Question

1. In a Quelling reaction test, the antibodies added to the sputum sample are reacting to what morphological feature on the bacterium which causes the bacterium to swell - a positive test result.

outer membrane

flagellum

capsule

cell wall

2. When the Western Blot is used to test for Lyme Disease what the procedure is testing for specifically in the individual is the presence of

  fragments of the bacterial outer membrane

the bacterium

specific DNA sequences from the bacterium

antibodies against the bacterium

3. Restriction enzymes, used in DNA fingerprinting, search for and cut pieces of ds DNA that are palindromes. Which below is a palindrome? (In the answers the top strand is listed first followed by it's complement)

CCCCCC GGGGGG

AAATTG TTTAAC

GAATTC CTTAAG

GTAAGC CATTCG

Answer 1

Ans 1: Correct option capsule

Explanation: This technique is used to detect the presence of Streptococcus pneumoniae which causes various diseases like pneumonia, meningitis, etc.

When the antibodies bind with the polysaccharides present on the capsule of the bacteria the refractive index of the capsule is changed. Hence capsule appears swollen when observed under the microscope.

The explanation for incorrect options:

• Antibodies are specific for the capsule they bind with capsule and not with the flagellum.
• Antibodies do not bind with the cell wall. The Capsule surrounds the cell wall and allows the bacteria to get an escape from the immune system. Hence antibodies target the capsule and bind with the capsule.

Ans 2: correct option: antibodies against the bacterium.

Explanation: Testing for Lyme disease is a two-step process. At first, the ELISA (enzyme-linked immunosorbent assay) test is done. If the result of this test is positive the second test western blot is done as a confirmatory test. In western blot, we look for the presence of IgG and IgM antibodies.

The explanation for the incorrect options:

Antibodies that bind to the bacterial outer membrane are further detected by western blot. Thus it's not bacterial outer membrane that is detected by western blot.

Antibodies do not bind with the specific DNA sequences from the bacterium thus these DNA sequences are not detected by western blot.

Ans 3: The sequence CCCCCC GGGGGG is the palindromic sequence.

Explanation: 5' CCCCCC GGGGGG 3'

3' GGGGG CCCCCC 5'

If we read the upper strand in 3' to 5' direction we will get the sequence similar to the complementary strand hence it is the palindromic sequence.

Incorrect options:

5' AAATTG TTTAAC 3'

3' TTTAAC AAATTG 5'

5' GAATTC CTTAAG 3'

3' CTTAAG GAATTC 5'

5' GTAAGC CATTCG 3'

3' CATTCG GTAAGC 5'

Explanation: In all the other sequences we will not get the sequence similar to the complementary strand when we read them in the reverse direction. Hence they are not palindromic sequences.