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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
Q

simple vs mixed/complex triglycerides?

A

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)

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26
Q

are animal, plant, fish triglycerides solid or liquid at room temp?

A

animal: solid

fish and plants: liquid

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27
Q

advantage of fats over polysaccharides?

A

acylgycerides carry more energy per carbon because they are more reduced

FA carry less h20 because they are nonpolar

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28
Q

describe the different energy use of glucose vs acylglycerides

A

glucose: (glycogen)
- short-term energy needs
- quick energy delivery

acylglycerides:

  • long term energy needs
  • good storage
  • slow delivery
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29
Q

how are triacylglyerols and monoacylglycerols digested?

conversion to lipoproteins

A

in the small intestine
by enzyme pancreatic lipase

monoacylglyerols:

  1. absorbed by intestinal cells
  2. converted to triacylglyerols
  3. assembled into lipoproteins
30
Q

what happens when you treat tri-acylglcerol with strong base of acid?

A

hydrolysis of the ester bond between glycerol and FA

ie. soap

31
Q

how are waxes formed?

describe role of waxes

A

condensation reaction between long FA and alcohol hydrocarbon chains

act as metabolic fuel and water impermeable coating

32
Q

structure of waves? how are they broken down?

A

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
Q

what are functions of structural lipids?

2 types?

A
  1. membrane function
  2. cell signalling

phospholipid and sphingolipids

34
Q

describe phospholipids

basic unit of phospho-acylglycerol?

structure?

A
  • 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
Q

chirality of glycerophospholipid?

chirality of glycerol?

A

glycerol: not chiral on it’s own ( has symmetry through C2)

36
Q

how many chiral centres in glycerophospholipid?

A

2

37
Q

what determines physical properties (and surface properties of membranes) of glycerophospholipid?

A

head group (X)

different organisms and different tissues have different lipids head groups

38
Q

what is the major component of most eukaryotic cell membranes?

A

phosphatidylcholine

X (head group) is choline

net charge of zero

prokaryotes can’t synthesize this = their membranes don’t contain it

39
Q

describe the charge of glycerophospholipids

A

amphipathic (hydrophillic and phobic)

head group is charged (phillic)

FA are phobic

40
Q

what bond is used in the glycerophospholipid between the head group and glyercol backbone?

A

phosphodiester linkage

41
Q

what gives cell membranes their overall positive or negative surface charges?

A

distribution of glycerophospholipids

42
Q

describe sphingolipids:

what is the backbone?

type of linkages?

subclasses?

A
  • 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
Q

where are sugar containing glycosphingolipids found?

A

outer face of plasma membranes

easily detectable by the immune system.

targets specific tissue membranes

nonpolar FA on inside
neg OH on outside

44
Q

what determines blood groups?

what determines the structure of sugar on head group in glycosphingolipids?

A

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
Q

what bond is inbetween polar head groups of phospholipids and glycolipids?

A

phospholipids: phosphodiester bond
glycolipids: glycosidic link

46
Q
  1. linkage between FA in triacylglyceroles, glycerophospholipids, galactolipids, and sulfolipids?
  2. in sphingolipids?
A
  1. ester link

2. amide link

47
Q

describe biologically active lipids?

2 major classes?

A

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

  1. sterols: generated from 2C (acetate) and through modification of other sterols
48
Q

why are steroids important?

A

digestion: bile salts act as fat solubilizers
hormones: human sex hormones

49
Q

what are the 4 types of phospholipases?

how do they differ?

A

4 types
1. phospholipase A1: cleaves C1 ester linked FA

  1. PPL A2: cleaves C2 ester linked FA
  2. PPL C: cleaves C3 phosphoester linked phosphoric acid
  3. 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
Q

2 classes of phospholipases?

A
  1. phospholipid specific lipases

2. broad substrate phospholipases

51
Q

role of phosphatidylinosital 4,5-bisphospahte?

example. maybe not important for final

A

found on intracellular side of cell membrane

hydrolysis is important for signalling pathway (protein kinase C)

52
Q

role of paracrine lipid hormone?

A

vital for signaling molecules

53
Q

enzymatic oxidation of arachidonic acid yields:

A

prostaglandins

thromboxanes

leukotrienes

54
Q

3 products of enzymatic oxidation of arachidonic acid?

example. potentially not important

A

prostaglandin: inflammation and fever. smooth muscle contraction in uterus
tromboxane: vasoconstrictor. platelet aggregation:

Leukotriene: smooth muscle contraction in lungs

55
Q

function of cholesterol:

A

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
Q

sterol structure?

A

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
Q

how does cholesterol accumulate in membrane?

A

cholesterol rigid structure favours interaction with saturate/transfat/unsat lipid

58
Q

how is cholestrol a fluidity buffer?

describe gel and liquid crystalline phases?

A

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
Q

what are lipid aggregates?

3 possible structures?

A
  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
Q

can storage lipids form micelles?

A

no they are completely NP

61
Q

can detergents form micelles?

A

yes

most detergents have polar head, charged group and rest is hydrophobic

62
Q

what do storage lipids form in aqueous solutions?

A

lipid droplets (they are NP)

63
Q

what is the cell membrane impermeable and permeable to?

A

impermeable: charged ion and large molecules or proteins
permeable: hydrophobic molecules, neutral gases, h2o

64
Q

what was the black membrane experiment used for?

A

used to determine what solutes cross the lipid bilayer down their electrochemical gradients

65
Q

layers of the cell membrane?

A

3 layers. 2 electron dense layers (inner and outer surfaces)

total: 5mn thick
3. 5-4nm of the middle hydrocarbon layer

66
Q

how can lipid molecules move on the cell membrane?

enzymes for catalyzed flip-flops?

A
  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
Q

are are membrane lipids distributed between inner and outer leaflets?

A

asymmetrically

68
Q

membranes of different cell organelles have different…

A

lipid composition

69
Q

cell membranes have many globular proteins where the phospholipids act as…

A

solvent

70
Q

3 classes of membrane proteins?

A
  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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