Items 205-210
A pregnant 39- years-old female has amniocentesis carried out because of concern about possible birth defect associated with pregnancy in older women. Strong reactivity with an antibody to glial fibrillary acidic protein (GFAP) is detected.
205. GFAP is
(A) found in neurons of the central nervous system
(B) a glycoprotein containing numerous sulfated side chains
(C) a constituent of the nuclear envelope
(D) a GTPase secreted by glial cells and active at low pH
(E) one of the proteins that form intermediate filaments
206. The women’s obstetrician informs her that
(A) her child is likely to born three months premature
(B) the test result suggest that she has AIDS
(C) the feturs has spina difida
(D) a cesarean delivery will be required
(E) she will probably give birth of triplets
207. A finding of positive immureactivity for which protein in a tumor mass is indicative that the tumor in of epinthelial origin?
208. Dance tangles of microfilaments are not most likely to be found in
(A) autopsy material from the brain of a victim of Alzahiemer’s disease
(B) benign tumors of the esophagus
(C) the lungs of patients recovering from carbon monoxide poisoning
(D) the liver of children suffering from acute lead poisoning
(E) spinal cord tissue of woman paralyzed due a dividing accident
209. Which of the following factors in most likely to be physiologically relevant to the disassembly of intermediate filaments?
(A) conjugation of the filaments with glycogen
(B) phosphorylation of intermediate filament protein subunits.
(C) covalent coupling to gamma tubulin sidechains.
(D) ATP concentration lower than 1 mM
(E) stimulation of protein kinases by free calcium levels greater than 100 micromolar
210. Which of the following is LEAST likely to be a structure or function with which intermediate filaments are associated?
(A) attachment of desmosomes
(B) binding to intergrins
(C) linkage of myosin and actin filaments.
(D) anchorage onto hemidesmosomes
(E) connection of the cytoskeleton to the plasma membrane.
ANSWER AND TUTORIAL OM ITEMS 205-210
The answers are: 205-E; 206-C; 207-A; 209-B; 210-C. Intermediate filaments are components of the cytoskeleton. Intermediate are typically 10 in diameter and are formed by the polymerization of the one or more members of a family of polypeptides. One of the main functions of intermediate filaments appears to be the “integration” of forces – applied to the plasma membrane – throughout the entire cytoskeleton. Intermediate filaments binds tightly and specifically to demosomes and hemidesmosomes, apparently via interaction with one or more subtypes of the tranmembrane proteins called intergrins. Although the disassembly of intermediate filaments at specific points in the cell cycle is not yet well understood, it is now known that phosphorylation of intermediate filament proteins favors disassembly of the filaments.
The proteins that form intermediate filaments differ from tissue to tissue and this difference are used in a number of clinical tests. Epithelial tissues have intermediate filaments made from a variety of keratins; the finding of keratin immunoreactivty in a tumor mass implies that the tumor is derived from epithelial tissue. Similarly, desmin, vimentin, GFAP, and neurofilemant proteins are diagnostic of muscle cells, connective tissues, glial cells in the CNS (including astrocytes), and neuronal cells, respectively. Field Nature - Portable Microscopes Fluorescence Microscopes.
Spina bifida is a development defect involving failure of the posterior end of the neural tube to close. In such situation, the amniotic fluid is found to contain GFAP. Among the many defects founds in patients with Alzheimer’s disease is the presence of numerous large aggregates (“tangles”) of neurofilaments.
