2.1.2e Lipids Flashcards
What are lipids
Lipids are macromolecules, composed of carbon, hydrogen & oxygen.
What are the 2 main types of lipids
- Triglycerides (the main component of fats & oils)
- Phospholipids
What are lipids soluble in
Organic solvents such as alcohols & acetone
Function of lipids
- STORAGE OF ENERGY for long-term use (eg. triglycerides)
- HORMONAL roles (eg. steroids sa. oestrogen & testosterone)
- INSULATION - both thermal (triglycerides) & electrical (sphingolipids)
- PROTECTION of internal organs (eg. triglycerides & waxes)
- STRUCTURAL components of cells (eg. phospholipids & cholesterol)
Lipid properties: compared to carbohydrates
The proportion of carbon to oxygen & hydrogen is smaller than in carbohydrates.
Property of lipids (involving reaction w water)
They are non-polar & hydrophobic (insoluble in water)
What is the mnemonic for the function of lipids
SHIPS
What are triglycerides & phospholipids an example of
Macromolecules - large molecules composed of several smaller ones, but not necessarily a polymer. Complex molecules w a relatively large molecular mass.
see showbie slide 5 for diagrams of types of lipids
How are triglycerides formed
Triglycerides are formed when condensation reactions occur between 1 glycerol & 3 fatty acid chains
What is the linkage within triglycerides
The hydroxyl (-OH) groups of glycerol combine with the carboxyl (-COOH) groups of the fatty acids to form an ester bond
- each ester bond is formed by condensation reaction
(see page 24 dia)
How are triglycerides broken down
During breakdown (eg for metabolism), these ester bonds are broken down by hydrolysis
What does the condensation reaction to form triglycerides cause
The condensation reaction results in the formation of 3 molecules of water
see showbie slide 6 for diagrams of triglyceride
Formation of the ester bond and release of water in triglycerides
- A H from glycerol combines w an OH from fatty acid to make water.
- The formation of an ester bond is a condensation reaction
- For each ester bond formed, a water molecule is released
- 3 fatty acids join to 1 glycerol molecule to from a triglyceride
- Therefore, for 1 triglyceride to form, 3 water molecules are released
see slide 9-13 for formation of triglycerides
2 types of triglycerides
Triglycerides can either be saturates or unsaturated, depending on the composition of the fatty acid chains
How do animals tend to store triglycerides
As fats (solid)
How do plants tend to store triglycerides
As oils (liquid)
How many different types of fatty acids are there
Over 70 different types, which vary in chain lengths, presence and number of double bonds
What are fatty acids
Long hydrocarbon chain that are found in certain types of lipids (triglycerides & phospholipids).
Fatty acids may differ in the length of the hydrocarbon chain & in the no. of double bonds
What are saturated fatty acids
- Fatty acids that possess no double bonds between their carbon atoms.
- The fatty acid is ‘saturated’ w hydrogen (have max no. of H atoms). This generates fats that are usually solid at room temp
Structure of saturated fatty acids
Linear in structure, originate from animal sources (eg fats) & are typicall7 solid at room temp
see slide 14-19, page 24 cgp for saturated & unsaturated fatty acids
What are unsaturated fatty acids
- Fatty acids with at least 1 double bond between carbon atoms
- causes the chain to kink
- either monounsaturated (1 double bond) or polyunsaturated (more than 1 double bond)
Structure of unsaturated fatty acids
Bent in structure, originate from plant sources (eg. oils). They are usually liquid at room temp.
Unsaturated fatty acids have at least 1 double bond between carbon atoms, which cause the chain to kink (see slide 15)
Eg of unsaturated fats; polyunsaturated
found in fish & some veg.
tuna, seeds
Eg of unsaturated fats: monounsaturated
found in plant-based foods & oils
avocados, olive oil
Eg of saturated fats from vegetables
coconut, palm oil
Eg of saturated fats
found in animal fats & dairy products
fatty meats, butter, milk
Eg of trans fats
found in fast foods & processed snacks
deep fried food, sweets
see slide 20 for types of fatty acids and their bonds table
What is a phospholipid
Phospholipids are macromolecules.
