Lecture 2 - Membrane Proteins Flashcards
Are proteins dynamic or static structures?
Dynamic
What does the structure of a membrane protein structure depend on?
Its function
If a protein was to change conformation, what would it require?
A specific biological signal
Do all living cells have membrane potentials?
YES
What is the importance of water in functioning proteins?
They need to be optimally hydrated to obtain their specific 3D structure
How does water interact with protein?
Dynamically constantly moving around forming hydrogen bonds
Fact to know:
Proteins are flexible and elastic, this is a key structural feature that enables function
What are the 3 modes of movement proteins in the membrane can do?
Lateral motion
Rotational motion
CONFORMATIONAL CHANGE
How are membrane proteins classified?
Based on their location/structural association with the membrane
What are the 2 groups of membrane proteins?
Peripheral proteins
Integral proteins
Where can peripheral proteins be located on the membrane?
External Membrane Face
Internal Membrane Face
How do peripheral proteins adhere to the membrane?
Via loose interactions/associations (non covalent) with INTEGRAL PROTEINS/LIPID head groups
What is the importance of Intracellular peripheral proteins and the Cortical cytoskeleton?
Provides flexibility and elasticity to membrane
Disperses forces throughout network protecting cell integrity
What is the function of extracellular peripheral proteins?
Enzymes
Antigens
Adhesive molecules with ECM
What are integral membrane proteins?
Proteins that have varying degrees of penetration of the lipid bilayer
How is the degree of penetration of integral membrane proteins determined?
The non polar and polar bond formed
Non polar (hydrophobic tails of bilayer)
Polar head groups and peripheral proteins interact with the polar residues of the peptide chains
What are lipid anchored proteins?
Type of integral protein where there’s a covalent link between the fatty acid group within the bilayer
Where is the functional protein located in a lipid anchored protein?
Outside the membrane
Able to move laterally
How are membrane proteins organised?
Very specifically and precisely in order to function correctly
What determines the positioning of membrane proteins?
The status of the near field electrical environment
What are the 3 ways that membrane proteins organise/interact?
Aggregation
Tethering (Extracellular and Intracellular)
Cell-cell interaction
Give 2 examples of aggregates:
Mitochondria (ET chain)
Lipid Rafts (Antigen presentation)
Give an example of External tethering::
Integral membrane proteins connect with ECM
What is internal tethering?
When membrane proteins connect with the cytoskeleton providing structure all strength and whole cell flexibility/elasticity
What is an example of a cell-cell interaction
Cadherins
What is the benefit of cadherins when forces are experienced?
They allow forces to be transmitted and dissipated through the tissue
What are the 3 mains structural components of the cortical cytoskeleton of the RBC plasma membrane?
Transmembrane proteins
Intermediate Anchoring Proteins connecting (1 & 3)
Long flexible/elastic force carrying proteins
What are the key transmembrane proteins in RBCs?
HCO3- / Cl- antiporter also called band 3.1 (TRANSPORTS CO2)
Glycophorin
What are the additional roles of Band 3.1 and Glycophorin?
Shaping RBC bioconcave architecture
Allow forces to be distributed throughout the whole structure
What does ankyrin do?
Binds spectrin to band 3.1 (HCO-3/Cl- Exchanger)
Links band 3.1 to cytoskeleton
Spectrin = cytoskeleton of RBC
What does Band 4.1, Adducin and Actin do?
Anchors Glycophorin
What is another name for spectrin?
Cytoskeleton
What is the function of spectrin?
It forms massive hexagonal lattice throughout whole RBC
What is the function of the cortical cytoskeleton?
Provides flexibility and elasticity for whole cell
Keeps membrane proteins in place
What would happen if the cytoskeleton proteins of RBCs were mutated?
Loss of RBC structural integrity
What is a common condition where the cytoskeleton proteins of red blood cells are affected?
Hereditary Spherocytosis
