Lecture 8: Biological Membranes Flashcards Preview

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Flashcards in Lecture 8: Biological Membranes Deck (54):

Features: General structure


sheetlike structures - 2 molecules thick - that form closed boundaries between different compartments


Features: Makeup of membranes


- lipids and proteins

- mass ratio ranges from 1:4 and 4:1

- never any higher/lower than this ratio

- vary for different membranes

- some also contain carbohydrates that are linked to lipids and or proteins


Features: spontaneous activity

- hydrophilic and hydrophobic moieties

- spontaneously form closed bimolecular sheets in aqueous media

- barriers to the flow of polar molecules


Features: proteins


- embedded in the lipid bilayer

- mediate distinctive functions

- serve as pumps, channels, recepctors, transducers and enzymes


Features: Interactions of membranes


noncovalent interactions, act cooperatively


Features: Symmetry of membranes


- asymmetric

- two faces (leaflets, layers) of biological membranes have different lipid compositions

- individual peripheral membrane membrane proteins are only associated with one side of th emmebrane while integral membrane proteins have different domains on different sides of the membranes


Features: Fluidity


- fluid structures

- lipids diffuse rapidly in the phase of th emmebrane, as do proteins unless anchored

- do not ROTATE across the membrane, can be considered as an oriented 2D solution


saturated vs unsaturated fatty acids

more unsaturated keep mem more fluid (lower temps)


Features: Polarized


- electrically polarized

- inside is -60mv

- membrane potential a key role in transport, energy conversion, excitability


What are lipids?

- consists mostly of hydrocarbons

- serve as fuel molecules and energy stores

- signal molecules and messengers

- one of the two main components of membranes


Three major types of lipids

- phospholipids

- sphingolipids

- steroids


Glycerol structure


3 alcohol groups

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Sphingosine structure


sphingosine makes up backbone and tail

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Fatty acids


- feature of phospholipids and glycolipids

- various lengths and degree of unsaturation

- fatty acids in biological systems usually ocntain even number of carbon atoms (14-24)

- unsaturated have at least one DB in cis

- polyunsaturated are separated by at least 1 methylene group


Fatty acid numbering

- start at carboxyl terminus

- methyl at distal (far) end is thne w-carbon and double bond is represented by ►with superscript


Ex: nutritionists number from the omega/terminal

Omega 3-6-9 has DBs beginning on each of those carbons


chemists number in opposite direction




chemist: 9-12-15 (from carboxyl terminus)

nutritionist: 3-6-9 (from end)

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What affects the fluidity of fatty acids?


- decreasing chain length


Glycerophospholipids structure


Head group:

- choline

- phosphate

- glycerol

1 saturated tail

1 unsaturated tail


*ester bonds (from joining alcohol and carboxylic acid)

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Breakdown of glycerophospholipids via phospholipases


- produces a variety of signal molecules such as diacylglycerol and inositol phosphates (including inositol 1,4,5 trisP)


phospholipases A1 and A2

phospholipases C and D


phospholipasesd A1 and A2


cleave fatty acids from a glycerophospholipid, producing lysophospholipids

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C and D phospholipases

hydrolyze on either side of the phosphate in the polar head group

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1 fatty acid chain


ester bond vs amide bond

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ABO Blood type


- blood genes exist in more than 2 alleles

- three alleles for blood

- attach different carbohydrates to membrane components

- Ia and Ib both code glycotransferases with different substrate specificity

- I gene is nonfunctional


Ia allele


- adds a-N-acetylgalactosamine to D galactose end of an oligosaccharide side chain of sphingolipid (H antigen

- makes A antigen


Ib allele

- encodes glycosyltransferase that joins  a-D galactose to the a-D-galactose end of H antigen

- creates b antigen


Resultant blood types

A (only AA or AO)

B (only BB or BO)

O (ii) --> do not produce



Sphingolipids and diseases


- defect of lysosomal enzymes involved in sphingolipid degradation results int he acucmulation of partial breakdown products (storage substances) causeing serious diseases

- dont properly degrade lipids

- BUT these diseases still result in 70-80% functionality. If the pathway was totally destroyed the person wouldnt be alive


Whata re steroids?

