19. In order to perform polymerase chain reactions (PCR), which of the following components is required?
(A) DNA ligase.
(B) Sense and antisense DNA primers encompassing the DNA region of interest.
(C) A vector with a selectable marker.
(D) An origin of replication specific for the bacterium Thermophilus aquaticus.

15. The heritable disorder Fragile X syndrome, a major cause of mental retardation, is caused by (A) production of enzymes that break the phosphate backbone. (B) X-ray. (C) presence of an extra chromosome in the sperm or egg. (D) duplication of multiple three-nucleotide repeats.

16. Excision repair corrects DNA by (A) detecting, removing, and replacing damaged or incorrect nucleotides in a single strand of DNA. (B) excising the incorrect base from a nucleotide. (C) removing extraneous groups such as methyl or oxygen added by mutagens. (D) correcting A=T to C-G transitions.

17. Histones and DNA have a strong attraction for each other because (A) DNA is positively charged and histones are negatively charged. (B) both DNA and proteins are hydrophobic. (C) DNA is negatively charged and histones are positively charged. (D) like substances share common charges.

18. Which one of the following is   NOT   a cis-regulatory element in gene transcription (A) bHLH-type protein. (B) promoter. (C) enhancer. (D) insulator.

20. The Nobel Prize in Physiology or Medicine 2019 was awarded for the discovery of what? (A) Cancer therapy by inhibition of negative immune regulation. (B) How cells sense and adapt to oxygen availability. (C) Mechanisms for autophagy. (D) Molecular mechanisms controlling circadian rhythm.

21. What is   NOT   true about Sanger sequencing? (A) It was developed by Frederick Sanger and colleagues in 1977. (B) The most widely used sequencing method for approximately 40 years. (C) A method based on in vitro DNA digestion. (D) Incorporation of chain-terminating dideoxynucleotides.

22. What is an "Okazaki fragment"? (A) The strand of nascent DNA which is synthesized in the same direction as the growing replication fork. (B) A short single-stranded nucleic acid utilized by all living organisms in the initiation of DNA synthesis. (C) Short sequences of DNA nucleotides which are synthesized discontinuously and later linked together by the enzyme DNA ligase to create the lagging strand during DNA replication. (D) A particular sequence in a genome at which replication is initiated.

23 The following DNA sequence is a region of a human genome that expresses a protein. If you want to down regulate the gene expression of this protein by making a 30 bp deletion in DNA, which position would be the most appropriate? (A) B. (B) C. (C) E. (D) All of the above. 

24. Following the figure in questions 3, if you want to truncate this protein by making a point mutation in DNA, which position would be the most appropriate? (A) B. (B) C. (C) E. (D) All of the above.

25. The first three bases of the 6-base recognition cleavage site of HindIII, a palindromic restriction enzyme, are AAG. What is the complete sequence of this 6 bp site? (A) AAGAAG. (B) AAGCTT. (C) AAGGAA. (D) AAGCUU.