After an animal dies, its muscles start to stiffen before the decomposition of tissues
relaxes the muscles again. Which of the following would you expect to explain this
muscle stiffening (i.e. rigor mortis)?
A.The myosin II heads in muscle fibers remain attached to actin filaments due to the
absence of Ca2+ in these cells.
B.The ATPase activity of muscle myosin II is inhibited by the elevated Ca2+.
C.The myosin II heads in muscle cells remain attached to actin filaments due to the
elevated Ca2+ in the muscle fibers.
D.Titin molecules unfold, preventing muscle relaxation.
E.The myosin II heads in muscle cells remain attached to actin filaments due to
covalent cross-linking.
For a complementation test to work, the mutations under study must be___
A.recessive.
B.dominant.
C.gain-of-function.
D.null.
E.conditional.
Three subunits of a protein complex have been resolved in a two-dimensional
polyacrylamide gel, as shown in the schematic drawing below. Indicate whether each of
the following better describes the a, b, or c subunit. Your answer would be a three-letter
string composed of letters a, b, and c only, e.g. cca.
( )It has the smallest apparent molecular weight.
( )It has the highest negative charge.
( )It has the lowest isoelectric point.
If this protein complex does not function normally, the ends of the eukaryotic
chromosomes would activate the cell’s DNA damage response, causing chromosomal
fusions and other genomic anomalies. What is this protein complex called?
A.Telomerase
B.T-loop
C.ORC
D.Shelterin
E.RecA
Which of the following features of DNA underlies its simple replication procedure?
A.The fact that it is composed of only four different types of bases
B.The antiparallel arrangement of the double helix
C.The complementary relationship in the double helix
D.The fact that there is a major groove and a minor groove in the double helix
Arsenate is a toxic ion that can interfere with both glycolysis and oxidative
phosphorylation. Arsenate resembles Pi (inorganic phosphate) and can replace it in
many enzymatic reactions. One such reaction is catalyzed by glyceraldehyde
3-phosphate dehydrogenase in step 6 of glycolysis. Upon completion of the reaction,
instead of the normal product, 1,3-bisphosphoglycerate, the mixed anhydride
1-arsenato-3-phosphoglycerate is formed; this undergoes rapid spontaneous hydrolysis
into arsenate plus 3-phosphoglycerate, the latter being a normal product of step 7 in
glycolysis. What would be the effect of arsenate poisoning in glycolysis?
A.It results in more ATP and NADH molecules generated for every glucose molecule.
B.It results in fewer ATP molecules generated per glucose molecule, but NADH
generation is not directly affected.
C.It brings glycolysis to an abrupt stop.
D.It results in fewer ATP and NADH molecules generated per glucose molecule.
E.It does not affect the number of ATP or NADH molecules generated per glucose
molecule.
Compared to cells of a normal tissue, which of the following occurs less frequently in
cells within a solid tumor?
A.Apoptosis
B.Necrosis
C.Cell division
D.Mitotic recombination
E.Stress
Three fundamental controls seem to have been subverted in essentially every type of
cancer. Choose these three among the following regulatory axes. Your answer would be
a three-letter string composed of letters A to F only, in alphabetical order, e.g. BDF.
(A)Wnt pathway
(B)Rb pathway
(C)RTK/Ras/PI3K pathway
(D)p53 pathway
(E)Hippo pathway
(F)GPCR/PKA pathway
You have set up a system of differential equations to describe the concentration of a
protein as a function of time based on transcription, translation, and degradation rates.
You simulate two conditions (1 and 2) that are identical except that the transcription
rate for the protein is set tenfold higher in one of them (1) compared to the other (2).
Starting from a concentration of zero, the time required to reach 50% of the final
steady-state concentration is ___
A.the same for conditions 1 and 2
B.tenfold longer for 1 compared to 2
C.tenfold longer for 2 compared to 1
D.less than tenfold longer for 1 compared to 2
E.less than tenfold longer for 2 compared to 1
Consider a human cell such as a hepatocyte. Which of the following compartments
occupies a larger volume in the cell?
A.Cytosol
B.Nucleus
C.Endoplasmic reticulum
D.Mitochondria
E.Peroxisomes
In which of the following organisms is systemic RNAi possible through feeding the
animal with the RNA?
A.Caenorhabditis elegans
B.Drosophila melanogaster
C.Mus musculus
D.Homo sapiens
E.All of the above
Which of the following is correct regarding the regulation and maintenance of Hox
gene expression in Drosophila?
A.Proteins of the Polycomb and Trithorax groups maintain inactive and active states of
Hox gene expression, respectively.
B.If Polycomb or Trithorax group genes are defective, Hox gene expression patterns are
still initiated, but cannot be correctly maintained.
