Alberts Molecular Biology of Cell - Chapter 005 Test Quiz Bank
With Questions & Answers 2023/2024
Cytoplasmcorrect answers Contents of a cell that are contained within its plasma membrane but, in the
case of eukaryotic cells, outside the nucleus
Cytosolcorrect answers Contents of the main compartment of the cell, excluding the nucleus and
membrane bounded compartments such as ER and mitochondria. the main site of protein degradation
Gated transportcorrect answers Movement of proteins through nuclear pore complexes between the
cytosol and the nucleus.
Organellecorrect answers Membrane-enclosed compartment in a eukaryotic cell that has a distinct
structure, macromolecular composition, and function.
Signal sequencecorrect answers Protein sorting signal that consists of a short continuous sequence of
amino acids.
TRUE OR FALSE
The biological membranes that partition the cell into functionally distinct
compartments are impermeable.correct answers FALSE
lipid bilayers themselves are impermeable to hydrophilic molecules but biological membranes, which
contain proteins in addition to the bilayer are not. they are selectively permeable
TRUE OR FALSE
Like the lumen of the endoplasmic reticulum (ER), the interior of the
nucleus is topologically equivalent to the outside of the cell.correct answers FALSE
the nucleus is topologically equivalent to the cytoplasm because the outer and inner membrane are
continuous with one another
TRUE OR FALSE
ER-bound and free ribosomes, which are structurally and functionally
identical, differ only in the proteins they happen to be making at a particular
time.correct answers TRUE
Ribosomes all begin translating mRNAs in the cytosol. the mRNAs for certain proteins encode a signal
sequence for the ER membrane. after synthesis, the nascent protein along with the ribosome and the
mRNA is directed by the signal sequence to the ER membrane. Ribosomes translating mRNA without
such a sequence remain free in the cytosol
TRUE or FALSE
Each signal sequence specifies a particular destination in the cell.correct answers TRUE
Signal sequences that specify particular cellular destinations have characteristic features that allow their
interaction with appropriate sorting receptors, which guide them to their target compartment
Is it really true that all human cells contain the same basic set of membrane-
enclosed organelles? Do you know of any examples of human cells
,that do not have a complete set of organelles?correct answers The vast majority of cells in the human
body do have a complete set of membrane enclosed organelles. Certain specialised cells do not. e.g. Red
Blood Cell. only a plasma membrane enclosed cytosol
Cells that make up the lens of the eye lack a mitochondria
Why do eukaryotic cells require a nucleus as a separate compartment
when prokaryotic cells manage perfectly well without?correct answers Eukaryotic gene expression is
more complicated. Prokaryotic cells do not have introns that interrupt the coding sequences on their
genes, so that an mRNA can be translated immediately after transcription. In eukaryotic cells most RNA
transcripts must be spliced before translation. The nuclear envelope separates the transcription and
translation processes in space and time.
What is the fate of a protein with no sorting signal?correct answers The protein will remain in the cytosol
Which
type of protein synthesis—in the cytosol or on the ER—do you think is
responsible for the majority of protein synthesis in a liver cell?correct answers In cells that do not
secrete large amounts of protein, the majority of protein synthesis is likely to occur in the cytosol.
List the organelles in an animal cell that obtain their proteins via gated
transport, via transmembrane transport, or via vesicular transport.correct answers The nucleus is the
only organelle that receives its proteins by gated transport.
The ER mitochondria and peroxisomes all receive their proteins by transmembrane transport, mediated
by specific protein translocators that reside in the membrane
The golgi apparatus, secretory vesicles, early and late endosome and lysosomes all obtain their proteins
via vesicular transport
Nuclear export signalcorrect answers Sorting signal contained in the structure of macromolecules and
complexes
that are transported from the nucleus to the cytosol through
nuclear pore complexes.
Nuclear Pore Complex (NPC)correct answers Large multiprotein structure forming a channel through the
nuclear
envelope that allows selected molecules to move between nucleus and
cytoplasm. It has a nuclear basket and each NPC contains aqueous passages, through which small water
soluble molecules can diffuse passively
How does selective import into the nucleus occur?correct answers The nuclear localization signal (NLS)
are responsible for the selectivity of the active nuclear import process.
To initiate nuclear import, most. NLS must be recognized by nuclear import receptors that are sometimes
called importins , export requires exportins. Importins and exportins belong to the karypherin family.
The importin finds the nuclear pore complex via FG repeats of the nucleoporins, of which there are 30
form the npc.
