671. The most stabilizing force for nucleic acids is
A. hydrogen bonds
B. electrostatic bond
C. Van der Waals
D. conformational entropy

672. A purine with an amine (NH2) group on the 6th carbon is
A. adenine
B. cytosine
C. thymine
D. guanine

673. Which of the following is found on RNA but not DNA?
A. Uracil
B. Deoxyribose
C. Phosphate
D. Adenine

674. Which of the following is a purine?
A. Cytosine
B. Adenine
C. Thymine
D. Uracil

675. Which of the following techniques was carried out by Nirenberg and Matthaei in 1961 to determine the first codon?
A. In vitro synthesis of a polypeptide using UUUUU
B. Labeled peptide binding to a ribosome
C. Mixed co-polymer mRNA synthesis
D. none of the above

676. Bacterial protein called catabolic activator protein (CAP) is an example of
A. negative control of gene expression
B. positive control of gene expression
C. second type of positive control of gene expression
D. none of the above

677. How many different codons are possible?
A. 3
B. 20
C. 64
D. An infinite number

678. The genetic code is
A. universal
B. universal except for rare exceptions in mitochondria and some protozoa
C. species-specific
D. kingdom-specific

679. Which of the following has been used as an evidence that primitive life forms lacked both DNA and enzymes?
A. RNA can both code genetic information and act as a catalyst
B. DNA and enzymes are only present in the most advanced cells
C. Advanced cells lack RNA
D. All of the above

680. Crick demonstrated that the genetic code involved three bases and suggested that the code was degenerated. What experimental technique Crick conducted to suggest genetic code degeneration?
A. Gel electrophoresis
B. Density gradient centrifugation
C. Frameshift mutagenesis
D. Restriction digests of the rII gene