The marking of a protein by polyubiquitylation to signify degradation ___
A.requires the hydrolysis of one ATP molecule to ADP per polyubiquitin chain.
B.involves covalent attachment of the target protein to the E1 enzyme.
C.is carried out by the proteasome complex.
D.is typically done on an arginine residue in the target protein.
E.involves the recognition of the target protein by an E2-E3 ligase.
Lysosomes are the principal site of cellular digestion. They ___
A.normally maintain a pH of about 2.0 to 2.5.
B.contain F-type ATPases that pump protons into the organelles.
C.contain heavily glycosylated membrane proteins.
D.are homogeneous in size and shape.
E.All of the above.
In the following schematic diagram of a cubic plant cell that has just left the meristem
zone, the cellulose microfibrils are shown as black lines. In which direction (1 or 2) do
you think the cell will elongate when the cell grows? If the cell wall is momentarily
dissolved, in what direction (3 or 4) would water tend to flow?
A.1; 3
B.1; 4
C.2; 3
D.2; 4
Expression of the Even-skipped (Eve) gene in early Drosophila embryos is under the
control of several transcription regulators. In one example, one of the Eve stripes is
positioned near the anterior region of the embryo, and its regulatory module contains
binding sites for Bicoid and Hunchback (activators) as well as Giant and Kr¼ppel
(inhibitors) such that the gene is expressed only in the region where concentrations of
the two activators are high and the concentrations of the two inhibitors are low. A
reporter gene can be placed under the control of this module, and it can be shown to
form a stripe in the same place in the embryo as the corresponding stripe of Eve.
Answer the following question(s) based on these findings.
What would you expect to happen to the pattern of reporter expression in flies that lack
the gene encoding Giant?
A.It would be expressed in all seven stripes.
B.It would be expressed in stripe 5 only.
C.It would expand to cover a broad anterior region of the embryo.
D.It would fail to express efficiently in the stripe 2 region.
E.It would be expressed throughout the whole embryo.
Phase variation helps protect the bacterium Salmonella typhimurium against the
immune system of its host by switching the orientation of a certain promoter. This
process ___
A.is carried out through a DNA transposition mechanism.
B.is irreversible.
C.can often result in the excision of the promoter from the chromosome altogether.
D.is mediated by enzymes that form transient covalent bonds with the DNA.
You infect human epithelial cells in culture with either nonpathogenic bacteria or Vibrio
cholerae, each without any further treatment, in the presence of MDC (an inhibitor of
clathrin-dependent endocytosis) or in the presence of filipin (an inhibitor of a
clathrin-independent endocytic pathway). You then measure the intracellular
concentration of cyclic AMP (in picomoles per milligram of total cell protein) and
summarize the results in the following table. Which row (1 or 2) do you think
corresponds to infection with V. cholerae? From these results, does cholera toxin enter
the cell in clathrin-coated vesicles?
A.Row 1; yes
B.Row 1; no
C.Row 2; yes
D.Row 2; no
Which of the following schematic drawings better depicts the end of mammalian
chromosomal DNA?
A.
B.
C.
D.
E.
There are six possible reading frames for any double-stranded DNA. In the following
schematic drawing of a genomic region in Escherichia coli, stop codons in each of these
frames are indicated by black bars. In which reading frame do you think the open
reading frame (ORF) is translated in this region? Write down the frame number as your
answer, e.g. 2.
How does talin activate the inside-out signaling through integrin?
A.It binds to both integrin subunits to bring them together in an interlocked
conformation.
B.It is a protein kinase that phosphorylates both integrin subunits and induces activation
by conformational change.
C.It competes with the subunit for binding to the subunit, therefore blocking
intimate – linkage.
D.It binds to the subunit, and dissociates the dimer into individual subunits that are
functionally active.
Retinoblastoma is an early-onset cancer of the retina with a rapid progression, and is
mostly diagnosed in children. In its hereditary form, multiple eye tumors usually arise
in both eyes, while the nonhereditary form usually causes fewer tumors in only one eye.
