Exam 2 Flashcards
What could be defined as an organized network of extracellular materials found beyond the immediate vicinity of the plasma membrane?
extracellular matrix
You place mammary gland epithelial cells in culture and then treat them with enzymes that digest the surrounding extracellular matrix. What happens?
the secretory and synthetic activities of the cells decrease
The basal lamina of which structure may thicken abnormally in long-term diabetics causing kidney failure?
the glomerulus
All collagen family members consist of __ chains arranged in a __
3, triple helix
Collagen fibrils are strengthened by covalent cross-links between __ and __ residues on adjacent collagen molecules
lysine, hydroxylysine
In the corneal stroma, the uniformity of collagen fiber size and the ordered packing of the fibers confers what property on the corneal stroma?
transparency
Basement membranes contain Type IV collagen, a non fibrillar collagen organized in a flattened network. The Type IV collagen trimer has some interspersed non helical segments. What property does this confer upon basement membranes?
flexibility
Type I collagen mutations cause a potentially lethal condition characterized by extremely fragile bones, think skin, and weak tendons. This condition is called
osteogenesis imperfecta
Type II collagen mutations alter the properties of cartilage tissue and are known to cause
dwarfism and skeletal deformities
Mutations in other collagen genes can lead to a variety of distinct but related defects in collagen matrix structure, one of which causes hyper flexible joints and highly extensible skin. These defects are usually referred to as
Ehler-Danlos syndromes
What substance joins proteoglycans together into gigantic complexes called proteoglycan aggregates? These complexes can occupy very large volumes
hyaluronic acid
If antibodies to fibronectin are exposed to an embryo through which neural crest cells are migrating, what happens?
neural crest cell movements are inhibited
What would be the effect on primordial germ cells when an embryo is exposed to laminin-specific antibodies?
their movement to the developing gonad is disrupted
The degradation of the extracellular matrix, along with cell surface proteins, is accomplished mostly by a __ -containing enzyme family called __
zinc, matrix metalloproteinases
What protein is thought to be secreted into the extracellular matrix that surrounds the lining of mature blood vessels, where it inhibits angiogenesis?
thrombospondin
What integral membrane protein family made of two membrane-spanning chains (a and b) is involved in attaching cells to their extracellular microenvironment?
integrins
In an integral, what structure is it that crosses the lipid bilayer?
a transmembrane helix
The activation of a membrane integrin by the binding of its cytoplasmic portion to molecules in the cytoplasm and the resultant increase in its affinity for an extracellular ligand is called
inside-out signaling
Evidence strongly suggests that the bent conformation of an integrin is __ and unable to bind its ligand
inactive
You are investigating the interactions of integrin a and b subunits and isolate the extracellular portion of an integrin as a soluble a/b heterodimer. The heterodimer lacks the associated transmembrane and cytoplasmic domains normally present as part of the molecule. You experimentally link the a and b subunits at the bases of their legs so that the ligand-binding regions of the a and b subunits approach one another. What is true about the molecules formed?
the molecules bind their ligand tightly
If experimentally linked a/b heterodimer integrin subunits are separated, what happens?
the molecules are unable to bind a ligand
What ion is not known to bind to integrins?
sodium
What kind of experiments have provided evidence that most interns have unique functions?
gene knockout experiments
You coat a Petri dish with fibronectin and proteoglycans and culture cells on the dish. The cells adhere to the dish. You repeat the experiment but this time add RGD tripeptides to the culture dish as the cells are added. What happens?
The cells do not adhere to the dish
You coat a Petri dish with fibronectin and proteoglycans and culture cells on the dish. The cells adhere to the dish. You repeat the experiment but this time add RGD tripeptides to the culture dish as the cells are added. The result of this experiment is an example of what biochemical process?
competitive inhibition
Why do cells flatten out as they make contact with a surface?
They send out projections that make increasingly stable attachments.
