All TAs hold their office hours in the lab (ESB 220)

BIO 126L
EXAM 2, Sample 1

Dr. Pratibha Saxena

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TA’S NAME

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NAME OF YOUR MIC 226/228 INSTRUCTOR


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INSTRUCTIONS: 

MIC 129 K EXAM II has 6 pages, and 29 questions.
There are a total of 200 points, accounting for 20% of your final grade.
Place your name at the top of each page and check that your exam is complete.

ANSWER ALL QUESTIONS.
Be brief and precise in your answers. DO NOT RAMBLE!
You must show your calculations where asked.

Copying and all other forms of cheating will be met with the appropriate disciplinary action.


In case you dispute the answer that is deemed correct, you MUST first submit to your TA your question and the reason that you think your answer is the best (not just right, but the best of the answer choices) along with references that support your viewpoint. This must be done within 1 week after the exams are returned.

YOU MUST HAND OVER YOUR COMPLETED EXAM TO YOUR TA WHEN LEAVING THE ROOM AND MAKE SURE THAT YOUR NAME HAS BEEN WRITTEN DOWN


GRADES WILL BE POSTED BY THURSDAY MAY 14 ON THE LAB DOORS

1. Answer True or False for the following. Correct the statements that are not true:  (2 pts each)

a. _____ Enrichment medium allows one type of organism to grow while inhibiting others.



b. _____ A change in the nucleotide sequence of an organism may result in the organism becoming auxotrophic.



c. _____ After conjugation with an Hfr strain, an F- strain may exhibit a new phenotype.



d. _____ An individual with an O negative blood type can receive blood from anyone.



e. _____ In agarose gel electrophoresis, smaller DNA fragments migrate farther as compared to the large DNA fragments.

Multiple choice: Circle the BEST answer (3 pts each)

2. The purpose of pasteurization at 80°C in the enrichment lab was... ?

a. to kill all cells

b. to kill vegetative cells

c. to select for gram + bacteria which can survive heat better than gram -.

d. to increase the mutation rate, allowing mutants to be isolated.

3. Which of the following selects for Gram NEGATIVE bacteria?

a. Mac Conkey’s agar	b. Blood agar
c. KIA agar	d. none of these

4. What is transferred in an Hfr X F- conjugation?

a. Carbohydrates	b. Nucleic acid
c. Lipid	d. Proteins

5. What is transferred between strains during cross-feeding?

a. substrate	b. enzymes
c. nucleic acids	d. all of these

 

6. Type II restriction endonucleases (the kind you used in the lab to digest lambda DNA), will most likely recognize and cleave a DNA fragment at the following site: (Keep in mind this only shows one of the two strands)

a. GGGTTT	b. ATCGGC
c. AACGTT	d. CGATGC

 

Fill in the blanks: (3 pts for each blank)

7. Decarboxylases are inducible enzymes. They are induced in the presence of the substrate, provided the environment is both ____________________ and __________________

8. KIA tubes offer important information in identification of microorganisms. 
A black color in this reaction is indicative of _________________.  The chemical name of the black precipitate is ____________________________ 

9. In agarose gel electrophoresis, DNA fragments move towards the _______________ electrode, because the DNA fragments are ___________________ charged.

10. At the end of Hfr X F- conjugation, the donor strain is ___________, and the recipient is _________________

11. A patient’s blood causes NO hemagglutination with anti-A, anti-B or anti-Rh antisera.  The patient’s blood type is _______________________ ; and the patient’s blood contains  _______________________ antibodies.

12. Simon’s citrate agar uses __________________ as the source of carbon. Organisms  capable of using this carbon source turn the agar ________________ (write down the color).

13. “Phenylalanine deaminase” test, uses _______________________ (name the reagent).  A positive reaction is indicated by the appearance of a ______________ color.

Short answers: Please be precise in your answers.

14. (8 pts) You have a chemically defined medium containing only a buffered carbon source.  Could you use this medium to enrich for any particular group of microorganisms?  If “Yes” which property of the organism allows it to do so.  If “No”, then why not?






15. (10pts)  Mention 5 characteristics of enterics.





16. (4 pts)  Briefly describe the difference between beta and gamma hemolysis.

17. (9 pts) Name a medium that you used in the lab to select for Gram positive microorganisms. Which component(s) of this medium allowed it to be selective for Gram positive microorganisms?






18. (10 pts) Why is it important to read your KIA tube’s results within 18 to 24 hours?  (Be brief and complete in your answer. Make sure you mention the problems both associated with early reading as well as those due to late reading)







19. (9 pts) Explain and interpret the following observation: 
A student wrote down the following results for the KIA tube: + / - / +







20. (5 pts) Besides Gram staining and morphological differences, Staphylococcus aureus and Streptococcus fecalis can be distinguished from one other by _________________ test.





21. (10 pts)  What is the function of the indicator strain in plaque assay?  How would the amount of indicator influence the assay?








22. (5 pts)  What is the main difference between a cell that is an Hfr and one that is F+.





23. (10 pts) At 25°C Serratia marcescens appears red, where as at 37°C it is colorless.  Is this a result of adaptation or mutation? How can you confirm this?








24. (15 pts) The following biochemical pathways describe three mutants having a defect at three  different steps. Use the information given below, to fill in the blanks.

Mutant 1: A------>B------>C------>D---X--->E

Mutant 2: A--X-->B------>C------>D-------->E

Mutant 3: A------>B------>C--X-->D------->E

List ALL the mutants that Mutant 1 can crossfeed: _______________

List ALL the mutants that Mutant 2 can crossfeed: _______________

List ALL the mutants that Mutant 3 can crossfeed: _______________

25. (12 pts) What will be the genotype of the recombinants obtained as a result of conjugation  between an Hfr (leu +, his -, and tetracycline sen) and an F- (leu -, his + and tetracycline resistant)?

Fill in the table below to show which of these organisms will grow on which medium. (F-, Hfr and/or recombinants)

Relevant genotype of the recombinants: _________________________

 

MEDIUM	ORGANISM(S) EXPECTED TO GROW
Minimal medium (M.M.)	_______________________
M.M.+ tetracycline	_______________________
M.M.+ leu + tetracycline	_______________________
Complete medium  (TSA)	_______________________

 

26. (10 pts) You need to find out the titer of a “Stock” solution of bacteriophage T7. To accomplish this, you made serial dilutions and used 0.1 ml of diluted phage solutions (from each tube) for the plaque assay. Next day you counted 50 plaques from the 10-3 dilution tube. (Show  your calculations)

Titer of the phage “Stock” is __________________________ (Use appropriate units) 







27. (6 pts) What is the importance of serotyping in microbiology labs in the health departments?






28. (5 Points) How are DNA bands visualized on an agarose gel after electrophoresis?   (Mention how it was done in your gel electrophoresis lab)








29. (5 pts) What is the main difference between agglutination and flocculation?
OR
What is the purpose of the Widal test?