Lipids + membranes Flashcards
Classify lipids.
-
simple lipids:
- triacylglycerols (fats/oils)
- waxes
-
complex lipids:
- phospholipids
- glycolipids
-
others:
- steroids
- ketone bodies, glycerol, hydrocarbons, vitamins, hormons, etc.
What can you say about the chainlength of naturally occuring fatty acids?
even no. of C-atoms (12-24)
What is the postfix of fatty acids?
How can they be abbreviated instead?
postfix:
- saturated: -anoic
- unsaturated: -enoic
alternative nomenclature:
- #C atoms : #double bonds, ex: 18:1
-
position of double bonds: ex: double bond btw C3/4, counted from terminal C
- 18:1; 3
- n-3
- Δ3
- ω3
What are unsaturated fatty acids?
Differentiate.
saturated = no double bonds, unsaturated = double bonds
- monounsaturated: 1 double bond
- polyunsaturated: 2+ double bonds
- eicosanoids: derived from arachidonic acid 20:4(Δ5,8,11,14)
What are eicosanoids?
Classify + brief description.
derived from arachidonic acid 20:4(Δ5,8,11,14)
-
prostanoids:
- prostaglandins: resp. for pain, fever, inflammation
- prostacyclins: inhibit platelet activation, vasodilator
- thromboxanes: clot formation
- leukotrienes: inv. in asthma + other processes
- lipoxins: resolve inflammation
What are prostaglandins?
Explain how they are formed.
Function?
cyclization btw C8 and C12 of arachidonic acid
→ cyclopentane ring
functions:
- produced by injured tissues
- involved in pain, fever, and inflammation
- not produced when anti-inflammatory drugs inhibit their synthesis (e.g. Aspirin)
Describe the geometrical isomerism of fatty acids.
Physiological effects?
in unsaturated fatty acids no rotation about double bonds, but if heated (hardened) rearrangement can occur
→ acyl chains either in cis or trans position
cis:
- naturally occuring isomeric form, 120°
- provides close molecular packing in cell membranes
trans:
- can cause cardiovascular diseases, diabetes mellitus
What are 3 famous ω3 (essential) fatty acids?
List some health benefits.
- α-linoleic acid (ALA)
- eicosapentaenoic acid (EPA)
- docohexaenoic acid (DHA)
health benefits:
- promote synthesis of prostaglandins/leukotrienes → anti-inflammatory
- vs. cancer
- vs. cardiovascular diseases
- vs. rheumatoid arthritis
- vs. Alzheimer disease
Explain the physical properties of fatty acids.
depend on chain length + saturation
Solubility:
- ↑ chains → ↑ hydrophobic → ↓ soluble
- double bonds ↑ solubility
Melting points:
- double bonds → acyl chain disorder and ↓ melting T
- unsaturated FAs solid at room T
What are triacylglycerols?
What is their function?
esters of glycerol + 3 fatty acids
→ main storage form of fatty acid in the body
What is important when it comes to labelling C atoms in glycerol?
What is the consequence?
C1 and C3 of glycerol not identical when viewed in 3D
→ sn-labeling used for C atoms
→ glycerol is prochiral (chiral when one of the above mentioned Cs modified)
How can triacylglycerols (TAGs) be decomposed?
Distinguish btw in vitro and in vivo.
- saponification: fat + base → soap
-
enzymatically: TAG + 2H20 ⇔ 2MAG + 2 fatty acid chains
- __pancreas lipase: hydrolyzes dietary fat molecules in the human digestive system
- cellular lipase: hydrolyzes TAGs in lipoproteins
What are waxes?
esters of long chain FA + long chain alcohols
What are glycerophospholipids?
Name an important biological function.
glycerol + 2 fatty acids + derivative of phosphoric acid
→ important components of cell membranes
What are lecithines?
Name important biological functions.
glycerophospholipids containing choline
function:
- nervous transmission (ex: acetylcholine)
- store labile methyl-groups
-
dipalmitoyl lecithin: surfactant of lung
→ absence: resp. distress syndrome
What is phosphatidylinositol?
Name important biological functions.
myoinositol + 1-3 esterified phosphate groups
function: act as second messengers
- membrane trafficking
- cell signaling
What are cardiolipins?
Function + consequences of a deficiency.
diphosphoacylglycerol → 4 fatty acids
function: essential for mitochondrial function
defficiency → heart failure, hypothyroidism, Barth syndrome
What are lysophopholipids?
