Biological molecules 2.1.2 Lipids

Question 1

What are lipids?

Answer 1

• lipids are molecules containing the elements carbon, hydrogen and oxygen.
• Generally fats that are lipids are solid at room temp and oils are liquid at room temp.
• Lipids are non polar molecules as the electrons in the outer orbitals that form bonds are more evenly distributed than in polar molecules. This means there are no positive or negative areas in the molecule so lipids are not soluble in water.

Question 2

Types of lipid macromolecules

Answer 2

• Triglycerides, phospholipids, glycolipids, cholesterol, steroid hormones, lipid based vitamins.
• Phospholipids, glycolipids and cholesterol are all components of membranes
• macromolecules = a large organic molecule.

Question 3

Triglycerides

Answer 3

• Made by combining one glycerol molecule with 3 fatty acids
• Glycerol is a part of the alcohol functional group
• fatty acids are in the carboxyl functional group (COOH), with a hydrocarbon attatched
• Both of these molecules contain hydroxyl groups, these hydroxyl groups interact leading to the formation of 3 water molecules and bonds between the fatty acids and glycerol molecules. (these are ester bonds and the process is called esterfication which is a condensation reaction)

Question 4

Functions of triglyceride

Answer 4

• Source of energy, can be used in respiration to provide twice as much energy per gram than carbohydrates or proteins.
• Energy storgae, for equivilant ammount of energy lipids have half the mass of carbohydrates and proteins). Facilitates movement of animals and seed dispersal in plants.
• Lipids are less dense than water so provides buoyancy
• Thermal insulator (bad conductor of heat)
• Provides electrical insulation (myelin sheath)
• protection, cushions and absorbs impact
• Reduces water loss (e.g. waxy cuticle)

Question 5

Fatty acids (in trigyleride)

Answer 5

• Methyl group (CH3)
• Long chain hydrocarbon (CH2)n
• The hydrocarbon chain is non polar/hydrophobic
• carboxyl group (COOH)

Question 6

Saturated fatty acids

Answer 6

• Have no double bonds present between carbon atoms
• They are called saturated because all carbon atoms have maximum number of bonds with hydrogen atoms
• e.g. palmatic acid (formula = C15 H31 COOH)
• General formula = Cn H2n+1 COOH

Question 7

Unsaturated fatty acids

Answer 7

• Has double bonds between some of the carbon atoms
• If there is just 1 double carbon bond it is called monosaturated, if there are 2 or more it is called polysaturated
• The presence of double bond causes molecules to kink or bend which makes them liquid at room temperature.
• General formula = Cn H2n-1 COOH

Question 8

Why are unsaturated fats liquid at room temp and saturated solid at room temp?

Answer 8

• Molecules of saturated fat can be packed tightly togther
• Molecules of unsaturated fats pack less closely togther due to kinks in structure so are liquid at room temp.

Question 9

How is margarine made?

Answer 9

• Hydrogenation of unsaturated vegetable oils to make them into saturated fats.

Question 10

Why do lipids contain more energy per gram than carbohydrates?

Answer 10

• There is a greater ratio of C-H bonds in fats compared to carbohydrates, the molecule can release more CO2 and H2O per mole when oxidised.

Question 11

The emulsion test

Answer 11

• Place 1cm of each solution into 3 seperate test tubes (Oil, water, milk)
• Add 2cm3 of ethanol to test tubes and shake thoroughly
• Add 2cm3 of water to test tubes and shake gently to mix and observe
• A positive test for lipids is cloudy solution and white emulsion in the test tubes.

Question 12

Phospholipids

Answer 12

• Are modified trigylcerides and contain the element phosphorus along with carbon, hydrogen and oxygen.
• Inorganic phosphate ions (PO4 3-) are found in the cyptoplasm of every cell
• Phosphate ions have extra electrons so are negatively charged, making them soluble in water.
• They are formed by one fatty acid being replaced by a molecule of phosphate. (look on pp for photo)

Question 13

Structure of phospholipids

Answer 13

• Look on pp for photo
• They have a non polar/hydrophobic tail and a polar/hydrophilic head

Question 14

Phospholipid bilayer

Answer 14

• Membranes are made out of a phospholipid bilayer
• The polar/hydrophilic head is in contact with the water and the hydrophobic tail is in the middle

Question 15

Phospholipids interacting with water

Answer 15

• They will form a layer on the surface of the water with phophate head in water and tail sticking out of water.
• Because of this they are called surface active agents or surfactants

Question 16

Glycolipids

Answer 16

• Membrane lipid with carbohydrate attached
• Often used for cell to cell recognition
• The carbohydrate is present on the extra cellular side of the cell membrane

Question 17

Sterols

Answer 17

• AKA steroid alcohols are another type of lipid found in cells, they are not fats or oils
• They are complex alcohol moleculesbased on a four carbon ring structure with a hydroxyl (OH) group at one end
• THe hydroxyl group is polar therefore hydrophillic and the rest of the molecule is hydrophobic.

Question 18

Cholesterol

Answer 18

• Is a sterol
• Manufactured primarily in the liver and intestines
• Important precurso for steroid hormones, fat soluble vitamins e.g. vitamin d, bile salts (helps emulsify fats in the small intestine).
• Important in formation of cell membranes as it is positioned between the phospholipids with the hydroxyl group at the periphery of the membrane. This adds to stability of the cell membrane and regulates their fluidity by keeping membranes fluid at low temperatures and stopping them from becoming too fluid at high temperatures.

Question 19

Biological roles of lipids

Answer 19

• Membrane formation and the creation of hydrophobic barriers.
• Hormone production
• Electrical insulation necessary for impulse transmission
• Waterproofing e.g. bird feathers

Question 20

Fats in our diet

Answer 20

• The presence of a double bond in unsaturated fats leads to a kink in the chain causing the lipid to be more liquid in nature
• Plants contain unsaturated triglycerides which normally occurs as oils
• Animals (generally not fish) contain saturated triglycerides or (solid) fats
• An unwanted product of the saturation of the hydrogenation is trans fats. These are unsaturated lipids in which the kinks that the double bonds naturally form have been reversed. They can increase the shelf life of products but are linked with coranary heart disease so are now usually removed from food.

Question 21

In triglyceride molecules, where are double bonds located?

Answer 21

within fatty acids only

Question 22

Cholesterol is essential for normal membrane functions because it:

Answer 22

regulates membrane fluidity

Question 23

What is the specific name for the process involving condensation reactions to create ester bonds called?

Answer 23

esterification