12. Which of the following is released by platelets in the vicinity of an injury?
(A) PDGF
(B) MPF
(C) protein kinase
(D) cyclin
(E) Cdk

8. In the formation of biofilms, such as those forming on unbrushed teeth, cell signaling serves which function? (A) formation of mating complexes (B) secretion of apoptotic signals (C) aggregation of bacteria that can cause cavities (D) secretion of substances that inhibit foreign bacteria (E) digestion of unwanted parasite populations

9. Which of the following is true of transcription factors? (A) They control gene expression. (B) They transcribe ATP into cAMP. (C) They initiate the epinephrine response in animal cells. (D) They regulate the synthesis of DNA in response to a signal. (E) They regulate the synthesis of lipids in the cytoplasm.

10. The toxin of Vibrio cholerae causes profuse diarrhea because it (A) modifies a G protein involved in regulating salt and water secretion. (B) decreases the cytosolic concentration of calcium ions, making the cells hypotonic. (C) binds with adenylyl cyclase and triggers the formation of cAMP. (D) signals IP3 to act as a second messenger for the release of calcium. (E) modifies calmodulin and activates a cascade of protein kinases.

11. If you were to observe the activity of methylated DNA, you would expect it to (A) be replicating nearly continuously. (B) be unwinding in preparation for protein synthesis. (C) have turned off or slowed down the process of transcription. (D) be very actively transcribed and translated. (E) induce protein synthesis by not allowing repressors to bind to it.

13. Which of the following is a protein maintained at constant levels throughout the cell cycle that requires cyclin to become catalytically active? (A) PDGF (B) MPF (C) protein kinase (D) cyclin (E) Cdk

14. To view and analyze human chromosomes in a dividing cell, which of the following is/are required? (A) electron microscope (B) radioactive staining (C) fluorescent staining (D) DNA stain and a light microscope (E) a stain particular to human cell

15. Why do RNA viruses appear to have higher rates of mutation? (A) RNA nucleotides are more unstable than DNA nucleotides. (B) Replication of their genomes does not involve proofreading. (C) RNA viruses replicate faster. (D) RNA viruses can incorporate a variety of nonstandard bases. (E) RNA viruses are more sensitive to mutagens.

16. A principal problem with inserting an unmodified mammalian gene into a plasmid and then getting that gene expressed in bacteria is that _____. (A) bacteria translate only mRNAs that have multiple messages (B) prokaryotes use a different genetic code from that of eukaryotes (C) bacteria cannot remove eukaryotic introns (D) bacterial RNA polymerase cannot make RNA complementary to mammalian DNA

17. Most of the dry mass of a plant is the result of uptake of _____. (A) water and minerals through mycorrhizae (B) carbon dioxide and oxygen through stomata in leaves (C) water and minerals through root hairs (D) carbon dioxide through stoma

18. Which of the following traits do archaeans and bacteria share? 1. composition of the cell wall; 2. presence of plasma membrane; 3. lack of a nuclear envelope 4. identical rRNA sequences. (A) 2 and 3 (B) 1 only (C) 3 only (D) 1 and 3 (E) 2 and 4