Beckers World of the Cell: chapter 7a

15) Where would you expect to find an organism possessing a cell membrane with the following composition: large proportions of cholesterol and a predominance of unsaturated fatty acids?
A) frozen wastelands
B) temperate regions
C) tropical regions
D) equa

a
(unsaturated fatty acids have a low transition temperatures, this keeps the membrane fluid even at lower temperatures)
(cholesterol is then needed to stabilize the membrane, because of kinks caused by double bonds)
(kolesterol �r en stel lipid, som med sin bulkiga struktur blockerar �mnen, som vill ta sig genom membranet)

16) A prokaryotic organism is isolated from a hydrothermal vent, where it has been observed to be thriving. Based on your knowledge of the plasma membrane, you would expect to find a predominance of
A) largely saturated fatty acids.
B) equal amounts of sa

a
(hydrothermal means hot water)
(largely saturated fatty acids: long-chain fatty acids and saturated "no double bonds" fatty acids have higher transition temperatures)
(you want that the transition temperatur is high in order to that the membrane does not melt)

17) Inactivation of a fluorescent dye in a very concentrated spot on a cell so that the fluidity of membranes is visualized is called
A) liposome formation.
B) SDS-PAGE.
C) photobleaching.
D) the freeze fracture technique.
E) ferritin conjugated lectins.

c

18) You are experimenting with a variety of lipids to determine their efficacy for use as drug delivery system liposomes. What is one feature of the individual lipid that would best ensure the use of a lipid for this purpose?
A) It must have a structure s

d

19) Hopanoids
A) are found in eukaryotes only.
B) are related to cholesterol.
C) are a type of glycolipid.
D) are a type of phospholipid.
E) all of the above

b
(hopanoids are sterol-like, choleterol-like)
(they appear to substitute for sterols in membrane structure in som prokaryotes)

20) The most common number of carbons in fatty acid hydrocarbon chains of membrane phospholipids is
A) 7.
B) 10.
C) 16.
D) 19.
E) 24.

c
("most fatty acids im membranes are between 12 and 10 carbons atom in lenght, with 16- and 18-carbon fatty acids especially in common" p.167)

21) Which of the following is a sterol-like lipid associated with the cell membrane of prokaryotes?
A) stearate
B) phytosterol
C) linoleate
D) palmitate
E) hopanoids

e
(still hopanoids ;-)
(a: stearate= saturated 18-carbon fatty acid = stearinsyra)
(b: phytosterol= sterol in plants)
(c: linolate = 2 double bonds, 18-carbon = linolsyra)
(d: palmitate = saturated 16-carbon = palmitinsyra)

22) To facilitate the regulation of membrane fluidity, E.coli has the enzyme
A) bacteriorhodopsin.
B) desaturase.
C) fatty acid convertase.
D) gangliosidase.
E) unsaturase.

b
(desaturase: = an enzyme that introduces double bonds into fatty acids)
(if it is getting colder the bacteria wants to maintain a fluid membrane, therefore the transition temperatur has to lower with help of this introduced double bonds, p. 172)

23) Which of the following disorders is the result of impaired glycosphingolipid metabolism?
A) leprosy
B) glycosphingolipid anemia
C) polydactyly
D) tuberculosis
E) Tay-Sachs disease

e
(gangliosides = glycosphingolipid)
(an enzyme for ganglioside degradation is lacking)
(therefore gangliosides accumulate in the brain, which is not god ;-)

24) The technique that allows various proteins to be differentiated based on size, once the proteins have been denatured, is
A) SDS-PAGE.
B) photobleaching.
C) liposome formation.
D) ferritin conjugated lectins.
E) the freeze fracture technique.

a
(SDS-PAGE = SDS-Polyacrylamide Gel Electrophoresis)
(electrophoresis = one of the most common approaches for separating molecules from each other)
(proteiner �r l�sta i SDS!)

25) Starting with shredded spinach leaves, you follow a procedure that allows for separation of cellular organelles. You are specifically looking for the fraction that contains the mitochondria. To identify this fraction you should test for the
A) phospho

e
(mitochondrion is the site of aerobic respiration)
(c: mitochondrion contains phospholipids but also cardiolipis in the inner membrane, because it was once a bacteria, according to wiki ;-)

26) With respect to the outer and inner faces of the lipid bilayer of the cell membrane, the composition of proteins is
A) asymmetrical.
B) identical.
C) not identical, but symmetrical.
D) highly random and varies throughout the cell.
E) a mirror image.

a

27) A means of detecting the presence of specific carbohydrate moieties on glycoproteins is
A) SDS-PAGE.
B) the freeze fracture technique.
C) photobleaching.
D) ferritin conjugated lectins.
E) liposome formation.

d
(lectin = plant proteins that bind specific sugar groups very tightly)
(p. 186: "Investigators visualize these lectins by linking them to ferritin, an iron-containing protein that shows up as an electron-dense spot when viewed with an electron microscope")

28) Localized regions of membrane lipids that contain proteins involved in cell signaling are known as
A) hopanoids.
B) membrane leaflets.
C) homeoviscous adaptation.
D) lipid rafts.
E) islands of hydropathy.

d
(lipid rafts = contains more highly saturated phospholipids and tight packed choleterol, as a result the rafts are thicker and less fluid then the rest of the mambrane)

29) Many integral membrane proteins have not been analyzed by X-ray crystallography. However,
transmembrane segments can be inferred using computer analysis of the amino acid sequence of the protein. This technique is known as
A) homeoviscous adaptation.

d
(wiki: A hydrophilicity plot is a quantitative analysis of the degree of hydrophobicity "group A" or hydrophilicity "group B and C" of amino acids of a protein. It is used to characterize or identify possible structure or domains of a protein.)
(p. 180)

