Biomembranes: Structure and Function

Comprehensive vocabulary flashcards covering the composition, structure, dynamics, transport mechanisms, and lipid rafts of biological membranes.

Functions of leaflet

Compartmentalizes cell organelles

Allows transport of ions

Energy storage

What allows ions to enter/exit leafleft

Permeable bilayer

What determines functionally of the leaflet

Proteins

What makes up the composition of leaflet

Cholesterol/ stigmasterol(plants)

Glycoproteins

Glycolipids

Different lipids involved in structure

Glycolipid

sterol

Fatty acids

Phospholipd

Major component of most bio membranes

Phospholipid

Which lipid class is amphipathic

Phospholipid

Cholesterol

How are phospholipid dynamic?

Lateral mobility

There is flipping between leaflets

Permeable membrane

Examples of phospholipids

Lecithin

Sphingomyelin

Phosphatidylserine

Phosphatidylethanolamine

Phospholipid structure

What are its derivatives

Lipid and steriod

Glycerol

What makes up the backbone of phospholipid

Phospholipid structure

What bonds connect their fatty acids

Ester

Phospholipids in humans

Phosphatidlyserine

Phosphatidylethanolamine

Phosphatidlylcholine

Types of membrane proteins

Intrinsic/transmembrane

Peripheral/extrinsic

Functions of transmembrane proteins

Transport

Enzymatic

Receptors

Cell communication

Adhesion to cytoskeleton And extra cellular matrix

Where do transmembrane proteins penetrate

Hydrophobic core

How are transmembrane proteins removed

By disrupting the bi layer

Location of transmembrane proteins

Lipid bilayer

Extrinsic membrane proteins

Do not interact with hydrophobic core

Location of peripheral membrane proteins

Extra/intracellular sides of membrane

Differentiate from peripheral and intrinsic membrane proteins

Extrinsic uses lipid anchors to insert itself into the membrane

Extrinsic interact with bilayer without completely crossing

How to extrinsic proteins interact with bilayer

Without crossing and not interacting with integral proteins

Where are membrane carbohydrates found

Outer leaflet

3 membrane carbohydrates

Proteoglycans(amino acid within fatty acid)

Glycolipids

Glycoproteins

Major functions of membrane carbohydrates

Cell recognition

3 membrane dynamics

Asymmetry

Fluidity

Lateral mobility(diffusion of a given membrane component)

Facilitated diffusion

Spontaneous movement of molecules across channel proteins from high-low conc

Types of active transport

Cotransport

Ion pump

Endocytosis

Lipid raft

Specialized micro domains that compartmentalize cellular processes

Properties of lipid raft

More rigid

Freely floats in bilayer

Types of lipid rafts

Caveolae

Planar

Cholesterol in lipid rafts

Holds rafts together

Lipid raft functions-10

Influences membrane fluidity

Assemblies signaling molecules’

Involved in apoptosis

Site for viral assembly-point of entry for virus

Regulates neurotransmission and receptor traffic

Leaflet

A single layer or monolayer of phospholipids that makes up half of a biological membrane bilayer.

What makes the leaflet of Archaebacterial Membrane special

Mono rather than bilayer

Phosphatidylcholine (Lecithin)

A major phospholipid found in biological membranes consisting of a glycerol backbone, two fatty acid chains, a phosphate group, and a choline head group.

Phosphatidylserine

One of the four major mammalian plasma membrane phospholipids that carries a negative net charge and is predominantly localized to the inner (cytoplasmic) leaflet.

Sphingomyelin

A prominent mammalian membrane phospholipid that is built on a sphingosine backbone rather than a glycerol backbone.

Cholesterol

An amphipathic lipid with a four-hydrocarbon-ring steroid nucleus that accounts for approximately $20\%$ of lipids in animal plasma membranes and is synthesized in the endoplasmic reticulum.

Plant Membrane Sterols

Sterol lipids such as stigmasterol and sitosterol that are present in the plasma membranes of plants in place of cholesterol.

Describe Glycolipid structure

Carbohydrates group attached to lipid

What sugar group heads Glycolipid

Glucose

Lipid tail of Glycolipid

Shingosine

Glycerol

Function of Glycolipid

Cell identification

Eg blood group

Fatty acids tail _________

Phospholipids

Which lipid normally has an even number of carbons

Fatty acids

Sterol structure

4 hydrocarbon groups

Where is sterol found

In the leaflet and bilayer

Describe sterols buffer function

Increases rigidly of boundary layer above body temperature (decreases fluidity)

Integral (Intrinsic) Membrane Proteins

Proteins that penetrate or fully span the hydrophobic core of the lipid bilayer and can only be extracted by disrupting the membrane bilayer.

Peripheral (Extrinsic) Membrane Proteins

Proteins loosely associated with the membrane surface via electrostatic interactions, lipid anchors, or bindings to integral proteins without entering the hydrophobic core.

Proteoglycans

Extracellular matrix and membrane molecules featuring a core protein linked covalently to long polysaccharide chains, which may span the bilayer or attach via a glycosylphosphatidylinositol (GPI) anchor.

Membrane Asymmetry

The unequal, non-random distribution of lipids, carbohydrates, and proteins between the inner (cytoplasmic) and outer (exoplasmic) leaflets of a bilayer.

Transition Temperature ($T_m$)

The specific temperature at which a lipid bilayer shifts between a solid-like, ordered gel state and a fluid-like, disordered liquid crystalline state.

Lateral Diffusion

The rapid sideways translation of phospholipids within the plane of the same monolayer, occurring at a frequency of approximately $10^7\text{ times per second}$.

Transverse Diffusion (Flip-Flop)

The very slow translocation of a phospholipid molecule from one leaflet across the hydrophobic core to the opposing leaflet, occurring spontaneously roughly once per month.

Selective Permeability

The property of the cell membrane allowing small hydrophobic molecules and small uncharged polar molecules to cross unassisted while excluding ions and large polar solutes.

Simple Diffusion

A form of passive transport where molecules move down their concentration gradient directly through the lipid bilayer without the assistance of transport proteins or energy consumption.

Facilitated Diffusion

The spontaneous passive movement of molecules or ions down their concentration gradient across a membrane aided by specific transmembrane channel or carrier proteins.

Osmosis

The passive transport and net movement of water molecules across a selectively permeable membrane in response to solute concentration differences.

Active Transport

The movement of ions or molecules across a biological membrane against their concentration gradient (from low to high concentration), requiring cellular energy expenditure ($\text{ATP}$).

Lipid Rafts

Small ($10\text{--}200\,\text{nm}$), dynamic, tightly packed membrane microdomains enriched in cholesterol (3- to 5-fold) and sphingolipids that compartmentalize specific cellular functions.

Planar Lipid Rafts

Non-caveolar glycolipid microdomains that remain continuous and flush with the plane of the surrounding plasma membrane.

Caveolae

Flask-shaped inward invaginations of the plasma membrane that contain caveolin proteins and function in receptor-independent endocytosis and signalling.

Caveolin

A specialized protein associated with caveolae that drives membrane curvature and regulates receptor-independent endocytic processes.