Lecture 8: Biological Membranes Flashcards
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
Sphingosine structure
sphingosine makes up backbone and tail
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
Linolenate
chemist: 9-12-15 (from carboxyl terminus)
nutritionist: 3-6-9 (from end)
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)
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
C and D phospholipases
hydrolyze on either side of the phosphate in the polar head group
Sphingolipids
1 fatty acid chain
ester bond vs amide bond
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
AB (AB)
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
micelle
- spherical structure with limited amphipathic molecules arranged with its hydrophobic regions in interior
bilayer
2D sheet with 2 lipid monolayers
vesicle
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)
Lipid rafts
groups of lipids linked to/associated with proteins
Types of membrane proteins
peripheral
integral
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
- single span a helix
- multiple span a helix
- multiple b-span (b barrel)
- nonspannign a helix
- fatty acyl or prenyl anchor
- lipid anchor with oligosaccharaide linker
- 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
