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A-level biology > Biological Molecules: Lipids > Flashcards

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
how do plants store triglycerides
- in the form of oils in their seeds and fruits
26
what are the main roles of triglycerides
- energy store - insulation (electrical) - buoyancy - protection
27
how are triglycerides used for insulation
- 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
how are triglycerides used in buoyancy
- the low density of the fat tissue increases the ability of animals to float more easily
29
how are triglycerides used in protection
the adipose tissue in mammals contains stored triglycerides and this tissue helps protect organs from the risk of damage
30
structure of a phospholipid
- a glycerol molecule bonded to two fatty acids and one phosphate ion
31
are phospholipids polar or non-polar
- the phosphate head is polar and so it is hydrophilic - fatty acid tails are non-polar and therefore hydrophobic
32
why are phospholipids integral to cell membranes
- 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
what type of lipid is amphipathic
phospholipids because they have both hydrophobic and hydrophilic parts
34
why do phospholipids form monolayers/bilayers in water
because they have both hydrophobic and hydrophilic parts
35
what are the roles of phospholipids
- 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
when do phospholipids act as a barrier to water soluble molecules
when a hydrophobic core is created as a result of a phospholipid bilayer forming
37
how do phospholipids allow cells to compartmentalise
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
how many water molecules are released in the formation of phospholipids
3
39
main function of phospholipids
cell membrane components
40
main function of triglycerides
energy storage
41
what is one disadvantage of the ethanol emulsion test
the result is qualitative and does not give a quantitative value as to HOW MUCH lipid may be present
42
what is a lipid soluble in
organic solvents such as alcohols not water or salt solutions
43
describe the process of the lipid emulsion test
- 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
properties of triglycerides
- have long hydrocarbon tails which contain large amounts of chemical energy - insoluble (form insoluble droplets in cells) - hydrophobic
45
properties of phospholipids
- hydrophilic at one end and hydrophobic at the other -
46
how do phospholipids form a bilayer
the fatty acids (hydrophobic) face inwards and the phosphate head (hydrophilic) faces outwards

A-level biology (7 decks)

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