You have grown neurons in a culture dish containing laminin and have induced axon
outgrowth. You now incubate the cells in the presence of various concentrations of two
secreted proteins (1 and 2). You then fix the cells, stain them with rhodamine-phalloidin
(a fluorescent dye that selectively labels actin filaments), and finally use a fluorescence
microscope to examine the axons. Some of the axon tips have lost their spread
morphology (with lamellipodia shrunk and filopodia retracted) and lack significant
fluorescence. You call these “collapsed cones.” In the following graph, the percentage
of cones that have collapsed is plotted as a function of concentration of proteins 1 and
2. Do you expect these proteins to be chemoattractants or chemorepellents in guiding
axonal growth cones? Which one is more potent?
A.Chemoattractants; protein 1 is more potent.
B.Chemoattractants; protein 2 is more potent.
C.Chemorepellents; protein 1 is more potent.
D.Chemorepellents; protein 2 is more potent.
E.Protein 1 is a chemoattractant, and protein 2 is a chemorepellent; protein 2 is more
potent.
Each gut stem cell …
A.is pluripotent.
B.divides approximately once a week.
C.gives rise to all four major epithelial cell types in the right proportions.
D.expresses Lgr5, just like the epithelial cells that derive from it.
E.All of the above.
Which of the following groups of proteins are pattern recognition receptors?
A.NOD-like receptors
B.Toll-like receptors
C.RIG-like receptors
D.C-type lectin receptors
E.All of the above
Judged by the average number of nucleotide-pair differences per 1000 nucleotide pairs,
which of the following pairs show the highest difference?
A.The genomes of S. cerevisiae and M. musculus
B.The genomes of two different E. coli strains
C.The ribosomal RNA genes from human and E. coli
D.The transfer RNA genes in a human and M. musculus
E.The genomes of two humans
If a hematopoietic cell is deprived of colony-stimulating factors, it typically …
A.dies by apoptosis.
B.differentiates randomly into several cell types.
C.differentiates randomly to one cell type.
D.enters a quiescent state.
E.divides without differentiating.
Which of the following evolutionary changes better explains morphological differences
between different animals despite many common molecular mechanisms governing
their development?
A.Changes in the types of genes responsible for key developmental processes.
B.Changes in regulatory DNA controlling expression of key developmental genes.
C.Changes in DNA-binding domains of key transcription regulators involved in
development.
D.Changes in coding sequences of key developmental genes.
E.Changes in copy number of key developmental genes.
Which of the following proteins do you expect to be enriched near the plus end of
microtubules?
A.Dynein
B.XMAP215
C. -Tubulin
D.Katanin
E.All of the above
Neuromuscular transmission involves the sequential activation of several ion channels.
Sort the following events to reflect the sequence leading to muscle contraction. Your
answer would be a five-digit number composed of numbers 1 to 5 only, e.g. 12543.
(A)Opening of voltage-gated Na+ channels in the muscle cell plasma membrane.
(B)Opening of Ca2+ release channels in the sarcoplasmic reticulum membrane.
(C)Opening of ionotropic acetylcholine receptors on the muscle cell plasma membrane.
(D)Opening of voltage-gated Ca2+ channels in the T tubules.
(E)Opening of voltage-gated Ca2+ channels in the motor neuron.
Which of the following structures is exclusively found in eukaryotic cells?
A.Plasma membrane
B.Cell wall
C.Chromosome
D.Ribosome
E.Lysosome
Evolutionary tracing has identified clusters of the most invariant amino acids in the
SH2 domain family. Which of the following is true regarding these sites?
A.Mutation in these sites generally keeps the protein functional.
B.The invariant amino acids generally have negatively charged side chains.
C.These sites correspond to the binding site for peptides containing phosphorylated
tyrosine.
D.The amino acids at these sites are generally hydrophobic.
E.These sites have evolved fast because they have critical functions.
The inactivation rate of voltage-gated Na+ and K+ channels can regulate the firing
frequency of neurons. Which of the following combinations results in the highest firing
frequency?
A.Rapid inactivation of both Na+ and K+ channels
B.Rapid inactivation of Na+ channels, slow inactivation of K+ channels
C.Slow inactivation of Na+ channels, rapid inactivation of K+ channels
D.Slow inactivation of both Na+ and K+ channels
In human cells, the alpha satellite DNA repeats ___
A.have a specific sequence indispensable for the seeding event that leads to chromatin
formation.
