Question

If the concentration of the Pumilio protein is uniform throughout the drosophila egg cytoplasm, then how does it inhibit the production of the Hunchback protein at the posterior end but not the anterior end of the embryo?

A.

The strongly reducing environment in the posterior parts of the embryo causes cleavage of intramolecular disulfide bonds to cause of activation of Pumilio

B.

Drosophila embryogenesis depends on a combination of processes described in all the above process

C.

High pH of the posterior end of the embryo causes local activation of Pumilio, which then suppresses Hunchback expression

D.

The protein Pumilio inhibits transcription of the hunchback mRNA only in the presence of Nanos, which is present in a decreasing gradient from posterior to anterior

E.

Specific kinases highly expressed in the posterior end of the embryo phosphorylate and activate the locally present Pumilo molecules, which then suppress the production of Hunchback

2. Draw the structures of the four DNA bases in your scrapbook and state the position of the substitutions on the central ring structure. Name the central ring structure

A.

A: 6-aminopurine; G: 2-amino 6-hydroxypurine; C: 2-hydroxy 4-aminopyrimidine; T: 2,4-dihydroxy-5-methylpyrimidine

B.

A: 4-aminopurine; G: 2-amino 4-hydroxypurine; C: 2-hydroxy 4-aminopyrimidine; T: 2,4- dihydroxy-5-methylpyrimidine

C.

A: 4-aminopurine; G: 2-amino 4-hydroxypurine; C: 2-hydroxy 4-aminopyrimidine; T: 2,6-dihydroxypyrimidine

D.

A: 4-aminopurine; G: 2-amino 4-hydroxypurine; C: 2-hydroxy 6-aminopyrimidine; T: 2,6-dihydroxy-5-methylpyrimidine

E.

A: 6-aminopurine; G: 2-amino 6-hydroxypurine; C: 2-hydroxy 4-aminopyrimidine; U: 2,4-dihydroxypyrimidine

3.

What is a chi sequence?

A.

5’-GGTGCTGG-3’; it is a site where the Rec D nuclease activity on the strand with the 5’-end is suppressed

B.

5’-GGGCGTGC-3’; it is a site where the RecBCD nuclease activity on the strand with the 3’-end is suppressed

C.

5’-GCTGGTGG-3’; it is a site where the Rec B nuclease activity on the strand with the 3’-end is suppressed

D.

5’- GCTGGTGG -3’; it is site at which an endonuclease cut is made

E.

5’-AAUAAA-3’; it is site at which an endonuclease cut is made

Answer 1

Correct answers

1.If the concentration of the Pumilio protein is uniform throughout the drosophila egg cytoplasm, then how does it inhibit the production of the Hunchback protein at the posterior end but not the anterior end of the embryo?

D. The protein Pumilio inhibits transcription of the hunchback mRNA only in the presence of Nanos, which is present in a decreasing gradient from posterior to anterior.

pumilio is a Drosophila gene which expressed maternally and there is uniformly dispersed throughout the embryo. Pumilio is required for embryonic development. During early embryonic development when the genome is transcriptionally silent maternally derived mRNA transcripts regulates the expression patterns of the embryo. During this stage, mRNA encoding Hunchback are regulated by Pumilio. Hunchback mRNA is distributed throughout the embryo but the protein must be restricted to the embryonic anterior. Nanos spatially restricts Hunchback expression by originating from the posterior pole and thus opposing the Hunchback gradient.

for repression of Hunchback there are Nanos response elements (NREs) whuch are the RNA sequences located in the 3′ untranslated region (3′ UTR) of Hunchback mRNA, These NREs are the binding sites for Pumilio. A trimeric Nanos-Pumilio-NRE complex is formed when Nanos partners with Pumilio on the NREs, This complax in turn represses Hunchback .

2. Draw the structures of the four DNA bases in your scrapbook and state the position of the substitutions on the central ring structure. Name the central ring structure.

A. A: 6-aminopurine; G: 2-amino 6-hydroxypurine; C: 2-hydroxy 4-aminopyrimidine; T: 2,4-dihydroxy-5-methylpyrimidine

3. What is a chi sequence?

C. 5’-GCTGGTGG-3’; it is a site where the Rec B nuclease activity on the strand with the 3’-end is suppressed.

In the genomes of enteric bacteria Chi sites are recombination hot spots. RecB acts as 3'-5' helicase, nuclease.