Many of the carriers of Sucrose–H+ symporters in the phloem play various role in transport, most of the transporters are found in source, path, and sink tissues. Some carriers are characterized such as;

a) SUT1, has high-affinity / low-capacity transporter found in the minor veins of source tissues, appears to be important in phloem loading.

b) Important role of SUT1 in phloem loading appears to be complemented by SUT4, which is low-affinity/high-capacity carrier

c) SUT2, appears to function as a sucrose sensor. This is indicated by findings showing that SUT2 is more highly expressed in sink and path tissues than in source leaves.

d) The major sucrose transporters in phloem loading into the companion cells and final uptake into companion cells appears to be the function of SUT4

Which of the following combination is correct?

#Question id: 2229

#Unit 2. Cellular Organization

The difference between pinocytosis and receptor-mediated endocytosis is that:

#Question id: 2230

#Unit 2. Cellular Organization

Which of these statements about the composition of biological membranes is false?

#Question id: 2231

#Unit 2. Cellular Organization

Membrane proteins:

I) are sometimes covalently attached to lipid moieties.

II) are sometimes covalently attached to carbohydrate moieties.

III) are composed of the same 20 amino acids found in soluble proteins.

IV) move across the membrane unless they are anchored

Which of the following combination is correct?

#Question id: 2232

#Unit 2. Cellular Organization

A GPI anchor

a. serves to attach some proteins to the cytosolic face of the plasma membrane.

b. contains phosphotidylserine.                      

c. may be cleaved to release the protein from the membrane.

d. contains sugar residues in addition to lipid components.

e. contains phosphoethanolamine.

#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.