Skeletal muscle cells consume enormous amounts of ATP. From the following list,
choose the two proteins that directly hydrolyze most of this ATP. Your answer would be
a two-letter string composed of letters A to F only, in alphabetical order, e.g. AF.
A.Troponin complex
B.Ca2+-release channel
C.Myosin light chains
D.Myosin heavy chain
E.Myosin light-chain kinase
F.Sarcoplasmic reticulum Ca2+-pump
Which of the following is NOT an example of a crawling cell?
A.Macrophage
B.Osteoclast
C.Keratocyte
D.Neural crest cell
E.Sperm
In the polymerization in vitro of actin filaments and microtubules from their subunits,
what does the “lag phase” correspond to?
A.Nucleation
B.Reaching steady state
C.Nucleotide exchange
D.ATP or GTP hydrolysis
E.Treadmilling
Sort the following from a low to a high contribution to the total mass of an E. coli
bacterium. Your answer would be a four-letter string composed of letters A to D only,
e.g. DCBA.
(A)Water
(B)Sugars
(C)Proteins
(D)Nucleic acids
Transmembrane proteins ___
A.are typically exposed only to one side of the membrane.
B.can be released from the membrane by a gentle extraction procedure such as salt
treatment.
C.are often further attached to the membrane via a GPI anchor.
D.are sometimes covalently attached to a fatty acid chain that inserts into the
membrane.
E.cannot contain sheets in the part of their structure that interacts with the membrane
interior.
The specific transfer RNA used for the incorporation of selenocysteine in proteins
recognizes the UGA codon, which is normally a translation stop codon. What prevents
this tRNA from reading through all the other “legitimate” UGA stop codons in the cells
and causing a massive, disastrous recoding?
A.The cells that have selenocysteine in their proteins do not normally use the UGA stop
codon and always use the other two stop codons (UAA and UAG) instead.
B.This tRNA is made in such a small amount that its side effects are negligible.
C.This tRNA only interacts with the UGA codon in the P site of the ribosome, and
therefore does not interfere with the normal function of the codon in translation
termination, which takes place in the A site.
D.The mRNAs encoding the selenocysteine-containing proteins also contain additional
sequences required for the recoding event.
The modified nucleotide shown below is normally found in mature___
A.tRNAs.
B.ribosomes.
C.spliceosomes.
D.snoRNAs.
E.All of the above.
Bistability in a biological system can be accompanied by hysteresis. Consider
switchlike cellular responses to a signal molecule, as shown in the following graphs. In
each graph, the solid curve corresponds to the change in cellular response when the
signal concentration is being increased over time, whereas the dashed curve
corresponds to the change when the signal concentration is being decreased. Which
graph do you think corresponds to a system with a greater degree of hysteresis? What
mechanism is responsible for this behavior?
A.Graph A; negative feedback
B.Graph A; positive feedback
C.Graph B; negative feedback
D.Graph B; positive feedback
Fill in the blank in the following paragraph regarding the recognition of tail-anchored
proteins by their targeting machinery. DO NOT use abbreviations.
“When the hydrophobic transmembrane ± helix at the C-terminus of an ER
tail-anchored protein emerges from the ribosome, the tail-anchored-binding domain
(TABD) of the Get3 ATPase binds to it. The job of TABD in Get3 is similar to that of
the flexible hydrophobic domain in the SRP54 protein of the signal-recognition particle,
in that it also has to recognize a degenerate set of hydrophobic – helices. Therefore, it
is not surprising that, just like the corresponding domain in SRP54, the binding site in
Get3 is rich in ___ residues.”
On the ribosome, the mRNA is read from ___, and the polypeptide chain is synthesized
from___
A.5′ to 3′; C- to N-terminus.
B.5′ to 3′; N- to C-terminus.
C.3′ to 5′; C- to N-terminus.
D.3′ to 5′; N- to C-terminus.
The gene clusters known as the Bithorax complex and the Antennapedia complex
contain…
A.a subset of segment-polarity genes.
B.segmentation genes.
C.homeobox-containing genes.
D.genes encoding chromatin repressors.
E.genes encoding chromatin remodelers.
The presence of which of the following provides the sample with the lowest electron
density?
A.Osmium
B.Lead
C.Uranium
D.Carbon
E.Gold
Which endocytic process is best depicted in the following schematic diagram?
A.Receptor-mediated endocytosis
B.Pinocytosis
C.Macropinocytosis
D.Phagocytosis
E.Entosis
On average, errors occur in DNA synthesis only once in every ten billion nucleotides
incorporated. Which of the following does NOT contribute to this high fidelity of DNA
synthesis?
