29. Which one of the following statements relating to lipids and membrane is correct?
(A) The non-polar interior of a lipid bilayer relies on salt bridges for its stability.
(B) Triacylglycerols are the simplest of the phospholipids.
(C) Cholesterol molecules are generally used to provide ion channels.
(D) The ability of species to migrate through a lipid bilayer increases with their polarity.
(E) Unsaturated fatty acyl groups used in phospholipids are normally cis isomers.

25. If a sample of DNA is found to have the base composition (molar ratios) of adenine, 40； thymine, 22； guanine, 19 and cytosine, 19, what conclusion can be drawn? (A) The DNA is a circular duplex. (B) The DNA is a linear duplex. (C) The DNA is single stranded. (D) The DNA has highly repetitive sequences. (E) The DNA has a high melting temperature.

26. Which of the following statements concerning cyclins is not correct? (A) They catalyze the phosphorylation of cyclin-dependent protein kinases. (B) They are regulatory subunits for enzymes that catalyze the phosphorylation of proteins. (C) They are activated and degraded during the cell cycle. (D) They can become linked to ubiquitin. (E) They contain specific amino acid sequences that target them for proteolysis. 

27. That the nature of genetic material is DNA is based on_______ . (A) the transforming material is heat-unstable (B) DNase digestion has no effects but RNase digestion can destroy the activity (C) the base composition of DNA is constant from one species to another (D) only DNA can enter the cell if E. coli is infected by T2 phage (E) UV absorption maximum is at 280 nm

28. Which one of the following statements relating to the common amino acids is correct? (A) Glutamine and asparagine have acidic side chains. (B) Valine and leucine have polar side chains containing an amide group. (C) Only phenylalanine and tyrosine absorb in the ultraviolet region near 270 nm. (D) There are three amino acids whose side chains carry a net positive charge at pH 5. (E) Methionine is one of three sulfur containing amino acids.

30. In a tissue that metabolizes glucose via the pentose phosphate pathway, carbon number 1 of glucose would be expected to end up principally in_______ . (A) glycogen (B) 3-phosphoglycerate (C) carbon dioxide (D) ribose-5-phosphate (E) pyruvate

31. Which one of the following statements relating to proteins is correct? (A) All proteins have quaternary structure. (B) Histidine is often found at the active site of globular proteins. (C) The primary structure of a protein describes the amino acid composition, but not the amino acid sequence. (D) Both alpha-helix and beta-sheet segments occur as secondary structural elements in all proteins. (E) When proteins are denatured, they can never be reconstituted back to a functional state.

32. The Type II glycogen disease (Pompe’s disease) is lack of _______. (A) glucose-6-phosphatase (B) glucose-1-phosphatase (C) lysosomal alpha-1 to 4- and 1 to 6- glucosidase (acid maltase) (D) debranching enzyme (E) branching enzyme

33. Severe combined immunodeficiency disease (SCID) is caused by deficiency of_______ . (A) adenosine deaminase (B) thymidine kinase (C) xanthine oxidase (D) DNA ligase (E) hypoxanthine-guanine phosphoribosyltransferase

34. Which one of the following statements about natural fatty acids is correct? (A) Molecules with odd and even numbers of carbon atoms are equally common. (B) All of the natural fatty acids are unsaturated. (C) Fatty acids provide a useful source of intermediates for gluconeogenesis. (D) Oxidation of fatty acids can lead to the production of ketone bodies. (E) The natural unsaturated fatty acids most commonly have their double bonds in trans geometry.

35. Which one of the following statements relating to lipids and membranes is correct? (A) Triacylglycerols are the major component of most cell membranes. (B) Clusters of cholesterol molecules are generally used to provide ion channels. (C) Na+ and K+ ions readily diffuse through the lipid bilayer. (D) Both saturated and unsaturated fatty acyl groups are used in typical phospholipids. (E) All phospholipids incorporate a glycerol unit as part of their structure.