L1 - Biological Membranes

Micelles

Spherical structures contain amphipathic molecules

Bilayer

Lipid aggregate in which two monolayers (leaflets) form a two dimensional sheet

Vesicles

Liposome forms spontaneously when a bilayer folds back on itself to form a hollow sphere

T/F: Membrane composition is the same between bilayers, leaflets, and locations.

FALSE

Liquid ordered state

gel like state in which all types of motion of individual molecules are strongly constrained

Liquid disordered state

state in which individual hydrocarbon chains are in constant motion (lateral and rotational)

Membrane Dynamics

at mammalian physiological temperatures (20-40C) biological membranes are fluid and maintained a transition state between Lo and Ld

Higher molecular weight ->______ melting point

higher melting point

Stacking and MW of hydrocarbon molecules contribute to a an _____ in melting point

increase

T/F: Membranes should be fluid enough for curvature but not rigid enough that they break

TRUE

Membrane composition _____ due to external factors and conditions

changes

As temp increases, membrane increases the amount of______ fatty acids and less _______ fatty acids

saturated; unsaturated

Cholesterol does/does not affect the melting temperature of a membrane

DOES NOT

Cholesterol acts as a “____” and broadens the temperature range while lowering repsonce

buffer

Fluid mosaic

pattern formed by individual lipid and protein units in a membrane. The pattern can change while maintaining the permeability of the membrane

Transporters

move specific organic solutes and inorganic ions across the membrane

Receptors

sense extracellular signals and trigger molecular changes in the cell

Ion channels

mediate electrical signaling between cells

Adhesion molecules

hold neighboring cells together

GPI-anchored protein

Exclusively on outer face and are clustered in certain regions

Microdomains

Lipid rafts; Clusters of cholesterol and sphingolipids that make the bilayer slightly thicker and more ordered than neighboring, phospholipid-rich regions; can be up to 50% of cell surface; Basically an island where proteins can aggregate to perform specific function

Lipids can easily laterally move but cannot easily go from…

one leaflet to another due to their amphitropic character. 

Membrane proteins facilitate the translocation of…

individual lipid molecules

Flippase (P-type ATPase) move; Utilizes _____

PE (Phosphatidylethanolamine) and PS (Phosphatidylserine) from outer to cytosolic leaflet; ATP

Floppase (ABC transporter) moves; Utilizes _____

phospholipids from cytosolic to outer leaflet; ATP

Scramblase moves; Utilizes

lipids in either direction toward equilibrium (diffusion); Ca²⁺

Curvature changes are central to the ability of biological membranes to undergo…

fusion with other membranes without losing continuity

v-SNARE

SNAP receptor located on the vesicle 

t-SNARE

SNAP receptor located on the target/membrane

As the vesicle approaches the membrane, the v-SNARE and t-SNARE recognize each other and start…

intertwining, which pulls the membranes together.

SNAP25 is located

on the target cell

Hemifusion

outer leaflets of both membranes come into contact

Complete fusion creates a fusion pore ->

pore widens and vesicle contents are released outside the cell

Botulinum toxins disrupt the interactions between SNARE proteins by

interacting with one of the three proteins and chewing them up.

Botulinum toxins and mechanisms have been applied clinically for

botox, preventing sweat, and migraines

v-SNARE, t-SNARE, and SNAP25 allows _______ to occur

exocytosis