A.Complementary base-pairing between the nucleotides
B.”Tightening” of the DNA polymerase enzyme around its active site to ensure correct
pairing before monomer incorporation
C.Exonucleolytic proofreading by the 3′-to-5′ exonuclease activity of the enzyme to
correct mispairing even after monomer incorporation
D.A strand-directed mismatch repair system that detects and resolves mismatches soon
after DNA replication
E.All of the above mechanisms DO contribute to the fidelity.
The citric acid cycle is summarized in the following figure. Answer the following
question(s) about this cycle.
In step 1 of the citric acid cycle drawn above, what is the molecule indicated with a
question mark?
A.O2
B.ATP
C.H2O
D.H+
E.Pyruvate
The AgeI restriction enzyme recognizes the sequence ACCGGT and cuts each strand
between the first (A) and the second (C) nucleotide. This can be represented as
A|CCGGT, with the vertical bar indicating the cleavage position. If a DNA fragment is
cut with AgeI at both ends, cutting a plasmid with which of the following enzymes
would then allow insertion of the fragment into the plasmid by simple ligation of sticky
ends?
A.FseI, with the recognition sequence GGCCGG|CC
B.AatI, with the recognition sequence AGG|CCT
C.BstZI, with the recognition sequence C|GGCCG
D.MroI, with the recognition sequence T|CCGGA
E.None of the above
A certain effector protein can be activated by phosphorylation at a key tyrosine residue.
An upstream kinase rapidly phosphorylates this tyrosine in the presence of a signal.
However, the kinase also phosphorylates and activates a slow-acting phosphatase that
can dephosphorylate the phosphotyrosine. Which curve in the following graph would
you expect to represent the activity of the effector molecule over time? The input signal
is present during the period indicated in gray. The dashed line represents the response in
the absence of the phosphatase.
Which of the following simplified diagrams better shows the changes in the
concentrations of three major cyclin-Cdk complexes (G1/S-Cdk, S-Cdk, and M-Cdk) in
the cell in different stages of the cell cycle?
You have devised genetic screens to identify gain- and loss-of-function mutations in the
Escherichia coli DNA ligase gene. One of the screens (1) seeks mutant cells that are
infected more readily with a ligase-deficient strain of T4 phage. The other screen (2)
seeks mutant cells that have increased radiation sensitivity at high temperatures.
Indicate whether each of the following descriptions better applies to screen 1 (1) or
screen 2 (2). Your answer would be a three-digit number composed of digits 1 and 2
only, e.g. 122.
( )It would identify gain-of-function DNA ligase mutants.
( )It would identify loss-of-function DNA ligase mutants.
( )It would identify conditional mutants.
Indicate true (T) and false (F) statements below regarding mitosis and the changes that
it brings about compared to interphase. Your answer would be a four-letter string
composed of letters T and F only, e.g. TFTF.
( )Microtubules become greatly stabilized in mitosis compared to interphase.
( )The number of ring complexes in the centrosomes increases greatly
during mitosis compared to interphase.
( )Chromosomes stabilize mitotic microtubules through activation of Ran monomeric G
protein.
( )A bipolar spindle can be formed even in the absence of centrosomes.
The lateral diffusion of a plasma membrane protein has been studied using the
fluorescence recovery after photobleaching (FRAP) technique in a cell under normal
conditions, and the following plot has been obtained. Under a different condition (e.g.
when a signaling pathway is turned on), the protein binds to a few other proteins and
protein complexes in the plasma membrane. As a result, its lateral diffusion coefficient
is reduced and a significant fraction of the molecules of this protein are immobilized in
large aggregates. How would you expect the FRAP curve to change under these new
conditions? The dotted line in each graph is the original curve shown for comparison.
The sliding clamp and the DNA helicase that function at the replication fork both have
three-dimensional structures resembling a ring with a central hole through which DNA
is threaded. Which of these proteins, the clamp (C) or the helicase (H), do you think has
a wider hole in its structure? Write down C or H as your answer.
You are studying the rising incidence of a certain subtype of cervical cancer in Oceania,
and are curious to know whether environmental factors are the dominant cause of the
disease. You collect the incidence statistics from indigenous populations as well as from
two different immigrant populations in three different countries, as shown in the
following table. Do these data appear to be consistent with a dominant role of
environmental risk factors (E) or a genetic background (G) for this type of cancer?
Write down E or G as your answer.
In the following graphs, the cellular response, as measured in real time by the
concentration of a certain active effector protein, is plotted over time for five cell types
(A to E) that are treated with three different concentrations of a signal molecule. During
the time period indicated by the horizontal gray bar, the signal molecule is present in
the culture media at a concentration of 1 nM (dotted curve), 5 nM (gray curve), or 25
nM (solid curve). Answer the following question(s) based on these graphs.
Which of the cell types A to E shows the fastest signal adaptation?