STRUCTURE AND FUNCTIONS OF MEMBRANE Flashcards
EXPLAIN THE IMPORTANCE OF MEMBRANES
COMPARTMENTALISATION = individual compartments with different functions can occur at the same time
BIOCHEMICAL PROCESSES = transport of electrons, oxidative phosphorylation, photosynthesis
INFORMATION PROCESSING - transmission of nerve impulses and effects of hormones
NAME FATTY SATURATED ACIDS
-Saturated fatty acids can be tightly packed by hydrophobic interactions of their chains
-> palmitic and stearic acids
NAME UNSATURATED FATTY ACIDS
have a coiled side chain, due to cis
double bonds, which keeps the membranes in a fluid state
-> as they are deformed due to cis bonds, they cannot effectively stick together
is Unsaturated fatty acids have kink(s) in their chains that limit how close their chains pack, hence they are more fluid
trans Unsaturated fatty acids are tightly packed because their rigid double bond and no kink in chains (reduced fluidity)
o linoleic acid, arachidonic acid - ω-6 fatty acids, essential
o linolenic acid - ω-3 fatty acids, essential
WHAT ARE THE PREDOMINATING LIPIDS OF MEMBRANES?
phospholipids
HOW ARE FATTY ACIDS CLASSIFIED?
a) Short Chain FA (up to 6 carbons)
b) Medium Chain FA (less than 12 carbons)
c) Long Chain FA (12 to 18 carbons)
d) Very Long Chain FA (more than 18 carbons)
WHICH TYPE OF FATTY ACIDS PREDOMINATE IN HUMAN FAT?
Long chain FA predominate in human fat (TAG, triacylglycerols)
LIST OF FATTY ACIDS
WHAT DO NATURAL OCCURING FATTY ACIDS OF ANIMAL LIPIDS CONTAIN?
Naturally occurring FA of animal lipids contain even number of carbons and cis double bonds
WHAT ARE THE COMPONENTS OF PHOSPHATIDIC ACID?
2x FFA + glycerol + H3PO4
-ester bonds
-precursor of all TAG and most phospholipids
WHAT ARE THE COMPONENTS OF GLYCEROPHOSPHOLIPID?
phosphatidic acid + another component (containing Nitrogen)
-at a high concentration of phospholipids, they start forming double layers of 7nm
thickness
-middle carbon of glycerophospholipids and TAG are chiral
4 OTHER COMPONENTS:
-choline
-serine
-ethanolamine
-myo inositol
NAME 4 GLYCEROPHOSPHOLIPIDS
phosphatidylethanolamine (cephalin) – formed by the attachment of ethanolamine
-phosphatidylserine – formed by the attachment of serine
-phosphatidylinositol – formed by the attachment of myo-inositol, on to inner leaflet
- phosphatidylinositol phosphate - phospholipid, other part of membrane – has signaling function
MAJOR MEMBRANE PHOSPHOLIPIDS^^^
other glycerophospholipids
-plasmalogen
-DIphosphatidylGLYCEROL = CARDIOLIPIN
WHAT DO SPHINGOPHOSPHOLIPIDS CONTAIN?
1 FA, sphingosine, phosphate, aminoalcohol
WHAT ARE SPHINGOMYELINS?
consist of:
- sphingosine = C18, 2x -OH, -NH2 (alcohol)
- ceramide = FA +sphingosine (amide bond)
- sphingomyelin = ceramide + H3PO4 + choline
->they form the myelin sheath of neurons
EXPLAIN GLYCOLIPIDS
-derived from sphingosine
-instead of phosphoric acid they have a sugar, usually galactose
-saccharide component -> galactose, glucose, oligosaccharide, N-acetylneuraminic acid
CEREBROSIDES = ceramide + monosaccharide
-> found in white matter myelin
GANGLIOSIDES = ceramide + oligosaccharide
-> ganglions
(globoside + one or more acidic sugar moieties)
GLOBOSIDES = ceramide + more than one sugar: galactose, glucose, N-acetylgalactose amine
SULFATIDE = cerebroside containing sulfatated galactose
WHAT ARE PHOSPHOLIPID FORMATIONS?
-> micelles – round structures made of phospholipids; surface is hydrophilic inner part is hydrophobic
-> bilayers – at high concentrations micelles independently turn into bilayers = membranes
-> liposomes – balls made of bilayer
WHAT IS THE POLARITY OF PHOSPHOLIPIDS?
amphoteric
-> hydrophilic head (phosphate and base)
-> hydrophobic tail (FA chain)
NAME THE 2 TYPES OF DIFFUSION IN THE MEMBRANE
-lateral
-transverse
EXPLAIN TRANSVERSE DIFFUSION IN THE MEMBRANE
-very slow
-rotation about their own axis
-flip flop movement
-membrane lipids exchange between layers this way
EXPLAIN LATERAL DIFFUSION IN THE MEMBRANE
-around 1 μm/s, considered fast
-sidewards movement
-membrane lipids move within the membrane monolayer this way
CHOLESTEROL
-in membranes mainly in non-esterified form
-stabilizes the speed of phospholipids in membrane – at lower temperature’s it speeds them up and protects them from solidifying and at higher temperatures it slows them down protecting them from dissolving
-It is the major precursor for the synthesis of vitamin D, of the various steroid hormones, including cortisol, cortisone, and aldosterone in the adrenal glands, and of the sex hormones progesterone, estrogen, and testosterone
-an animal sterol found in the body tissues (and blood plasma) of vertebrates. It can be found in large concentrations within the liver, spinal cord, and brain
about 20% of membrane lipid mass
* Rigid (compact) but not planar (chair conformation)
* Packed within the spaces between adjacent phospholipid molecules (in „kinks“ of unsaturated FA) with its –OH
oriented to the polar heads of a neighboring phospholipids
* Found in both membrane leaflets
EXPLAIN THE FUNCTION OF GASEOUS ANAESTHETICS AND GIVE 2 EXAMPLES
dissolve in membrane and protect against the movement of substances/ions, which disrupts the transmission of nerve impulses and causes the patient to fall unconscious
EG: diethyl ether, halothane (2-brom-2-chlor-1,1,1-trifluorethane)
HOW HYDRPPHOBIC AND HYDROPHILIC SUBSTANCES ACT DIFFERENTLY IN WATER
EXPLAIN THE MOVEMENT OF MOLECULES THROUGH THE MEMBRANE
FREE DIFFUSION: non polar and polar small substances
FACILITATED DIFFUSION: large polar substances and charged substances
WHAT ARE MEMBRANE PROTEINS?
