Cell and Molecular Biology -- Biology 20A

Transcription

1 Cell and Molecular Biology -- Biology 20A Midterm Exam Name You will not need it, but you may take up to 1.5 hr for the exam. Class will resume with lecture at 2:45 pm (sorry). Each numbered question has equal value: 50 x 4 = 200 points. NOTE: Words have specific meanings. No attempt is being made to trick you, but please read each question carefully.

2 1. Which of the following particles is most important to the chemistry of compounds? a. hadron d. electron b. neutron e. photon c. quark 2. What are the differences among hydrogen atoms, hydrogen ions and hydrogen molecules a. the number of electrons d. the number of photons b. the number of neutrons e. both a and c c. the number of protons 3. What element is most important to the cell in terms of energy and information storage and transfer? 4. Complete the following equations for radioactive decay of carbon isotopes: C > N β C > Be β 5. Which of the two forms of carbon in the previous queston is used in positron emission (PET) scanning? 6. Transition metals are characterized by having partially filled d-orbitals. What is the significance of this for biology? 7. When an atom absorbs a photon a. light is given off d. it becomes radioactive b. an electron goes to higher energy e. the nucleus decays

3 d. an isotope is formed 8. Oxygen and sulfur are in the same column of the periodic table. What is the most fundamental thing that they therefore have in common? 9. What is the orbital hybridization of an alkane carbon and the geometry of the atoms around it? 10. For each pair of structures circle the one that predominates at low ph: - + a. CO 2 H CO 2 b. NH 2 NH Which of the following has a stereioisomer? a. CO 2 H b. CO 2 H c. CH 2 OH d. CHO CH C=O CH 2 CHOH CH CH 3 CH 2 CH 2 OH CO 2 H CO 2 H 12. Draw the valence shell electron configuration of H 2 O and O 2 and add the appropriate number of protons and electrons in order to balance the equation. 2 H O H > O O 13. What biological process is responsible for the most significant conversions of this type? 14. Draw the open chain form of any aldohexose.

4 15. Complete the following structure for the α-anomeric form of glucose: 16. What are the formal oxidation states of the carbons in: CO 2 CH 2 OH 17. How many electrons are added, on average, to the typical carbon during the reduction of carbon dioxide to glucose? 18. During what process does the transformation in the previous question typically take place? 19. How many stereoisomers are there of the TCA cycle intermediate succinate. (Do not count succinate in your total). CO 2 H CH 2 CH 2 CO 2 H 20. Draw two amino acids linked together in a peptide bond. They may be either specific or generic.

5 21. Identify by name any four of the eight amino acids whose side chains are shown here. CO 2 H CONH 2 H NH 2 CH 3 CH 2 CH 2 CH 2 S CH 2 CH 2 CH 2 CH 2 CH 2 CH For the previous question, for the four amino acid side chains not ididentified by name, indicate whether each is polar, non-polar or charged at physiological ph. 23. Identify the class of molecules to which the following compound belongs: O CH 2 O-C-CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 O CH-O-C-CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 2 -CH 3 CH 2 OPO 4 = 24. Draw all of the products of complete hydrololysis of the compound in the previous question.

6 25. If the α- and β- anomers of glucose are so easily interconvertible, why do starch and cellulose not easily interconvert into each other? 26. What is the difference between a micelle and a vesicle? 27. What is the principal type of bonding (and between what) that holds together the secondary structure of proteins? 28. How many different trinucleotides are there? How many tripeptides? 29. In double-stranded DNA or RNA, a purine is always paired with a(n) 30. Money tends to get concentrated in places where it is already concentrated (i.e., the rich get richer). How is this phenomenon different from the behavior of solutes in solutions?

7 31. At equilibrium H = T S, meaning that all the energy in the system (enthalpy) is in the form of entropy. How does this affect the ability of the system to do work ( G)? 32. Match: ribosome protein transport Golgi protein encoding vesicle protein targetting nucleus protein sysnthesis 33. Give two examples of things chloroplasts and mitochondria have in common. 34. How do cis-double bonds affect the fluditiy of membranes? 35. What is it about the lipid bilayer that makes it such an effective barrier to the passage of water and ions?

8 36. When mammalian muscle goes from resting to working the breakdown of glycogen causes a large increase in the flux of glucose into the system. The production of carbon dioxide increases, but not nearly as dramatically. Why? What happens to all the carbon? 37. What chemical form is the immediate storage compound for most of the energy resulting from the TCA cycle? 38. How do membranes play a critical role in both photosynthesis and respiration? 39. The dark reactions use the reducing power stored by photosynthesis to produce what key intermediate? a. NADPH d. acetyl-coa b. glyceraldehyde 3-phosphate e. pyruvate c. glucose-1-phosphate 40. Cyanide blocks the ability of the electron transport chain to pass electrons to oxygen. How does that explain the fact that fermenting organisms are relatively tolerant of cyanide? ec. Identify the molecule on the front page of this exam.