Question

QUESTION 26

Which of the following will have the LEAST influence on the efficiency of transformation in E. coli bacteria?

A. heat shock

B. calcium chloride treatment

C. chilling on ice

D. using high concentrations of DNA

E. electrical field

QUESTION 31

1. Heat can disrupt hydrogen bonding between DNA strands. Which of the following DNA strands would denature at the LOWEST temperature?

   	A.	90% AT and 10% GC
   	B.	70% AT and 30% GC
   	C.	10% AT and 90% GC
   	D.	30% AT and 70% GC
   	E.	50% AT and 50% GC

QUESTION 32

1. You are a researcher studying the genetic basis of colon cancer. You have been working with a colon cancer cell line to determine the expression levels of different genes that might contribute to cancer formation. You obtain the DNA methylation status of five genes of interest (the data are shown in the table below). The plus (+) sign indicates the level of DNA methylation; more plus signs correlates with increased methylation levels.

   Gene	Methylation levels
   1	++
   2	+++++
   3	+++
   4	++
   5	+

   
   Based on the information shown above, which gene would you predict to have the highest rate of transcription?

   	A.	gene 5
   	B.	gene 2
   	C.	gene 1
   	D.	gene 3
   	E.	gene 4

Answer 1

Question 26

Answer: Chilling on ice will have the least influence on the transformation efficiency in E. coli. This because chilling on ice is used to stabilize the bacteria cell membrane and decreasing the time on incubation on ice will not have effect transformation efficiency. Hence, option C is the correct answer. Heat shock during transformation is an important step because it helps in uptake of the plasmid DNA. Calcium chloride treatment is used to make the E.coli cells competent. Highly competent cells will increase the transformation efficiency. Using high concentration DNA will decrease the transformation efficiency. Optimum electrical field is essential for transformation of E.coli cells during electroporation. Hence, options A, B, D and E are incorrect answer.

Question 31

Answer: DNA with high AT content and low GC content will require lowest temperature to denature DNA. This because the number of hydrogen bonds between A-T is two and G-C is three. The energy required to break two hydrogen bonds between A-T is less than the three hydrogen bonds between G-C. Hence, option A (90% AT and 10% GC) is the correct answer and options B, C, D and E are incorrect.