1.5-LIPIDS Flashcards
Lipids is a varied group of substances but what characteristics do they share? (4)
contain carbon, hydrogen and oxygen
proportion of oxygen to carbon and hydrogen smaller than in carbohydrates
insoluble in water
soluble in organic solvents i.e. alcohols and acetone
What are the main groups of lipids?
triglycerides (fats and oils)
phospholipids
Where is one of the roles of lipids?
in the cell membrane (cell-surface membranes and membranes around organelles)
What does phospholipids contribute to?
the flexibility of membranes and the transfer of lipid-soluble substances across them
What is a role of lipids? (1)
source of energy
when oxidised, lipids provide more than twice the energy as the mass of carbohydrates and release valuable water
What is a role of lipids? (2)
waterproofing
lipids are insoluble in water and so useful as waterproofing. both plants ans insects have waxy, lipid cuticles that conserve water, while mammals produce an oily secretion from the sebaceous glands in skin
What is a role of lipids? (3)
insulation
fats are slow conductors of heat and when stored beneath the body surface help to retain body heat. also act as electrical insulators in myelin sheath around nerve cells
What is a role of lipids? (4)
protection
fat is often stored around delicate organs i.e. kidneys
What is the state of fats and oils at room temperature (10-20℃)?
fats are solid
oils are liquid
Why are triglycerides so called?
as they have three (tri) fatty acids combined with glycerol (glyceride)
What does each fatty acid form?
forms an ester bond with glycerol in a condensation reaction
What does the hydrolysis of a triglyceride produce?
produces glycerol and three fatty acids
What is the same in all triglycerides?
the glycerol molecule
Where does the difference in the properties of different fats and oils come from?
variation in the fatty acids
How many fatty acids are there?
over 70 different fatty acids
What do all the fatty acis have?
a carboxyl (-COOH) group with a hydrocarbon chain attached
What is the fatty acid known as if this chain had no carbon-carbon double bond?
describes as saturated, because all the carbon atoms are linked to the max no. of hydrogen atoms
What is it called when there is a single double bond?
mono-unsaturated
What is it called if more than one double bond is present?
polyunsaturated
What does it mean for triglycerides to have a high ratio of energy-storing carbon-hydrogen bonds to carbon atoms?
an excellent source of energy
What does it mean for triglycerides to have low mass to energy ratio?
makes them good storage molecules because much energy can be stored in a small volume
How is triglycerides being good storage molecules especially beneficial in animals?
as it reduces the mass they have to carry as they move around
What property do triglycerides have by being large, non-polar molecules?
insoluble in water
What does triglycerides being insoluble in water mean?
their storage does not affect osmosis in cells or the water potential of them
What happens due to triglycerides having a high ratio of hydrogen to oxygen atoms?
release water when oxidised and therefore provide an important source of water, especially for organisms living in dry deserts.
What are phospholipids similar to?
lipids
How are phospholipids different to lipids?
one of the fatty acid molecules is replaced by a phosphate molecule
Do fatty acids repel or attract water?
repel water (are hydrophobic)
Do phosphate molecules repel or attract water?
attract water (are hydrophilic)
What two parts is a phospholipid made up of?
a hydrophilic ‘head’
a hydrophobic ‘head’
What does the hydrophilic ‘head’ do?
interacts with water ( attracted to it) but not with fat
What does the hydrophobid ‘head’ do?
orients itself away from water but mixes readily with fat
What are molecules that have two ends (poles) that behave differently said to be?
polar
What does them being polar mean?
when these polar phospholipid molecules are placed in water they position themselves so that the hydrophilic heads are as close to the water as possible and the hydrophobic tails are as far away from the water as possible
What makes phospholipids polar molecules?
having a hydrophilic phosphate head and a hydrophobic tail of two fatty acids
What does phospholipids being polar molecules mean?
in an aqueous environment phospholipids molecules form a bilayer within cell-surface membranes
What does the bilayer within cell-surface membranes result in ?
a hydrophobic barrier is formed between the inside and outside of a cell
What do the hydrophilic phosphate ‘heads’ of phospholipids molecules do?
help to hold at the surface of the cell-surface membrane
What does the phospholipid structure allow them to form?
glycolipids by combining with carbohydrates within the cell-surface membrane
Why are these glycolipids important?
in cell recognition
What is the cloudy colour due to in test for lipids?
any lipid in the sample being finely dispersed in the water to form an emulsion
What happens to light passing through this emulsion?
it is refracted as it passes from oil droplets to water droplets, making it appear cloudy