Treatment may involve a combination of chemotherapy, radiotherapy, and other
therapies and the majority of patients can be cured if given the right treatment.
However, survivors of one form of retinoblastoma (and not the other form) have a
markedly increased frequency of subsequent neoplasms that can lead to other cancers
later in life, especially soft-tissue sarcomas. These patients should therefore be closely
monitored throughout their lives. Which gene is affected by the primary driver mutation
in this cancer as well as the later sarcomas? Which form of retinoblastoma do you think
is associated with a higher risk of subsequent neoplasms?
A.p53; hereditary
B.Rb; hereditary
C.Ras; nonhereditary
D.p53; nonhereditary
E.Rb; nonhereditary
Multidomain glycoproteins in the extracellular matrix have binding sites for many other
macromolecules. These glycoproteins …
A.can serve as tracks along which cells can migrate.
B.can bind to growth factors and influence cell signaling.
C.can bind to cell-surface receptors.
D.can serve as repellents to forbid cell migration.
E.All of the above.
Malignant cancer cells that have entered the bloodstream can imitate lymphocytes in
exiting the bloodstream and entering underlying tissues in the process of metastasis.
This “lymphocyte mimicry” can be summarized as …
A.an initial cadherin-dependent rolling followed by an integrin-dependent adhesion and
emigration.
B.an initial cadherin-dependent rolling followed by an I-CAM-dependent adhesion and
emigration.
C.an initial cadherin-dependent rolling followed by a selectin-dependent adhesion and
emigration.
D.an initial selectin-dependent rolling followed by a cadherin-dependent adhesion and
emigration.
E.an initial selectin-dependent rolling followed by an I-CAM-dependent adhesion and
emigration.
The type III secretion system of pathogenic bacteria …
A.is a general secretion system found only in Gram-positive bacteria.
B.is used to inject effector proteins directly into the cytoplasm of host cells.
C.is similar to the eukaryotic secretion system.
D.is similar to the bacterial conjugation apparatus.
E.All of the above
Indicate whether each of the following phosphorylation events typically activates (A) or
inactivates (I) the protein that is being phosphorylated. Your answer would be a
four-letter string composed of letters A and I only, e.g. IIIA.
( )Phosphorylation of Cdc25 by M-Cdk
( )Phosphorylation of condensin subunits by M-Cdk
( )Phosphorylation of kinesin-5 by Aurora-A
( )Phosphorylation of Ndc80 subunits by Aurora-B
Sort the following events to reflect the sequence during smooth muscle contraction
upon delivery of muscle stimulation. Your answer would be a five-digit number
composed of digits 1 to 5 only, e.g. 13452.
(A)Activation of the myosin light-chain kinase
(B)Interaction of myosin head with actin
(C)Phosphorylation of myosin
(D)Calcium release into the cytoplasm
(E)Activation of calmodulin
You have engineered the X chromosomes in female mice such that one X chromosome
expresses green fluorescent protein when active, while the other expresses red
fluorescent protein. You have used these mice to study cancer in females. You know
that each tumor is a clonal cellular proliferation, meaning all of its proliferating cells are
descendants of a single original cancer-causing cell. It follows that, unless
X-chromosome inactivation is perturbed in tumors, ___
A.all tumor cells in one mouse should express the same fluorescent protein (either red
or green), but tumor cells from different mice can show either red or green
fluorescence.
B.the cells in any tumor should all express the same fluorescent protein (either red or
green), but independently derived tumors in the same mouse can show either green or
red fluorescence.
C.different cells within each tumor can express different fluorescent proteins, and the
tumors would therefore show yellow fluorescence, but each cell shows either red or
green fluorescence.
D.each cell can express both fluorescent proteins and would therefore emit yellow
fluorescence, and the tumors would glow in yellow as well.
E.different tumors would show red, yellow, or green fluorescence.
Which of the following is true regarding maternal-effect genes?
A.Bicoid and Nanos are maternal-effect genes.
