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AS Biology > Lipids - Biological Molecules > Flashcards

Lipids - Biological Molecules Flashcards

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1
Q

Describe the emulsion test for lipids

A
  • dry and grease free test tube
  • add ethanol to sample
  • shake tube to dissolve
  • add water and shake
  • cloudy white colour indicates the presence of a lipid
  • a negative test shown by a clear solution
    (if testing a sold crush/grind before dissolving)
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2
Q

What elements do lipids contain?

A

Carbon, hydrogen and oxygen
But lower ratio of O to C and H than carbs

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3
Q

Are lipids soluble?

A

Non-polar molecules
So insoluble in water
But soluble in alcohols and acetone (organic solvent)

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4
Q

What are other properties of lipids?

A

Generally hydrophobic
Don’t form polymers

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5
Q

What are the types of lipids?

A

Triglycerides - fats and oils
Phospholipids - found in cell-surface membrane

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6
Q

How is triglyceride an energy + water source?

A
  • energy and metabolic water source
  • when oxidise provide more that twice the energy than the same mass of carbs and release valuable water
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7
Q

How are triglycerides buoyancy aids?

A
  • called blubber in aquatic animals and used a buoyancy aid
  • less dense than muscle or bone
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8
Q

How are triglycerides insulation?

A
  • heat: slow conductors of heat
  • electrical: myelin sheath around nerve cells helps speed up transmission of impulse
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9
Q

How are triglycerides waterproof?

A
  • insoluble in water and useful in providing waterproof protection
  • mammals produce waterproof layer from skin
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10
Q

How are triglycerides used as protection?

A
  • fat stored around delicate organs e.g. kidney
  • cuticle of lead
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11
Q

What do triglycerides consist of?

A

3 fatty acids and glycerol (see notes for diagram)

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12
Q

How is glycerol shown?

A

(See notes)
Sometimes written as

CH2OH
I
CH2OH
I
CH2OH

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13
Q

What do fatty acids consist of?

A

Carboxyl group (COOH)
Hydrocarbon chain

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14
Q

What do variations in properties come from?

A

As glycerol is always the same, variations in properties in different fats and oils come from variations in the fatty acids.

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15
Q

What are fatty acids?

A

There are over 70 different fatty acids
All have an acidic COOH group and hydrocarbon chain attached (R group)

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16
Q

What are saturated fatty acids?

A

Hydrocarbon chain has only single bonds (between carbon atoms)

17
Q

What are unsaturated fatty acids?

A

Hydrocarbon chain has at least one double bond (between carbon atoms)

18
Q

What are the properties of saturated fatty acids?

A

-long straight chains
- most animal fats
- solid at room temp

19
Q

What are the properties of unsaturated fatty acids?

A

-plant and fish fats
- vegetable oils
- liquid at room temp
- kinks made by double bonded C prevent molecules from packing tightly together

20
Q

What reaction takes place between fatty acids and glycerol?

A

A condensation reaction occurs between glycerol and fatty acids to form an ESTER BOND

21
Q

Where must water molecules come from in the condensation reaction?

A

H from OH group on glycerol
OH from carboxyl group on fatty acids
Must be from exact positions

22
Q

Explain emulsion test for lipids

A

Lipid will dissolve in ethanol
But will not in water -forming cloudy white emulsion

23
Q

How is structure related to function for triglycerides?
Pt 1

A

High proportion of C-H bonds for number of C atoms (bonds store energy)
- excellent source of energy

High proportion of H to O atoms
- release water when oxidised, so useful source of water (especially for animals living in dry climates)

Large non polar molecules making them insoluble
- storage doesn’t affect the water potential of the cell and so no effect on osmosis

24
Q

How is structure related to function of triglycerides?

A

Low mass to energy ratio
- good storage molecule because a great deal of energy can be stored in a small volume

25
Q

Draw condensation reaction between triglyceride and phosphoric acid to make a phospholipid

A

See notes

26
Q

What is the structural difference between a triglyceride and a phospholipid?

A

One of the fatty acids is replaced by a phosphate group
Shown as P

27
Q

What are the properties of phospholipids?

A
  • phosphate is -vely charged and attracts water HYDROPHILIC
  • fatty acid molecules are HYDROPHOBIC and repel water
  • a phospholipid has a
    HYDROPHILIC HEAD
    HYDROPHOBIC TAIL
28
Q

What is the structure of a phospholipid?

A

Polar head
Attracts water
Hydrophilic

Fatty acid tails
Repels water
Hydrophobic

29
Q

What are the adaptations to function (phospholipid)? Bilayer

A
  • polar molecule with hydrophilic head and hydrophobic tail with 2 fatty acids
  • in aqueous environment molecules form a bilayer within cell-surface membrane
  • forms a hydrophobic barrier between inside and outside of cell
30
Q

What are the adaptations to function (phospholipid)? Micelles

A
  • can self-assemble into micelles
  • useful in the absorption of molecules that aren’t easily soluble
31
Q

What are the adaptations to function (phospholipid)? Glycolipids

A
  • structure allows them to combine with carbohydrates within cell-surface membrane to form glycolipids
  • important in cell recognition

AS Biology (21 decks)

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