Lipids and Proteins

Question 1

Draw/describe the basic structure of a triglyceride?

Answer 1

One glycerol molecule attached to three fatty acids in a E shape

Question 2

Describe how the structure of a protein depends on the amino acids it contains (6 marking points)

Answer 2

• the structure of a protein is determined by the position of amino acids/ ionic bonds/ hydrogen bonds/R groups
• the primary structure is the sequence of a/a
• the secondary structure is formed by H bonds: Alpha helix and Beta pleated sheets
• tertiary structure is caused by interactions between a/a
• this determines the specific shape of the protein, e.g// enzyme’s active site, complementary shape of antibodies to receptors
• the Quaternary structure involves multiple polypeptide chains joined together

Question 3

Give 5 functions of lipids (phospholipids and triglycerides)?

Answer 3

• Energy source; when oxidised they release up to 2x the amount of energy than CHOs
• Insulation; for example myelin, which helps nerve signals travel
• Protection; surround and protect vital organs
• Cell membranes; phospholipids make up cell membranes
• Waterproofing; waxy cuticle and glands in skin

Question 4

How is a triglyceride formed?

Answer 4

• One glycerol molecule reacts with 3 fatty acids
• condensation reaction (releases water)
• ester bonds are formed

Question 5

What properties of triglycerides make them suited for their function?

Answer 5

• Insoluble in water (non-polar); so does not impact the water potential of cells
• High ratio of O to H atoms; release water when oxidised - good for organisms in dry
• High ratio of energy storing C-H bonds; good source of energy
• low mass:energy ratio; lots can be stored in a smaller mass, reduces the mass animals have to carry

Question 6

What 2 functional groups are involved in the formation of peptide bonds?

Answer 6

COOH on one a/a and NH2 on the other

Question 7

What two elements is a peptide bond between?

Answer 7

C-N

Question 8

What 3 types of bond can be formed in the tertiary structure of a protein?

Answer 8

• Hydrogen bonds
• disulfide bridges
• ionic bonds

Question 9

Describe a test that could be carried out to confirm the presence of lipids. Include a positive result

Answer 9

• add ethanol to sample
• add water and shake
• white emulsion will form if lipids are present

Question 10

Describe a test that could be carried out to confirm the presence of proteins. Include a positive result

Answer 10

• add sample to test tube and add equal volume NaOH
  -add a few drops of dilute copper (II) solution
• if proteins are present, turns from blue to violet

Question 11

How are phospholipids arranged in a cell membrane?

Answer 11

• form a bilayer
• hydrophobic tails facing inwards, away from water
• hydrophilic heads face outwards, towards water
• this way the hydrophobic heads have minimal contact with water

Question 12

How are phospholipids suited for their function?

Answer 12

• hydrophobic tails; prevent water soluble substances from moving in/out of the cell
• hydrophilic heads and hydrophobic tails mean a bilayer is formed

Question 13

Give 4 functions of proteins

Answer 13

• transport proteins
• enzymes
• antibodies
• structural proteins