Cell and molecular biology (alberts) EXAM QUESTIONS AND CORRECT ANSWERS(VERIFIED ANSWERS)|AGRADE

Cell and molecular biology (alberts) EXAM
QUESTIONS AND CORRECT
ANSWERS(VERIFIED ANSWERS)|AGRADE
Cytoplasm - ANSWER-Contents of a cell that are contained within its plasma
membrane but, in the case of eukaryotic cells, outside the nucleus
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 membraneenclosed 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
The golgi apparatus, secretory vesicles, early and late endosome and lysosomes all
obtain their proteins via vesicular transport
Nuclear export signal - ANSWER-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) - ANSWER-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? - ANSWER-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 kary