CELL AND MOLECULAR BIOLOGY
PRACTICE STUDY GUIDE TESTED
QUESTIONS
●● Cytosol
Answer: 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 transport
Answer: Movement of proteins through nuclear pore complexes between
the
cytosol and the nucleus.
●● Organelle
Answer: Membrane-enclosed compartment in a eukaryotic cell that has a
distinct
structure, macromolecular composition, and function.
●● Signal sequence
Answer: 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.
Answer: 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.
Answer: 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.
Answer: 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.
Answer: 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?
Answer: 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?
, Answer: 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?
Answer: 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?
Answer: 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.
Answer: 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
PRACTICE STUDY GUIDE TESTED
QUESTIONS
●● Cytosol
Answer: 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 transport
Answer: Movement of proteins through nuclear pore complexes between
the
cytosol and the nucleus.
●● Organelle
Answer: Membrane-enclosed compartment in a eukaryotic cell that has a
distinct
structure, macromolecular composition, and function.
●● Signal sequence
Answer: 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.
Answer: 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.
Answer: 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.
Answer: 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.
Answer: 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?
Answer: 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?
, Answer: 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?
Answer: 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?
Answer: 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.
Answer: 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
