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NAME ___________________________________
BIOLOGY 205, SECTION 006
EXAM 2
SPRING 2010
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+ QUESTIONS WILL BE GRADED ON BOTH HOW CORRECT AND HOW COMPLETE YOUR
ANSWER IS.
+ PLEASE USE ONLY THE ALLOTTED SPACE TO ANSWER EACH QUESTION. BE CONCISE.
1. (2 points) What is the term for short-range cell-cell communication via secreted local mediators that act on
adjacent cells?
(A) Endocrine signaling
(B) Paracrine signaling
(C) Contact-dependent signaling
(D) Delta-Notch signaling
2. (2 points) A small molecule that is formed in the cytosol, or released into it, in response to an extracellular
signal and that helps to relay the signal to the interior of the cell.
(A) Neurotransmitter
(B) Tyrosine kinase
(C) GTP-binding protein
(D) Second messenger
3. (2 points) Communicating cell-cell junction that allows ions and small molecules to pass from the
cytoplasm of one cell to the cytoplasm of the next.
(A) Gap junction
(B) Desmosome
(C) Contact-dependent signaling
(D) Enzyme-coupled receptor
4. (2 points) Protein composed of three subunits, one of which is activated by the binding of GTP.
(A) Ras
(B) Cyclic-AMP-dependent kinase (PKA)
(C) G-protein-coupled receptor (GPCR)
(D) Heterotrimeric G protein
5. (2 points) Protein that contributes to the desensitization of GPCRs by binding to their intracellular domain
after they have been activated by ligand binding.
(A) IP3 receptor
(B) Arrestin
(C) Protein kinase C
(D) Adenylyl cyclase
6. (2 points) Cell surface receptor that activates a tyrosine kinase that is noncovalently bound to the receptor.
(A) Cytokine receptor
(B) Receptor tyrosine kinase
(C) TGFbeta receptor
(D) SMAD family
7. (2 points) A kinase that is involved in intracellular signaling pathways activated by cell surface receptors
that phosphorylates inositol phospholipids.
(A) Janus kinase (JAK)
(B) TOR kinase
(C) AKT kinase
(D) PI-3 kinase
8. (2 points) System of protein filaments in the cytoplasm of a eukaryotic cell that gives the cell its shape and
the is required for cytokinesis.
(A) Actin cytoskeleton
(B) Microtubule cytoskeleton
(C) Intermediate filaments
(D) Lamins
9. (2 points) A protease inhibitor that prevents the cleavage of cohesin until its ubiquitination by the anaphase
promoting complex and subsequent proteolysis.
(A) Separase
(B) Securin
(C) Condensin
(D) Chiasma
10. (2 points) Channel-forming protein that associates with the mitochondrial outer membrane to trigger the
intrinsic apoptotic pathway.
(A) Cytochrome c
(B) BCL-2
(C) Bak
(D) Apoptosome
11. (2 points) An essential component of the S-phase checkpoint that triggers cell cycle arrest pending
successful DNA repair.
(A) p53
(B) Cdc6
(C) S-Cdk
(D) Caspase
12. (2 points) Class of intermediate filament proteins that contribute to the mechanical stability of skin.
(A) Vimentin
(B) Desmin
(C) Keratin
(D) Lamin
13. (2 points) Adhesive structures that mediate cell-cell connections between epithelial cells.
(A) Hemidesmosomes
(B) Gap junctions
(C) Lamellipodia
(D) Desmosomes
14. (2 points) Actin-binding protein that organizes actin filaments in to long parallel arrays at the apical
surfaces of epithelial cells.
(A) Arp
(B) Villin
(C) Filamin
(D) Cofilin
15. (2 points) Microtubule-based motor protein that powers the beating of cellular protrusions such as cilia and
flagella.
(A) Cytoplasmic dynein
(B) Axonemal dynein
(C) Kinesin
(D) Bi-polar kinesin
16. (2 points) Chromosomal structures formed during “cross-over” between sister chromatids during meiosis.
(A) Kinetochores
(B) Centromeres
(C) Chiasma
(D) Telomeres
17. (2 points) During what stage of the cell cycle does centriole duplication occur?
(A) G1
(B) S-phase
(C) G2
(D) Prometaphase
18. (2 points) An enzyme that is activated by the presence of giacylglycerol (DAG) and cytoplasmic calcium
released from the ER.
(A) Protein kinase C
(B) Protein kinase A
(C) Calcium-calmodulin-dependent kinase
(D) Akt kinase
19. (2 points) A protein that terminates the elongation phase of growing actin filaments to maintain the
population as short filaments during cellular protrusion.
(A) Arp
(B) Capping protein
(C) Cofilin
(D) Myosin I
20. (2 points) A class of secreted signaling factors that induce the receiving cells to enter mitosis.
(A) Mitogens
(B) Growth factors
(C) TGFbeta
(D) Survival factors
21. (10 points) The anaphase promoting complex (APC) is responsible for the initiation and completion of
anaphase (or the end of mitosis) by inactivating two classes of proteins. What are these two proteins and
how does the APC inactivate them?
M-cyclin and securin. APC is a ubiquitin ligase that polyubiquitinates its targets thus marking them for
destruction by the proteosome.
22. (10 points) During anaphase, chromosome movements are driven by two types of transport: anaphase A and
anaphase B movements. How are these two types of transport different and what is the basis of the forces
produced?
Anaphase A is the movement of chromosomes to spindle poles and is driven by the depolymerization of
kinetochore microtubules. Anaphase B is overall elongation of the spindle (pole-to-pole distance) and is
mediated by the combination of interpolar microtubule growth and antiparallel sliding.
23. (10 points) You are examining the cellular response to a new drug. You treat cells with the drug and
measure the intracellular levels of diacylglycerol and find that they increase as a response to the treatment.
With what type of receptor would you predict the drug interacts and how is the rise in intracellular
diacylglycerol used to change cellular physiology or metabolism?
A GPCR. Activation of the GPCR activates heterotrimeric G proteins which in turn activate
phospholipase C to cleave inositol lipids in to DAG and IP3. IP3 stimulates calcium release from the ER
and this calcium pulse, in combination with DAG in the membrane, activate protein kinase C.
24. (10 points) Mitochondria play a critical role in the process of intrinsic programmed cell death. Briefly
describe the role that they play and the molecules involved from initiation of the process to the activation of
executioner caspases.
Bax and Bak bind to the outer mitochondrial membrane forming channels that allow the release of
cytochrome c. Cytochrome c then binds to a cytosolic adaptor that clusters inactive initiator procaspase
molecules and promotes their proteolytic auto-activation. These in turn activate executioner caspases.
25. (10 points) Certain classes of drugs affect muscle contraction by binding to the troponin complex and
increasing its affinity for calcium ions. What effects would these drugs have on muscle contractility and why?
Increased affinity of troponin for calcium would lead to a longer, more stable interaction between actin
and myosin, thus increasing muscle contractility.
26. (10 points) What are the similarities and differences between the reactions that lead to the activation of
heterotrimeric G proteins and the reactions that lead to the activation of Ras?
Heterotrimeric G proteins and Ras are similar in that they undergo a cycle of activation by binding to
GTP and inactivation by GTP hydrolysis.
They are different in the upstream activators are GPCRs in the case of trimeric G proteins and RTKassociated activating proteins in the case of Ras. They are also different in that trimeric G proteins form
a trimeric complex in the inactive state that dissociates upon activation while Ras is a monomer
throughout its cycle.