- Structure is similar to triglyceride, but one fatty acid chain replaced with a phosphate group
Structure of phospholipids
- Glycerol plus 2 fatty acids & a phosphate group
- The ‘polar head’ refers to the glycerol & phosphate. It is hydrophilic, meaning it attracts water
- The fatty acids ‘tails’ are hydrophobic, meaning they repel water
(see slide 21-25, page 24 for structure)
Why do phospholipids form bilayer in water
Phospholipids are amphipathic (they have both hydrophobic & hydrophilic parts). As a result, phospholipid molecules form monolayers or bilayers in water
Function of phospholipids
- Play crucial role in forming plasma membrane of cells
- In an aqueous environment, being polar means a bilayer can be formed
- They form a bilayer w the fatty acid ‘tails’ facing into eachother, & the ‘polar heads’ facing outwards & dissolving in the aqueous intra- and extracellular fluids
- The hydrophilic heads can be used to hold at the surface of the cell surface membrane
- Their structure allows them to form glycolipids w carbohydrates which are important on the cell surface membrane for cell recognition
- Ideal for forming cell surface membranes as they enable integration of other molecules into the ‘mosaic’ & help regulate movement of molecules in & out of cells
What is cholesterol
Sterols (steroid alcohols) are another type of lipid found in cells
Where is cholesterol manufactured
Manufactured primarily in the liver & intestines
Structure of cholesterol
Has a hydrocarbon ring structure attached to a hydrocarbon tail
Has a 4 carbon ring structure w a polar hydroxyl (OH) group at one end
(see slide 29)
Function of cholesterol
- Important in the formation & fluidity of cell surface membranes & in the production of certain hormones eg. testosterone
- Forms a small, thin molecule that fits into the lipid bilayer giving strength & stability
- Needed to make Vitamin D
Is cholesterol soluble in water
NO. Like all lipids, cholesterol is insoluble in water. In order to be transported in the bloodstream, insoluble cholesterol is combined w proteins to form soluble lipoproteins
There are 2 major lipoproteins
What are the 2 major lipoproteins
- Low-density lipoproteins
- High-density lipoproteins
What are Low-density lipoproteins (LDLs)
LDLs - BAD
Triglycerides (from fats in our diet) combine w cholesterol & proteins to form LDLs which transport the cholesterol to our body cells
Function of Low-density lipoproteins
- Carry cholesterol from the liver to the rest of the body
- Bind to receptors on cell surface membranes before being taken up by the cells where the cholesterol is involved in the synthesis & maintenance of cell membranes
- Excess LDL overload on these membrane receptors, results in high blood cholesterol levels, which may be deposited in the artery walls forming atheromas
What are High-density lipoproteins (HDLs)
HDLs - GOOD
‘H’ for ‘Hoover’. HDLs are made when triglycerides (from fats in diet) combine w cholesterol & proteins. They have a higher % of protein & less cholesterol compared to LDLs, hence their higher density
Function of High-density lipoproteins
- HDLs scavenge & ‘hoover’ up excess cholesterol in the arteries & carries it to the liver where it is broken down & passed out of the body
- This lowers the blood cholesterol levels, & helps remove the fatty plaques of atherosclerosis
What is ‘bad’ about LDLs and ‘good’ about HDLs
- LDLs raise blood cholesterol levels & are associated w the formation of atherosclerotic plaques, whilst HDLs lower blood cholesterol levels.
Therefore, it is desirable to maintain a higher HDL:LDL ratio in the blood
Dietary factors that increase cholesterol levels
High intake of certain types of fats will differently affect cholesterol levels in blood
- SATURATED fats increase LDL levels (& HDL as shown in studies, but much more LDL), raising blood cholesterol levels
- TRANS fats increase LDL levels & decrease HDL levels, significantly raising blood cholesterol
- UNSATURATED fats increasing HDL levels, lowering blood cholesterol
- MONOSATURATED fats helps removal of LDLs from blood
- POLYSATURATED fats increase activity of the LDL receptor sites so the LDLs are actively removed from blood
Exam q: Compare LDLs & HDLs
LDL carry cholesterol from liver to body cells
- Bind to receptors on cells which takes in cholesterol
- Raises blood cholesterol
- Increase deposition of fats in artery wall
- Form plaques/atheromas
HDL carry cholesterol from body to liver
- Bind to receptors on liver cells
- Liver takes in excess cholesterol
- Reduces blood cholesterol
- Therefore reduces deposition of fats
- Decreases risk of plaques/atheromas
Why is health advice constantly changing
As technology develops and so our understanding of biological processed increases
What is food synergy according to health advice
It is now generally believed that nutrients do not work in isolation but as part of the combined effect of a whole range of nutrients - food synergy
Why is the data used in health advice reports often flawed
- Bc the subjects involved in the studies often do not provide accurate info when diet is concerned. Ppl tend to underestimate what they eat, forget what they have eaten & dont know the exact ingredients of meals (particularly if eating out)
- Ppl are also different due to genetics & so respond diffrerently to different nutrients
Structure of a triglyceride: the fatty acids
- Fatty acid molecules have long ‘tails’ made of hydrocarbons.
- The ‘tails’ are hydrophobic. These tails make lipids insoluble in water
Basic structure of a fatty acid
page 24 cgp
Property -> function of triglycerides
Used as energy storage molecules in animals & plants
Long hydrocarbon tails of fatty acids contain lots of chemical energy -> lipids contain twice as much energy per gram as carbohydrates
Insoluble -> so they dont cause water to enter the cells by osmosis, which would make them swell
How are triglycerides insoluble
Triglycerides bundle tg as insoluble droplets in cells bc the fatty acid tails are hydrophobic
The tails face inwards, shielding themselves from water w their glycerol heads
Where are phospholipids found
In cell membranes of all eukaryotes & prokaryotes. They make up what’s known as the phospholipid bilayer
Property -> function of phospholipids
Phospholipid heads are hydrophilic & tails are hydrophobic -> form a double layer w thier heads facing out towards the water on either side
Centre of the bilayer is hydrophobic -> water-soluble substances cant easily pass through it, so membrane acts as a barrier to those substances
Property -> function of cholesterol
Small size, flattened shape -> allows it to fit in between the phospholipid molecules in the membrane
At higher temps, they bind to the hydrophobic tails of the phospholipids, causing them to pack more closely tg -> makes the membrane less fluid & more rigid
At lower temps, cholesterol prevents phospholipids form packing too close tg, & so increases membrane fluidity
