What is a cell membrane Flashcards
Why are membranes important?
- Forms an outer boundary of every cell
- Selectively permeable- controls entry of nutrients and exit of waste
- Maintains an ion concentration gradient between inside and outside of cell
- Participates in joining of cells to form tissues/organs
- Enables cells to respond to changes in environment
- Membrane functions are crucial for cell survival
Two main constituents of a cell wall?
Protein and lipid
What are many functional differences between cell types due to?
Variations in the composition of their plasma membranes
Phospholipid molecule description?
Hydrophillic head
Glycerol backbone
Hydrophobic fatty acid chains (Tails)
How is cell membrane arranged in water?
With the hydrophilic head groups oriented towards the water and the hydrophobic tail groups oriented away from the water
Name for structure of cell membrane?
Phospholipid Bilayer
What gives the cell membrane it’s Fluidity?
Phospholipids rotate, move laterally, flex, twirl, vibrate in their own half of the membrane millions of times per second. (They however do not flip)
What stiffens the cell membrane?
Cholesterol molecules
Phospholipid bilayer membranes are impermeable to@
Charged ions (Almost any water soluble substance)
What molecules can cross lipid bilayer?
Water, oxygen, CO2, NH3, (Small uncharged polar molecules)
Why can water get through the membrane?
Can fit through the gaps made by phospholipid molecules when they move
3 basic functions of lipid bilayer?
Forms Basic structure of membrane
Hydrophobic barrier interior serves as a barrier
Responsible for membrane fluidity- change cell shape
2 types of membrane proteins?
Peripheral or Integral (Or docking- marker acceptors)
Peripherally associated membrane proteins?
Not embedded within the membrane
Adhere tightly to the cytoplasmic/ extracellular surfaces of the Plasma membrane
Integral Membrane Proteins?
Associated with lipid bilayer in 3 ways
1) Proteins that span the lipid bilayer once or several times (Transmembrane Proteins)
2) Proteins that are embedded but do not cross the bilayer
3) Proteins that are linked to a lipid component of the membrane of a fatty acid derivative that intercalates into the membrane
What are peripheral proteins bonded to?
Non-covalently bonded with integral proteins
5 main functions of integral proteins?
1) Ligand Binding Receptors
2) Adhesion molecules
3) Can carry out trans-membrane movement of water molecules
4) Can be enzymes
5) Can participate in intracellular signalling
Docking- marker acceptor proteins?
Located on inner membrane surface
Interact with secretory vesicles leading to exocytosis of vesicle contents.
Glycocalyx formed by?
Glycoproteins and glycolipids
What serves as self-identity markers on cells?
Short carbohydrate chains on the outer membrane surface
These enable cells to interact with and identify one another
Carbohydrates Role?
Self-identity Markers- enable cells to interact with and identify each other
Role in tissue growth- cells don’t overgrow territory
3 types of specialized cell junction?
Tight Junctions
Desmosomes
Gap junctions
Tight Junctions
Join the lateral edges of epithelial cells near their lumenal (apical) membranes (can be tight or leaky junctions)
Desmosomes
Adhering junctions that anchor cells together, especially in tissues subject to stretching eg skin, heart, uterus
Gap junctions
‘Communicating junctions that allow the movement of charge carrying ions and small molecules between two adjacent cells.
Basolateral membrane faces the?
Blood
Example of muscles that Gap junctions help?
Heart muscles to contract and relax in coordination-
Allows rapid spread of electric activity
