1) After mixing a heat-killed, infectious smooth strain of bacteria with a livin
ID: 71447 • Letter: 1
Question
1) After mixing a heat-killed, infectious smooth strain of bacteria with a living non-infectious rough strain, you discover that some of the living cells are now infectious. Which observations would provide the best evidence that the ability to infect is a HERITABLE trait?
a. DNA is passed from the heat-killed strain to the living strain.
b. Protein is passed from the heat-killed strain to the living strain.
c. The infectivity in the living strain is especially virulent.
d. Descendants of the living cells are also infectious.
e. Both DNA and protein passed from the heat-killed strain to the living strain.
2) Which of the following important inferences made by Watson and Crick was NOT possible from just observing the X-ray micrograph of DNA made by Rosalind Franklin?
a. the shape is helical
b. diameter of the helix
c. height of one turn
d. base pairing of AT and GC
e. all of the above
3) The single-stranded DNA molecule 5'-ACCGGA-3' can form a double helix with a DNA molecule of sequence ____, to form a double-stranded DNA molecule held together by ____ hydrogen bonds:
A) 5'-ACCGGA-3', 12.
B) 5'-TCCGGT-3', 6.
C) 3'-ACCGGT-5', 12.
D) 3'-TCCGGT-5', 16.
E) 3'-TGGCCT-5', 16.
Explanation / Answer
1.
The DNA is passed from heat killed, infectious smooth strain to living, non-infectious rough strain by the process of transformation and therefore, the non-infectious strain is converted to an infectious strain. Hence, option (a) is correct.
2.
The structure of DNA as double helix was proposed by Watson and Crick and they got the idea of DNA structure of DNA as double helix by observing the X ray diffraction picture of DNA worked out by Rosalind Franklin. But the X - ray diffraction picture of DNA exhibited the 3 dimensional structures but not given the idea about shape, diameter, height of one turn and base pairing in the DNA double helix. Hence, the option e is correct.
3.
The DNA sequence 5` - ACCGGA-3' forms complementary base pairing with DNA sequence 3'-TGGCCT-5', 16. The base A pairs with T by 2 hydrogen bonds and G pairs with C by 3 hydrogen bonds and hence, the total number of hydrogen bonds in the sequence are 16. Therefore, the option E is correct.
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