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PID Number ______-______

HOUR EXAM I

BIOLOGY 108

FALL, 2004

In the spirit of the honor code, I pledge that I have neither given nor received help on this exam.

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1. (12 points) Below is a diagram of a bacterium.

Is this a gram-negative or a gram-positive organism? (circle one)

Label the indicated parts.

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

What is the composition in terms of major macromolecules of a.______

b.______

c.______

d. ______

If this bacterium were of the other type with respect to the Gram stain, what would be 3 major differences in the cell structure?

1.
2.
3.

2. (16 points) Fill in the following table with respect to bacterial growth.

Organism and medium / Conditions / Growth rate (fast, medium, slow, or none) / biochemical process producing energy / Electron donor / Final electron acceptor
E. coli with glucose and nutrient broth
(rich medium) / aerobic
37o
E. coli with glucose and nutrient broth / anaerobic
37o
E. coli with CO2, NO3, H2SO4 , and salts / aerobic
37o
Thiobacillus in medium with H2SO3 , and salts / aerobic
25o

3. (7 points) Bacterial growth curve

Identify each of the four phases of bacterial growth shown in the above graph.

A.______

B.______

C.______

D.______

What is the doubling time of the cells in phase B (to within 20 min.)? ______

In which phase are most bacteria in nature? ______

4. (4 points) Some bacteria, such as Bacillus subtilis, form spores under conditions in which growth can no longer be supported. Sporulation has many distinct stages and different proteins are made in each stage. At the level of transcription, explain how the bacterium regulates transcription so that the mRNA needed for various sporulation proteinsis made at the correct stages.

5. (7 points) The presence or absence or specific small molecules can influence the level of transcription of an individual gene. There are 2 major mechanisms of regulation of transcription. Label the molecules involved in the regulation of the genes below.

  1. What type of mechanism is depicted above? ______
  1. Will this scenario lead to transcription? ______
  1. What is the corepressor in this system? ______
  1. How many proteins will a prokaryote make from this message (when the operon is expressed) ? ______

6. (17 points) One example of positive control of transcription is the regulation of the maltose operon. What is the major type of protein involved in positive control? ______

Fill in the following table (using + and -) to indicate the phenotype of the various E. coli genotypes listed below.

E. coli genotype / Protein B made / Ability to grow on minimal media with maltose
In presence of maltose / In absence of maltose
Wild type
A+p+abs+K+B+M--
A+p+abs+(ATG of K) K+B+M--
A--p+abs+K+B+M+
A+p--abs+K-B+M--
A--p+abs+K+B+M--

A=activator, p=promoter, abs=activator binding site, K=maltose transport protein, B=lamB maltose porin, M=maltase needed to digest maltose, =is a deletion

What would happen if the A+p+abs+K+B+M--bacterium was infected with lambda? ______

7. (8 points) B. pertussis is the bacteria which causes whooping cough in humans. In order to invade hosts, B. pertussis must sense its environment and regulate the expression of sets of genes. For example, B. pertussis makes a toxin only in the presence of host cells. In order to study the reguation of the production of this toxin, you make a mutant of B. pertussis which no longer makes toxin. You clone and sequence the mutated gene and find that it encodes a DNA binding protein. Suggest a hypothesis for how this gene could be involved in the regulation of toxin biosynthesis.

_

In your continued study, you isolate another gene in which mutations abolish toxin biosynthesis. This gene encodes a membrane protein. Suggest a hypothesis for how this second gene could be involved in the regulation of toxin biosynthesis.

If your hypothesis is correct what will be the phenotype (with respect to toxin production) of a mutant

a. in which the first gene is placed behind the lambda PR promoter? ______

b. in which the second gene is placed behind the lambda PR promoter? ______

8. (8 points)Shown below are the components of the chemotaxis system in E. coli.

Fill in the table with the phenotype of each of the listed mutants.

Mutation / Phenotype
Delete cheA
Delete cheZ
CheY mutant in which the histidine which is phosphorylated is replaced by glycine
  1. In the presence of a constant chemoattractant, E. coli will exhibit ______methylation of the receptor transducer proteins.
  1. In the presence of an increased chemoattractant, E. coli will exhibit ______sensitivity over time.

9. ( 6 points)

a. How does growth in the presence of histidine (an amino acid) effect the amino acid phenylalanine biosynthetic operon expression in E. coli bacteria with a mutation of Phe t-RNA synthetase so that it puts histidine on Phe-t-RNA? Describe the mechanism of this regulation.

b. In a trpR-- (R=repressor gene) bacterium, if you deleted region 3 of the attenuator, will tryptophan biosynthetic enzymes be made in the absence of tryptophan? ______

In the presence of tryptophan? ______

10. ( 7 points) Fill in the following table indicating the major genes in each category for each virus.

virus / immediate early genes / early genes / late genes
T4 / XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
T7 / XXXXXXXXXX
XXXXXXXXXX
XXXXXXXXXX
Herpes

11. (8 points) Fill out the following indicating the type of plaques (clear, cloudy, or none) which would be formed if  of the indicated genotype infected the strains of E. coli shown. The genetic map of  is given below.

PR cro tR1 CII tR2 Q tR3 PRlate SR...A...

______

xis att int CIII tL1 N PL CI PRMPRE

 genotype / bacterial host
E. coli K12 (-) / E. coli K12 ()
wild type
PR no longer binds CI
PR replaced with Ptrp and the cells are grown on minimal medium
PRM replaced with Ptrp and the cells are grown on minimal medium