- family of organic compoudns whose multiple (usually 4) fused rings share carbons

- in most cases an -OH is attached to at least 1 ring

- part of membranes or function as hormones to carry messages




deficiency of 17b-hydroxysteroid dehydrogenase 3


- reduces production of testosterone and can result in dev of male pseudohermaphroditism

- male doesnt go through puberty completely


Amphipathic membranes


- polar, hydrophobic head and nonpolar, hydrophilic tail


Basic forms of membrane

- micelle

- bilayer

- vesicle

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- spherical structure with limited amphipathic molecules arranged with its hydrophobic regions in interior




2D sheet with 2 lipid monolayers



open bilayer is relatively unstable and can spontaneously self-associate into a hollow vesivle, closed bilayer or liposome, enclosing aqueous activity


steps of lipids to membrane


unfavorable (planar phospholipid bilayer with edges exposed to water)


favorable ( sealed compartment formed by phospholipid bilayer)


* no energy needed (favorable)


Disrtibution of lipids a membrane


- asymmetric

- different lipids and proteins can be concentrated differently on either side


Fluid mosaic model


biological membranes

- consist of lipid bilayer in which membrane proteins are embedded

- considered an oriented 2D liquid- in which lipids and proteins diffuse more or less freely within the plane

- contain some defined structures or domains (protein complexes, lipid rafts)

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Lipid rafts


groups of lipids linked to/associated with proteins

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Types of membrane proteins





peripheral proteins


membrane proteins that lack exposed hydrophobic groups and do not penetrate the bilayer


integral proteins


- membrane proteins are amphipathic - hydrophobic an dhydrophilic regions or domains

- some extend across the lipid bilayer since they have 1 or mroe transmembrane proteins

- some partially embedded


interactions of proteins in the membrane


- independednt and interact noncovalently

- some have fattya cids or other lipids groups covalently attached and are referred to as anchored

- membrane spanning structures including b-strands, a-helices

- sequences of 20 consecutive nonpolar amino acids suggests a membrane spannins a -helical region of a protein


a helix in membrane IDd by

- 20 consecutive nonpolar amino acids


Types of membrane proteins


1. single span a helix

2. multiple span a helix

3. multiple b-span (b barrel)

4. nonspannign a helix

5. fatty acyl or prenyl anchor

6. lipid anchor with oligosaccharaide linker

7. peripheral mebrane



6 major functions of membrane proteins


- transport

- enzymatic activity

- signal transduction

- cell-cell regognition

- intercellular

- attachment to cytoskeleton and extraellular matrix


How are double bonds made in hydrocarbons?


oxidation aka dehydrogenation


How many carbons must be in fatty acid chain to find DBs?

- at least 16


Allergic reactions


- venom has phospholipases

- they break down erythrocytes

- immune reaction also occurs in response to degradation products


antivenom deactivated phospholipases


phospholipase C products


diacylglycerol and inositol 1,4,5 trisphosphate


diacylglycerol: activation of protein kinases, phosph in signaling pathways

inositol: increases Cell Ca2+, binding and reg


Determining blood type


- agglutination --> molecules join/link together


- add antibodies to blood sample

- A blood produces anti B antibodies, reacts with anti A

- B produces antiA, reacts with anti B antibodies

- AB blood produces no antibodies, blood reacts with both anti a and B

- O produces all antibodies, doesnt react with anti A or anti B antibodies


Importance of cholesterol

- NEED for cellular membranes

- hydrophobic but must be transported through hydrophilic blood

- carried in bowl like structure

- too much can build up and cause heart disease or stroke (plaque)


steroids and gender determination


- activate hundreds of transcription factors

- can change complete expression patters


male vs female


where are lipids made?

-golgi apparatus

- "melt" into membranes


membrane protein complexes


- do not move, cannot free flow

- like cytochrome C


hydropathy index

certain types of proteins and aas more likely to be span membrane

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