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LDSCI211 (Biochem 1) > Lipids and membranes > Flashcards

Lipids and membranes Flashcards

1
Q

what are the 2 common properties that lipids share?

A
  1. insolubility in aqueous or water based solutions

2. solubility in organic or non-polar solvents

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2
Q

when you increase the number of C in a lipid, what happens to solubility?

A

inc # C = dec solubility = molecule will e bigger = more van de waals interactions holding it together

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3
Q

what are the 5 biological functions of lipids?

A
  1. storage of energy:
    - reduced compounds (high available energy)
    - hydrophobic nature (good packing)
  2. membrane structure
    - main component
  3. signaling molecules
    - hormones (steroids)
    - vit A and D (hormone precursors
  4. cofactors for enzymes
    - vit K: blood clot formation
  5. Antioxidants:
    - vit E: protects membranes (membranes are easily damaged by free radicals)
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4
Q

what are the two types of lipids? major difference?

A
  1. complex lipids (has FA)

2. biologically active lipids (no FA but are derived from FA)

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5
Q

what are the 2 types of complex lipids?

polar or non polar?

A

storage (non polar)

structural (polar)

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6
Q

2 types of storage lipids?

polar or non polar?

A

triglycerides and waves

nonpolar

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7
Q

2 types of structural lipids?

polar or non polar?

A

phospholipids
sphingolipids

polar

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8
Q

2 types of biologically active lipids?

A

prostaglandins

steroids

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9
Q

structure of a fatty acid?

A

amphipathic molecules
3-35 C hydrocarbon chains
carboxylic acid group

general chemical formula: CH3 (CH2)n COOH
n= or > than 2

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10
Q

describe FA waxy solids at room temp

A

FA with c10 or higher

saturated hydrocarbon chains

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11
Q

describe FA oily liquids at room temp

A

FA with c9 or lower

saturated of unsaturated hydrocarbon chains

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12
Q

how to name FA?

describe structure of 18:2 (delta 9,12)

A

refer to table 10-1

18 carbons. 2 double bonds at 9th and 12th carbon

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13
Q

what is the pKa of the COOH group on fatty acids?

what affects the pKa in FA?

pH of fully ionized FA?

A

less than 5

lower pKa means stronger acid. COOH group will have lower pKa (or higher acidity) if R group is very EN = low electron density on H because electrons are pulled towards the R group

fully ionized FA is pH 7

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14
Q

do natural FA have even or odd number of C?

A

even number

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15
Q

are natural FA branched or un-branched?

A

un-branched

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16
Q

what are the effects of saturation or unsaturation of a FA

3 main physical property changes?
ie. why is saturated FA solid at room temp?

A

double bonds (from unsaturation) affects the positions of FA tails

DB produces kinks therefore:
1. sat FA are more packed than un-sat
2 less ordered packing leads to weaker intermolecular interactions (van der waal)
3. lower mp for unsat FA

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17
Q

what is numbered carbon #1 in FA?

A

numbering starts with the COOH end

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18
Q

what defines the physical properties are FA?

A

physical properties (solubility and mp) are defined by:

  1. hydrocarbon chain length
  2. degree of saturation
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19
Q

how is solubility and mp affected with an increase in chain length of a FA?

effects in decrease in degree of saturation in a FA

A

when chain length increases, solubility in water decreases (becomes more nonpolar) and mp increases (higher van der waals)

decrease in deg of sat = become more unsaturated = add more DB

  • more DB = less ordered packing = water intermolecular interactions = takes less thermal energy to melt = lower mp
  • also more DB = less packed
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20
Q

what essential FA can humans not produce?

A
  1. linoleic acid (omega 6)

2. linolenic (omega 3)

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21
Q

what does omega 3 FA inhibit?

A

formation of thromboxane (an eicosanoid) required for platelet aggregation and clot formation.

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22
Q

what are the 3 major types of omega 3 FA ingested in foods?

what happens to them once eaten?

which 2 are the effective PUFAs?

A

alpha-linolenic (ALA)

eicosapentaenoic acid (EPA)

docosahexaenoic acid (DHA)

once eaten, the body converts ALA to EPA and then to DHA. Thus effective PUFAs are EPA and DHA

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23
Q

describe formation of trans FA.