FG for phenylalanine and glycine
Rancorrect answers Monomeric GTPase present in both cytosol and nucleus that is required
for the active transport of macromolecules into and out of the nucleus
,through nuclear pore complexes.
nuclear laminacorrect answers Fibrous meshwork of proteins on the inner surface of the inner nuclear
membrane.
Nuclear import receptorcorrect answers Protein that binds nuclear localization signals and facilitates the
transport
of proteins with these signals from the cytosol into the nucleus
through nuclear pore complexes
also known as Importin
Nuclear Localisation Signal (NLS)correct answers Sorting signal found in proteins destined for the nucleus
and which enable
their selective transport into the nucleus from the cytosol through the
nuclear pore complexes.
outer nuclear membranecorrect answers The portion of the nuclear envelope that is continuous with the
endoplasmic
reticulum and is studded with ribosomes on its cytosolic surface.
TRUE OR FALSE
The nuclear membrane is freely permeable to ions and other small molecules
under 5000 daltons.correct answers TRUE
due to the perforated membrane
TRUE OR FALSE
To avoid the inevitable collisions that would occur if two-way traffic
through a single pore were allowed, nuclear pore complexes are specialized
so that some mediate import while others mediate export.correct answers FALSE
individual nuclear pores mediate transport in both directions. its unclear how traffic is avoided
TRUE OR FALSE
Some proteins are kept out of the nucleus, until needed, by inactivating
their nuclear localization signals by phosphorylation.correct answers TRUE
gene regulatory proteins are usually regulated in this way. preventing gene activation or repression until
the proper time
TRUE OR FALSE
All cytosolic proteins have nuclear export signals that allow them to be
removed from the nucleus when it reassembles after mitosis.correct answers FALSE
resident cytosolic proteins are efficiently excluded from reassembling nuclei by the mechanism or
reassembly. the nuclear envelope is initially closely applied to the surface of the chromosomes, excluding
all proteins except those bound to mitotic chromosomes. once the envelope is complete, other residents
of the nucleus are imported via their nuclear localisation signals.
The inner and outer nuclear membranes form
a continuous sheet, connecting through the nuclear pores. Continuity
implies that membrane proteins can move freely between the two
, nuclear membranes by diffusing through the bilayer at the nuclear pores.
Yet the inner and outer nuclear membranes have different protein compositions,
as befits their different functions. How do you suppose this
apparent paradox is reconciled?correct answers - proteins on the inner membrane are anchored by
interactions with components of the nucleus such as the nuclear lamina and chromosomes.
- the nuclear pore proteins may restrict the free diffusion of other proteins as they are a boundary
between the inner and outer layer.
How is it that a single nuclear pore complex can efficiently transport proteins
that possess different kinds of nuclear localization signal?correct answers Transport is mediated by a
variety of nuclear import receptors that are encoded by a family of related genes.
How do you suppose that proteins with a nuclear export signal get into
the nucleus?correct answers proteins with a nuclear export signal also have a nuclear localisation signal,
therefor allowing them to shuttle between the nucleus and cytoplasm.
Nuclear localization signals are not cleaved off after transport into the
nucleus, whereas the signal sequences for import into other organelles
are often removed after import. Why do you suppose it is critical that
nuclear localization signals remain attached to their proteins?correct answers at each mitosis, the
contents of the nucleus and the cytosol mix when the nuclear envelope disassembles. when the nucleus
reassembles, the nuclear proteins must be selectively reimported. by contrast, the contents of other
organelles never mix wit the cytosol. at mitosis, the ER and Golgi break up into vesicles which retain the
luminal contents.
How does the Ran-GTP-GDP cycle in nuclear export/import work?correct answers Ran can exist in a gdp
and gap bound form. In the cytosol, the ran gdp Form dominantes, due to ran gap, gtpase activating
protein.
Rangdp is imported into the nucleus via its own import receptors.In the nucleus, ran gtp dominates due
to rangef (gdp/gtp nucleotide Exchange factor)
The gradient of these two forms drives the nuclear transport in the appropriate direction
Mitochndriacorrect answers Membrane-enclosed organelles, about the size of bacteria, that carry out
oxidative phosphorylation and produce most of the ATP in eukaryotic
cells.
has a double membrane.
contain DNA and ribosomes but still require protein import from cytosol.
Mitochondrial hsp70correct answers Part of a multisubunit protein assembly that is bound to the matrix
side
of the TIM23 complex and acts as a motor to pull the precursor protein
into the matrix space.--> ratchet
Multisubunit protein assembly that transports proteins across the mitochondrial
outer membrane.correct answers TOM complex
Mitochondrial precursor proteincorrect answers Protein encoded by a nuclear gene, synthesized in the
cytosol, and subsequently
