3.1.3 & 3.1.4 Lipids and Properties of Proteins

Question 1

Structure of a triglyceride (2)

Answer 1

Glycerol molecule
3 fatty acids

Question 2

Structure of a phospholipid (3)

Answer 2

1 glycerol molecule
1 phosphate group (attached to glycerol)
2 fatty acid chains
The two fatty acids also bond to the glycerol via two condensation reactions bonded with two ester bonds

Question 3

How are triglycerides formed? (3)

Answer 3

Three condensation reactions between one molecule of glycerol and three molecules of fatty acid
( Not a polymer because it’s not many repeated units)

Question 4

In a triglyceride, how many water molecules are lost?

Answer 4

3

Question 5

In a triglyceride, how many condensation reactions occur?

Answer 5

3

Question 6

What is the bond formed in a triglyceride?

Answer 6

Ester bond (3 ester bonds)

Question 7

Fatty acids can either be?

Answer 7

Saturated or Unsaturated

Question 8

What is the structure of a saturated fatty acid?

Answer 8

The hydrocarbon chain has only single bonds between the carbons. It’s fully saturated holding the maximum amount of hydrogen

Question 9

What is the structure of an unsaturated fatty acid?

Answer 9

The hydrocarbon chain consists of at least one double bond between carbons

Question 10

Properties of triglycerides

Answer 10

• Energy storage- due to the large energy-storing carbon-hydrogen bonds compared to the carbon bonds, a lot of energy is stored in the molecule

• Act as a metabolic water source- due to the high ratio of hydrogen to oxygen atoms. Triglycerides can release water if they’re oxidised which is essential for animals in the desert e.g. camels

• Don’t affect water potential and osmosis- they’re large and hydrophobic, making them insoluble so repel water

• Lipids have a low mass. A lot can be stored without increasing that mass and preventing movement

Question 11

Properties of phospholipids

Answer 11

• Hydrophilic ‘head’ due to negative charge on phosphate group

• Attracts water and repels fats as it’s charged

• Fatty acid chain is not charged

• Known as the hydrophobic ‘tail’ and it repels water, but will mix with fats and other lipids

Question 12

Dipeptides

Answer 12

They are formed when two amino acids are joined by a condensation reaction where a water molecule is removed and forms a peptide bond

Question 13

Polypeptides

Answer 13

They are formed by the condensation of many amino acids that form multiple condensation reactions that are joined by peptide bonds

Question 14

What is the primary structure of a protein?

Answer 14

The order/sequence of the amino acids in the polypeptide chain- this is a polymer. The primary structure determines the location of the ionic,hydrogen and disulfide bonds in the tertiary structure.

(This is made straight after translation in protein synthesis)

Question 15

What is the secondary structure of a protein?

Answer 15

This is when the primary structure is folded or modified by twisting so we can have an alpha helix or a beta-pleated sheet that are held in place by hydrogen bonds.

The sequence of amino acids causes parts of a protein molecule to bend into an alpha helix shape or fold into beta-pleated sheets.

Question 16

What is the tertiary structure?

Answer 16

The tertiary structure is further folding and modifying the secondary structure to create a unique 3D shape and that shape is held in place by ionic, hydrogen and sometimes disulfide bonds.
The location of the bonds determined by the primary structure also determines how it folds and the 3D shape.

Question 17

What is the quaternary structure?

Answer 17

The quaternary structure is still the unique 3D shape with the same bonds but it’s a protein that is made up of more than one polypeptide chain.