Membranes

In the amphipathic design of membranes what are the outer and inner leaflets enriched with respectively?

Outer: Phosphotidyl-choline, sphingomyelin, and glycolipds

Inner: Phsphatidyl-serine (negative), phosphatidyl-ethanolamine

What is Cholesterol needed for in membrane?

Strengthen/ Stiffenf bilayer while allowing mid bilayer to remain fluid

How do phospholipids move in bilayer?

Lateral: polar heads move w/n SAME leaflet very fast

Rotation/flexion: Hydrophobic tails benindg or rotating within SAME leaflet to adjust packing

Flip flop: Very long process, rare without enzymes moving polar head through hydrophobic core to other side

Function Classes of membrane associated proteins & their functions:

Transporters: move solutes across bilayer

Receptors: Sense extracellular signals and initiate intracellular cascades

Anchors: Link cytoskeleton to ECM

Enzymes: Catalyze reactions at the membrane surface

Explain Sodium Potassium Pump

Extracellular contains high Na and low K

Intracellular contain low Na and high K

Moving Na out and K in against gradient requires ATP for energy (active transport)

ATP phosphorylated into ADP + P, pyruvate binds to receptor/pump creating conformational change that lets 3 Na out and 2 K in pyruvate removed from receptor/pump creates conformational change allowing 2 K in

Explain Epinephrine pathway

7-pass receptor, adrenal medulla, stress fear exercise trigger

epinephrine binds to beta-adrenergic receptor activating bound G-protein to disassociate, alpha portion of g-protein disassociates and binds to adenyl cyclase activating it, ATP converted to cAMP which activates protein kinase A which activates phosphorylase to break down glycogen into glucose to be released into blood stream

Explain Glucagon pathway

7 pass receptor, alpha cells in pancreas, low glucose levels trigger

Glucagon binds to glucagon receptor on liver cells, G protein activated, alpha subunit activates adenyl cyclase, adenyl cyclase makes cAMP, binds to PKA which activates multiple enzymes to glycogen phosphorylase (turn glycogen into glucose), glycogen synthase (stop glycogen production), stimulate gluconeogenesis

Increasing glucose in blood

Explain PDGF receptor

PDGF released in response to injury or cell growth demand, binds to PDGF receptor (tyrosine kinase), receptor dimerizes (attaches to another PDGF receptor), they psophorylate each other, attracts other signalling proteins for proliferation (MAPK), survival (AKT), and migration & growth (PKC/Ca)

Explain Adenylate Cyclase

Second Messenger enzyme activated by alpha subunit of G protein to turn ATP into cAMP

Explain cyclo-oxygenase-1

Archidonic acid released activates COX-1 receptor, converts prostaglandin into PGH2 which is the precursor to other products responsible for clotting, protecting stomach lining and regulating blood flow and kidney function

Define Integral Proteins

Transmembrane Proteins

Embed 1 or more hydrophobic alpha helices and beta barrels across bilayer requiring detergent for removal

Define Peripheral Proteins

Non-covalently bounded to lipid head groups or with other proteins and can be removed with pH change or salt

Covalent Lipid Anchor Types:

Leaves polypeptide either on cytosolic or exoplasmic side

Fatty Acid: Myristate (14:0) or palmitate (16:0) attached to N-terminal Gly

Prenyl: Farnesyl (C15) or Geranyl (C20) chains added to C-terminal Cys

GPI: complex glycolipid added to C-terminus to display the protein on extracellular surface

Explain translocation of PKC

signaling pathway makes diacylglycerol, PKC binds to DAG non covalently and becomes anchored to membrane (peripheral protein), activating it

Explain Phospholipase A2 translocation

Stimulus (injury) —> Intracellular Ca rises —> Ca binds to Phospholipase A2 —> cPLA2 changes shape moving to membrane —> PLA2 cleaves phospholipids releasing arachidonic acid—> arachidonic acid converted to prostaglandins

Example of restricting movement of integral proteins by anchoring cytoplasmic portion to intracellular cytoskeleton

Spectrin-actin networks form scaffold under membrane maintaining shape

Ankyrin binds to Band 3 restricting Band 3s lateral movement

Glycophorin & protein 4.1 anchor cytoskeleton to membrane stabilizing vertical interactions

Example of restricting movement of integral proteins by tight junctions keeping them in specific domains

Epitelial cells are held together by tight junctions so Protein A able to move within surface but not into portion of membrane abuts adjacent cells

How to see lateral diffusion of protein FRAP & Heterokyrons?

FRAP- dye and bleach are see if fluorecent returns yes = mobile no = anchored

Heterokyrons: 2 different cells fuse together, see how integral proteins redistribute move freely = evenly distribute across membrane or stay separated = anchored or. restricted movement

Glycocalyx

Outer leaflet of membrane rich in carbohydrates, some covalently bonded to glycolipids and glycoproteins, other peripheral glycoproteins

Epithelial cells have to glycocalyx parts with different components one of which is facing basil lamina the other the free epithelial surface

Contributes to protection, hydration barrier, cell-cell recognition, filtration, immune interactions

ECM

Bigger/ more complex than glycocalyx, main components are integrin, fibronectin, collagen, proteoglycan, influence development, migration, proliferation, shape and function of cells that contact it