I\'m struggling with microbiology. Here is the problem I\'m trying to solve. I h
ID: 121757 • Letter: I
Question
I'm struggling with microbiology. Here is the problem I'm trying to solve. I have only gained a basic understanding of lac operons and trp operons at this point. Can you possible solve this for me? Please discuss the lac operon in yourself. Last night you slept and were environmentally lac-. If you had a glass of milk this morning, you are now lactose+. Explain the genetic to phenotypic flow. Also, discuss the trp operon in you. Last night you slept and were environmentally trp+. If you had a slab of turkey bacon containing lots of tryptophan this morning, you are now trp-. Explain the genetic to phenotypic flow.
Explanation / Answer
Ans. At cellular level, the genetic to phenotype flow consists of following steps-
I. Step 1: Induction the gene: There must be some intracellular signals that trigger the initiation of gene transcription. For example, for induction of Lac operon, lactose must be there in the environment. Without these inducers and similar molecules. Regulator, a gene can’t switch between ON and OFF conditions.
II. Transcription: When appropriate stimuli are present, the gene is transcribed into mRNA.
III. Translation: The mRNA is translated into protein. The protein is the “phenotype” of the gene.
The fundamental difference between Lac and Trp operon that-
Lac operon is an Inducible System. In absence of effector, the repressor binds to operator and keeps the gene in OFF condition. So, the gene remains OFF in absence of effector.
The effector (E, here lactose) molecule binds to repressor (R). The (Effector-Repressor) complex can no longer bind to the operator. Thus, transcription is set ON. Since, the effector induces (triggers or initiate) gene transcription, it is called an Inducible system. The operon mediates catabolism of lactose sugar.
Trp operon is a Repressible System. In absence of effector, the repressor can NOT bind to operator and keeps the gene in ON condition. So, the gene remains ON in absence of effector.
The effector (E, here tryptophan) molecule binds to repressor (R). The (Effector-Repressor) complex now binds to the operator shutting OFF gene transcription. Since, the effector represses (inhibits/ stops) gene transcription, it is called a Repressible system.
The operon mediates anabolism of tryptophan amino acid.
Now, coming to the point-
#1. Lac operon: Humans don’t have Lac operon but many microbes in the gut (ex- E. coli) have Lac operon.
When environment is changed from Lac- (operon is OFF) to Lac+ (operon is ON) through intake of milk, the effector molecule (Lactose in milk) binds to repressor protein, thus the transcription of gene expression is set ON.
Genetic to Phenotype flow- Step 1: Lac operon is turned ON by the lactose molecule.
Step 2: The three genes of Lac operon (gene z, y and a) are transcribes to produced their respective mRNA.
Step 3: The mRNAs are translated into their respective enzymes which further catabolize lactose.
#2. Lac operon: Humans don’t have Lac operon but many microbes in the gut (ex- E. coli) have Trp operon.
When environment is changed from Trp+ (operon is ON) to Trp- (operon is OFF) through intake of turkey, the effector molecule (Tryptophan) binds to repressor protein, thus the transcription of gene expression is set OFF. It’s an obvious thing, when tryptophan is supplied abundantly through food, there is no need of synthesizing tryptophan using trp operon.
Genetic to Phenotype flow- Step 1: Trp operon is turned OFF by the tryptophan amino acid molecules.
Step 2: The genes of the operon are no longer transcribed to yield their respective mRNA.
Step 3: In absence of mRNA, no enzymes involved in Trp anabolism is produced. So, Trp amino acid is no longer synthesized using trp operon.