the permease. lac A is the gene for a transacetylase. lac I, on a different part of the DNA, codes for the lac repressor, the protein which can bind to the operator.
18How the lac operon worksWhen lactose is NOT present, the cell does not need the enzymes. The lac repressor, a protein coded for by the lac I gene, binds to the DNA at the operator, preventing transcription.When lactose is present, and the enzymes for using it are needed, lactose binds to the repressor protein, causing it to change shape and come off the operator, allowing RNA polymerase to find the promoter and transcribe.
http://www.med.sc.edu:85/mayer/genreg1.jpg
19Lactose is not actually the inducer
Low basal levels of beta-galactosidase exist in the cell. This converts some lactose to the related allolactose which binds to the lac repressor protein.
Synthetic inducers such as IPTG with a similar structure can take the place of lactose/allolactose for research purposes.
http://www.search.com/reference/Lac_operon
20Glucose is the preferred carbon source
Positive regulation• Presence of lactose is not enough
– In diauxic growth graph, lactose is present from the start. Why isn’t operon induced?
• Presence of glucose prevents positive regulation– NOT the same as inhibiting– Active Cyclic AMP receptor protein (CRP) needed to
bind to DNA to turn ON lactose operon (and others)– Presence of glucose (preferred carbon source) prevents