Membrane biology and transport Flashcards
What model is used for the cell membrane?
Fluid mosaic model
What are phospholipids?
The basic component of cell membranes
Hydrophillic Head
Hydrophobic tail
What is cholesterol’s role in the membrane?
To regulate fluidity
How much of the membrane volume is protein?
Around 50%
What protein % does mitochondrial membranes have?
80%
What are the three types of integral proteins?
Single, Multipass and Polytopic
What are single transmembrane proteins?
Only passes through the membrane once
What are Multipass transmembrane proteins?
The protein passes through the membrane multiple times
What are polytopic transmembrane proteins?
Passes through the membrane multiple times but as a beta-sheet
What is a Amphipathic protein?
Passes through the extracellular side of the membrane once
What is a Hydrophobic loop protein?
The protein enters the extracellular side of the membrane multiple times
What does a electrostatic protein do?
Binds to the hydrophillic parts of the membrane
What do anchored proteins do?
Covalently bond to the lipid “anchor” Glycosylphosphatidylinositol (GPI)
How is fluidity affected?
Cholesterol - More cholesterol = less fluid
Temperature - Lower temp = less fluid
Phospholipids - Longer chains = less fluid
Saturated chains = less fluid
What is a lipid raft?
An area that’s rich in cholesterol and sphingomyelin
How does membrane permeability change?
Charge
Polarity
Size
How does facilitated diffusion work?
High -> low concentration
Uses channels/carriers
e.g. Ion channels, Water via aquaporins
How does active transport work?
Low -> high concentration
Uses ATP
e.g. Ion pumps
How are channels/carriers controlled?
Ligand gated
Mechanically gated
Always open
Voltage gated
How do voltage-gated ion channels work?
They detect changes in membrane potential
Na+, K+, Ca2+ channels
Inactivation causes refractory period
What do amino acids do in ion channels?
They selectively filter different ions
What do amino acids do in voltage channels?
They have a voltage sensing helix
What is endocytosis?
The cell engulfs an external substance and contains it within a vesicle
What is exocytosis?
Cell secretes a substance contained within a vesicle
How are ion gradients established?
Through precise control of which ions enter/exit
What do membrane potentials allow?
Electrical signalling and excitability
Energy production
What is the purpose of receptors?
Allows a molecule to affect the cell without entering
What is the largest and most diverse group of receptors?
G-Protein coupled receptors
What does an activated G protein activate?
A second messenger
