MIC205B Exam 1 Key

September 20, 2007

Instructor: Dr. Stephen Billington

 

Part 1 MULTIPLE CHOICE: Read each question and the answers carefully. Circle the correct answer on the test paper. Each correct answer is worth 3 points, for a Part 1 total of 45 points. Correct answers are underlined below

 

JUSTIFICATIONS: If you are unsure of an answer, you may write a short explanation next to the question on the test paper (this may earn you points if your answer is wrong, but you can justify it).

 

1.         Monosaccharides are joined together using

 

a. ester linkages

 

b. glycosidic bonds

 

c. peptide bonds

 

d. crazy glue

 

2.         The primary structure of a protein refers to

 

a. the three dimensional structure of the protein

 

b. the interactions of the protein with other proteins

 

c. the sequence of amino acids in the protein

 

d. the presence of D-amino acids

 

3.         Nucleotides are composed of

 

a. a sugar, a nitrogenous base and a phosphate

 

b. an amino acid, a nitrogenous base and a phosphate

 

c. a glycerol molecule and three fatty acids

 

d. two sugar molecules linked by a glycosidic bond

 

4.         The process of modifying a molecule after it diffuses into the cell to maintain a concentration gradient is called

 

a. group translocation

 

b. passive diffusion

 

c. active transport

 

d. osmosis

 

5.         Long carbon chains that are completely bonded to hydrogen are

 

a. unsaturated

 

b. liquid at room temperature

 

c. saturated

 

d. polyunsaturated

                                                                                          

6.         Peptidoglycan is a polymer of the alternating sugars

 

a. glucose and galactose

 

b. ribose and deoxyribose

 

c. alanine and cytosine

 

d. N-acetylglucosamine and N-acetylmuramic acid

 

7.         In the β-form of glucose,

 

a. the hydroxyl group on carbon 1 is below the ring

 

b. the hydroxyl group on carbon 1 is above the ring

 

c. the hydroxyl group on carbon 2 is missing

 

d. the hydroxyl group on carbons 2 and 3 are missing

 

8.         The plasma membrane is

 

a. impermeable to all molecules

 

b. impermeable to H₂O

 

c. permeable to all molecules

 

d. selectively permeable

 

9.         D-amino acids are found in

 

a. proteins

 

b. peptidoglycan

 

c. carbohydrates

 

d. DNA

 

10.       The Sec protein secretion system is used

 

a. by Gram negative cells to transport proteins across both membranes

 

b. to transport proteins across the peptidoglycan layer of bacterial cells

 

c. to transport proteins across the plasma membrane  of bacterial cells

 

d. to transport nutrients into the cells against a concentration gradient

 

11.       If the genome of a virus has the following composition 155 A, 133 C, 133 G and 155 U. What type of nucleic acid is the genome made of?

 

a. double stranded DNA

 

b. single stranded RNA

 

c. single stranded DNA

 

d. double stranded RNA

 

12.       Which of the following is NOT a component of the Gram negative lipopolysaccharide

 

a. Lipid A

 

b. core polysaccharide

 

c. teichoic acid

 

d. repeating O-side chain

 

13.       Which of the following macromolecules are not formed by polymerization

 

a. lipids

 

b. carbohydrates

 

c. proteins

 

d. nucleic acids

 

14.       Active transport

 

a. requires energy input

 

b. does not require energy input

 

c. allows H₂O to enter the cell

 

d. requires a concentration gradient

 

15.       Penicillin acts as an antibiotic by

 

a. preventing the cross linking of peptidoglycan tetrapeptides

 

b. cleaving the glycosidic bonds between N-acetylglucosamine and N-acetylmuramic acids

 

c. preventing the formation of ester linkages in phospholipid synthesis

 

d. Cleaving crosslinked peptidoglycan molecules

Part 2 SHORT ANSWER: Read each question carefully and answer each question in the space provided. Each correct answer is worth 5 points, for a Part 2 total of 45 points.

 

JUSTIFICATIONS: Again, if you are unsure of an answer, you may write a short explanation next to the question on the test paper.

 

16.    a.   True OR False? Lipids are polar and dissolve in water. This is an important property for the formation of bacterial membranes.

 

__FALSE_________

 

         b.   True OR False? Bacterial membranes are fluid, allowing proteins and phospholipids to move laterally through the membrane.

