_simple lipids:_ triacylglycerols (fats/oils) waxes _complex lipids:_ phospholipids glycolipids _others:_ steroids ketone bodies, glycerol, hydrocarbons, vitamins, hormons, etc.

Lipids + membranes Flashcards by LV D

Classify lipids.

simple lipids:
- triacylglycerols (fats/oils)
- waxes
complex lipids:
- phospholipids
- glycolipids
others:
- steroids
- ketone bodies, glycerol, hydrocarbons, vitamins, hormons, etc.

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What can you say about the chainlength of naturally occuring fatty acids?

even no. of C-atoms (12-24)

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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 C^3/4, counted from terminal C
- 18:1; 3
- n-3
- Δ³
- ω³

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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)}

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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

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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)

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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

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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

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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

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What are triacylglycerols?

What is their function?

esters of glycerol + 3 fatty acids
→ main storage form of fatty acid in the body

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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)

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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

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What are waxes?

esters of long chain FA + long chain alcohols

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What are glycerophospholipids?

Name an important biological function.

glycerol + 2 fatty acids + derivative of phosphoric acid
→ important components of cell membranes

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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

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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.

1. **fat globules of dietary fat broken down** into microscopic droplets 2. ↑ **surface area** 3. 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 T_M_: interaction w/ hydrocarbon tails of FA → **increases fluidity** * _above T_M_: limits disorder → **limiting fluidity** _{Tm = transition from crystalline phase to more liquid-like phase of membrane}