25. Which of the following is NOT a post-translational modification?
(A) Phosphorylation.
(B) Glycosylation.
(C) Acetylation.
(D) Methylation.
(E) Ubiquitination.

21. Which of the following is true of chromatin? (A) Heterochromatin has more acetyl groups on the histones. (B) Heterochromatin has fewer methyl groups on the DNA. (C) Active genes are not bound by nucleosomes. (D) Sequence-specific DNA binding proteins can only activate transcription. (E) The chromatin structure on a particular gene may be different in different cells.

22. In E. coli, biosynthesis of tryptophan can be repressed. The repressor protein of the trp operon (A) is activated by the binding of tryptophan. (B) is inactivated by the binding of tryptophan. (C) is not affected by tryptophan. (D) is activated by the binding of free tRNA. (E) is only synthesized in the presence of tryptophan.

23. The major lipids found in membranes are (A) triacylglycerols and cholesterol. (B) cholesterol and sphingomyelin. (C) phospholipids, glycolipids, and cholesterol. (D) phospholipids and free fatty acids. (E) cholesterol, inositol, and glycolipids.

24. During glycolysis NADH is produced in the cytosol. Under aerobic conditions, what is the primary fate of this NADH? (A) It accumulates in the cytosol. (B) It diffuses into the mitochondria. (C) It transfers its reducing equivalents directly to NADP+. (D) The reducing equivalents are transferred by a shuttle system to the mitochondrial electron transport system. (E) It is used to reduce glucose to sorbitol.

26. Which one of the following components is NOT necessary in an expression plasmid to be useful in the construction of recombinant DNA? (A) A multiple cloning site. (B) A tag coding sequence. (C) A promoter and a terminator. (D) Multiple cloning sites. (E) A coding sequence that is for antibiotic resistance.

27. Inheritance of phenotype sometimes does not directly involving the nucleotide is termed epigenetic inheritance. The epigenetic inheritance (A) only refers to genomic imprinting. (B) only effects female offspring. (C) only effects male offspring. (D) only refers to X inactivation. (E) can result in the expression of different alleles in different generations.

28. Which of the following is a possible application of tandem mass spectrometry? (A) Cell-specific gene expression. (B) Gene regulation. (C) Elucidation of metabolic pathways. (D) Tumor profiling. (E) Determination of the amino acid sequence of a peptide.

29. Which of the following is NOT correct regarding homeotic genes? (A) Homeotic genes encode transcription factors. (B) Homeotic genes are the only genes that contain the homeobox. (C) Homeotic genes are found in clusters called complexes. (D) The proteins encoded by homeotic genes contain DNA-binding domain. (E) Homeotic genes activate other developmental genes.

30. Ribosomes attached to rough ER are the site for synthesis of many types of secretary proteins. Which of the following mechanism is typically used for nascent protein insertion into the mammalian ER membrane? (A) Pretranslational. (B) Cotranslational. (C) Post-translational. (D) Cotranscriptional. (E) All of the above.

31. MPF is a cyclin-Cdk complex that was discovered first in Xenopus egg. Its activity fluctuates during cell cycle. Which of the following is NOT its characteristic? (A) Fluctuation of the cyclin concentration is the same as MPF activity. (B) The peak of the MPF activity is G2 phase. (C) The peak of the MPF activity is M phase. (D) The breakdown of the MPF occurs abruptly during M phase. (E) The activity of the MPF promotes mitosis by phosphorylating various proteins. .