How is tRNA splicing different from mRNA splicing in eukaryotic cells?
A.tRNA splicing does not proceed via transesterification reactions.
B.tRNA splicing is carried out by proteins only.
C.tRNA splicing does not create a lariat intermediate.
D.tRNA splicing involves RNA endonuclease and RNA ligase activities.
E.All of the above.
The following schematic drawing shows two integrin molecules. Which molecule (a or
b) is depicted in its active configuration? Which side of the plasma membrane (1 or 2)
represents the cytosol?
A.a; 1
B.a; 2
C.b; 1
D.b; 2
As shown in the following drawing, a researcher has engineered three pairs of LoxP
sites (for conservative site-specific recombination) in a region that contains three
reporter genes coding for red, yellow, or cyan fluorescent proteins, respectively. Each
type of LoxP sequence (shown as a black, gray, or white arrowhead) is specific,
meaning it does not recombine with the other types of LoxP sequences. Upon Cre
recombinase activation, depending on which recombination event occurs first (which
we assume is random), a number of possible combinations of reporters can remain in
the final DNA. For each of the following combinations, indicate whether it can (C) or
cannot (N) result from this recombination scheme. Do not consider the re-integration of
excised DNA, which happens very rarely. Your answer would be a six-letter string
composed of letters C and N only, e.g. CCCCNN.
( )Red and yellow
( )Red only
( )Yellow only
( )Cyan only
( )Yellow and cyan
( )Red and cyan
A geneticist has devised a strategy to study protein translocation into the endoplasmic
reticulum (ER) in yeast cells. She is interested in two different signal sequences that are
thought to operate via slightly different translocation mechanisms. Using genetic
engineering, she has fused the first signal sequence to a protein whose cytosolic
expression is absolutely necessary for cell survival in the selective medium, but is
inactive when in the ER. In the same cell, she has also fused the second signal sequence
to a toxic protein whose cytosolic expression leads to cell lysis but is harmless when in
the ER. Whereas wild-type cells undergo lysis upon the expression of these fusion
proteins, she has been able to identify viable mutants, each of which has a
loss-of-function mutation in a gene encoding a protein involved in membrane
translocation. The products of these genes are probably ___
A.involved in the general transport of proteins into the ER, regardless of the type of
signal sequence.
B.involved in the transport of proteins with the first signal sequence but not the second
one.
C.involved in the transport of proteins with the second signal sequence but not the first
one.
D.involved in the transport of proteins with a novel signal sequence (i.e. neither the first
signal sequence nor the second one).
Considering the diagrams below that show hydrogen-bond donors and acceptors as well
as hydrophobic groups in four DNA base pairs, which of the following do you think is
the most difficult to accomplish by DNA-binding proteins?
A.Distinguishing between A-T and T-A in the major groove
B.Distinguishing between A-T and C-G in the major groove
C. Distinguishing between C-G and G-C in the major groove
D.Distinguishing between C-G and G-C in the minor groove
E.Distinguishing between C-G and T-A in the minor groove
In a gene that normally contains three exons, which of the following changes probably
will NOT activate the nonsense-mediated mRNA decay pathway? The sizes of exons 1
to 3 are 100, 150, and 200 nucleotide pairs, respectively.
A.A nonsense mutation in exon 1
B.A nonsense mutation in exon 2
C.A mutation in the first intron resulting in the inclusion of a large intronic fragment in
the mature mRNA.
D.A frameshift mutation in exon 1
E.A mutation in exon 2 leading to its loss through exon skipping.
What is the typical thickness of a lipid bilayer such as the plasma membrane of our
cells?
A.0.5 nm
B.5 nm
C.50 nm
D.100 nm
E.500 nm
The structural formulas for the 20 naturally occurring amino acid residues are shown in
the panel below. Answer the following question(s) with the help of this panel.
Which of the amino acids shown above has the most limited combinations of phi ( )
and psi ( ) angles in its Ramachandran plot? Write down the one-letter abbreviation for
it, e.g. A.
You have purified a multisubunit extracellular protein that has several interchain
disulfide bonds. Which of the following chemicals would you add to your purified
protein mixture if you wanted to eliminate the disulfide bonds?
A.NaCl, a salt
B.SDS, an ionic detergent and denaturing agent
C.H2O2, an oxidizing reagent
D.Tris, a buffering agent
E.DTT, a reducing agent
The Steel factor/Kit signaling pathway plays an important role in the migration of many
types of cells during development as well as in the adult animal. Not surprisingly,
loss-of-function mutations in Steel factor result in cell migration defects. Selective
inactivation in these cells of which of the following proteins might be expected to
rescue (i.e. partially restore to normal) the defective phenotype of Steel loss-of-function
mutants?