30) Cell-cell communication in plants takes place via specialized structures called
A) plasmodesmata.
B) desmids.
C) gap junctions.
D) cell wall pores.
E) connexons.

a

31) The likely number of and locations of transmembrane segments of integral membrane proteins is inferred by
A) X-ray crystallography.
B) SDS-PAGE.
C) western blot.
D) hydropathic analysis.
E) affinity labeling.

d
("once the amino acid sequence of a membrane protein is known the number and positons of transmembrande segments can be inferre from hydropathy plot" p. 180)
(a computer program identify clusters of hydrophobic amino acids)
(c: western blotting = used in electrophoresis to detected polypeptides)

1) Which of the following is NOT a function of membranes?
A) define cell boundaries
B) compartmentalization
C) information storage
D) regulation of transport
E) cell-cell communication

c
(information storage is a function of nucleus)

2) Which is NOT a model for membrane structure?
A) Overton lipid coat
B) Langmuir monolayer
C) Gorter and Grendel bilayer
D) Singer and Nicholson fluid mosaic
E) Watson and Crick double helix

e
(Watson and Crick discovered the DNA double helix structure)

3) Temperature has a dramatic effect upon cell membranes. This influence can readily make a cell membrane more solid or more fluid in response to the temperature. This is an example of
A) liquidation.
B) membrane flexibility.
C) phase transition.
D) membr

c
(phase transition = change in the state of a membrande between a fluid state and a gel state)

4) Two cells with different cell-surface markers are fused in the presence of polyethylene glycol (PEG). The cells are then placed at 0�C. What do you expect to observe about the individual cell markers?
A) The markers will evenly disperse throughout both

d
(because ist is to cold)

5) Which of the following molecules would NOT readily cross an intact cell membrane by simple diffusion?
A) water
B) glucose
C) oxygen
D) fatty acids
E) ethanol

b

6) With regard to the semipermeable nature of the plasma membrane, which of the following would readily cross without the aid of a transport protein?
A) calcium ions
B) glucose
C) water
D) amino acids
E) DNA

c

7) You are examining an electron micrograph of cells obtained from a new deep-sea life form. Upon closer examination, you notice that there are two dark lines separated by a lightly stained region. These results are similar to the observation of which per

a
(Robertson described the "unit membrane", each membrane appears as two dark lines separated by a highly stained central zone ... that gives the appearance of "railroad track" in the TEM)
(b: Gorter and Grendel = lipid bilayer 1925)
(c: Unwin and Henderson = transmembran segments)
(d: Overton = lipid nature of membrane 1890s)
(e: Singer and Nicolson = fluid mosaic model 1972)

8) The scientist(s) who developed the "sandwich" model of the cell membrane is (are)
A) Overton.
B) Langmuir.
C) Gorter and Grendel.
D) Davson and Danielli.
E) Robertson.

d
(Davson and Daniellie described 1935 the membrane as lipid bilayers that are coated on both sides with thin sheets of protein)
(protein-lipid-protein = sandwich)
(a: Overton = lipid nature of membrane1890s)
(b: Langmuir = lipid monolayer 1900s)
(c: Gorter and Grendel = lipid bilayer 1925)
(e: Robertson = unit membran "railroad" 1960)

9) With respect to the outer and inner faces of the lipid bilayer of the cell membrane, the composition of lipids is
A) asymmetrical.
B) identical.
C) not identical, but symmetrical.
D) highly random and varies throughout the cell.
E) a mirror image.

a
(proteiner och lipider har en asymmetrisk f�rdelning i cellmembranet, undantag f�r kolesterol!)

10) Based on the composition of cell membranes, the most prominent lipids are
A) phospholipids.
B) glycolipids.
C) cholesterol.
D) phytosterol.
E) cerebrosides.

a
(phospholipids = phosphoglycerides and sphingolipids)
(b: glycolipids= adding a carbohydrat groups to lipids, involved in signaling)
(c and d: steroles in animal / plant cells)
(d: cerebrosides= kind of glycolipids)

11) Of the following lipids, which is found in approximately equal amounts in both the outer and inner portions of the lipid bilayer?
A) cholesterol
B) glycolipid
C) phosphatidylserine
D) phophatidylethanolamine
E) phophatidylinositol

a
(cholesterol = necessary for maintaining and stabilizing membranes)
(b: glycolipid = outer membrane)
(c,d,e: are all phospholipids "which are more prominent in the inner membrane, where they are involved in transmitting varous kinds of signals from the plasma membrane to the interior of chells")

12) A prokaryotic organism is isolated from a glacier, where it has been observed to be thriving. Based on your knowledge of the plasma mem- brane, you would expect to find a predominance of
A) largely saturated fatty acids.
B) equal amounts of saturated

d
(largely unsaturated fatty acids: "tend to have lover transition temperatures" that is godd because it is cold in a glacier)
("the kinks caused by double bonds in fatty acids prevent the hydrocarbon chains from fitting togehter snugly")
(d.v.s. de stelnar inte till, som m�ttade fettsyror)

13) Based on your knowledge of the chemistry of the cell membrane, which of the following compounds would you couple with a new drug in order to achieve better uptake by cells?
A) carbohydrates
B) polar amino acids
C) lipids
D) several mannose-6-phosphate

c

14) Cholesterol
A) is found in abundance in prokaryotic cell membranes.
B) intercalates between the fatty acid chain within the bilayer.
C) increases permeability for small cations.
D) destabilizes the cell membrane.
E) is found only in plants.

b
(to intercalate = infoga)
(cholesterol stabilizes the membrane)
(a: procaryotic cells = bacteria, they have hopanoids which are sterol-like molecules)
(e: in plants mostly phytosterols)