Why do liposomes not fuse with one another spontaneously when suspended in an
aqueous environment?
A.Because fusion requires a large number of flip-flops, which are very rare.
B.Because the hydration shell of the polar head groups of the lipids needs to be
removed.
C.Because fusion requires micelle formation.
D.Because of the rapid lateral diffusion and rotation of the lipid molecules.
The genotypes of 400 colorectal cancer tumors are tabulated below, where the number
of tumors with or without mutations in each of the two cancer-critical genes, -catenin
and Apc, are indicated. Which row (a or b) corresponds to those with a mutant Apc
gene? Which column (1 or 2) corresponds to those with a mutant -catenin gene?
A.a; 1
B.a; 2
C.b; 1
D.b; 2
You have studied the circadian clock in a certain mouse strain by monitoring the
physical activity (e.g. wheel-running) of a few mice over an extended period of time.
For the first week, you kept the mice under normal 12 hr light /12 hr dark cycles; they
were then transferred to constant darkness. You have plotted the average activity of the
mice in the following graph. The light and dark conditions are represented with white
and gray backgrounds, respectively. The activity in each day is plotted in black in one
row of the graph, and consecutive days are arranged from the top to the bottom. The
horizontal axis represents the time of the day. Based on these results, what is the most
accurate estimate for the free-running period of the circadian clock in this mouse strain?
A.About 25 hr
B.About 24.5 hr
C.About 24 hr
D.About 23.5 hr
E.About 23 hr
In terms of molecular function, what do Ras and myosin have in common?
A.They normally bind to GTP.
B.They couple the hydrolysis of a bound nucleoside triphosphate to protein movements.
C.They switch between two distinct conformations controlled by protein
phosphorylation and dephosphorylation.
D.They are multisubunit proteins and contain a scaffold subunit.
E.All of the above.
How has pathogenicity in pandemic strains of Vibrio cholerae been acquired?
A.By transformation
B.By transduction
C.By conjugation
D.By vertical gene transfer
Consider a genetic network consisting of gene A whose product activates the
transcription of gene R. Imagine that the concentration of protein A is suddenly changed
by a significant amount. The following graphs show how the concentration of protein R
would then change over time to reach steady state again. The two curves (1 and 2) in
each graph correspond to systems that have different transcription rates for A. For one
of the two graphs (A or B) a negative feedback loop is present, in which protein R
represses the transcription of gene A. Which conclusion is correct according to these
results?
A.The negative feedback loop makes the system slower in reaching the steady state.
B.With negative feedback, the steady-state concentration is less sensitive to fluctuations
in kinetic rate constants.
C.Higher transcription rates for gene A result in lower steady-state levels of protein R
both with and without negative feedback.
D.All of the above.
In the following schematic diagram of a nuclear pore complex, on which side is the
cytosol located? What is the approximate diameter of the pore, as indicated by the
vertical bar?
A.Right; 1
B.Right; 0.1
C.Left; 1
D.Left; 0.1
Voltage-gated cation channels in the plasma membrane of a neuron open when the
membrane potential passes a threshold value that is about 20 mV above the resting
potential. This corresponds to a change of about 4 x 106 newtons per coulomb in the
magnitude of the electric field across the membrane compared to the resting state. The
tetrameric channels have a voltage-sensing helix S4 in each of their four subunits. Most
S4 helices contain seven residues with positively charged side chains. The charge
carried by each such residue is about 1.6 x 10-19 coulombs. By reaching threshold
depolarization, what are the magnitude and the direction of the collective force that the
four S4 helices in the channel experience as a result of the change in the electric field?
The force that particles of charge q in an electric field E experience is calculated as F =
q.E.
A.18 pN, toward the cell interior
B.18 pN, toward the cell exterior
C.90 pN, toward the cell interior
D.90 pN, toward the cell exterior
E.45 pN, toward the cell interior
An enzyme acts on a tyrosine residue in a target protein to create a binding site for the
SH2 domain. This enzyme is most specifically ___
A.an isomerase.
B.a nuclease.
C.a phosphatase.
D.a kinase.
