1. Trp Operon a. Biosynthetic operon i. Trp regulation is
Trp Regulation
1. Trp Operon a. Biosynthetic operon i. Trp regulation is used to synthesize Trp amino acid b. Two methods of control of the Trp operon: i. Repression 1. This is a coarse control ii. Attenuation 1. This is a fine-tuning 2. Repression: Tryptophan repressor binds DNA only when Trp is present
a. The Trp operon has genes: E, D, C, B, A b. There is a promoter site and an operator site c. And upstream of the first gene is a leader region (trpL) i. It is involved in attenuation d. The repressor binds to the operator i. It isn’t in the right conformation to bind on its own ii. When the repressor is complexed with Trp, it represses the operon 1. Thus, it is a self-regulated cycle a. When there is a lot of Trp, you don’t want to make more (so the Trp operon is repressed) 3. Attenuation = “to lessen something” (another way of regulation) a. Definition of attenuation: “Termination of transcription before the start of the first gene” b. A Rho-independent terminator is located in the leader sequence i. BUT it does not always cause termination ii. It’s a regulated terminator
Attenuated RNA
iii. Attenuated RNA 1. It’s kind of like abortive transcription 4. In the leader sequence, there are two competing mRNA structures can form depending on Trp levels in cell
a. In a terminator structure: 1 & 2 pair and 3 & 4 pair and it’s followed by a chain of U’s b. In an antiterminator structure: 1 is free, 2 & 3 are paired, and 4 is free 5. How does the cell sense the level of tryptophan? a. The charging of tRNAs is very sensitive to amino acid concentrations b. Translation is very sensitive to levels of charged tRNAs in cell c. Ex: if there is a lot of tryptophan, there is a lot of charged tRNAs in the cell with tryptophan, and translation speeds up b/c there is a constant supply of Trp to build peptide chains
6. Leader sequence
a. Part of the leader sequence is translated (leader peptide) i. In the middle of the leader peptide are 2 Trp codons 1. This make the translation of the leader peptide sensitive to charged Trp-tRNAs, which in turn is sensitive to the level of Trp in the cell b. Ribosome pausing determines which secondary structure will form i. 1 with 2 and 3 with 4 ii. 1 free, 2 with 3, and 4 free 7.
Ribosomes pause at one of two places: a. Pauses at the stop codon if tryptophan is high in the cell i. Normally, when the ribosome gets to a stop codon, there is a pausing as it waits to see if any other tRNAs will come in, and then release factors finally arrive ii. *Every stop codon causes pausing at the site b. Pauses at the Trp codon if tryptophan is low in the cell
8. The whole purpose of the leader sequence is to see if we have charged TrptRNAs in the cell a. It is a little bit of a waste of energy b. You see that the two Trp codons come at the beginning (in region 1), so if the ribosome pauses at the Trp codon b/c the levels of Trp are low, region 1 will be blocked from binding with region 2
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ c. With high levels of Trp, the ribosome stops at the stop codon i. Blocks regions 1 and 2 ii. 3 and 4 pair iii. Attenuation occurs d. The whole operon is NOT synthesized i. There is Rho-independent termination transcription stops early
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ e. With low levels of Trp, the ribosome starts making the leader peptide (since there is a lack of Trp), and it stops at the Trp codon at the beginning of region 1 i. Blocks region 1, but NOT region 2 1. 2 and 3 bind, and 4 is left on its own f. Genes are translated into proteins
9. Structure of Trp Operon
1. Trp Operon a. Biosynthetic operon i. Trp regulation is used to synthesize Trp amino acid b. Two methods of control of the Trp operon: i. Repression 1. This is a coarse control ii. Attenuation 1. This is a fine-tuning 2. Repression: Tryptophan repressor binds DNA only when Trp is present
a. The Trp operon has genes: E, D, C, B, A b. There is a promoter site and an operator site c. And upstream of the first gene is a leader region (trpL) i. It is involved in attenuation d. The repressor binds to the operator i. It isn’t in the right conformation to bind on its own ii. When the repressor is complexed with Trp, it represses the operon 1. Thus, it is a self-regulated cycle a. When there is a lot of Trp, you don’t want to make more (so the Trp operon is repressed) 3. Attenuation = “to lessen something” (another way of regulation) a. Definition of attenuation: “Termination of transcription before the start of the first gene” b. A Rho-independent terminator is located in the leader sequence i. BUT it does not always cause termination ii. It’s a regulated terminator
Attenuated RNA
iii. Attenuated RNA 1. It’s kind of like abortive transcription 4. In the leader sequence, there are two competing mRNA structures can form depending on Trp levels in cell
a. In a terminator structure: 1 & 2 pair and 3 & 4 pair and it’s followed by a chain of U’s b. In an antiterminator structure: 1 is free, 2 & 3 are paired, and 4 is free 5. How does the cell sense the level of tryptophan? a. The charging of tRNAs is very sensitive to amino acid concentrations b. Translation is very sensitive to levels of charged tRNAs in cell c. Ex: if there is a lot of tryptophan, there is a lot of charged tRNAs in the cell with tryptophan, and translation speeds up b/c there is a constant supply of Trp to build peptide chains
6. Leader sequence
a. Part of the leader sequence is translated (leader peptide) i. In the middle of the leader peptide are 2 Trp codons 1. This make the translation of the leader peptide sensitive to charged Trp-tRNAs, which in turn is sensitive to the level of Trp in the cell b. Ribosome pausing determines which secondary structure will form i. 1 with 2 and 3 with 4 ii. 1 free, 2 with 3, and 4 free 7.
Ribosomes pause at one of two places: a. Pauses at the stop codon if tryptophan is high in the cell i. Normally, when the ribosome gets to a stop codon, there is a pausing as it waits to see if any other tRNAs will come in, and then release factors finally arrive ii. *Every stop codon causes pausing at the site b. Pauses at the Trp codon if tryptophan is low in the cell
8. The whole purpose of the leader sequence is to see if we have charged TrptRNAs in the cell a. It is a little bit of a waste of energy b. You see that the two Trp codons come at the beginning (in region 1), so if the ribosome pauses at the Trp codon b/c the levels of Trp are low, region 1 will be blocked from binding with region 2
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ c. With high levels of Trp, the ribosome stops at the stop codon i. Blocks regions 1 and 2 ii. 3 and 4 pair iii. Attenuation occurs d. The whole operon is NOT synthesized i. There is Rho-independent termination transcription stops early
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ e. With low levels of Trp, the ribosome starts making the leader peptide (since there is a lack of Trp), and it stops at the Trp codon at the beginning of region 1 i. Blocks region 1, but NOT region 2 1. 2 and 3 bind, and 4 is left on its own f. Genes are translated into proteins
9. Structure of Trp Operon
