Membrane Transport and Excitable Cells Flashcards
What are integral membrane proteins?
Spans the plasma membrane, functions include channeling or transporting molecules across the membrane.
What are peripheral proteins?
Attached to integral proteins. Can be enzymes, involved in attachment functions and shape changes, or act as receptors if they are on the cell surface
What is the cytoskeleton?
A structure that helps cells maintain their shape and internal organization. Anchors to the plasma membrane
What is the glycocalyx?
Mix of carbohydrates attached to lipids and proteins on outer face. Allows cells to recognize one another
What happens to the glycocalyx when the cell becomes cancerous?
It changes, and can even change repeatedly, making it difficult for the immune system to keep up
What is the function of cholesterol?
Reduces general membrane fluidity and stabilizes its structure.
What does excess cholesterol do?
Causes the membrane to lose flexibility
What are tight junctions?
Fusion of adjacent plasma membranes to prevent passage of molecules in between cells
What are desmosomes?
Anchoring junctions: molecular linking of cells to resist mechanical stress
What are gap junctions?
Molecular channels between cells to allow passage of cytoplasmic molecules
What are connexons?
An assembly of 6 proteins called connexins that form the pore for a gap junction between the cytoplasm of 2 adjacent cells
Connexons are ___ tissues
Electrically excitable
What are some functions of plasma membranes?
Transport, intercellular joining, enzymatic activity, cell-cell recognition, receptors for signal transduction, attachment to extracellular matrix
Plasma membranes provide:
A selectively permeable, hydrophobic barrier between the interstitial fluid and the cytoplasm
What is interstitial fluid?
A filtrate of blood
What does interstitial fluid contain?
Salts, sugars, amino acids, vitamins, hormones, metabolites, O2, CO2 and other gases
How do water soluble molecules get across the plasma membrane?
Facilitated diffusion
What is facilitated diffusion?
The passive movement of molecules across the cell membrane via the aid of a membrane protein. Requires a source of ATP
What are 2 examples of facilitated diffusion?
Carrier proteins and channel proteins
Characteristics of facilitated diffusion for water soluble substances
1) Specific
2) Not ATP requiring
3) Limited by carrier/channel saturation
4) movement DOWN a concentration gradient
What is carrier-mediated facilitated diffusion?
Molecules are “helped” through the membrane by a membrane component
When is carrier-mediated facilitated diffusion used?
With lipid insoluble molecules that are too large to pass through membrane channels/pores
What are leaky channels?
Some ion channels that are always open
Channel mediated facilitated diffusion is ___ due to ___ and ___ of ___ that line the channels
Selective
Pore size
Charges
Amino acids
What are gated channels?
Ion channels that require some signal in order to be activated and opened
What are aquaporins?
Water channels on many cells
What is osmolarity?
Total concentration of solute particles in a solution
What is tonicity?
Ability of a solution to change the shape of a cell by altering its water content
What is an isotonic solution?
Solutions that contain the same concentration of water and solutes as the cell cytoplasm
What is a hypertonic solution?
The solute concentration is higher than that inside the cell, and the solutes cannot cross the membrane
What is a hypotonic solution?
The solute concentration is lower than that inside the cell
Molecules that are ionically bonded have ___ than those that are covalently bonded
Greater osmotic power
How are hypertonic solutions used in patients?
Used carefully and with monitoring for edema; pull water out of swollen cells
How are hypotonic solutions used in patients?
Used carefully and with monitoring to rehydrate severely dehydrated patients
Active transport requires ATP because the substance is:
1) Too large for pores and is lipid insoluble
2) Moving against its concentration gradient
Active transport requires a carrier. What does it do?
Combines specifically and reversibly with a substance to help it across the plasma membrane
Unlike facilitated diffusion, active transport solute pumps move substances:
AGAINST their concentration gradients
What is a symporter?
A membrane protein that facilitates the simultaneous transport of two distinct substances across the cell membrane in the SAME DIRECTION
What is an antiporter?
A membrane protein that transports two molecules across the cell membrane at the same time in the OPPOSITE DIRECTION
Does passive transport require energy?
No
Oxygen and water enter the cell through:
Simple diffusion
How do aquaporins work?
The inside of the channel protein is hydrophilic, drawing water to/through it