To what is the cytoplasmic domain of integrins in the region of a focal contact connected via various adaptors?
actin of the cytoskeleton
The tightest attachment between a cell and its extracellular matrix is seen at the site where an epithelial cell is attached to the underlying basement membrane. The specialized adhesive structure found at such a site is called a(n) ________.
hemidesmosome
Filaments connected to the dense plaque underlying the membrane in a hemidesmosome course outward into the cytoplasm. These filaments are composed of the protein _____ and are best known as ______.
keratin, intermediate filaments
Epidermolysis bullosa, an inherited blistering disease, is caused by
genetic alterations in any one of a number of hemidesmosomal proteins
Focal adhesions
collect information about the chemical properties of the extracellular environment
Which of the following proteins are known to be associated with focal adhesions?
actin and myosin
Cells were allowed to bind to beads that had been covered with a coating of fibronectin. When the membrane-bound beads were pulled by an optical tweezer, the resultant mechanical stimulus was transmitted into the cell interior. What response did this cause?
It generated a wave of Src kinase activity.
Mesenchymal stem cells were grown on a soft, pliable substratum. Into what type of cells did they develop?
nerve cells
Mesenchymal stem cells were grown on a substratum of moderate stiffness. Into what type of cells did they develop?
muscle cells
Mesenchymal stem cells were grown on a very stiff substrate. Into what type of cells did they develop
osteoblasts, which give rise to bone cells
The filaments associated with hemidesmosomes are
keratin filaments and intermediate filaments
In which disease do individuals produce antibodies that bind to proteins present in hemidesmosmes? It causes the lower layer of the epidermis to lose attachment to the underlying basement membrane and thus to the underlying connective tissue layer of the dermis. The leakage of fluid into the space beneath the epidermis results in severe blistering of the skin.
bullous pemphigoid
Which disease is an inherited blistering disease that can occur in patients with genetic alterations in any one of a number of hemidesmosomal proteins, including the α6 or β4 integrin subunit, collagen VII or laminin-5?
epidermolysis bullosa
What proteins have been shown to be altered by genetic mutations in patients who suffer from epidermolysis bullosa?
the α6 integrin subunit, the β4 integrin subunit, collagen VII, laminin-5
You disaggregate cells from two different developing organs and mix them together. Initially, they form a mixed clump. What happens next?
The cells sort themselves out so that each cell adhered only to cells of the same type
________ are members of an integral membrane glycoprotein family that bind to specific sugar arrangements in oligosaccharides that project from the surfaces of other cells.
Selectins
Lymphocytes are isolated and labeled with radioactive isotopes. They are then exposed to frozen tissue sections of a lymphoid organ. What happens?
The lymphocytes selectively adhere to the endothelial lining of venules in peripheral lymph nodes.
The binding of lymphocytes to the endothelial lining of venules in peripheral lymph node frozen tissue sections could be blocked in what way? This demonstrated the existence of what kind of molecule?
Treatment with antibodies against specific lymphocyte surface glycoproteins, selectins
While most IgSF members are involved in various aspects of immune function, some of them mediate ________ cell-cell adhesion
calcium-independent
The bonds that selectins form with their ligands become _______ when the interaction is __________
stronger, placed under mechanical stress
What is thought to be the origin of immunoglobulins?
They may be derived from cell-adhesion receptors in invertebrates.
What is the function of most IgSFs?
mediating specific interactions of lymphocytes with cells needed for the immune response
L1 is an IgSF molecule that has been shown to be important in neural development; it is thought that it may be involved in axon growth within the embryonic nervous system. What evidence supports this statement?
People who die of L1-deficiency are often missing two large nerve tract
Patients that have died of L1-deficiency disease are missing a nerve tract that ________.
1) runs between the brain and the spinal cord
2) runs between the two halves of the brain
3) runs between the spinal cord and cerebellum
4) runs between the brain and the endocrine system
1 and 2
You genetically engineer nonadhesive cells to express one variety of cadherins and then mix the cells in various combinations. You then monitor their interactions. What do you observe?