B.A female homozygous for a loss-of-function maternal-effect gene mutation can be
fully normal, but her offspring will show the phenotype.
C.The offspring of a female homozygous for a loss-of-function maternal-effect gene
mutation will show the phenotype regardless of the paternal genotype.
D.The second-generation offspring of a male homozygous for a loss-of-function
maternal-effect gene mutation can show the phenotype.
E.All of the above.
The free-energy change ( G) for a simple reaction, A –> B, is 0 kJ/mole at 37°C when
the concentrations of A and B are 10 M and 0.1 M, respectively. What is the free-energy
change for the reaction when the concentrations of A and B are instead 0.01 M and 1 M,
respectively? Recall that G° = -5.9 x log(Keq). Write down your answer as a number
with the appropriate sign (+ or -) and in kJ/mole, e.g. +11.8 kJ/mole.
X-chromosome inactivation in female mammals occurs mostly randomly early in
development, resulting in a heterogeneous cell population, with each cell having
inactivated one or the other of its X chromosomes and passing on the same
X-inactivation choice to its offspring. The inactivated X chromosome is generally
hypermethylated and transcriptionally inactive. You are studying a newly discovered
type of colon tumor in women that has a morphology distinct from that of other colon
adenomas. You extract chromosomal DNA from the tumor cells. You then either keep
the DNA untreated, or digest the DNA with a methylation-sensitive restriction enzyme
that only cleaves its recognition DNA sequence if the sequence is not methylated.
Finally, you amplify by polymerase chain reaction (PCR) a locus on the X chromosome
known to be polymorphic in length (i.e. it is expected to be of different sizes in different
X chromosomes). The locus has a restriction site for the mentioned enzyme, such that
cleavage would prevent PCR amplification. You quantify the amount of PCR products
corresponding to shorter and longer versions of the locus, and obtain the results shown
in the following table. Do these data appear to be in better agreement with a
monoclonal (M) or a polyclonal (P) origin of cancer? A monoclonal origin would mean
that all cells in the tumor are the clonal descendants of a single abnormal cell, while a
polyclonal tumor is composed of cells from different lineages. Write M or P as your
answer.
In the following simplified diagram of cell divisions in a multicellular species, the
germ-cell and somatic-cell lineages are depicted. Which of the indicated cells (1 or 2)
represents the germ line? Write down 1 or 2 as your answer.
In the following schematic drawing of the cytosolic side of human red blood cell
plasma membrane, which of the labeled proteins is spectrin?
Indicate whether each of the following descriptions is shared (S) or not shared (N)
between macrophages and neutrophils in destroying invading pathogens in vertebrates.
Your answer would be a four-letter string composed of letters S and N only, e.g. SSSS.
( )They use a respiratory burst and create toxic reactive oxygen species to kill engulfed
pathogens.
( )They are normally found in most tissues even before pathogen invasion.
( )They are long-lived and normally survive long after activation.
( )They secrete pro-inflammatory cytokines upon encountering invading pathogens.
The phosphorylation state of a human protein follows the oscillatory pattern shown in
the first graph below. The protein is phosphorylated by two kinases (1 and 2), both of
which are activated in an oscillatory pattern. Kinase 1 oscillates in congruence with the
circadian rhythm, while kinase 2 oscillates at a higher frequency and is independent of
the circadian clock. The second graph shows the phosphorylation state of the same
protein in mutant cells lacking one of the kinases mentioned above. Which kinase (1 or
2) do you think is missing in these mutant cells? Write down 1 or 2 as your answer.
Which of the time points (A to E) in the following schematic drawing of the
mammalian cell cycle represents the restriction point?
Fill in the blank in the following paragraph. Do not use abbreviations.
“Growth and branching of blood vessels by the process of … creates a highly branched
network of blood vessels and capillaries to ensure that almost every cell within our
body has access to nutrients and oxygen from a nearby capillary. This process is distinct
from de novo vasculogenesis during embryonic development.”