C.The remodeled chromatin at the Hox complex is heritable through cell generations.
D.If all the Hox genes in an embryo are deleted, segmentation still occurs but distinct
segment identities are lost.
E.All of the above.
The two chromosomes in each of the 22 homologous pairs in our cells …
A.have the exact same DNA sequence.
B.are derived from one of our parents.
C.show identical banding patterns after Giemsa staining.
D.usually bear different sets of genes.
E.All of the above.
Indicate true (T) and false (F) statements below regarding P-bodies. Your answer would
be a four-letter string composed of letters T and F only, e.g. TTFT.
( )P-bodies are membrane-enclosed organelles scattered throughout the cytoplasm.
( )mRNAs that are to be degraded are transferred from P-bodies to stress granules
containing decapping and exonuclease enzymes.
( )When translation initiation is blocked, stress granules typically shrink.
( )mRNAs associated with stress granules are primed for translation.
The homologous chromosome pairs in our cells do not carry identical sequences in all
loci. This heterozygosity (difference between the two copies) can be altered in cancer:
in fact, loss of heterozygosity at many loci is observed in cancer cells, through an
increase in either homozygosity (two identical copies) or hemizygosity (i.e. loss of one
copy). Researchers can take advantage of this loss of heterozygosity in cancer cells to
identify genomic loci that contain cancer-critical genes. What type of gene would you
expect to find in chromosomal regions with a loss of heterozygosity? Proto-oncogenes
(P) or tumor suppressor genes (T)? Write down P or T as your answer.
Consider the two feed-forward loops below containing three transcription regulators A,
B, and C, where A receives the input signal and C generates the output. In the so-called
coherent loop (left), A activates C both directly and indirectly, whereas in an incoherent
loop (right), A activates C via one route and inactivates it via the other. Answer the
following question(s) based on these network motifs.
Considering the two particular feed-forward designs shown, would you expect the
coherent (C) or the incoherent (I) loop to have a stable output and respond best to input
signals that are above a certain threshold? Write down C or I as your answer.
Fill in the blank in the following paragraph.
“During intense €anaerobic’ physical exercise, the high energy demand in the muscle
cells leads to an accumulation of lactic acid in these cells and their surrounding tissues.
Similarly, the yeast Saccharomyces cerevisiae can produce ethanol when grown
anaerobically. The lactate or ethanol production takes place in a process called …”
Indicate whether each of the following descriptions applies to transformed cell lines
(T), nontransformed cell lines (N), or both (B). Your answer would be a four-letter
string composed of letters T, N, and B only, e.g. BBNN.
( )They can be thawed and recultured after long-term storage in liquid nitrogen.
( )They often grow only when attached to a surface, such as that of a culture dish.
( )They proliferate to very high densities.
( )They usually cause tumors when injected into immunocompromised animals.
Indicate if each of the following descriptions matches messenger RNAs (M), ribosomal
RNAs (R), or transfer RNAs (T). Your answer would be a four-letter string composed
of letters M, R, and T only, e.g. RRRT.
( ) They contain codons.
( ) They contain anticodons.
( ) They are (covalently) attached to amino acids.
( ) They are at the core of a complex that carries out protein synthesis.
In isoelectric focusing, is the low-pH end close to the anode (A; positive electrode) or
cathode (C)? Would you use octylglucoside (O; a nonionic detergent) or SDS (S) for
separation of proteins by this technique? Would a highly basic protein be near the
high-pH (H) or low-pH (L) end of the strip at the end of the experiment? Write down
your answer as a three-letter string using the letters in the parentheses above, e.g. ASH.
Indicate whether each of the following descriptions better applies to proto-oncogenes
(P) or tumor suppressor genes (T). Your answer would be a four-letter string composed
of letters P and T only, e.g. PPPT.
( )Cancer mutations in these genes are usually recessive.
( )Cancer mutations in these genes include gene duplications.
( )Cancer mutations in these genes are responsible for most hereditary cancers.
( )Cancer mutations in these genes are commonly in the form of nonsense (truncating)
mutations that abort protein synthesis.
Tom40 is a nuclear-encoded essential subunit of the TOM complex in the outer
mitochondrial membrane. It is a -barrel protein that forms the pore through which
precursor proteins enter the intermembrane space from the cytosol. Indicate true (T) and
false (F) statements below regarding the Tom40 protein. Your answer would be a
four-letter string composed of letters T and F only, e.g. TTTF.
( )Incorporation of new Tom40 in the outer membrane requires preexisting Tom40 in
that membrane.
( )Formation of new TOM complexes is dependent on the SAM complex.
( )Tom40 is partially translocated through the outer membrane and is then transferred in
the plane of the membrane to fold into its native conformation.
( )Tom40 is translocated through the inner membrane as a precursor.