Hello, I need help with these six questions:
1) Which of the following molecules is the most likely to cross the membrane by simple diffusion?
c) A steroid.
d) An amino acid.
e) A peripheral protein.
2) Cellular membranes are fluid because:
a) small amounts of water passing through the membranes can make them fluid.
b) the phospholipids that make up the membranes are not covalently linked to each other.
c) membrane proteins of various sizes and density disrupt the integrity of the lipid bilayer.
d) old phospholipids are constantly being removed and new phospholipids are constantly being added to membranes.
e) each half of the bilayer literally “floats” on the other half.
3) Most cells in metazoans employ the Na+-K+ pump to keep intracellular Na+ concentration low and K+ concentration high. A disproportionally large amount of energy is consumed in this cellular process versus others. What is the purpose of keeping intracellular Na+ concentration low?
a) the energy stored in the Na+ gradient across the cell membrane can be harvested to perform other tasks.
b) a high concentration of Na+inside the cell will upset the intracellular charge balance of molecules.
c) removing Na+ from the cytoplasm keeps the cell isotonic with the extracellular environment.
d) Na+ tends to disrupt and weaken hydrogen bonds, thereby affecting protein functions.
e) the precise function of the Na+-K+pump is still controversial.
4) Across the plasma membrane of the cell, Na+concentration is high on the outside and low in the inside, and the K+concentration is the reverse. Which of the following statement regarding transport of these two ions is most likely to be correct?
a) the concentration gradients of both ions can be overcome by antiporters.
b) it is easier to export Na+then to import K+.
c) there is a tendency for Na+to diffuse out of the cell.
d) import of Na+requires input of energy.
e) the concentration gradients of the two ions cancel each other such that there is no net gradient.
1) The lipid bilayers that constitute the plasma membrane and the endomembrane system of a eukaryotic cell:
a) have about the same total surface area.
b) house about the same integral membrane proteins.
c) serve about the same function.
d) have about the same composition.
e) store about the same content.
5) When acids are added, a buffer helps prevent a drop in pH by:
a) becoming a weak acid.
b) becoming more soluble in water.
c) removing protons from solution.
d) preventing water from ionizing.
e) all of the above.
6) a-helices and b-pleated sheets are common folding patterns among most polypeptides. This is because:
a) formation of a-helices and b-pleated sheets is independent of the primary structure of polypeptides.
b) a-helices and b-pleated sheets are the result of the most common amino acid sequences found in polypeptides.
c) a-helices and b-pleated sheets form wherever there are hydrophobic regions within the polypeptide.
d) helical and pleated structures are natural configurations of any long, linear macromolecules.
d) all of the above.