Lipids

What are lipids

What are lipids

a diverse group of non-polar molecules that contain carbon, hydrogen and oxygen.

What solvents do lipids dissolve in

Non-polar solvents, such as alcohol, (does not include water-a polar solvent).

What are fatty acids

A carboxylic acid with a long, non-polar hydrocarbon tail.

What is the difference between saturated and unsaturated fatty acids

Saturated fatty acids only have single C-C bonds in the hydrocarbon tail giving a straight tail. Unsaturated fatty acids have at least on double or triple C-C bond in the hydrocarbon tail giving a bent tail.

What are essential fatty acids

Fatty acids that must be included in the diet since they cannot be synthesised by the body.

What are triglycerides

3 fatty acids and glycerol

How are triglycerides formed

In a condensation reaction between glycerol and 3 fatty acids (may be the same or different). Forming one molecule of a triglyceride releases 3 water molecules.

What is the bond between a glycerol and a fatty acid called and how many are there in triglycerides

An ester bond. There are 3 in triglycerides.

what do animals and plants store triglycerides as

animals store them as fats while plants store them as oils

What is the difference between fats and oils

In fats, most of the fatty acids are saturated meaning the triglyceride is solid at room temperature (as the triglycerides can pack more closely to each other). In oils, most of the fatty acids are unsaturated meaning the triglyceride is liquid at room temperature.

Roles of triglycerides

• Energy store: Important, high energy stores and are insoluble so can be stored in cells. They are found in the adipose tissue in mammals and in seeds and fruits in plants.

• Thermal insulation: Insulating layer beneath the skin reduces heat loss.

• Buoyancy: Fats are less dense than water e.g. blubber in whales.

• Shock absorber: Deposited around vital organs to protect the from impact.

What enzymes hydrolyse triglycerides

lipases

How are triglycerides energy stores

The fatty acids contain many C-H bonds that can be broken to release energy to produce ATP.

What is the aerobic respiration of fatty acids an important source of

metabolic water

How are triglycerides and most other lipids transported in the blood

As lipoproteins as they are non-polar and insoluble in water so they are complexed with proteins that are soluble for transport in the plasma.

What are phospholipids

A glycerol bonded to 2 fatty acids by ester bonds and a phosphate group.

What is the hydrophilic region of a phospholipid

The polar, phosphate-containing head

What is the hydrophobic region of a phospholipid

The non-polar fatty acid tails.

In water, what 3 structures can phospholipids arrange themselves in

liposome (circular bilayer), micelle, or bilayer

Why do phospholipids form these structures

The polar heads interact with water to face outwards, while the non-polar tails interact with each other to face inwards or towards each other to exclude water.

What forms the structural basis of all biological membranes

The phospholipid bilayer

How can phospholipids be modified

By the addition of a small organic molecule to the phosphate group or in glycolipids, the phosphate group is replaced with a carbohydrate chain.

What is cholesterol

A small non-polar molecule with 4 carbon-based rings and a single polar OH group at one end.

Role of cholesterol

• Helps regulate the fluidity of membranes by preventing it from becoming too fluid or too solid.

• Cholesterol is also used in the synthesis of the steroid hormones e.g. testosterone, and oestrogen

Why is excess cholesterol in humans a problem

• It may be deposited in the walls of blood vessels leading to atherosclerosis (narrowing of artery).

• Also, excess cholesterol in bile may lead to gall stones in the gall bladder.

Where a receptors for steroid hormones usually found and why that location

In the cytoplasm as they are small and hydrophobic so can easily pass through the hydrophobic part of the plasma membrane.