describe rigidity of trans FA

A

-form by partial hydrogenation of unsat FA and cis-DB isomerization to trans-DB

  • DB can rotate like SB = increased rigidity in the molecule.
  • results in reduced membrane fluidity, flexibility and function
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24
Q

describe formation and structure of acylglycerols

A
  • results from condensation rxns between one glycerol sugar with one, two or three FA.
  • glycerol (backbone) and FA are linked by an ester linkage
  • triacylglycerol has a center of asymmetry (chiral carbon) at the 2nd C atom
  • most abundant form of metabolic storage lipids in animal and plant cells (energy storage and rapid source of energy))
  • can be present as insoluble forms
  • animal triglycerides are solid. plant and fish triglycerides are oil at room temp
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25
simple vs mixed/complex triglycerides?
if all FA are the same length = simple triacylglyceride (has no chiral carbon) if all FA have different lengths and degree of saturation = mixed/complex tracyglyceride (has a chiral carbon)
26
are animal, plant, fish triglycerides solid or liquid at room temp?
animal: solid | fish and plants: liquid
27
advantage of fats over polysaccharides?
acylgycerides carry more energy per carbon because they are more reduced FA carry less h20 because they are nonpolar
28
describe the different energy use of glucose vs acylglycerides
glucose: (glycogen) - short-term energy needs - quick energy delivery acylglycerides: - long term energy needs - good storage - slow delivery
29
how are triacylglyerols and monoacylglycerols digested? conversion to lipoproteins
in the small intestine by enzyme pancreatic lipase monoacylglyerols: 1. absorbed by intestinal cells 2. converted to triacylglyerols 3. assembled into lipoproteins
30
what happens when you treat tri-acylglcerol with strong base of acid?
hydrolysis of the ester bond between glycerol and FA ie. soap
31
how are waxes formed? describe role of waxes
condensation reaction between long FA and alcohol hydrocarbon chains act as metabolic fuel and water impermeable coating
32
structure of waves? how are they broken down?
DON'T contain glycerol broken down with strong acids and bases to FA and alcohol hydrocarbons have higher melting temp than tri-acylglycerides (because long hydrocarbon chains)
33
what are functions of structural lipids? 2 types?
1. membrane function 2. cell signalling phospholipid and sphingolipids
34
describe phospholipids basic unit of phospho-acylglycerol? structure?
- one of major components of cell membranes - phosphatidic acids are neg charged at pH7 andis the basic unit of phospho-acylglyerol structure of phospho-acylglycerol: - made up of 1,2-diaclglycerol ( 2 FA plus glycerol) linked to phosphoric acid - 2 FA are linked to 1st and 2nd OH of glycerol by *ester bonds* - 1st FA is usually saturated, 2nd FA is unsaturated (kink) - phosphoric acid is linked to 3rd OH of glycerol by *phospho-ester bond* - head groups: alcohol based compounds linked to phosphatidic acids -refer to diagram
35
chirality of glycerophospholipid? chirality of glycerol?
glycerol: not chiral on it's own ( has symmetry through C2)
36
how many chiral centres in glycerophospholipid?
2
37
what determines physical properties (and surface properties of membranes) of glycerophospholipid?
head group (X) different organisms and different tissues have different lipids head groups
38
what is the major component of most eukaryotic cell membranes?
phosphatidylcholine X (head group) is choline net charge of zero prokaryotes can't synthesize this = their membranes don't contain it
39
describe the charge of glycerophospholipids
amphipathic (hydrophillic and phobic) head group is charged (phillic) FA are phobic
40
what bond is used in the glycerophospholipid between the head group and glyercol backbone?
phosphodiester linkage
41
what gives cell membranes their overall positive or negative surface charges?
distribution of glycerophospholipids
42
describe sphingolipids: what is the backbone? type of linkages? subclasses?
- backbone is a long chain amino alcohol sphingosine (*NOT glycerol*) - FA attaches to sphingosine (*amide linkage*) at C2 of spingosine chain one FA + sphingosine = ceramide (structurally similar to diacylglycerol) polar head group is attached to C1 by a *glycosidic or phosphodiester bond* subclasses (determined by head group) 1. phosphoryl choline + spingosine = sphingomyelin 2. sugar group + sphingosine = cerebroside 3. combination of sugars (or oligosaccharide) + sphingosine = ganglioside refer to diagram -know which parts are FA spingosine, amide link,
43
where are sugar containing glycosphingolipids found?
outer face of plasma membranes easily detectable by the immune system. targets specific tissue membranes nonpolar FA on inside neg OH on outside
44
what determines blood groups? what determines the structure of sugar on head group in glycosphingolipids?
type of sugar located on head groups in glycosphingolipids determined by expression of specific glycosyltransferases 1. *inactive* glycosyltransferase: has O antigen 2. glycosultransferase that transfers N-acetylgalactosamine group: has A blood group 3. glycosyltransferase that transfers galactose: B group
