B1.1 - lipids (2e)

Question 1

what are the hydrophobic properties of lipids?

Answer 1

lipids are non-polar substances in living organisms that dissolve in non-polar solvents but have limited solubility in aqueous solvents

• lipids contain regions of hydrocarbon
• because the C-H bonds are non-polar covalent bonds, lipids are non-polar

Question 2

what molecules do lipids include?

Answer 2

lipids contain regions of hydrocarbon

Question 3

how can lipids be identified?

Answer 3

lipids can be identified by their low proportion of oxygen to carbon atoms, as they have areas of hydrocarbon (C-H bonds)

Question 4

what is glycerol?

Answer 4

glycerol is a three-carbon molecule, each of which is bonded to a hydroxyl group
- each hydroxyl group can be involved in a condensation reaction to form a covalent bond
- what binds to each of glycerol’s hydroxyl groups determines the type of lipid formed

Question 5

how can glycerol form triglycerides?

Answer 5

triglycerides - one glycerol molecule can link three fatty acid molecules, via their carboxyl group

Question 6

how can glycerol form phospholipids?

Answer 6

phospholipids - one glycerol molecule can link two fatty acid molecules and one phosphate group
- this molecule is important for forming cell membranes

Question 7

what is the solubility of lipids?

Answer 7

lipids have limited solubility in aqueous solvents, but they do dissolve in non-polar solvents

Question 8

what are the roles and structures of phospholipids?

Answer 8

role = forming cell membranes

structure = glycerol, 2 fatty acids, phosphate group

Question 9

what are the roles and structures of steroids?

Answer 9

role = hormones

structure = 3 six-carbon rings and 1 five-carbon ring

Question 10

what are the roles and structures of triglycerides (fats and oils)?

Answer 10

role = energy storage and thermal insulation

structure = glycerol and 3 fatty acids

Question 11

what are the roles and structures of wax?

Answer 11

role = waterproof coating

structure = long alcohol and 1 fatty acid

Question 12

what are saturated fatty acids?

Answer 12

have no double carbon (C=C) bonds, which means the melting point is relatively high (solid at room temperature) and is why its consumption is correlated with an increased risk of coronary heart disease

Question 13

what are monounsaturated fatty acids?

Answer 13

have one double carbon (C=C) bonds, which means the melting point is lower than the equivalent saturated fatty acid, particularly if it is a cis unsaturated fatty acid and so the lipid is liquid at room temperature

Question 14

what are polyunsaturated fatty acids?

Answer 14

have more than one double carbon (C=C) bonds, which means the melting point is lower than the equivalent saturated fatty acid, particularly if it is a cis unsaturated fatty acid, meaning the lipid is an oil at room temperature

Question 15

what are cis unsaturated fatty acids?

Answer 15

in cis unsaturated fatty acids, the two hydrogen atoms on either side of the C=C double bond are on the same side of the fatty acid molecule

Question 16

what are trans unsaturated fatty acids?

Answer 16

in trans unsaturated fatty acids, the two hydrogen bonds on either side of the C=C double bond are on the opposite sides of the fatty acid molecule

Question 17

why do trans fatty acids have a higher melting point than cis fatty acids, and what can this cause?

Answer 17

trans fats tend to have a higher melting point than the equivalent cis fatty acid, which links their consumption to coronary heart disease
- this is because the bends in cis fatty acids are packed less tightly than trans fatty acids

Question 18

how do the properties of triglycerides make them suitable for long-term energy storage functions?

Answer 18

• adipose tissue is composed of cells that store triglycerides
• lipids are more efficient energy stores than carbohydrates because they release more energy per gram, approximately twice as much
• when energy intake is exceeded, condensation reactions form more triglyceride molecules
• when sufficient food is not available, hydrolysis occurs to release glycerol and fatty acids to be used in respiration

Question 19

how do the properties of triglycerides make them as thermal insulators to aid maintenance of body temperature even in cold habitats?

Answer 19

seals, walruses and whales are all endotherms and have a thick layer of fat, called blubber, between their skin and muscles
- this blubber helps to trap the heat generated by the metabolic reactions inside the animal

Question 20

what causes the the formation of phospholipid bilayers?

Answer 20

the formation of phospholipid bilayers in water or aqueous solutions is a consequence of the hydrophobic and hydrophilic regions of these amphipathic molecules

Question 21

how is the bilayer structure in phospholipids formed?

Answer 21

• the hydrophobic fatty acid tails are not attracted to water, and so face inwards, away from the water of the cytoplasm (intracellular) or surrounding fluid (extracellular)
• the hydrophilic phosphate heads are attracted to the water and face outwards.

Question 22

what are steroids?

Answer 22

steroids are a sub-category of lipids; they are a group or hormones that are made from cholesterol

Question 23

how can steroids be identified?

Answer 23

they can be identified by having a low proportion of oxygen to carbon and having a ring structure made of three 6-carbon rings and one 5-carbon ring

Question 24

what are some examples of steroids?
where are they produced?
what is their role?

Answer 24

oestradiol - the strongest naturally occurring oestrogen hormone, which is important of female reproductive development

testosterone - a hormone that is important for male reproductive development

• these are both produced in the gonad and are involved in the development of primary and secondary sex characteristics

Question 25

why are steroids soluble in the lipid bilayer of cells?

Answer 25

• this is because the non-polar/hydrophobic steroid molecule can interact with the hydrophobic core of the bilayer
• this allows them to pass through the plasma membrane and nuclear membrane by simple diffusion

Question 26

what is the effect of hormones once they are in the nucleus?

Answer 26

once in the nucleus, the hormones impact the process of transcription, affecting the production of mRNA molecules and therefore gene expression