New version page

UT BIOL 3030 - Biomembranes

Upgrade to remove ads

This preview shows page 1 out of 3 pages.

Save
View Full Document
Premium Document
Do you want full access? Go Premium and unlock all 3 pages.
Access to all documents
Download any document
Ad free experience

Upgrade to remove ads
Unformatted text preview:

Lecture 9: Biomembranes- Composition and Organization of Lipid Bilayerso Biological membranes Are impermeable to water-soluble molecules and ions Have a gluey consistency with fluid-like properties- Phospholipids spontaneously form lipid bilayerso Leaflet  structure of phospholipid  minimizes contact of hydrophobic chains with water by aligning themselves tightly togethero No membrane can have an “edge” with exposed hydrocarbon fatty acyl chainso Endocytosis: Segment of plasma membrane buds inward and eventually pinches off as a separate vesicle- Phospholipid is a generic termo Refers to any amphipathic lipid with a phosphate-based head and 2-chain hydrophobic tailo Phosphoglycerides = most abundant  Glycerol backbone, two esterified fatty chains make up tail Saturated or unsaturated  Head is polar group estrified to phosphate 4 major head groups: Plasmalogens: group of Phosphoglycerides- Contain one fatty chain attached to glycerol by ester linkage and long hydrocarbon chain- Abundant in heart/brain tissue- Greater chemical stabilityo Sphingolipids = derived from sphingosine Structure consists of amino alcohol with long HC chain and long fatty acid attached in amide linkage to the sphingosine amino group Some have phosphate-based polar head group, most abundant being sphingolipid Sphingomyelin contains a phosphocholine head group Some have polar head groups as sugars and are not linked to tails via phosphate groups  glycolipidso Sterols (cholesterols): Basic structure is four-ring isoprenoid-based HC for tail and single polar hydroxyl for head group Sterols differ for different types of organisms:- Animals = cholesterol- Plants = stigmasterol- Fungi = ergosterol- Fluidity of the Membraneo Individual phospholipids can mov laterally throughout bilayero Factors affecting speed of molecules moving within and across layers include: Temperature  increase can cause disorder in tails, decreasing thickness of bilayer and making it more fluid-like  Structure of HC tails  long tails pack tightly, decreasing fluidity  kinks disrupttight packing and cause increase fluidity Number of cholesterol molecules in bilayer  cholesterol restricts random movements of tails  lower cholesterol causes slight increase in fluidity- Composition and Organization of Lipid Bilayerso Biomembranes are classified by its composition of lipids and proteinso Movement of membranes from one compartment to another can selectively enrich certain membranes  responses to environmento Lipid type can dictate membrane thicknesso Lipid composition affects membrane curvature Large Head, long tail  flat bilayer Small head, long tail  curved bilayer Combination of lipids  combination of shapeso Exoplasmic and cytoplasmic leaflets are composed of different lipidso PS ad PI lipids carry negative charge and therefore interact on cytoplasmic face with positively charged a.a. PI face cytoplasm  involved in cell signaling PS face cytoplasm  activates blood clotting enzymeso Flippases: relocate lipid between faces  requires ATPo Lipid rafts: microdomains  more ordered, less fluid- Membrane Proteins: Structure and Basic Functionso 3 types: integral, lipid-anchored, and peripheral Integral membrane proteins contain at least one hydrophobic membrane-spanning domains Transmembrane proteins and glycolipids are asymmetrically oriented in bilayero Integral proteins: 3 domains: cytosolic (hydrophilic), exoplasmic (hydrophilic), and membrane spanning (hydrophobic) Hydrophobic residues interact with HC core of bilayer All TM proteins have one or more alpha helices or multiple beta sheetso Lipid-anchored Covalently bound to lipids  does not enter bilayer Acylation: fatty acid attached to glycine residue Prenylation: HC attached to cysteine residue GPI anchor: attach cell-surface proteoglycanso Peripheral Do not contact hydrophobic core Interacts with integral or lipid-bound proteins Inside  can be cytoskeletal proteins Outside  can be ECM or cell wall proteins- Multimeric Membrane Proteinso Alpha-helical protein segments often have polar or charged residueso Side chains guide assembly/stability of multimeric proteinso Beta-sheet protein segments: Hydrophilic, hydrophobic


View Full Document
Download Biomembranes
Our administrator received your request to download this document. We will send you the file to your email shortly.
Loading Unlocking...
Login

Join to view Biomembranes and access 3M+ class-specific study document.

or
We will never post anything without your permission.
Don't have an account?
Sign Up

Join to view Biomembranes 2 2 and access 3M+ class-specific study document.

or

By creating an account you agree to our Privacy Policy and Terms Of Use

Already a member?