Actin filaments that are held together by the cross-linking protein fimbrin are not
contractile. This is probably because …
A.the very weak cross-linking by this protein cannot convert myosin II activity into a
coherent contraction.
B.fimbrin arranges the actin filaments in parallel bundles in which all the plus ends
point to the same direction.
C.the very tight packing of actin filaments by this small protein excludes myosin II
filaments and other large proteins.
D.fimbrin arranges the actin filaments into gel-like networks in which myosin II
activity does not produce contraction.
E.fimbrin is a large protein that binds to several actin filaments and resists contraction.
Cellulose is deposited onto the plant cell wall in highly ordered crystalline aggregates
by the cellulose synthase complex embedded in the plasma membrane. Would you
expect cell wall deposition to continue following treatment of plant cells with a drug
that depolymerizes microtubules? Would you expect these cells to be able to switch the
orientation of the microfibril pattern between successive lamellae?
A.Yes; yes
B.Yes; no
C.No; yes
D.No; no
Which of the following is true regarding heterochromatin in a typical mammalian cell?
A.About 1% of the nuclear genome is packaged in heterochromatin.
B.The DNA in heterochromatin contains all of the inactive genes in a cell.
C.Genes that are packaged in heterochromatin are permanently turned off.
D.The different types of heterochromatin share an especially high degree of
compaction.
E.Heterochromatin is highly concentrated in the centromeres but not the telomeres.
Overproduction of cadherins such as E-cadherin …
A.is often found in cancers originating from epithelia.
B.is induced by the transcription regulatory protein Twist.
C.induces epithelial-mesenchymal transition.
D.leads to stronger cell-cell adhesion.
E.All of the above.
While examining the crystal structure of a membrane protein, you find several
phospholipid molecules bound to the protein. You know that these lipids ___
A.are thought to help stabilize many membrane proteins.
B.may enhance the crystallization of the bound membrane proteins.
C.interact specifically with the protein.
D.can have head groups of various sizes and charges depending on the protein.
E.All of the above.
Which of the following conditions is NOT expected to provide protection against HIV-1
infection of helper T cells?
A.A loss-of-function mutation in the CCR5 gene
B.Treatment with enfuvirtide, a membrane-fusion inhibitor
C.Treatment with concanamycin A, an inhibitor of endosomal proton pumps
D.Treatment with AMD-070, a CXCR4 antagonist
E.Treatment with PRO-542, a soluble decoy protein containing CD4 sequences
Which mammalian blood cell type undergoes the developmental event shown
schematically in the following drawing as part of its maturation?
A.Monocyte
B.Megakaryocyte
C.Erythrocyte
D.Lymphocyte
E.Granulocyte
Studying the expression of a transcription regulatory protein in two cell types, you have
performed experiments showing that the mRNA encoding the protein is present at
comparable levels in the cytosol of both cell types. However, based on the expression of
its target genes, you suspect that the protein activity might be significantly different in
the two cell types. Which of the following steps in expression of the gene encoding this
protein is more likely to be differentially controlled in these cell types?
A.Transcription
B.Translation
C.mRNA transport
D.mRNA degradation
Which of the following cell populations in our body has the highest mitotic index?
A.Neurons
B.Hepatocytes
C.Red blood cells
D.Fibroblasts
E.Skeletal myocytes
Which division in meiosis is more similar to mitosis? In which division do sister
chromatids separate from each other?
A.Meiosis I; meiosis I
B.Meiosis I; meiosis II
C.Meiosis II; meiosis I
D.Meiosis II; meiosis II
ATP is the main energy currency in cells, and it can especially be used to drive
condensation reactions that produce macromolecular polymers. How does ATP
normally catalyze the condensation reaction, which by itself is energetically
unfavorable?
A.It transfers its terminal phosphate to an enzyme and is released as ADP.
B.It transfers its two terminal phosphates to an enzyme, and is released as AMP.
C.It covalently attaches to both of the substrates.
D.It transfers either one or two terminal phosphate(s) to one of the substrates and is
released as either ADP or AMP.
E.It covalently attaches to the enzyme, forming an enzyme-AMP adduct.
How does the expression of Delta on the surface of a cell activate the expression of
certain genes in the nucleus of its neighboring cell?
A.Delta binding activates Notch, which activates a transcriptional activator through the
JAK€STAT pathway.
B.Delta binding leads to the stabilization of a cytoskeleton-associated transcriptional
activator.
C.Delta binding releases the intracellular tail of Notch, which enters the nucleus and
converts a transcriptional repressor into a transcriptional activator.
D.Delta binding leads to Notch-mediated recruitment of protein complexes to the
plasma membrane, resulting in the degradation of a transcriptional repressor.
E.Delta binding leads to the proteolytic cleavage of Notch and inhibition of its activity
as a transcriptional repressor, leading to the activation of target genes.
The equilibrium constant for the reaction that breaks down each molecule of substrate A
to one molecule of B and one molecule of C is equal to 0.5. Starting with a mixture
containing only molecules A at 1 M concentration, what will be the concentration of
molecule A after reaching equilibrium under these conditions?
A.0.5 M
B.0.25 M
C.0.125 M
D.0.333 M
E.0.667 M
Which of the following is NOT true about the nuclear subcompartments?
A.Nucleoli, Cajal bodies, and speckles are examples of such subcompartments.
B.Each specialized subcompartment has a distinct biochemical environment and a
selected set of proteins and/or RNA molecules.
C.The subcompartments are constitutively present in a cell except during nuclear
divisions.
D.They are likely to be organized by a tethered network of macromolecules in gel-like
structures.