The genetically engineered cells adhered preferentially to cells expressing the same cadherins.
Cadherins appear to be important in holding cells together in __________ tissues.
tightly cohesive
Calcium ions form bridges between
successive domains of a given cadherin molecule
What determines the strength of adhesion between apposing cells held together by cadherins?
d) the number of cadherins in a cluster connecting the cells
57) The loss of cadherin function may be instrumental in what disease state?
c) the spread of malignant tumors
58) When tight junctions, gap junctions and desmosomes are arranged in a specific array, the assortment of surface specializations is called a(n) __________.
d) junctional complex
59) From the apical surface to the basal surface of an epithelial cell, what is the order of cell junctions observed in the junctional complex?
a) tight junction, belt desmosome, spot desmosomes, gap junctions
60) What type of cell adhesion molecule is associated with cells being held together by adherens junctions at the site of the junction?
e) cadherins
61) What can be described as a tightly adherent, polarized cell layer?
c) an epithelium
62) What can be described as solitary, nonadhesive, nonpolarized migratory cells?
a) a mesenchyme
63) Which of the following is typified by an epithelial-mesenchymal transition or EMT?
1) formation of the mesoderm during gastrulation in a chick or mammalian embryo
2) cells breaking away from a from a cohesive epiblast
3) fusion of sperm and egg
4) formation of cartilage
e) 1 and 2
64) Which of the following tissues are typically derived from mesenchymal cells?
e) mesodermal tissues, blood and muscle
65) Which of the following tissues are typically not derived from mesenchymal cells?
b) ectodermal tissues
66) The cells of the epiblast of a developing mammalian embryo display what cell adhesion molecules on their surfaces, molecules that presumably promote their close association with one another?
b) E-cadherins
67) What is thought to promote the release of future mesoderm cells from an epithelium and their transformation into mesenchymal cells?
a) a stoppage in the expression of E-cadherin genes
68) Which tissues below are typically derived from the single-celled epithelium on the dorsal surface of a chick embryo after gastrulation?
b) skin, ectodermal tissues and nervous system
69) Which tissues below are not typically derived from the single-celled epithelium on the dorsal surface of a chick embryo after gastrulation?
a) muscle
70) What changes in the central region of the dorsal surface of the single-celled epithelial layer of a chick embryo lead to the formation of the primitive nervous system?
1) a stoppage in the expression of E-cadherin genes
2) a stoppage in the expression of N-cadherin genes
3) an elevation in the expression of N-cadherin genes
d) 1 and 3
71) Which tissues below are typically derived from the cells on the dorsal surface of a mammalian embryo after gastrulation that express N-cadherins and stop expressing E-cadherins?
a) skin
b) only brain
c) only spinal cord
d) only neural tube
e) brain, spinal cord and neural tube
e) brain, spinal cord and neural tube
72) Which tissues below are not typically derived from the cells on the dorsal surface of a mammalian embryo after gastrulation that express N-cadherins and stop expressing E-cadherins?
a) skin
73) Cadherin clusters of adherens junctions _____________.
1) connect the external environment to the actin cytoskeleton
2) do not require calcium ions to perform their function
3) provide a pathway for signals to be transmitted from the cell exterior to the cytoplasm
4) connect the external environment to the vimentin cytoskeleton
e) 1 and 3
74) Desmosomes are particularly numerous in tissues _____________.
a) that are subjected to mechanical stress
b) like cardiac muscle
c) like the epithelial layers of the skin
d) like the epithelial layers of the uterine cervix
e) All of these are correct.
e
75) The cadherins of the desmosomes ____________.
