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Lac Operon
| Question | Answer |
|---|---|
| What is gene regulation in Bacteria? | Bacteria adapt to changes in their surroundings by using regulatory proteins to turn groups of genes on and off in response to various environmental signals. |
| How does E. Coli regulate the expression of its genes? | according to the food sources that are available to it. |
| What is an operon? | a cluster of bacterial genes along with an adjacent promoter that controls the transcription if those genes. |
| A regulatory gene | lacl |
| The structural genes | LacZ, LacY, lacA |
| What happens when the genes in an operon are transcribed? | a single mRNA is produced for all the genes in that operon. |
| Why is the mRNA said to be polycistronic? | it carries the information for more than one type of protein |
| What is the operator? | it is a short region of DNA that lies partially within the promoter and that intersects with a regulatory protein that controls the transcription of the Operon. |
| What is a promoter? | like a doorknob, in that the promoters of many operons are similar. The operator is like the keyhole in a doorknob, in that each door is locked by only a specific key, which in this case is a specific regulatory protein. |
| What does the regulatory gene lacI produce? | an mRNA |
| What does an mRNA produce? | a Lac repressor |
| What does the repressor do? | it keeps RNA polymerase from transcribing the structural genes. In other words it inhibits transcription of the lac operon. |
| In the absence of lactose, what does the lac repressor bind to? | It binds to the operator, and keeps RNA polymerase from transcribing the lac genes |
| What is negative regulation? | IT is the effect of the lac repressor on the lac genes, it would be a waste for a bacterial cell to express lac genes if lactose was not present |
| What happens if lactose is present? | the lac genes are expresses because allolactose binds to the Lac repressor protein and keeps it from binding to the lac operator. |
| What is Allolactose? | it is an isomer of lactose |
| What does Allolactose bind to? | an allosteric site on the repressor protein causing a "shape" change..this means the repressor wont bind to the operator and falls off. RNA polymerase can then bind to the promoter and transcribe the lac genes. |
| Why is Allolactose called an inducer? | because it turns on, or induces the expression of the lac genes |
| What happens when enzymes encoded by the lac operon are produced? | they break down lactose and allolactose and eventually releases the repressor to stop transcription |
| LacZ | B-galactosidase |
| LacY | Lactose permease |
| LacA | Transacetylase |
| What will bacteria use before it uses lactose? | Glucose |
| What happens when both glucose and lactose are present? | the genes for lactose metabolism are transcribed to a small extent |
| When does maximal transcription of lac operon occur? | only when glucose is absent and lactose is present |
| What is cAMP | cyclic AMP |
| What is CAP | catabolite activator protein |
| Hpw is the concentration of cAMP inversely proportional to the concentration of glucose. | As the concentration of glucose decreases, the concentration of cyclic AMP increases. |
| What is cAMP derived from? | ATP |
| What happens in the presence of lactose and absence of glucose? | cyclic AMP joins with CAP that binds to the lac promoter and lets transcription occur (works very efficiently) |
| What is the function of LacZ? | breakdown of lactose to glucose and galactose |
| What is the function LacY? | transport of lactose into the cell |
| What is the function of lacA? | unknown |
Created by:
sammiexox