Chapter 18

Chapter 18 - Chapter 18: Regulation of Gene Expression...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
Chapter 18: Regulation of Gene Expression 18.1: Bacteria often respond to environmental change by regulating transcription Two ways of how bacteria can synthesize tryptophan 1) Feedback inhibition- allows cell to adapt to short-term fluctuations in the supply of a substance it needs 2) Cells can adjust the production level of certain enzymes (they can regulate the expression of the genes encoding the enzymes ⇓ ⇓ - Operons: The basic concept o Transcription units that makes tryptophane (has promotor and five genes that code for proteins that make up tryptophan) o Operator= the “switch” that controls the whole cluster of funtioally related genes o Operon= together, the promotor, operator, and the 5 genes make up an operon o Trp operon is typically “switched” on, meaning that the RNA polymerase can bind to the promotor and transcibe the genes of the operon o Trp repressor= a specific protein that can “switch” off the trp operon by binding itself to the operator and blocking the attachment of RNA polymerase to the promotor, preventing the transcription of the genes Trp repressor is the product of a regulatory gene called trpR An allosteric protein that is expressed continuously and is always present Has two alternative shapes, one active and inactive Typically, it is synthesized in an inactive form o If trp binds to the trp respressor>>active form>>turning off the operon o Trp functions in a system as a corepressor because it can switch on and off 1
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
- Repressible and inducible operons: 2 types of negative gene regulation o Trp operon is an example of repressible operon because it is able to repress transcription o Lac operon is an example of inducible operon because it induced transcription o lacI= regulatory gene that codes for an allosteric repressor protein that can switch off the lac operon by binding to the operator (similar to trp operon) Difference: is active by itself, binding to the operator and switching the lac operon off Inducer- inactivates the repressor So if lac is lacking, the lac repressor is active, and the genes of the lac operon is silenced So if lac is added into the cells environment, allolactose binds to the lac repressor and alters its conformation, nullifying the repressor’s ability to attach to the operator o Inducible enzyme- synthesis is induced by chemical signal (allolactase) o Repressible enzyme- function in anabolic pathways, which synthesize essential end products from raw materials (precursors) o Trp and lac operons involve the negative control of genes because the operons are switched off by the active form of the repressor protein - Positive Gene Regulation 2
Background image of page 2
o When glucose and lactose are both present in its environment, E.coli preferably uses glucose o When there’s a lack of glucose, E.coli uses lactose as energy source to
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 7

Chapter 18 - Chapter 18: Regulation of Gene Expression...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online