A researcher has grown monolayers of cells from either of two epithelial cell lines on a
permeable supporting membrane that separates two electrolyte chambers. One of the
cell lines (A) has been derived from the mammalian kidney and forms epithelial sheets
resembling those lining the renal collecting duct and the urinary bladder. The other (B)
is derived from the mammalian small intestine. The researcher has measured the
voltage (V) and electrical current (I) across the monolayer and has plotted the results in
the graph below. Which line (1 or 2) in the graph do you think corresponds to cell line
A? Recall that current (I) is related to the applied voltage (V) by the equation I = V/R,
in which R is the electrical resistance. Write down 1 or 2 as your answer.
Which of the following is correct regarding the mutation rate of genomic DNA in
different organisms?
A.Human cells have a much higher mutation rate compared to bacteria when the rate is
normalized to a single round of replication over the same length of DNA.
B.Mutation rates limit the number of essential genes in an organism’s genome.
C.Mutations in the somatic cells cannot be lethal.
D.Even if the mutation rate was 10 times higher than its current value, germ-cell
stability in humans would not have been affected.
E.All of the above.
It is a model organism used to study various cell and developmental processes such as
the growth of developing body parts in the right place and with the correct shape. It
develops from a fertilized egg to an adult in a little over a week, and has been a favorite
of geneticists for almost a century. Some of its cells have giant chromosomes whose
banding patterns have been extremely helpful in classical genetic studies. Which of the
following describes this organism?
A.It is a vertebrate.
B.Its genome is only 10 million nucleotide pairs long.
C.There are many more duplicate genes in this organism compared to humans.
D.Although useful for genetic studies, the molecular mechanisms governing its
development are irrelevant to human development.
E.It normally only reproduces sexually.
Which of the following illnesses is NOT associated with infection with the pathogen
indicated?
A.Cervical cancer associated with human papillomavirus infection
B.Cancer in chickens associated with Rous sarcoma virus infection
C.Colon cancer associated with Vibrio cholerae infection
D.Stomach cancer associated with Helicobacter pylori infection
E.Atherosclerosis associated with Chlamydia pneumoniae
In each of the following comparisons, indicate whether the molecular clock is expected
to tick faster on average in the first (1) or the second (2) case. Your answer would be a
four-digit number composed of digits 1 and 2 only, e.g. 2222.
( )1: The exons, or 2: the introns of a gene
( )1: The mitochondrial, or 2: the nuclear DNA of vertebrates
( )1: The first, or 2: the third position in synonymous codons
( )1: A gene, or 2: its pseudogene counterpart
In the following schematic diagram of a simple columnar epithelium lining the
digestive tract, indicate which position (A to F) along the basal-apical axis better
corresponds to each of the following features. Your answer would be a six-letter string
composed of letters A to F only, e.g. FEDABC.
( )Basal lamina
( )Cell apex
( )Adherens junctions
( )Gap junctions
( )Hemidesmosomes
( )Tight junctions
Imagine that 1 L of a solution containing each of the 20 naturally occurring amino acids
at 50 mM concentration each (total concentration of 1 M) is allowed to polymerize in a
perfectly stepwise fashion such that at each step, a random amino acid can be
incorporated into a growing polypeptide. The steps are repeated, until eventually the
solution is only composed of 40-mers (and virtually all of the monomers have been
used). What fraction of all 40-mers can possibly be present in this solution? Round your
number to four decimal places. Avogadro’s number is 6 x 1023.
Reference: FACS Data Analysis
You have been studying the effect of loss-of-function mutations in the Cdk inhibitor
protein (CKI) p21. You add the drug fucoxanthin to cell cultures harboring either
wild-type or mutant versions of the p21 gene. Fucoxanthin is known to induce
cell-cycle arrest in G1. After a day, you add the thymidine analog BrdU to the culture
media, collect the cells after an hour, treat them with anti-BrdU antibody and the
fluorescent DNA stain DAPI, and finally subject them to fluorescence-activated cell
sorting (FACS). The FACS data can be viewed as a two-dimensional dot plot composed
of thousands of dots, in which each cell is represented by one dot at coordinates that
correspond to the intensities of the DAPI fluorescence signal (X axis) and BrdU
fluorescence signal (Y axis) for that cell. Answer the following question(s) according to
the simplified dot plot below, generated from your experiment.
Indicate which boxed region (1, 2, or 3) in the FACS plots corresponds better to each of
the following phases of the cell cycle. Your answer would be a three-digit number
composed of numbers 1 to 3, with each number used once, e.g. 312
( )G1 phase
( )S phase
( )G2 and M phases
Indicate whether each of the following descriptions better applies to connective (C) or
epithelial (E) tissues. Your answer would be a four-letter string composed of letters C
and E only, e.g. EEEE.
( )Cells are usually distributed sparsely in the extracellular matrix.
( )Gap junctions are rarely found.
( )Direct cell-cell attachments are common.
( )Cells are tightly associated into sheets.
Indicate whether each of the following groups of genes typically creates a transient
pattern in the developing embryo (T) or a long-lived pattern that is preserved (L). Your
answer would be a five-letter string composed of letters T and L only, e.g. TTTLT.
( )Egg-polarity genes
( )Pair-rule genes
( )Hox genes
( )Gap genes
( )Segment-polarity genes
For the Human Genome Project, cloning of large segments of our genome was first
made possible by the development of yeast artificial chromosomes, which are capable
of propagating in the yeast Saccharomyces cerevisiae just like any of the organism’s 16
natural chromosomes. In addition to the cloned human DNA, these artificial vectors
were made to contain three elements that are necessary for them to function as a
chromosome. What are these elements? Write down the names of the elements in
alphabetical order, and separate them with commas, e.g. gene, histone, nucleosome.