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biology > Biological Molcules - Lipids > Flashcards

Biological Molcules - Lipids Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

what are lipids and what do they contain

A

lipids are macromolecules. they contain large amounts of carbon and hydrogen atoms with fewer oxygen atoms.

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2
Q

what are lipids soluble and insoluble in

A

lipids are soluble in organic solvent (e.g alcohol)
and insoluble in water

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3
Q

what are the three important groups of lipids

A

triglycerides (fats and oils)
phospholipids
cholesterol

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4
Q

give an example of lipids functioning as energy storage

A

adipose tissue of vertebrates, oil in fruits and seeds

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5
Q

give an example of the structural function of lipids

A

phospholipid bilayer of cell membrane

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6
Q

give an example of the thermal insulation function of lipids

A

to reduce heat loss e.g penguins

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7
Q

give an example of the electrical insulation function of lipids

A

myelin sheath of neurone axons

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8
Q

give an example of the cushioning/protection function of lipids

A

to protect vital organs e.g heart and kidneys

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9
Q

give an example of the waterproofing function of lipids

A

birds feathers and plant leaves

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10
Q

give an example of the buoyancy function of lipids

A

aquatic animals like whales

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11
Q

give an example of lipids functioning in hormone production

A

testosterone, oestrogen, cortisol

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12
Q

describe the structure of triglycerides

A

one molecule of glycerol attached to three fatty acids by ester bonds

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13
Q

describe the structure of glycerol

A

alcohol with three carbons and 3 OH groups

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14
Q

describe the structure of fatty acids

A

carboxyl group: COOH
hydrocarbon tail: carbon and hydrogen, varies in length and structure (2-20 carbons long)

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15
Q

give a property of fatty acids

A

hydrophobic - making them insoluble in water

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16
Q

describe saturated fatty acids

A

all of the carbon atoms form the maximum number of bonds with hydrogen atoms. there are NO double bonds between carbon atoms

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17
Q

describe unsaturated fatty acids

A

there is at least one double bond between carbon atoms. this causes the chain to kink

18
Q

describe monosaturated fatty acids

A

there is just one double bond

19
Q

describe polysaturated fatty acids

A

there are two or more double bonds

20
Q

why are polyunsaturated fats liquid at room temperature

A

the kinks caused by double bonds mean that the molecules cannot pack as closely together

21
Q

how are triglycerides formed

A

a condensation reaction occurs between the COOH group of the fatty acid and the OH group of the glycerol.
the bond formed is an ester bond

22
Q

what is the name for the reaction forming triglycerides

A

esterification

23
Q

how can triglycerides be broken down

A

the ester bonds can be broken down by hydrolysis reactions

24
Q

what is the main function of triglycerides

A

compact energy store

25
Q

why are triglycerides a good compact energy store

A

they contain a high proportion of C-H bonds and therefore release about twice as much energy per gram as carbohydrates

26
Q

why are triglycerides insoluble in water and why is this useful

A

they are non-polar. therefore, they do not affect osmosis in cells

27
Q

why are lipids useful for desert animals

A

respiration of lipids releases water

28
Q

what other functions do triglycerides have

A

thermal insulation, buoyancy (less dense than water), electrical insulation, protection, storage of fat-soluble vitamins e.g A and D

29
Q

describe the structure of phospholipids

A

similar to triglycerides but a phosphate group replaces one of the fatty acids ie one molecule of glycerol attached to a phosphate group and two fatty acids

30
Q

describe the phosphate group in phospholipids

A

negatively charged polar head. hydrophilic

31
Q

describe the fatty acid chains in phospholipids

A

uncharged, non-polar tails. hydrophobic

32
Q

what are the three behaviours of phospholipids in water

A

-form a single layer on water with their heads in the water and their tails sticking up

  • form micelles in water: tiny balls with the tails pointing in and the heads on the outside
  • bilayer can form with two rows of phospholipids: tails pointing inwards and heads outwards
33
Q

describe the main function of phospholipids

A

form a key role in cell membranes

34
Q

why are phospholipids useful in cell membranes

A

flexibility and stability: the phospholipids can move within a layer but not out of the layer
selective permeability: the non-polar tails makes the membrane a barrier to the movement of large polar molecules, but small and non-polar molecules can diffuse through

35
Q

why do organisms living in colder climates often have an increased number of unsaturated fatty acids in their phospholipid membranes

A

more kinked molecule; less uniformly packed together, ensures fluidity of membranes at lower temperatures

36
Q

describe the structure of cholesterol

A

a sterol; a lipid not made from fatty acids and glycerol
cholesterol is a small hydrophobic molecule

37
Q

what are the functions of cholesterol

A

found in cell membranes where it regulates fluidity
Vitamin D, steroid hormones e.g testosterone, and bile are manufactured from cholesterol

38
Q

how can the substances manufactured from cholesterol pass through the cell surface membranes

A

simple diffusion

39
Q

describe the method for the emulsion test for lipids

A

crush material and mix well with ethanol
decant or filter the suspension to remove any solid particles
carefully pour the ethanol solution onto some water in a clear test tube - don’t mix

40
Q

what are the positive and negative results for the emulsion test

A

positive: a milky white emulsion forms on top of the water
negative: solution remains clear

41
Q

why will the emulsion test not work for milk

A

milk will cause the solution to appear milky white regardless of whether or not there are lipids present

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