Biological Molecules: Lipids Flashcards

1
Q

what is a lipid

A

a macromolecule which contains carbon, hydrogen and oxygen

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2
Q

what are the two types of lipid

A
  • triglycerides
  • phospholipids
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3
Q

two main characteristics of triglycerides

A
  • non-polar
  • hydrophobic (insoluble in water)
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4
Q

how does the chemical make-up of lipids differ from carbohydrates

A

lipids have a lower proportion of carbon to hydrogen and oxygen

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5
Q

why are triglycerides insoluble in water

A
  • there are no exposed -OH groups

the -OH on the end of each of the 3 fatty acid chains bonds with one of the 3 -OH groups on the glycerol molecule

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6
Q

what is the composition of a triglyceride

A

three fatty acid molecules bonded to one glycerol molecule

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7
Q

what type of organic compound is glycerol

A

an alcohol

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8
Q

what is a fatty acid made up of

A

a methyl group at one end of a hydrocarbon chain (known as the R group and typically 4 to 24 carbons long) with a carboxyl group at the other end

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9
Q

what is the shorthand for the chemical formula of a fatty acid

A

RCOOH

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10
Q

what are the two types of fatty acid

A
  • unsaturated
  • saturated
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11
Q

how do triglycerides vary

A

the fatty acids

  • the length of the hydrocarbon chain
  • presence, number and location of double C=C bond
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12
Q

what is the difference between mono- di- and poly- unsaturated fatty acids

A

refers to how many double bonds are present

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13
Q

structure of a cis-fatty acid

A

CH2 groups are both at the tops bond of each carbon

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14
Q

structure of a trans-fatty acid

A

CH2 groups are top left and bottom right of the carbons

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15
Q

difference between cis- and trans- unsaturated fats

A

cis- fats can be metabolised by enzymes

trans- fats can’t form enzyme-substrate complexes and are therefore not metabolised (much more unhealthy than cis)

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16
Q

how do triglycerides form

A
  • by esterification when an ester bonds forms between -OH group on glycerol and -COOH group of the fatty acid

this is called a condensation reaction

  • the H from glycerol and OH from fatty acid bond to release a water molecule
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17
Q

equation for the formation of a triglyceride

A

glycerol + 3 fatty acids -> 3H2O + triglyceride

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18
Q

biological molecules in order of energy per gram

A
  • lipids
  • proteins
  • carbohydrates
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19
Q

which type of fatty acid is healthiest

A
  • unsaturated
20
Q

what type of fatty acid are oils

A

unsaturated

21
Q

how are lipids used to produce atp

A
  • they contain many carbon-hydrogen bonds with little oxygen (they are highly reduced)
  • they are then oxidised during cell respiration
  • which causes the bonds to break
  • which releases energy used to produce atp
22
Q

why are triglycerides good as energy stores

A
  • hydrophobic so don’t cause osmotic water uptake
  • store more energy per gram (due to their hydrocarbon chains)
  • large so doesn’t osmose out of cell
  • the oxidation of carbon-hydrogen bonds releases large numbers of water molecules during cellular respiration
23
Q

why are unsaturated fats liquid at room temperature

A

the presence of double bonds adds kinks to the fatty acid chains which alters their properties

24
Q

how do mammals store triglycerides

A

as oil droplet in adipose tissue (helps them to survive when food is scarce such as hibernating bears)

25
Q

how do plants store triglycerides

A
  • in the form of oils in their seeds and fruits
26
Q

what are the main roles of triglycerides

A
  • energy store
  • insulation (electrical)
  • buoyancy
  • protection
27
Q

how are triglycerides used for insulation

A
  • triglycerides are part of the composition of the myelin sheath that surrounds the axon

this provides insulation which increases the speed of transmission of nerve impulses

  • triglycerides are also a part of the adipose tissue layer below the skin which acts as insulation against heat loss
28
Q

how are triglycerides used in buoyancy

A
  • the low density of the fat tissue increases the ability of animals to float more easily
29
Q

how are triglycerides used in protection

A

the adipose tissue in mammals contains stored triglycerides and this tissue helps protect organs from the risk of damage

30
Q

structure of a phospholipid

A
  • a glycerol molecule bonded to two fatty acids and one phosphate ion
31
Q

are phospholipids polar or non-polar

A
  • the phosphate head is polar and so it is hydrophilic
  • fatty acid tails are non-polar and therefore hydrophobic
32
Q

why are phospholipids integral to cell membranes

A
  • the phosphate head interacts with water but not with fats and the fatty acid tails move away from water but mixes readily with fats. therefore we can control what goes in and out of a cell (anything polar at least) ——- this is because the phospholipids form a bilayer which creates a hydrophobic core meaning water soluble substances cannot easily pass through
  • The hydrophilic phosphate heads form H-bonds with water allowing the cell membrane to be used to compartmentalise
    This enables the cells to organise specific roles into organelles helping with efficiency
  • Composition of phospholipids contributes to the fluidity of the cell membrane
    If there are mainly saturated fatty acid tails then the membrane will be less fluid
    If there are mainly unsaturated fatty acid tails then the membrane will be more fluid
  • Phospholipids control membrane protein orientation
    Weak hydrophobic interactions between the phospholipids and membrane proteins hold the proteins within the membrane but still allow movement within the layer
33
Q

what type of lipid is amphipathic

A

phospholipids because they have both hydrophobic and hydrophilic parts

34
Q

why do phospholipids form monolayers/bilayers in water

A

because they have both hydrophobic and hydrophilic parts

35
Q

what are the roles of phospholipids

A
  • they are integral to cell membranes
  • they can form a hydrophobic core which acts as a barrier to water-soluble molecules
  • they allow cells to compartmentalise
36
Q

when do phospholipids act as a barrier to water soluble molecules

A

when a hydrophobic core is created as a result of a phospholipid bilayer forming

37
Q

how do phospholipids allow cells to compartmentalise

A

the hydrophilic heads form H-bonds with water allowing the cell membrane to be used to compartmentalise

this enables the cells to organise specific roles into organelles, helping with efficiency

38
Q

how many water molecules are released in the formation of phospholipids

39
Q

main function of phospholipids

A

cell membrane components

40
Q

main function of triglycerides

A

energy storage

41
Q

what is one disadvantage of the ethanol emulsion test

A

the result is qualitative and does not give a quantitative value as to HOW MUCH lipid may be present

42
Q

what is a lipid soluble in

A

organic solvents such as alcohols

not water or salt solutions

43
Q

describe the process of the lipid emulsion test

A
  • add ethanol
  • shake
  • add water
  • shake
  • if lipids are present a milky white emulsion will form and the more lipid present the more obvious the colour
  • no lipid present = clear solution

if food is solid it should be ground up first

44
Q

properties of triglycerides

A
  • have long hydrocarbon tails which contain large amounts of chemical energy
  • insoluble (form insoluble droplets in cells)
  • hydrophobic
45
Q

properties of phospholipids

A
  • ## hydrophilic at one end and hydrophobic at the other
46
Q

how do phospholipids form a bilayer

A

the fatty acids (hydrophobic) face inwards and the phosphate head (hydrophilic) faces outwards