Biol 1610 - Class 21 and 22 Post-class

The beaker in the illustration contains two solutions of salt with different concentrations (measured by molarity, M). The two solutions are separated by a membrane that is permeable to water but not to salt.

diffusion of water from A to B but no diffusion of salt

The random movement of molecules within a solution is referred to as:

diffusion.

Secondary active transport uses a pre-established ion gradient to move a second compound across the plasma membrane. The pre-established ion gradient arises from:

hydrolysis of ATP

The interior region of a phospholipid bilayer is characterized as:

hydrophobic.

Lipid bilayers spontaneously form to orient the _____ tails _____ to minimize their contact with water.

hydrophobic; inside

Where must the SRP receptor be located in a cell?

in the membrane of the rough endoplasmic reticulum

The class of organic molecules defined by a physical property rather than a structure are the:

lipids

The beaker in the illustration contains two solutions of salt with different concentrations (measured by molarity, M). The two solutions are separated by a membrane that is permeable to both salt and water. What will occur in this container?

net diffusion of water from A to B and of salt from B to A

A protein that is found in the Golgi apparatus was synthesized:

on ribosomes located on the rough ER.

A beaker of water is separated by a selectively permeable membrane that allows the passage of water but not ions. A solution of 4% sodium chloride (NaCl) is placed on one side of the membrane and pure water is placed on the other side of the membrane. The solutions are allowed to equilibrate. At this point, which process is going on?

osmosis

Which substance could most easily cross a synthetic membrane composed of phospholipids but not proteins?

oxygen (O2)

The lipid components of cellular membranes often include:

phospholipids and cholesterol.

Which choice is considered an integral membrane protein?

a protein with its amino-terminus in the cytoplasm and its carboxy-terminus in the extracellular space

What factors are required for net movement of a substance to occur by facilitated diffusion?

All of these choices are correct. *a plasma membrane *a concentration gradient *a transport protein

Phospholipids spontaneously form a variety of structures in aqueous solution. Which choice best describes this property?

All of these choices are correct. *the ability of vesicles to fuse with the plasma membrane (exocytosis) *the ability of vesicles to bud off from the plasma membrane (endocytosis) *the first cells *formation of lipid bilayers

Why does active transport of molecules across a membrane require ATP?

An input of energy is needed to allow the movement of molecules from an area of low concentration to one of higher concentration.

Consider the events that describe the progress of a protein that will be secreted from the cell. Which of the following sequences of events correctly? 1. SRP binds to the growing polypeptide chain and to the ribosome. 2. Translation resumes. 3. SRP binds to its receptor. 4. The signal sequence is cleaved. 5. Protein synthesis begins in the cytosol. 6. Translation pauses.

5 → 1 → 6 → 3 → 2 → 4

Suppose you are studying the transport of a certain polar molecule across the plasma membrane of cells in culture. Over a period of time, you measure the concentration of a polar molecule inside and outside of the cells. You find that the concentration of the molecule is higher in the cell and is gradually increasing. You also measure the ATP concentration inside the cell and find that it is decreasing. Which of the following is probably responsible for the transport of this polar substance into the cell? (Select all that apply.)

- active transport - facilitated diffusion

Read the following scenarios and indicate which of the following processes they describe. 1. Sodium ions (Na+) move through sodium channels in a synthetic membrane 2. Sodium molecules move randomly around a solution of sodium chloride in water, frequently colliding with other sodium ions and chloride ions 3. Water molecules move into the cytosol of a cell placed in a hypotonic solution 4. Water molecules move into the cytosol of a cell placed in pure water 5. The action of sodium-potassium pumps moves sodium ions (Na+) out of a cell and potassium ions (K+) into a cell.The action of sodium-potassium pumps moves sodium ions (Na+) out of a cell and potassium ions (K+) into a cell.The action of sodium-potassium pumps moves sodium ions (Na+) out of a cell and potassium ions (K+) into a cell 6. Glucose molecules move into cells lining the intestine against their concentration gradient driven by the movement of sodium ions (Na+) into the cells down their concentration gradient.

1. (d) facilitated diffusion 2. (c) diffusion 3. (e) osmosis 4. (e) osmosis 5. (a) primary active transport 6. (b) secondary active transport

If FRAP is performed on two membranes, one at 25ºC and the other at 40ºC, which one of the following results would most likely be observed?

Both membranes would recover fluorescence in the bleached area, but the membrane at the warmer temperature would recover more rapidly.

Which molecule would most likely require a transport protein to cross the plasma membrane of a red blood cell?

C6H12O6 (glucose)

Secondary active transport in yeast and plant cells uses the _______ concentration gradient, whereas animal cells use the ______________ gradient.

H+ .... Na+/K+

Although the phospholipid molecules can be in constant lateral movement, they very rarely flip from one side of the bilayer to the other. Which of the answer choices could explain this?

The head groups are repelled by the hydrophobic membrane interior.

Predict how phospholipids would arrange if they were placed in a nonpolar solution rather than a polar solution like water.

The phospholipid tails would orient toward the solution, and the heads would cluster away from the solution.

A beaker contains two solutions of salt dissolved in water. The two solutions have different concentrations of salt (measured by molarity, M) and are separated by a membrane that is permeable to both salt and water. The salt and water will move through the membrane by diffusion.

There will be a net movement of salt from side B to side A and net movement of water from side A to side B.

The plasma membranes of some plant cells use transport proteins to move protons out of the cell against their concentration gradient. This is an example of:

active transport.

The sodium-potassium pump is an example of:

an antiporter.

Why do some plasma-membrane transporters use the energy of ATP move to ions against their concentration gradient?

because the concentration gradient allows some transporters to move other molecules against their concentration gradients.

A phospholipid molecule in a membrane can:

both spin (rotate around its vertical axis) and move side-to-side (lateral movement).

Suppose you are studying the transport of a certain polar molecule across the plasma membrane of cells in culture. Over a period of time, you measure the concentration of a polar molecule inside and outside of the cells. You find that the concentration of the molecule is lower in the cell but is gradually increasing. You also measure the ATP concentration inside the cell and find that it is not changing. Which of the following is probably responsible for the transport of this polar substance into the cell?

facilitated diffusion

Which component of a phospholipid is found in the interior of a lipid bilayer?

fatty acids

What is responsible, in part, for keeping the cytoplasm of red blood cells isotonic with the blood plasma and thereby preventing either lysis or shrinking of the cells?

the sodium-potassium pump

Amino acids with hydrophobic side chains are often found in the region of an integral membrane protein that spans the membrane.

true