A.Kit, the receptor for Steel
B.Bax, an essential apoptotic protein
C.Endothelin-3, a survival factor for neural crest cells
D.Fibronectin, a multi-adhesive protein of the extracellular matrix
E.FGF4, a growth factor
How does Helicobacter pylori persist in the hostile environment of the stomach?
A.By expressing adhesin proteins that bind to molecules on the surface of gastric
epithelial cells
B.By producing the enzyme urease, which locally neutralizes the gastric acid
C.By chemotaxis, using flagella, toward gastric epithelial cells
D.By producing toxins that target both epithelial cells and immune cells
E.All of the above
Which of the following is NOT the role of molecular chaperones in the folding of
cellular proteins?
A.They assist proteins in folding into their correct conformations.
B.They help prevent formation of protein aggregates.
C.They specify the final three-dimensional shape of proteins.
D.They catalyze the folding of proteins in the crowded environment of the cell.
E.They make the protein-folding process in the cell more reliable.
A point mutation in the gene encoding the subunit of hemoglobin can lead to
sickle-cell anemia. Due to formation of mutant hemoglobin aggregates, red blood cells
in affected individuals can adopt a sickle-like shape that interferes with their normal
function. Interestingly, individuals carrying this mutation are less vulnerable to malaria
infection by Plasmodium falciparum, which replicates inside red blood cells.
Accordingly, would you expect the frequency of the mutated hemoglobin allele to be
higher in West Africa (A) or in Europe (E)? Write down A or E as your answer.
This large and complex general transcription factor has a DNA helicase activity that
exposes the template for RNA polymerase II transcription. It also has a kinase activity
that phosphorylates the C-terminal domain of the polymerase on Ser5 leading to
promoter clearance. It is___
A.TFIIB
B.TFIID
C.TFIIE
D.TFIIF
E.TFIIH
The eukaryotic chromosomes are organized inside the nucleus with a huge compaction
ratio of several-thousand-fold. What is responsible for such a tight packaging?
A.The various chromatin proteins that wrap and fold the DNA
B.The nuclear envelope which encapsulates the chromosomes
C.The nuclear matrix that provides a firm scaffold
D.All of the above
What do the enzymes topoisomerase I and topoisomerase II have in common?
A.They both have nuclease activity.
B.They both create double-strand DNA breaks.
C.They both require ATP hydrolysis for their function.
D.They both can create winding (tension) in an initially relaxed DNA molecule.
E.All of the above.
In the following simplified diagram, the activation of a hypothetical allosteric protein is
plotted as a function of effector molecule concentration. Which curve (A to E) do you
think corresponds to a condition in which activation requires the highest number of
effector molecules bound to each protein?
Indicate true (T) and false (F) statements below regarding cell proliferation in human
somatic cancer cells. Your answer would be a four-letter string composed of letters T
and F only, e.g. TFFF.
( )Cancer cells show replicative cell senescence.
( )Cancer cells maintain their telomeres by inhibiting the enzyme telomerase.
( )Some cancer cells do not rely on telomerase for telomere lengthening.
( )Most cancer cells lack telomeres.
Myelomas are cancers of blood plasma cells€white blood cells that are normally
responsible for producing large quantities of antibodies. In the following “Circos plot”
for myelomas in a hypothetical mammalian genome, the interchromosomal
rearrangements are indicated by red lines and variations in copy numbers are indicated
in blue. The positions of named genes are indicated with arrows. On which
chromosome do you expect to find the antibody genes? Write down the chromosome
number (1 to 5) as your answer.
If two genomic polymorphic sites were randomly and independently associated with
each other, one would expect the frequency of observing a combination of their allelic
forms in an individual to be equal to the multiplication product of the probability of the
alleles occurring separately. In many cases, however, this is not true. The degree of
deviation from random association can be quantified and summarized in diagrams such
as the one below. In this diagram, eight SNPs in a genomic region are shown and their
pairwise deviation from random association is color-coded by different shades of red,
such that the darkest red shade indicates the furthest deviation from random association.
In contrast, those pairs that associate randomly are colored white. For example, SNPs A
and F seem to associate randomly as indicated by the corresponding box marked with
black borders. From this diagram, two haplotype blocks can be readily detected. What
subset of the shown SNPs is not part of any of the two blocks? Write down the letter(s)
as your answer, in alphabetical order, e.g. CEH.
Gout patients have high uric acid levels in their blood and suffer from arthritis in their
joints as a result of formation of intracellular and extracellular uric acid crystals. Would
you expect treatment with glucocorticoids (G), which inhibit prostaglandin synthesis, or
with tumor necrosis factor (TNF) to be normally used to treat such patients?