45
what bond is inbetween polar head groups of phospholipids and glycolipids?
phospholipids: phosphodiester bond glycolipids: glycosidic link
46
1. linkage between FA in triacylglyceroles, glycerophospholipids, galactolipids, and sulfolipids? 2. in sphingolipids?
1. ester link | 2. amide link
47
describe biologically active lipids? 2 major classes?
dont contain FA or glycerol backbone can be generated from FA occurs in smaller amounts in cells and tissue role: recruit other cellular proteins to function classes: 1. prostaglandins: generated through modification of FA 2. sterols: generated from 2C (acetate) and through modification of other sterols
48
why are steroids important?
digestion: bile salts act as fat solubilizers hormones: human sex hormones
49
what are the 4 types of phospholipases? how do they differ?
4 types 1. phospholipase A1: cleaves C1 ester linked FA 2. PPL A2: cleaves C2 ester linked FA 3. PPL C: cleaves C3 phosphoester linked phosphoric acid 4. PPL D: cleaves phosphoesterlinked X or head groups (refer to diagram) PPL differ by where they cleave the ester linkage -don't cleave ethyl linkages as in sphingosine
50
2 classes of phospholipases?
1. phospholipid specific lipases | 2. broad substrate phospholipases
51
role of phosphatidylinosital 4,5-bisphospahte? | example. maybe not important for final
found on intracellular side of cell membrane hydrolysis is important for signalling pathway (protein kinase C)
52
role of paracrine lipid hormone?
vital for signaling molecules
53
enzymatic oxidation of arachidonic acid yields:
prostaglandins thromboxanes leukotrienes
54
3 products of enzymatic oxidation of arachidonic acid? | example. potentially not important
prostaglandin: inflammation and fever. smooth muscle contraction in uterus tromboxane: vasoconstrictor. platelet aggregation: Leukotriene: smooth muscle contraction in lungs
55
function of cholesterol:
prevents close packing of lower end of the FA hydrocarbon = decreases mp of lipid bilayer promotes tight packing of the upper ends of the FA hydrocarbon tails = increases mp of bilayer
56
sterol structure?
3 parts: - four fused rings. rigid and planar. hydrophobic - flexible and branched hydrocarbon/alkyl side chain - OH polar head amphipathic molecule (acts as structural lipid)
57
how does cholesterol accumulate in membrane?
cholesterol rigid structure favours interaction with saturate/transfat/unsat lipid
58
how is cholestrol a fluidity buffer? describe gel and liquid crystalline phases?
prevents sudden change in pH. avoids sudden gel to crystal phase allows membrane to tolerate changes in temperature without losing property gel phase:fully extended and packed hydrocarbon chains liquid phase: disordered and fluid chains refer to chart (slide 348): cholesterol creates slower rate of change when temp increases
59
what are lipid aggregates? | 3 possible structures?
1. lipid micelles - small spherical - h2o excluded from interior - head to tail ratio > 1 - free FA and detergents favour this conformation ie. soap 2. lipid bilayer - 2 monolayer - sheet like structure - water is excluded from interior - head to tail ratio = 1 - phosphoacylglycerides and sphingolipids favors this 3. liposomes - derived from lipid bilayer, folded back onto itself - encloses water on interior. acts as barrier between 2 environments
60
can storage lipids form micelles?
no they are completely NP
61
can detergents form micelles?
yes | most detergents have polar head, charged group and rest is hydrophobic
62
what do storage lipids form in aqueous solutions?
lipid droplets (they are NP)
63
what is the cell membrane impermeable and permeable to?
impermeable: charged ion and large molecules or proteins permeable: hydrophobic molecules, neutral gases, h2o
64
what was the black membrane experiment used for?
used to determine what solutes cross the lipid bilayer down their electrochemical gradients
65
layers of the cell membrane?
3 layers. 2 electron dense layers (inner and outer surfaces) total: 5mn thick 3. 5-4nm of the middle hydrocarbon layer
66
how can lipid molecules move on the cell membrane? enzymes for catalyzed flip-flops?
1. diffuse laterally 2. spin on axis no uncatalyzed flip-flop motion catalyzed flipflop enzymes: 1. flippases (uses ATP) 2. floppases (uses ATP) 3. scramblase (no ATP)
67
are are membrane lipids distributed between inner and outer leaflets?
asymmetrically
68
membranes of different cell organelles have different...
lipid composition
69
cell membranes have many globular proteins where the phospholipids act as...
solvent
70
3 classes of membrane proteins?
1. integral or intrinsic MP: transverse bilayer one or several times. Can be extracted from membrane with detergents 2. anchored MP: inked covalently to FA in inner or outer leaflet (don't transverse bilayer entirely). Detergent can extract from the membrane 3. peripheral/associated MP: associates or interacts with transmembrane protein. (don't transverse bilayer)

LDSCI211 (Biochem 1) (8 decks)

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