lecture 6- membrane structure and composition

Biological membranes are responsible for _____ cells and

intracellular organelles.

delimit

Biological membranes does what? and what is it made of

enclosing or separating

layers of material made of amphiphilic molecules that act as a selective permeability barrier

What is the structure of the plasma membrane and most intracellular membranes that encapsulate organelles are described as what?

Lipid bilayer

polar head are hydrophobic or hydrophilic and they face what ?

Hydrophilic

Face the cytoplasm and the extracellular space

Fatty acyl chains tails are hydrophobic or hydrophilic and they face what ?

Hydrophobic

Face each other in the plane of the membrane

Amphipathic

Molecules containing hydrophilic and hydrophobic domains

Unsaturated fatty acid tails are ___ because the kinks prevent tight packing.

more fluid

longer chains are more or less fluid

longer chains are less fluid.

Membrane lipids with saturated fatty acid tails are more ___ because they pack tightly.

Rigid

When heat is added to membrane what consistent would be seen?

Fluid like consistency

Glycerophospholipids structure

Head group with choline, ethanlamine, serine,glycerol, inositol

phosphate

glycerol back bone

one saturated and one unsaturated fatty acids

Sphingophospoholipids

(sphingomyelins) Structure

Head group with choline

Phosphate

Sphingosine Backbone

Fatty chain tail

saturated fatty acids

Glycerophospholipids

(plasmalogens) Structure

Head group with choline, ethanlamine, serine,glycerol, inositol

phosphate

glycerol back bone With ether bond

Fatty chain tail saturated fatty acids

Phosphatidylinositol is a key component of many what?

many signaling pathways, and is located primarily in the cytoplasmic leaflet of the plasma membrane

Pulmonary Surfactant is a ?

a surface-active lipoprotein complex formed by alveolar cells in lungs.

DiPalmitoyl-PhosphatidylCholine (DP-PC) is the ___ of surfactant, sometimes called Lecithin (a generic name for amphiphilic films).

main lipid component

DPPC ___(and allows air to inflate the lungs more easily) by adsorbing to the air-water ___ of alveoli, with hydrophilic head groups in the water and the hydrophobic tails facing towards the air.

reduces water surface tension….interface

Respiratory Distress Syndrome can occur in ____; It is the most common cause of death in premature babies.

in neonates;

The molecular basis of respiratory distress syndrome is an _____ of surfactant caused by abnormal Lecithin / Sphingomyelin ratio in amniotic fluid.

insufficiency of surfactant

Glycolipids are what?

Glycolipids are lipids with one or more carbohydrates

attached

Are glycolipids more abundant or less abundant than phospholipids ?

less

Carbohydrates of glycolipids are always oriented to face

the ___ of the cell

outside

Glycolipids are a component of the “____” on cells,

known as the ___

“coating” on cells,

known as the glycocalyx

Glycolipids participate in what interactions?

cell-cell

Sphingoglycolipids are a source of ____, and can act as receptors for toxins, such as cholera toxin and tetanus toxin

blood group antigens

• Glycolipids also protect what?

epithelial cell membranes exposed to harsh environments, such as low pH and degradative enzymes

Reduced degradation causes

Lipid accumulation diseases

Neumann pick disease

sphingomyelin in brain and RBCs

Fabry disease

Glycolipids → ceramide trihexoside in brain heart kidney

Krabbe disease

Glycolipids , particularly galaocerebroside in ogliodendrocytes

Gaucher disease

Glucocerebrosides in RBCs liver and spleen

Tay sachs disease

GM2 gangliosides In neurons

Meracheomaric leukodystrophy

Sulfatide compounds in neural tissue

What’s the characteristics of cholesterol?

Cholesterol is also amphipathic, with a polar hydroxyl group, and hydrophobic steroid nuclei and hydrocarbon tails.

Cholesterol influences what at both low and high temperatures?

Membrane fluidity

Cholesterol does what with phospholipids ?

it “slips through” or insert itself between phospholipids and fills spaces between rails of phospholipids with unsaturated , lined fatty acid tails

Integral membrane proteins

span the entire membrane one or more times

Lipid anchored membrane proteins –

proteins with covalent attachment to a lipid

Glycoproteins –

transmembrane or lipid anchored proteins with extracellular-facing carbohydrate groups

Peripheral membrane proteins –

proteins associated with lipids (always face the cytoplasm)

Lipid-anchored proteins are also considered to be integral membrane proteins , why?

because they can only be removed from membranes by disrupting the entire membrane structure

Hydropathy plots are used for what?

to determine the overall structure of integral membrane proteins by identifying regions with a-helical segments

Integral membrane proteins associated with?

Cell-cell and cell-extracellular

matrix adhesion proteins

• Ion channels

• Transport proteins

• Hormone and growth factor

receptors

lipid anchored membrane proteins associated with ?

G-proteins – signaling, post-translational modification of effector molecules

Glycoproteins – glycocalyx, adhesion, signaling, antigenic immune regulation

Peripheral membrane proteins associated with

Cytoskeletal filaments – corralling integral and lipid-anchored proteins, “stabilizing” peripheral proteins

Enzymes – signal transduction, protein processing

The fluid mosaic model of membranes

Although the biological membranes are stable structures, the lipids and proteins with them are relatively relatively fluid

What physical barriers restricts movement?

tight junctions, or anchoring to the cytoskeleton

Phosphatidylserine has the ability to what?

Act as “eat me “ signals to attract macrophages

What’s a plasmalogin ?

A special lipid restricted to the peroxisome

Caveolae do what

Cholesterol homeostasis

Endocytosis

Signaling

Mechanoprotection

Lipid rafts have what and do what?

Enriched in shingolipids, cholesterol

Cholesterol transport

Endocytosis

Signal transduction

Molecules can be clustered Tg and considered “micro compartmentalization