80. Which of the following metal ions in heme can bind oxygen reversibly?
(A) Fe²⁺
(B) Mg²⁺
(C) Ca²⁺
(D) None of above

76. How does glycogen enter glycolysis? (A) Directly as glucose 6-phosphate (B) Through direct hydrolysis to form glucose (C) Through conversion to fructose 6-phosphate or fructose 1-phosphate (D) Through phosphorolytic cleavage to form glucose 1-phosphate and subsequent conversion to glucose 6-phosphate

77. How are the urea cycle and the citric acid cycle interconnected? (A) Both cycles share the same enzymes (B) The urea cycle is a branch of the citric acid cycle (C) Both cycles use the same intermediates (D) The urea cycle and the citric acid cycle are not interconnected

78. In which organs does gluconeogenesis primarily occur in mammals? (A) Brain, muscles, and erythrocytes (B) Liver, kidney, and small intestine (C) Pancreas, lungs, and spleen (D) Stomach, gallbladder, and bladder

79. Which of the following is responsible for reducing molecular O2 to H2O in the respiratory chain of mitochondria? (A) NAD-linked dehydrogenase (B) Cytochrome oxidase (Complex IV) (C) Succinate dehydrogenase (Complex II) (D) Superoxide dismutase (SOD)

1. To possess optical activity, a compound must be: (A) a carbokydrate. (B) a hexose. (C) asymmetric. (D) colored. (E) D-glucose.

2. A major component of RNA but not of DNA is: (A) adenine. (B) cytosine. (C) guanine. (D) thymine. (E) uracil.

3. In the Watson-Crick model for the DNA double helix (B form), the A-T and G-C base pairs share which one of the following properties? (A) The distance between the two glycosidic (base-sugar) bonds is the same in both base pairs, within a few tenths of an angstrom. (B) The molecular weights of the two base pairs are identical. (C) The number of hydrogen bonds formed between the two bases of the base pair is the same. (D) The plane of neither base pair is perpendicular to the axis of the helix. (E) The proton-binding groups in both base pairs are in their charged or ionized form.

4. Which of the following does not apply to the construction or use of a DNA library? (A) Determining the location of a particular DNA sequence in a DNA library requires a suitable hybridization probe. (B) Genomic libraries are better for expressing gene products than cDNA libraries. (C) Many segments of DNA from a cellular genome are cloned. (D) Specialized DNA libraries can be made by cloning DNA copies of mRNAs. (E) The DNA copies of mRNA found in a cDNA library are made by reverse transcriptase.

5.Which vitamin is derived from cholesterol? (A) A (B) B12 (C) D (D) E (E) K

6. The shortest o helix segment in a protein that will span a membrane bilayer has about_____amino acid residues. (A) 5 (B) 20 (C) 50 (D) 100 (E) 200