 

____TRUE________

 

17.       In the space below, draw the formation of a β1-4 glycosidic bond between two glucose molecules using structural formula. Include reactants and products.

 

 

 

 

 

 

 

 

 

 

 

 

 

18.    DNA and RNA are polymerized in the 5’-3’ direction. What do the 5’ and 3’ numbers refer to?

 

___Carbons 5 and 3 on adjacent deoxyribose or ribose sugars. These carbons are connected through phosphate in a phosphodiester bond

 

19.    a.   Fill in the blanks. A peptide bond is formed between the carboxyl group of one amino acid and the amino group of the next amino acid.

 

         b.   Fill in the blank. The start of a protein is called the amino or N- terminus and the end of a protein is called the carboxyl or C- terminus.

 

20.    a.   True OR False? Peptidoglycan is an almost impermeable barrier that excludes most nutrients from the cell.

 

FALSE

 

         b.   True OR False? The outer membrane of Gram negative bacteria is more permeable than the plasma membrane.

 

TRUE

 

21.    Fill in the blanks. DNA contains four nitrogenous bases; the pyrimidines cytosine and thymine, and the purines adenine and guanine.

 

22.    a.   True OR False? The secondary structure of protein refers to the local folding of amino acids into structures such as α‑helices and β‑sheets.

 

TRUE

 

         b.   The quaternary structure of proteins refers to multiple polypeptide subunits coming together to form a functional protein.

 

TRUE

 

23.    Fill in the blanks. In the Gram stain, following decolorization with the alcohol, Gram negative cells will be colorless, while Gram positive cells will retain their purple/violet color. This results from the dehydration of peptidoglycan in the Gram positive cell wall, which traps the crystal violet-iodine complex inside the cell.

 

24.    a.   Fill in the blanks. In Gram negative bacteria, the Type II secretion system transports proteins across the outer membrane, while the Type I secretion system transports proteins directly from the cytoplasm to the external environment.

 

         b.   True OR False? Both Type I and Type II secretion systems require energy in the form of ATP.

 

TRUE

 

Part 3 SHORT ESSAY: Answer TWO of the following questions in the space provided. Each correct answer is worth ten points, for a total of 20 points for Part 3.

 

25.    Using a schematic diagram describe the structure of peptidoglycan in Gram negative and Gram positive bacteria. Label the sugars and amino acids, and indicate any unusual bonds.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

26.    Describe the fate of bacterial cells in hypotonic and hypertonic solutions. Describe what happens to these cells if the cell wall is removed.

 

Hypotonic solutions are those where solute concentrations are greater inside the cell than outside the cell. As a result water (which can move freely through bacterial membrane and cell walls) moves into the cell. Bacterial cells are protected in hypotonic solutions by the strength of the peptidoglycan in the cell wall which maintains the integrity of the cell. Even though the cell membrane expands, the cell wall prevents the cell from lysing. Cells without cell walls are osmosensitive. In hypotonic solutions, water will move into the cell, and the cell will expand and eventually burst.

 

Hypertonic solutions and those where solute concentrations are greater outside the cell than inside the cell. As a result water moves out of the cell. Bacterial cells are sensitive to high external solute concentration because when water moves out of the cell the cytoplasm dehydrates. Even though the cell wall maintains cell shape, the plasma membrane will shrink away from the cell wall in a process called plasmolysis and the cell will eventually die. Cell without cell walls are very sensitive to hypertonic conditions, as water rushes out of the cell and the cell shrinks and dies.

 

 

 

27.    Describe the structure of deoxyribonucleic acid, including nucleotides (and their components), bonds between nucleotides and bonds between DNA strands.

 

In DNA, nucleotides are composed of deoxyribose, phosphate and one of four nitrogenous bases (adenine, cytosine, guanine and thymine)

 

Nucleotides are linked by phophodiester bonds forming a sugar phosphate backbone where deoxyribose sugars are linked by phosphate groups through carbons 3 and 5. The nitrogenous base is attached to carbon 1 of deoxyribose

 

DNA is double stranded, and the two strands are linked though hydrogen bonding between the nitrogenous bases. A only binds with T (2 H-bonds), while C only binds with G (3 H-bonds) 

 

 

 

 

 

 

 

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