Giardia intestinalis can cause disease in several different mammalian species, including humans. Giardia organisms (G. intestinalis) that infect humans are similar morphologically to those that infect other mammals, thus they have been considered a single species. However, G. intestinalis has been divided into different subgroups based on their host and a few other characteristics. In 1999, a DNA sequence comparison study tested the hypothesis that these subgroups actually constitute different species. The following phylogenetic tree was constructed from the sequence comparison of rRNA from several subgroups of G. intestinalis and a few other morphologically distinct species of Giardia. The researchers concluded that the subgroups of Giardia are sufficiently different from one another genetically that they could be considered different species

Which of the following changes would a modern systematist be most likely to make after learning of the results of the rRNA analyses?

#Question id: 2233

#Unit 2. Cellular Organization

Membrane proteins may interact with biomembranes through

a. covalently attached fatty acid molecules.

b. covalently attached lipid molecules.

c. noncovalent protein-protein interactions.

d. hydrophobic α-helical domains.

e. noncovalent protein-lipid interactions.

#Question id: 2234

#Unit 2. Cellular Organization

Which of the following statement(s) is (are) true of transmembrane proteins?

a. All contains a hydrophobic α helix.

b. Some serve as membrane attachment sites for peripheral membrane proteins.

c. Some contain more than one membrane-spanning domain.

d. All are asymmetrically oriented in the lipid bilayer.

#Question id: 2235

#Unit 2. Cellular Organization

The generation and maintenance of a membrane electric potential requires which of the following:

a. active pumping of ions       

b. ion-specific membrane channel proteins

c. ATP                                    

d. a generally permeable membrane

#Question id: 2236

#Unit 2. Cellular Organization

The partition coefficient K, the equilibrium constant for partitioning between oil and water, for butyric acid is about 10^–2, and for 1,4-butanediol it is about 10^–4.  You add liposomes containing only water to a solution with an initial concentration of 1 mM butyric acid and 100 mM 1,4-butanediol outside the liposomes.  What is the relative rate of diffusion of the two substances into the liposome interior?

#Question id: 2237

#Unit 2. Cellular Organization

Glucose enters erythrocytes via a GLUT-1 uniporter. As the levels of glucose in the bloodstream decrease between meals, what happens to the glucose in the cells?

#Question id: 2238

#Unit 2. Cellular Organization

Consider the transport of glucose into an erythrocyte by facilitated diffusion.  When the glucose concentrations are 5 mM on the outside and 0.1 mM on the inside, the free-energy change for glucose uptake into the cell is:  (These values may be of use to you:  R = 8.315 J/mol·K; T = 298 K; 9 (Faraday constant) = 96,480 J/V; N = 6.022×10²³ /mol.)