Flashcards in 3 Physiology: Cell Membrane Deck (68)
The cell membrane is the boundary between?
an ordered intracellular environment (the intracellular fluid; ICF) and a less-ordered extracellular fluid (ECF) or disordered external environment
If the membrane was a simple static structure that merely prevented the admixture of these two environments, most cells would?
Death of the cell may be delayed if energy-rich molecules are stored within the cell, and in extraordinary cases, cell death may be delayed almost indefinitely if the cell drastically curtails its energy requirements, i.e., if it lowers its metabolic rate, as is seen in spore- forming bacteria
HOWEVER CELL MEMBRANE IS NOT A STATIC STRUCTURE
The energy required for maintenance of internal order is derived from?
energy-rich molecules obtained from the ECF
The stored energy-rich molecules are derived from?
molecules obtained from the environment, and the bacterium must respond to information from the environment in order to initiate sporulation (and later, to reverse it).
In many cases, it is the membrane which receives this information.
What is The Cell Membrane?
is a Dynamic, Heterogeneous, Fluid Structure
Describe a dynamic structure
unlike a static one, undergoes change.
Over the course of a cell’s lifespan, its membrane continuously exhibits changes in structure which reflect changing emphasis of function
An example of change in a dynamic cell membrane
the membranes of numerous cell types exhibit an increase in the number of glycoprotein molecules which allow for the passage of glucose through the membrane subsequent to a meal
What are two functions of the cell membrane?
allow passage of (some) molecules
they change shape
An example of change in a dynamic cell membrane
phagocytosis, wherein a cell membrane undergoes considerable changes in shape as it surrounds and engulfs a molecule or cell which has made contact with the membrane
The functions of the cell membrane are made possible by the actions of what?
of distinctly different molecules in and associated with the membrane, i.e., the cell membrane is a heterogeneous structure.
Common component molecules of cell membranes include?
proteins and glycoproteins
Describe how the cell membrane is a fluid structure?
Molecules (especially proteins and glycoproteins) can be experimentally labeled with various markers such as fluorescent dyes.
Microscopic examination of cells reveals movement of the dyes, which therefore indicates the movement of the proteins and glycoproteins in the membrane
the most common molecules in the cell membrane are?
What is a “fluid mosaic” (the cell membrane is often referred to as this)?
a structure composed of a large number of different molecules (a mosaic) which move within the membrane (fluid).
How are Phospholipids arranged?
arranged in a bilayer, with polar (hydrophilic) components in contact with extracellular and intracellular fluid, and nonpolar (hydrophobic) components making up the bulk of the thickness of the membrane.
What is also found in both monolayers of the membrane?
What are found in the outer monolayer of the membrane?
Some proteins/glycoproteins are embedded where? And these such molecules are called what?
in only one of the two monolayers and therefore are in contact with either the extracellular fluid or the intracellular fluid, while other proteins/glycoproteins span the entire membrane and are in contact with the extracellular and intracellular fluids.
Such molecules are termed TRANSMEMBRANE PROTEINS.
List the functions of the cell membrane
a) It regulates the passage of substances into and out of the cell by the processes of diffusion, facilitated diffusion and active transport (and by other processes such as exocytosis, endocytosis and phagocytosis).
b) It receives information in physical and/or chemical form from the ECF/extracellular environment
c) It catalyzes chemical reactions, i.e., it possesses enzymes
d) It serves structural functions, such as attachment and movement
e) Organelles are subcellular membrane-bound compartments. Organelle
membranes also regulate passage, receive information, catalyze reactions and serve structural function.
Diffusion results from what?
from a greater frequency of collisions between molecules where they exist at a higher concentration than where they exist at a lower one.
diffusion is a manifestation of the laws of?
thermodynamics in that a high concentration of molecules in one place and a low concentration in another is an example of order, while an equal concentration of molecules in two places is an example of disorder.
A number of small, nonpolar molecules are able to easily what?
diffuse through the phospholipid bilayer of the cell membranes.
Paramount amongst these are the gases O2 and CO2.
Other molecules which share the combined hydrophilic/hydrophobic character of phospholipids and cholesterol can do what?
also pass through the membrane with relative ease.
Such molecules include fatty acids and steroid hormones (which are derivatives of cholesterol).
Larger polar/hydrophilic molecules, on the other hand, CAN or CANNOT diffuse through the phospholipid bilayer?
Numerous polar molecules do, however, diffuse through cell membranes by way of?
What allows for the passage of an ion such as Na+ or K+?
these proteins form a water-containing pore or channel
Ion channels are characterized as?
specific (i.e., they usually allow only one or two ions to diffuse “down” its/their concentration gradient/s.)
What may influence the rate at which ions move through protein channels?
electrical forces as well as diffusion because ions are charged
What are Leak Channels?
channels that are always open