1) have a different domain structure from classical cadherins
2) are referred to as desmogleins
3) are called desmocollins
d) 1, 2 and 3
76) Pemphigus vulgaris __________.
a) is characterized by a loss of epidermal cell-cell adhesion
b) is an autoimmune disease
c) is characterized by severe blistering of the skin
d) is caused by the production of antibodies against one of the desmoglzins
e. all are correct
e
77) Attachment of an integrin to its ligand can induce which of the following responses within a cell?
a) changes in cytoplasmic pH
b) changes in cytoplasmic C2+ ion concentration
c) protein phosphorylation
d) gene expression
e) All of these are correct.
e
78) Mammary gland epithelial cells are removed from a mammary gland and grown on a bare culture dish. What happens to them?
1) Nothing happens.
2) They lose their ability to synthesize milk proteins.
3) They appear as flattened, undifferentiated cells.
4) They become even more differentiated and proliferate at a high rate.
e) 2 and 3
79) When undifferentiated mammary gland epithelium cells that had been grown on a bare culture dish are cultured in the presence of certain extracellular molecules (e.g., laminin), what, if anything happens to them?
1) There is no change in these cells.
2) They regain their differentiated appearance.
3) They differentiate into muscle and bone cells.
4) They become organized into milk-producing, gland-like structures.
e) 2 and 4
80) Laminin is thought to stimulate mammary gland cells to differentiate into milk-producing gland-like structures. How does laminin accomplish this?
1) Laminin stimulates the mammary cells by binding to cell-surface integrins.
2) Laminin stimulates the mammary cells by binding to cell-surface selectins.
3) Laminin binding at the cell surface activates kinases at the inner surface of the membrane.
4) Laminin binding at the cell surface activates kinases on the membrane’s outer surface.
e) 1 and 4
81) What forms the barrier of the tight junctions that seals off the space between adjacent cells?
a) paired rows of aligned integral membrane proteins
82) Which tight junction will form a tighter seal?
a) one with a single strand of aligned integral membrane proteins
b) one with a number of parallel, interconnected strands of aligned integral membrane proteins
c) tight junctions containing a special kind of phospholipid
d) tight junctions containing a special kind of carbohydrate
e) one with a number of parallel, interconnected strands of interdigitated integral membrane
b
83) One small region of a human kidney tubule known as the thick ascending limb (or TAL) has tight junctions that are permeable to magnesium (Mg2+) ions. What is thought to account for the permeability of this tight junction to magnesium ions?
b) Loops of claudin molecules that extend into the extracellular space form pores in the TAL.
84) Animals lacking the claudin-1 gene suffered from ___________.
a) uncontrolled water loss
85) Despite the presence of the blood-brain barrier, what cells, oddly enough, can pass through the blood-brain barrier by sending a signal that opens up the junction?
b) immune system cells
86) The opening in the center of a connexon that allows the passage of solutes between cells is called a(n) ________.
b) annulus
87) Each connexon in a gap junction is constructed of ___ connexin subunits.
c) 6
88) During gap junction formation, connexons in apposing cells become tightly connected through extensive noncovalent interactions of __________.
b) connexin subunit extracellular domains
89) What kind of molecule does not pass through a gap junction?
d) ribosomes
90) A new type of communication system has been discovered that consists of thin, highly elongated tubules capable of conducting cell-surface proteins, cytoplasmic vesicles and calcium signals from one cell to another. This system is referred to as ________.
d) tunneling nanotubes
91) Which animal cell structure do plasmodesmata in plants most closely resemble?
d) gap junctions
92) What explains the fact that plants lack the specialized junctions seen in animal cells?
c) the presence of the cell wall
93) What lines the plasmodesmata?
d) the plasma membrane
94) The dense central structure that is derived from the smooth endoplasmic reticulum and usually seen in the plasmodesmata is called a(n) ________.
b) desmotubule
95) From what cell organelle does the desmotubule appear to be derived?
a) SER of the two cells
96) You are studying a plant and inject fluorescein, a fluorescent dye, into a single cell on the surface of the plant. After a brief period of time, the dye spreads to cells neighboring the injected cell. What do you conclude?
d) The cells are connected by plasmodesmata.