proteins which are integrated into the phospholipid bilayer cell membrane
WHAT FORMS MICELLES?
cone shaped amphiphilic molecules
WHAT FORMS BILAYERS?
cylinder amphiphilic shaped molecules
EG: PHOSPHOLIPIDS
EXPLAIN PERIPHERY PROTEINS
- do not go across whole membrane
- placed on inner or outer sheet of cell membrane
-enzymes or receptors
-polar
-weak interactions with lipid membrane
EG: spectrin of erythrocytes, cytochrome C and ATP-ase of mitochondria and acetylcholinesterase in electroplax membranes
EXPLAIN INTEGRAL PROTEINS
penetrate across the phospholipid membrane once or several times
o function as ion channels, membrane receptors or ensure the transport of
different substances across the membrane
o transport membrane proteins allow easier diffusion of substances across the membrane
-strong interactions with bilayer
-non polar
EG: membrane bounded enzymes, drug and hormone receptors, antigen and rhodopsin.
WHAT IS THE EQUATION FOR OSMOTIC PRESSURE?
π = ci * R * T
(ci - osmolarity – concentration of all osmotically active particles [Osmol/L]
o ci (osmol/L) = i * c (mol/L))
WHAT IS THE OSMOLARITY OF BLOOD PLASMA?
300 mOsmol/L
EXPLAIN THE DIFFERENT TYPES OF OSMOTIC SOLUTIONS
hypertonic – higher concentration of particles - plasmolysis (water leaves cell)
isotonic – balanced concentration – nothing is happening
hypotonic – lower concentration of particles - plasmoptysis (water goes into cell and
causes it to break)
EXPLAIN MEMBRANE POTENTIAL
- membrane potential is formed by the different concentration of ions inside and outside the cell – inside mainly
negative charge, outside positive - inside - K+ and negatively charged proteins
- outside - Na+ a Cl-
- two forces apply here
o electrical – because all molecules are charged, they attract or repel each other - K+ and Na+ want to go in, Cl- and proteins want to go out
o concentration - K+ and proteins want to go out, Na+ and Cl- want to go in
o when these two forces are put together, they form an electrochemical gradient
- because K+ want to go in (due to the electrical force) but even out (due to the concentration gradient), these two forces
will compete and K+ will partly leak out of the cell causing a more positive charge outside than inside
CARBOHYDRATES OF THE ABO BLOOD SYSTEM
WHAT ARE THE DIFFERENCES BETWEEN PASSIVE AND ACTIVE TRANSPORT?
Active transport uses energy (ATP) for the moving the molecules in and out of the cellular membranes and therefore remain active, while in passive transport the molecules do not use energy for their movements
-Active transport moves from regions of high-low concentrations = AGAINST GRADIENT
Passive transport moves from regions of low-high concentrations = ALONG GRADIENT
-Active transport is fast unidirectional upwards
Passive is slow bidirectional downwards
-Active transport = Endocytosis, Exocytosis, Proton pumps and Sodium potassium pumps
Passive transport = osmosis and diffusion
TRANSPORT OF MEMBRANE PROTEINS
rER → GA→ membrane
TRANSPORT OF LYSOSOMAL PROTEINS
rER → GA → lysosome
TRANSPORT OF PROTEINS FOR EXPORT
rER (proteosynthesis, posttranslational modifications)
→ transport vesicles → GA: more posttranslational modifications (phosphorylation, glycosylation, removal of saccharides) → secretion vesicles → exocytosis
EXPLAIN RAFT DOMAINS
WHERE DO GLYCOLIPIDS OCCUR?
only in the outer leaflet of the plasma membrane
WHICH MOLECULES ACCOUNT FOR AROUND 18% OF ALL HUMAN PHOSPHOLIPIDS?
plasmalogens and ether phospholipids
-> high in heart and brain
WHERE IS CARDIOLIPIN ABUNDANT?
inner mitochondrial membrane
WHICH MOLECULES OCCUR IN THE INNER LEAFLET OF PLASMA MEMBRANE?
phospholipids with serine, ethanolamine and inositol
WHAT DO THE MOST ABUNDANT PHOSPHOLIPIDS CONTAIN?
choline
WHICH PHOSPHOLIPID PREDOMINATES IN THE OUTER LEAFLET OF CELL MEMBRANE?
phosphatidyl choline predominates
-phosphatidylserine is also here
HOW IS MEMBRANE FLUIDITY AFFECTED BY LIPID COMPOSITION?
higher presence of unsaturated or shorter FA (and lower amount of cholesterol) increases membrane fluidity at lower temperature, whereas long saturated FA (or trans FA) and
more cholesterol stabilize membranes and make them less permeable
