Lecture 15 Flashcards
What membrane defines the cell boundary?
Plasma membrane
What defines enclosed compartments
Organelles (mitochondria, golgi etc.)
What controls movement of material into and out of the cell/organelles
Plasma membrane and organelles
What allows response to external stimuli
Plasma membrane
What enables interactions between cells
Plasma membrane
(Ex. Tissues, muscles need to communicate with each other)
What provides a scaffold for biochemical activities
Mitochondria and chloroplasts
(Energy transduction)
Describe the structure of plasma membrane
Trilaminar structure is the lipid bilayer
Lipid bilayer is made up of phospholipids
Proteins are embedded in/associated with the phospholipid bilayer
What is the fluid mosaic model of biological membranes
Fluid: components are mobile
Mosaic: diverse ‘particles’ (protein, carbs and cholesterol penetrate the lipid layer) the components can interact
Describe the phospholipid structure
Glycerol backbone: 2 fatty acid chains and polar head group linked by a phosphate residue
Phospholipids are amphipathic
( hydrophilic and hydrophobic)
How will phospholipids try to organize themselves
In it’s most stable form, liposomes
Micelles only have one hydrophobic chain
Where does phospholipid synthesis occur?
Multiple step process at the interface of the cytosol and ER membrane
What does the ER membrane contain
Molecular machinery (enzymes) for synthesis and distribution
What are the 3 membrane proteins? Where are they located?
- Integral - many different functions, span the lipid bilayer, extracellular and extends from membrane
- Peripheral - associate with surfaces of the lipid bilayer
- Lipid-anchored- attach to a lipid in the bilayer (associated but do not span it)
What are the functions of integral proteins
- Transport of nutrients and ions
- Cell to cell communication (gap junction)
- Attachment (through receptors)
Describes lipids movement in relation to a leaflet
Lipids move easily, laterally within leaflet
Lipid movement between leaflets are slow and difficult
How do membrane proteins move within the biylayer
They diffuse
Restricted movement ( rapid is spatially limited and long range diffusion is slow)
Biochemical medication can change mobility (important for signal transduction)
Describe the structure of biological membranes
Properties that all membrane share: about 6nm thick, stable, flexible, capable of self assembly
Unique features: different types of lipids and proteins for different functions, differences between cells and organelles within them
What is contained in the inner membrane of the mitochondria?
Very high concentration of proteins that are needed for electron transport chain and ATP synthesis
What is the structure and purpose of the myelin sheath
Low amounts of protein and made up of multiple layers of the plasma membrane
Serves as insulation and increases the speed of electrical impulses almond the myelinated fiber
What are the leaflets of the membrane? What are the functions?
Each layer of the bilayer
Allows for movement of proteins and communication between cells
Each leaflet has distinct structure in many plasma membranes
Outer leaflet contains glycolipids and glycoproteins
How does temperature affect fluidity of biological membranes
Hotter temps increase fluidity (Liquid crystal)
Lower temps decrease fluidity (crystalline gel)
How does membrane fluidity change with the nature of the lipid
Membrane fluidity is crucial for cell function
Unsaturated lipids increase fluidity
Saturated lipids reduce fluidity
How does lipid composition of membrane change in response to changes in temp
- Desaturation of lipids
- Exchange of lipids chains
What does a balance between an ordered (rigid) and disordered (fluid) structure allow
Mechanical support and flexibility
Membrane assembly and modification
Dynamic interactions between membrane components (ex. proteins can come together reversibly)
How does cholesterol control membrane fluidity
A bidirectional regulator
At high temps, stabilizes the membrane and raises the melting point
At low temps, it intercalates between phospholipids and prevents them from clustering together and stiffening
How will cholesterol change the fluidity of membrane in a liquid crystal state versus a crystalline gel state
Overall changes packing and flexibility of lipids
Added to a liquid crystal membrane: fluidity decreases
Added to a crystalline gel membrane: fluidity will increase