97) Which of the following is not a function of the plant cell wall?
a) It allows plant cells to develop osmotic turgor pressure that pushes against their surrounding walls.
b) It provides mechanical support for individual cells and serves as a type of “skeleton” for the whole plant.
c) It protects cells against damage from mechanical abrasion, osmotic influx of water & pathogens.
d) It prevents cell-cell interactions.
e) It can be a source of signals that alter activities of cells that it contacts.
d
98) The enzyme embedded in the plant cell membrane that catalyzes the growth of a cellulose molecule is called _________.
b) cellulose synthase
99) Which plant cell wall molecule is economically important as a component essential for the production of jams and jellies?
b) pectin
100) What class of plant cell proteins facilitates plant cell growth by causing a localized relaxation of the cell wall, which allows the cell to elongate at that site in response to turgor pressure generated within the cell?
c) expansins
101) What type of protein also seen in animal cells spans the plant plasma membrane and is thought to transmit signals from the cell wall to the cytoplasm?
a) protein kinase
102) Cell walls of young, undifferentiated plant cells must be able to grow along with the cells of which they are a part and thus exhibit extensibility. What are they known as?
a) primary walls
103) The thicker walls seen in mature plants that no longer allow extensive growth of the cell wall are known as _______.
b) secondary walls
104) How is the structure of the mature plant cell wall similar to the structure of the corneal stroma of the chicken embryo?
d) Both contain adjacent layers of fibers that are arranged perpendicular to each other.
1) Who was the first to report that certain rare inherited diseases were caused by the absence of specific enzymes?
b) Archibald Garrod
2) Alcaptonuria is a genetic disease that is characterized by _________.
a) urine turning dark upon exposure to the air
3) An alcaptonuric lacks the enzyme that oxidizes what metabolite?
c) homogentisic acid
4) What did Archibald Garrod call diseases like alcaptonuria?
e) inborn errors of metabolism
5) What did Beadle and Tatum use to generate mutations in their experimental organism?
b) irradiation with ultraviolet light
6) Beadle and Tatum’s research suggested that __________.
c) a gene carries the information for the construction of a particular enzyme
7) What was the new name of Beadle and Tatum’s hypothesis after it was discovered that some enzymes were composed of more than one polypeptide chain?
b) the One Gene – One Polypeptide hypothesis
8) Why has the One Gene – One Polypeptide hypothesis had to be modified?
b) Genes can be spliced differently to generate a variety of related polypeptides.
9) Which scientist is best known for his work on sickle cell anemia and proving the mechanism that causes the disease?
d) Vernon Ingram
10) What difference between sickle cell and normal hemoglobin is apparently responsible for all of the symptoms associated with sickle cell anemia?
a) The difference is a valine substitution in the mutant sickle cell hemoglobin for a glutamic acid in the normal molecule.
11) The enzyme in eukaryotes that is responsible for the synthesis of RNA from a DNA template is called _______.
b) DNA-dependent RNA polymerase
12) The site on DNA to which RNA polymerases bind before initiating transcription is called the ______.
promoter
13) What provides the energy that drives the polymerization of RNA from a DNA template?
c) ribonucleoside triphosphate precursors
14) The reverse reaction of nucleic acid synthesis almost never happens. What prevents it?
d) Nucleic acid synthesis is coupled to the highly exergonic pyrophosphate hydrolysis.
15) While RNA polymerase is a processive enzyme that remains attached to the DNA over long stretches of template, it must be associated _______ enough so that it can move from nucleotide to nucleotide along the template.
b) loosely
16) Once the σ factor leaves the core enzyme, what happens?
b) The core enzyme continues synthesis.
17) The nucleotide at which transcription is initiated is called _____.
b) +1
18) Sequences of DNA that are similar, seemingly conserved and seen in association with genes in roughly the same location from gene to gene in bacteria are called ________. They are generally the most common version of such a conserved DNA sequence, but some variation in the sequence can occur from one gene to another.
c) consensus sequences
