The researchers set up the following experiment: 1. Each yeast strain is diluted
ID: 206056 • Letter: T
Question
The researchers set up the following experiment: 1. Each yeast strain is diluted in phosphate buffer solution so that there is the same concentration 2. Lysis buffer, which dissolves the cell membrane and releases the cytosol into the solution, is 3. ONPG is added to each tube. After 15 minutes, the researchers use a spectrophotometer to of cells in each tube. added to each tube. measure the A420 for each reaction. units are a measure of how much active enzyme there is present in a solution. The higher the The Aso is used to calculate the Activity Units of each tube, measured in velocity/mL. Activity Activi ty Units, the more active enzyme is present. Their data is shown in the table below. Yeast Strain Activity Units (velocity/mL) 3.6 95.3 241.7 6.2 1. (1 pt) Why do the researchers have to lyse the cells? 2. (1 pt) What protein/enzyme is encoded by the lacZ gene? (2 pts) The lacZ gene is placed in front of a promoter that normally binds to another gene. What is the protein that is encoded by the gene to which this promoter belongs? What is that protein's function? 3. (2 pts) Based on your previous answer and what you know about transcription, is this a housekeeping gene or a responsive/differentiated gene? Include in your answer the definition of both terms and why this gene belongs to the category you've chosen. 4.Explanation / Answer
1. Why do the researchers have to lyse the cells?
Lysing of cells break the cell membrane and releases the cytosol to the solution. As a result, the enzyme produced by the yeast can be studied. Without lysing the cells it is difficult to extract the enzyme of our interest. Hence, researchers have to lyse the cells to study the activity of the enzyme.
2. What protein or enzyme is encoded by the lacZ gene?
The gene lacZ encodes a protein called beta-galactosidase. This protein has enzymatic property and converts lactose into galactose and glucose.
3. The answer to question 3
The protein encoded by the gene to which the promoter belongs is the lac operon repressor. This protein is encoded by the gene lacI.
In the absence of lactose, the lac operon repressor protein inhibits the binding of RNA polymerase to the promoter of lacZ gene. As a result, the expression of beta-galactosidase by lacZ is blocked.
4. The answer to question 4
Based on the previous answer the gene lacI is a responsive gene. The activity of lac repressor protein is positively or negatively regulated by the absence or presence of lactose.
Housekeeping genes: Genes which are essential for the basic functioning of cells are called housekeeping genes
Responsive/ differentiated gene: Genes which are under regulation by other biomolecules are called responsive/ differentiated genes. There are of two types: a. Inducible genes b. Repressible genes