Cell Surface Flashcards
What are the functions of the cell surface membrane
- Barrier between the cell and its environment
- Maintaining different intracellular and extracellular environments
- Site of chemical reaction
- Protect vital components
- Allow cell communication
What are the predominant phospholipids in biological membranes
- phosphatidylcholine
- phosphatidylserine
- phosphatidylethanolamine
- sphingomyelin
What effect does cholesterol have on the fluidity of the membrane and how does it do this
- Makes the membrane less fluid and more rigid.
- Intercalates between the phospholipids, a tighter packed bilayer
What 3 processes does the fluidity of biological membranes allow
- Signalling - lipids and membrane proteins are able to diffuse rapidly to interact.
- Ensure membranes are shared equally between daughter cells
- Allows membranes to fuse together (endo and exocytosis)
What do transmembrane regions of integral proteins contain and what is their significance
- Mainly contain hydrophobic amino acids.
- These amino acids interact with phospholipid tails
What are the 6 functions of membrane proteins
- Transport
- Catalysis (enzymes)
- Signal transduction
- Cell recognition
- Intercellular joining
- Attachment (to cytoskeleton or intracellular matrix)
List the 4 Intracellular signal transduction lipids
- Phosphatidylinositol
- Diacylglycerol
- Ceramide
- Sphingosine-1-phosphate
Where do Intracellular signal transduction lipids come from and what proportion of phospholipids do they make up
- Derived from lipids in the plasma membrane.
- Minor proportion of phospholipid content
Give some features of Intracellular signal transduction lipids due to their specificity
- Rapidly generated and destroyed by enzymes
- Spatially and temporally generated depending on when and where they are needed
- Bind to specific regions
What drives passive transport across biological membranes
- Concentration gradients
What is the difference between facilitated and simple diffusion
- Facilitated involves membrane proteins, simple does not
What 3 factors affect the ability of a solute to cross the membrane in simple diffusion
- Hydrophobicity
- Size - Large uncharged polar molecules cannot pass through whereas smaller ones can
- Charged - Ions are too polar to pass through
What are the 2 classes of proteins involved in facilitated diffusion
- Channel proteins-
- Uniporter carrier proteins
What factors do channel proteins discriminate based on
- Size
- Charge
What are channels (proteins)
- Hydrophilic pores through the membrane
- Non-directional ion channels
- Gated channels (more control than simple pore)
- Fast
What factors do uniporter proteins discriminate based on
- Solute must be complimentary to the binding site. Highly selective
How do uniporter carrier proteins work
-Substrate binds and induces conformational shape change.
- The shape change moves the substrate across membrane and releases into the cell
- Slow
Why do cells maintain electrochemical gradients
- Drive transport across membranes
- Maintains osmotic balance
- Electrical forces inside and outside the cell must be balanced)
Why is ATP required in active transport
- Solutes are moved against their electrochemical gradients, this requires energy
What are the 3 ways that active transport occurs
- ATP- driven pumps - Couples hydrolysis of ATP with the transport of solute
- Coupled transporters - Couples movement of a solute with the concentration with the movement of a solute against it
- Light-driven pumps - Couples transport of solute against gradient with the input of energy from light
What are the 2 types of ATP- driven pumps active transport
- Symport- When both solutes move in the same direction
- Antiport - When the solutes move in opposite directions
Describe the Na+ and K+ example of ATP driven active transport
- 3Na+ moves out of the cell while 2K+ moves in
- Na+ binds to the catalytic unit to activate ATPase, and hydrolysis of ATPase causes a conformational change
- Na+ is released out of the cell and K+ bind extracellularly, dephosphorylation of the subunit causes conformational change.
- K+ released into the cell
Describe the Na+/ glucose example of symporter active transport
- Na+ is in high concentration inside the gut whereas glucose concentration is low.
- Binding of glucose is dependent on the binding of Na+
- Glucose becomes more likely to bind to symporter as concentration of Na+ is higher outside the cell
Describe the Na+/ Ca2+ example of antiporter active transport (CARDIAC)
- Concentration of Na+ and Ca2+ outside the cell is higher
- Antiporter moves 3Na+ outside the cell (along its gradient), for every 1Ca2+ out (against its gradient).
