Membranes and membrane transport Flashcards
What are the properties of the plasma membrane?
1- Forms the outer boundary of the cell 2- It’s selectively permeable 3- Controls the entrance of nutrients and exit of waste products. 4- Mantain the difference in concentration between the inside and the outside of the cell. 5- Particippiate in the joining of cells to form tissues and organs. 6- Allow cells to interact in different ways with the same extracellular fluid.
What are the three main components of the plasma membrane that form the fluid mosaic models?
-Phospholipid bilayer -Proteins -Carbohydrates
Describe phospholipids:
They have a phosphate group that links a substituent group to a glycerlo unit (this form the hydrophilic and polar head) and two fatty acids chains (that form the hydrophobic and nonpolar tails).
What happens to phospholipids in acqueous environment?
They thend to form a lipid bilayer.
What is a lipid bilyaer?
Is a double layer of lipid molecules with an hydrophobic inner core.
Describe the structure of the lipid bilayer
It has a trilaminar structure with the hydrophobic tails buried in teh centre of the bilayer away from water and the hydrophilic heads lined up on both sides in contact with water.
State the properties of the lipid bilayer:
1- Is fluid because phospholipids are not held togeterh by covalent bonds. 2- Cholesterlo contributes to both the fluidity and the stability of the membrane. 3- The phospholipids are constantly moving 4- The phospholipid bilayer is impermeable to charged molecules and water soluble molecules.
State the functions of the lipid bilayer:
1- It forms the basic sctructure of the plasma membrane 2- Its hydrophobic interior serves as a barrier between the inside and the outside of the cell. 3-It’s responsable for the fluidity of the membrane.
What are the two kinds of membrane proteins?
1- Integral membrane proteins 2- Peripheral membrane proteins.
Describe integral membrane proteins:
They are noncovalently embedded in the phospholipid bilayer by their hydrophobic regions.
What are transmembrane proteins?
They are integral proteins that extend through the entire thickness of the lipid bilayer one or several times.
Describe peripheral membrane proteins:
Polar molecules that don’t penetrate the membrane, instead they adhere tightly to the cytoplasmic or extracellular surface.
State the seven functions of membrane proteins:
1) Ligand Binding Receptor 2) Cell Adhesion Molecules (CAM) 3) Channels 4) Carriers and pumps 5) Membrane-bound enzymes 6) They participate to intracellular signaling 7) Docking marker acceptor
Describe Ligand Binding Receptor
Sites that recognize and bind with specific extracellular chemical messengers.
Describe cell adhesion molecules (CAM)
They can either protrude from the outer membrane surface and form hooks and loops or span the plasma membrane where they serve as structural link between the outer membrane surface and its extracellular sorroundings.
Why are CAMs important?
Because they hepl regulating cell shape, growth and differentiation and allow the cell to adapt to its immediate sorroundings.
What are channels?
Water filed pathways that serve as conduits that allow water molecules and ions to flow passively through the lipid bilayer.
What are carriers?
They can either facilitate the trnasport of a specific molecules or couple transport of a molecule with the transport of a solute
What is the function of membrane-bound enzymes?
They control specific chemical reactions.
What are docking marker acceptors?
They are located on the inner membrane surface and allow the docking of vesicles for exocytosis
What are the two different kinds of membrane carbohydrates?
Glycoproteins and glycolipids and they form the glycocalix.
What are the two functions of membrane carbohydrates?
1) They act as self identity markers that enable cells to identify and interact with one another. 2) They have a role in tissue growth and prevent cells to trespass across the boundary of neighbouring tissues.
What are the three different forms of cell adhesion?
-CAMs -Extracellular Matrix -Specialized cell junctions.
What are the three different type of cell junctions?
1) Tight junctions 2) Gap Junctions 3) Desmosomes.
Describe tight junctions:
Adjacent cells bind firmly with one another at points of direct contact to seal of the passageway betweent cells.
Describe desmosomes:
Adhering jucntions that anchor cells together.
What are the two units that constitute a desmosome:
A pair of plaques and a strong filament containing cadherin that extend across the space between the two cells attaching the plaques at both sides.
Describe gap junctions:
Comunicating junctrions that allow the movement of charge molecules between two adjacent cells.