Exam 6: Lipids, Membranes, and the First Cells

What region of a steroid is hydrophilic?

Glucose diffuses slowly through artificial phospholipid bilayers. The cells lining the small intestine, however, rapidly move large quantities of glucose from the glucose- rich food into their glucose- poor cytoplasm. Using this information, which transport mechanism is most probably functioning in the intestinal cells?

What do phospholipids and triglycerides have in common?

Use the following information when answering the corresponding questions). Rhodopsins are light- sensitive molecules composed of a protein opsin) and retinal derivative of vitamin A). Opsin is a membrane protein with several a- helical segments that loop back and forth through the plasma membrane. There are two classes of rhodopsins. According to Oded Beje, one class has relatively slow dynamics a photocycle of approximately 0.5 second) and is well suited for light detection. The second class has faster dynamics a photocycle of approximately 0.02 seconds) and is well suited for chemiosmosis-pumping of protons or chloride ions across cell membranes. Oded Beje was the first, in September 2000, to report on a rhodopsin proteorhodopsin) found in the domain Bacteria. [ -Which of the following best describes this particular protein?

Which of the following best describes how CFTR functions?

The text states that ribonucleotides can diffuse through some types of liposomes. It's likely that the lipids present early in chemical evolution had short chains. Would liposomes formed from these types of lipids be more or less permeable to ribonucleotides than if early cells formed from long- chained lipids?

Suppose some blood cells were in an isotonic solution. What would happen to them?

Which of the following increases the strength of the hydrophobic interactions in lipid bilayers and thus makes them less permeable to polar molecules?

Which of the following substances would most likely require a protein to facilitate its diffusion across a cell membrane?

Valine, a nonpolar amino acid, shows up in the wrong place in the hemoglobin of sickle- cell anemia, causing the disease. This is due to a genetic mutation. The result of this mutation is that hemoglobin molecules-which transport oxygen in red blood cells-stick together, causing the red blood cells to become distorted, but without having any significant effect on oxygen binding. Based on what you know about protein structure and the polarity of amino acids, predict where the mutated valine would most likely be found.

You have just discovered an organism that lives in extremely cold environments. Which of the following would you predict to be true about the phospholipids in its membranes, compared to phospholipids in the membranes of organisms that live in warmer environments?

Why does cholesterol lower membrane permeability?

Use the following information when answering the corresponding questions). Rhodopsins are light- sensitive molecules composed of a protein opsin) and retinal derivative of vitamin A). Opsin is a membrane protein with several a- helical segments that loop back and forth through the plasma membrane. There are two classes of rhodopsins. According to Oded Beje, one class has relatively slow dynamics a photocycle of approximately 0.5 second) and is well suited for light detection. The second class has faster dynamics a photocycle of approximately 0.02 seconds) and is well suited for chemiosmosis-pumping of protons or chloride ions across cell membranes. Oded Beje was the first, in September 2000, to report on a rhodopsin proteorhodopsin) found in the domain Bacteria. [ -Proteorhodopsin consists of a single polypeptide chain. What is the highest level of structure found in this protein?

You have a planar bilayer with equal amounts of saturated and unsaturated phospholipids. After testing the permeability of this membrane to glucose, you increase the proportion of unsaturated phospholipids in the bilayer. What will happen to the membrane's permeability to glucose?

The term phospholipid can best be described by which of the following?

Which of the following is the best explanation for why cholesterol decreases the permeability of biological membranes?

In secondary active transport

In an experiment involving planar bilayers, a solution of table salt sodium and chloride ions in water) is added on the left side of the membrane, while pure water is added on the right side. After 30 minutes, the researchers test for the presence of ions on each side of the membrane. The right side tests negative for ions. What can you conclude?

GLUT- 1 is an example of what?

Steroids are