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 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 Ran - ANSWER-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 lamina - ANSWER-Fibrous meshwork of proteins on the inner surface of the inner nuclear membrane