What is the biological relevance of lysolecithine?
glycerophospholipids + only 1 acyl group + -OH
ex: lysolecithine → metabolism of phospholipids
MNEMONIC: lys<strong>OH</strong>phospholipids
structure of lysolecithine
What are ether phospholipids?
Explain one group of phospholipids.
Function?
phospholipids w/ ether linkage instead of ester at C1
ex: plasmalogens (C1=C2 double bond)
location and function:
- 10 - 30% of all phospholipids in brain/heart
- protective effect against ROS
structure of a plasmalogen
What are sphingophospholipids?
Name an important biological function.
sphingosine (1 acyl group + 1 head group) + esterified phosphate group
→ important components of cell membranes
What are sphingomyelins?
Name important biological functions.
ceramide + phosphocholine/-ethanolamine
function:
- outer layer of cell membranes (esp. lipid rafts)
- myelin sheats → cell signaling
- apoptosis
What are glycosphingolipids?
Important function?
ceramide + sugars
→ specify cell identity
blood group antigens:
- –O
- –A (+GalNac)
- –B (+Gal)
What are glycophospholipids?
What is their function and where can they be mostly found?
phospholipid + carbohydrate chain
location / function:
- in brain/nervous tissue
- in outer layer of plasma membrane → glycocalyx
Explain the structure of steroids.
How do they prevail in nature?
Properties?
phenantrene + cyclopentane ring
each ring either “boat” or “chair” (naturally: chair, more stable)
properties:
- low solubility in H20 (like other lipids)
- __transported by proteins
- can pass through cell membranes
What is the most important steroid?
Functions?
cholesterol
- precursor of steroids in bile acids, adrenocortical hormones, sex hormones, Vit D, cortisol
- esp. in nervous tissue, plasma membranes
Explain different ways of self-orientation of lipids.
What is the reason for that behavior?
lipids = amphipathic (= hydrophobic/-philic end)
- micelle: polar heads outside, nonpolar tails inside
- liposomes: either multi-/unilamellar. double layers formed with aqueous content inside
- emulsion: emulsifying agent needed (on surface) → stabilize much larger nonpolar particles (main bulk)
Differentiate btw bile acids.
General structure.
- prim. conjugated bile salts: synthesized in liver
- sec. conjugated bile salts: result from bacterial actions in the colon
amphipathic = hydrophobic + hydrophilic
- cholesterol-derived portion: hydrophobic (methyl groups) + hydrophilic (-OH groups)
- amino acid portion: polar = hydrophilic.
Explain the detergent effect of bile acids.
- fat globules of dietary fat broken down into microscopic droplets
- ↑ surface area
- available for digestion by lipases (cannot access the inside of lipid droplets)
Which substances can pass through membranes formed by lipid bilayers?
lipid soluble, non-polar (gases, small molecules) can diffuse through
water soluble, polar cannot → need membrane channels
What is protein lipidation?
Examples.
anchoring of proteins to lipid bilayer
- isoprenylation
- cholesterylation
- glycophophatidylinositol
- myristoylation
- S-prenylation
- S-acylation
List some functions of membrane proteins.
act as
- enzymes
- pumps, transporters, channels
- structural components
- antigens, receptors
What is lateral diffusion?
lipids + non-anchored membrane proteins can float freely in the plane of their membranes
What is flip-flop?
transverse movement of lipids across the membrane
e.g. as response to eat-me-signal
List which structures cause the asymmetric apperance of membranes.
regional heterogeneities
outside:
- choline-containing phospholipids
- sugars of glycosphingolipids/glycoproteins
inside:
- aminophospholipids
What is the function of flippases, floppases and scramblases?
- flippases: phospholipids _from I_nside to outside
- floppases: phospholipids _from O_utside to inside
- scramblases: phospholipids in both directions
Differentiate btw membrane proteins.
Examples.
integral membrane proteins
- require use of detergents for solubilization
- amphipathic → 2 hydrophilic ends, intervening hydrophobic region
- can span membrane once/multiple times
- ex: transporters, ion channels, G proteins
peripheral membrane proteins
- do not require use of detergents for solubilization
- bound to hydrophilic regions of integral proteins
- ex: ankyrin bound to spectrin → maintenance of donut shape of RBCs
What is the function of cholesterol?
modifies fluidity of membranes
- below TM: interaction w/ hydrocarbon tails of FA → increases fluidity
- above TM: limits disorder → limiting fluidity
<u>Tm </u>= transition from crystalline phase to more liquid-like phase of membrane
