Chapter 8: Cell Membranes Flashcards
The plasma membrane is referred to as a “fluid mosaic” structure. What does the term refer to?
The fluid aspect of the membrane is due to the lateral and rotational movement of phospholipids, and embedded proteins account for the mosaic aspect.
Consider the currently accepted fluid mosaic model of the plasma membrane. Where in the plasma membrane would cholesterol most likely be found?
in the interior of the membrane
The steroid cholesterol, wedged between phospholipid molecules in the plasma membranes of animals, helps stabilize the membrane.
Functions of membrane protein
Intercellular joining, transport, cell-cell recognition, enzymatic activity, signal transduction, attachment to the cytoskeleton and extracellular matrix
Which of the following functions of membrane proteins is important in tissue formation during embryonic development in animals?
Cell-cell recognition is an important function of membrane proteins, and this cell-cell recognition is important in tissue formation during embryogenesis.
Membrane proteins with short sugar chains form identification tags that are recognized by other cells.
Membrane carbohydrates function primarily in *
.Variations in carbohydrate structure distinguish one species from another, one individual from another, and even one cell type from another.
cell-cell recognition.
Where in the membrane would carbohydrates most likely be found?
Membrane carbohydrates are covalently bonded to lipids or proteins and extend out from the external side of the plasma membrane as a means of *
on the outside (external) surface of the membrane
cell identification.
The asymmetrical distribution of membrane proteins, lipids, and carbohydrates across the plasma membrane is determined as the membrane is being constructed.
The two lipid layers may differ in specific lipid composition.
Parts of proteins that are exposed on the cytoplasmic side of the endoplasmic reticulum are also exposed on the cytoplasmic side of the plasma membrane.
Every integral membrane protein has a specific orientation in the plasma membrane.
read
When the concentration is the same on both sides of the membrane, passive transport continues, but the rate of transport is the same in both directions.
Passive transport permits the solute to move in either direction, but the net movement of solute molecules occurs down the concentration gradient of the molecule.
read
Cells A and B are the same size, shape, and temperature, but cell A is metabolically less active than cell B. and cell B is actively converting oxygen to water in cellular respiration. Oxygen will diffuse more rapidly into cell __________ because __________.
B … the diffusion gradient in cell B is steeper
diffusion into the cell will continue because the concentration gradient favors movement in that direction.
Facilitated diffusion of solutes may occur through * in the membrane.
channel or transport proteins
The concentration of solutes in a red blood cell is about 2%, but red blood cells contain almost no sucrose or urea. Sucrose cannot pass through the membrane, but water and urea can. Osmosis would cause red blood cells to shrink the most when immersed in which of the following solutions?
No. If the membrane is permeable to urea, then urea will simply diffuse through the membrane until it reaches equilibrium. This will increase the solute concentration inside the cell relative to outside, and water will enter osmotically.
Correct. When a cell is placed in a hypertonic environment, water will leave the cell, causing it to shrink.
Example of active transport:
The sodium-potassium pump hydrolyzes ATP and results in a net positive change outside the cell membrane. This is how the sodium-potassium pump generates voltage across the cell membrane.
To pump glucose up its concentration gradient, sodium moves down its concentration gradient, and the distribution of sodium ions across the membrane forms an electrochemical gradient that drives this mechanism.
The movement of sodium down its gradient drives glucose up its gradient, and because sodium is at different concentrations on either side of the membrane and as sodium has a +1 charge, an electrochemical gradient also exists.
read
Cotransport proteins allow a single ATP-powered pump to drive the active transport of many different solutes. The electrochemical gradient created by a single ATP-dependent pump can drive the transport of many different solutes using cotransport proteins.
read
The movement of protons through the cotransport protein cannot occur unless sucrose moves at the same time. The obligate coupling of proton movement to sucrose movement prevents the energy of the proton gradient from being lost if sucrose is not present.
read
