Question

17. a. (2 pts) When discussing prokaryotic gene regulation, define the term constitutive:

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b. (2 pts) Which of the following partial diploids is constitutive? As a reminder a partial diploid contains two copies of the genes shown below. The genes before the slash are on the bacterial chromosome. The genes after the slash are on a plasmid.

a. lacI⁺ lacO⁺ lacZ⁺/lacI⁺ lacO⁺ lacZ⁺     b. lacI^- lacO⁺ lacZ⁺/lacI⁺ lacO⁺ lacZ+      

c.lacI⁺ lacO^c lacZ⁺/lacI⁺ lacO⁺ lacZ⁺   d. lacI^s lacO⁺ lacZ⁺/lacI⁺ lacO⁺ lacZ⁺

19. (6 pts) Outline the differences between these three bacterial strains (one or two sentences)

F – strain ________________________________________________________________

F + strain _________________________________________________________________

Hfr strain__________________________________________________________________

20 a. (2 pts) Which of the above strains can donate genes to another bacterium? _____ and ______.

b. (1 pt) Which of the above is the recipient in a conjugation gene-mapping experiment? ______.

c. (1 pt) Name of structure formed during conjugation which permits transfer of genetic information? _______.

22. a. (4 pts) In 1 or 2 sentences define transformation in bacteria __________________________

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b. (2 pts) Most laboratory bacterial strains cannot naturally undergo transformation. Term for bacterial strain which through heat-shock/other method is rendered able to undergo transformation _________

Answer 1

•Prokaryotic gene regulation is a sequential [-on and off-] process of transcription and translation by regulatory proteins.

•Gene regulatory protein is the product [expressed ] of regulatory gene , may act as activator or repressor. The binding of activator protein to the target DNA site [near promotor region] increases the rate of transcription [positive control]. The binding of repressor protein to the target DNA site decreases the rate of transcription [negative control].

•Constitutive Expression:- A typical bacterium contains several thousand genes , some genes are very important to the life of cell and hence they are remain active at all time. Thus their expression occur Constitutively, meaning that they are expressed at a reasonably constant rate and not subjected to regulation. A housekeeping gene is typically a constitutive gene that is transcribed at a relatively constant level.

• Constitutively expressed genes, are always "on“; In Contrast inducible as well as repressible or, indeed, facultative genes. These are on and off expression which regulated by inducer [activator] or repressor.

•Mutant gene of an inducer operon are always transcribed , even in the absence of inducer. And it is now called constitutive mutant.

•Eg:- in constitutive Lac mutation , all three lac operon genes are transcribed at all times and not turn off, even in the absence of lactose.

•b. lacI- lacO+ lacZ+/lacI+ lacO+ lacZ+  = is constitutive . Because it shows mutation in I [repressor] and here represented as I-

•F- Cells are Cell lacking F [fertility factor]plasmid . The bacterium  F-, can only act as the recipient, during conjugation.

•F+ Cells are Cells containing F - factor on plasmid . The bacterium is F+ is the donor. ...

•The integrated strains F+ and F- of are called Hfr, because of the high frequency of recombination. [that occurs when mated with F- bacteria.]

•Hfr cells can become F+, but F+ cells cannot become Hfr. Hfr are able to conjugate with only other Hfr cells, and F+ cells are able to conjugate only with other F+ cells.

•Out of the above strains F + strain and Hfr strain can donate genes to another bacterium.

•F – strain is the recipient in a conjugation gene-mapping experiment.

•Conjugation tube is formed during conjugation which permits transfer of genetic information. The special surface appendage is present on bacterial cell called PILI. Pili are used during conjugation that’s why it is also called sex pili , which is shorter in length than flagella but larger than fimbrae.

•The term transformation is define as the absorbance [taken up] of foreign DNA [naked] material from surrounding medium [environment. ]