B.can be seen to be packaged into alternating blocks of chromatin, one of which
contains the histone H3 variant CENP-A.
C.are sufficient to direct centromere formation.
D.are necessary for centromere formation.
E.All of the above.
You have obtained leaf samples from three strawberry varieties A, B, and C. You isolate
the cells, extract their nuclei, and stain them with propidium iodide, a fluorescent dye
that binds quantitatively to DNA. You then use a fluorescence-activated cell sorter
(FACS) machine to sort the nuclei based on their fluorescence. Guessing from the
results, presented in the following histograms, which variety would you expect to yield
larger strawberries?
A.Variety A
B.Variety B
C.Variety C
D.They should all be the same
Soon after the discovery of nerve growth factor (NGF), researchers injected newborn
mice with rabbit antiserum (i.e. serum that contains antibodies) against NGF. They
observed massive nerve cell death compared to appropriate control injections. Up to
99% of the neurons in some parts of the developing peripheral nervous system died
after about a week of daily injections. These results suggest that …
A.NGF signaling sensitizes developing nerve cells to apoptotic signals.
B.developing neurons undergo apoptosis in the presence of rabbit proteins.
C.developing neurons require NGF for apoptosis.
D.developing neurons undergo cell death in the absence of NGF.
E. NGF signaling is sufficient for survival of the developing neurons.
The differentiation of bone marrow stromal cells into bone or fat cells depends on
chemical and mechanical signals. In each of the following conditions, indicate whether
you would expect the stromal cells to differentiate into bone (B) or fat (F) cells. Your
answer would be a three-letter string composed of letters B and F only, e.g. FBB.
( )The cells are embedded in a stiff hydrogel.
( )The cells are embedded in a soft hydrogel.
( )The cells are treated with a Rho inhibitor. The monomeric GTPase Rho is required
for the assembly of actin stress fibers and actin-myosin bundles.
Mice whose immune systems had previously rejected a tissue transplant from a certain
strain of donor mouse received another transplant shortly afterward, either from the
same donor strain or a new one. All of the recipient mice eventually rejected the
transplant. However, one group did so more quickly than the other group. Do you think
this group received the graft from the original mouse strain (O) or the new strain (N)?
Write down O or N as your answer.
The following mRNA sequence is taken from the middle of exon 3 in a mature mRNA
that has 12 exons. Knowing that this mRNA does not undergo nonsense-mediated
decay, which of the reading frames shown is the correct one for this mRNA? Write
down 1, 2, or 3 as your answer.
Indicate true (T) and false (F) statements below regarding G-protein-coupled receptors
(GPCRs). Your answer would be a five-letter string composed of letters T and F only,
e.g. TTFFF.
( )All GPCRs share a similar structure composed of seven transmembrane helices.
( )All GPCR ligands (signal molecules) have a similar structure.
( )GPCRs have only been found in multicellular organisms, consistent with their role in
intercellular signaling.
( )The hormone insulin is recognized by a GPCR on the surface of its target cells.
( )Once activated, a GPCR molecule can activate multiple molecules of G protein to
amplify the incoming signal.
In the schematic drawing of an antibody molecule below, indicate which letter (A to E)
corresponds to each of the following features. Your answer would be a five-letter string
composed of letters A to E only, e.g. DAECB.
( )N-terminus
( )C-terminus
( )Light chain
( )Antigen-binding site
( )Disulfide bond
Indicate whether each of the following transport processes occurs via the mechanisms
described as gated transport (G), transmembrane transport (T), or vesicular transport
(V). Your answer would be a five-letter string composed of letters G, T, and V only, e.g.
VTTTG.
( )Import into nucleus
( )Export from nucleus
( )Import into mitochondria
( )Return from Golgi to ER
( )Return from ER to cytosol
Imagine two spherical cells, one of which is 5000 times larger in volume than the other.
The smaller is a prokaryote, and the larger cell is a eukaryote with 20% of its volume
confined in a spherical nucleus. If the diameter of the prokaryotic cell is 0.7
micrometers, what is the diameter of the nucleus in the eukaryotic cell in micrometers?
Write down your answer as a number only.