E.a synthase.
In the simplified diagram below depicting exocytosis of synaptic vesicles, which
components (A to D) correspond to each of the following? Your answer would be a
four-letter string composed of letters A to D only, e.g. DBCA.
( )Ca2+
( ) Complexin
( ) Synaptotagmin
( ) SNARE complex
The genetic information carried by a cell is passed on, generation after generation, with
astonishing fidelity. However, genomes are still altered over evolutionary time scales,
and even their overall size can change significantly. Which of the following
genome-altering events has increased the size of the mammalian genome the most?
A.Transposition
B.Point mutation
C.Chromosomal deletion
D.Chromosomal inversion
E.Chromosomal translocation
A microtubule appears as a left-handed helix due to an approximately 0.9-nm stagger in
the lateral contacts between adjacent protofilaments. In the lateral contacts, – and
-tubulins in one protofilament interact with – and -tubulins, respectively, in the
neighboring protofilament, except for a longitudinal discontinuity along the
microtubule called the seam. Along the seam, lateral contacts have to be made between
different tubulins (i.e. -tubulin with -tubulin). Which of the following do you think is
acceptable as the repeat distance of tubulin monomers along a protofilament?
A.4 nm
B.5 nm
C.6 nm
D.7 nm
E.10 nm
Which of the following cell types in our body are typically renewed independently of
stem cells? Your answer would be a string composed of a subset of the letters A to E in
alphabetical order, e.g. BDE.
(A)Red blood cells
(B) Cells of pancreatic islets
(C)Hepatocytes of the liver
(D)Epithelial cells of the epidermis
(E)Neutrophils of the blood
The nicotinic acetylcholine receptor is an ionotropic receptor that can be activated by
nicotine, a stimulant drug found in cigarettes. Additionally, -bungarotoxin, a neurotoxin
found in the venom of some snakes, binds preferentially and tightly to the closed
conformation of the receptors. Another drug, donepezil, is a potent acetylcholinesterase
inhibitor used to treat patients with Alzheimer’s disease. If applied at a neuromuscular
junction, indicate whether each of the compounds (1) acetylcholine, (2) nicotine, (3)
-bungarotoxin, and (4) donepezil would enhance (E) or suppress (S) the Ca2+ influx in
the muscle cells. Your answer would be a four-letter string composed of letters E and S
only, e.g. EESS.
Fill in the blanks in the following paragraph regarding genome evolution. In your
answer, separate the two missing phrases with a comma, e.g. protein, plasma
membrane. Do not use abbreviations.
“Conservation of genomic sequences between humans and chickens is mainly due to
___ selection, whereas the conservation observed between humans and chimpanzees is
mostly due to the short time available for mutations to accumulate. Even the DNA
sequences at the ___ position of synonymous codons are nearly identical between
humans and chimpanzees.”
Indicate true (T) and false (F) statements below regarding programmed cell death by
apoptosis. Your answer would be a four-letter string composed of letters T and F only,
e.g. TTTF.
( )Apoptosis is the final fate of almost all cells in an adult animal.
( )Even perfectly healthy cells may undergo apoptosis.
( )DNA damage that cannot be repaired inhibits apoptotic pathways.
( )Apoptosis is the main form of programmed cell death in plant cells as well as in
animal cells.
Indicate whether each of the following statements is true (T) or false (F) regarding all
the cell-surface immunoglobulin molecules produced by a single, mature, nave B cell.
( )They all have the same heavy chain.
( )They all have the same light chain.
( )They all have the same antigen-binding site.
In the following schematic diagram of five pairs of alternative RNA splicing patterns,
which pair depicts exon skipping only? In exon skipping, an exon is spliced out of the
RNA transcript along with its flanking introns. In the diagram, exons are colored dark
blue and introns are colored yellow. Light blue indicates possible exons.
If heart surgery is necessary in a newborn, the thymus is sometimes removed to gain
better access to the heart. If a lymph node of such a patient is later studied in a
microscope, one particular area of the node is found to have an unusually low number
of cells. Looking at the drawing below, what is the name of this area?
