BIOLOGICAL MOLECULES - lipids

Question 1

describe how to test for lipids in a sample?

Answer 1

1. take a completely dry and grease free test tube
2. to 2cm^3 of sample being tested, add 5cm^3 of ethanol
3. shake the tube thorougly and dissolve any lipid in the sample
4. add 5cm^3 of water and shake gently
5. a milky white emulsion indicates the presence of a lipid
6. as a control, repeat the procedure using water instead of the sample; the final solution should remain clear.

Question 2

How do triglycerides form?

Answer 2

they are formed by the condensation reaction between 1 molecule of glycerol and 3 fatty acids, forming ester bonds

Question 3

are lipids soluble in water?

Answer 3

they are insoluble in water

Question 4

what are lipids soluble in?

Answer 4

organic solvents such as alcohol and acetone

Question 5

what are the properties of triglycerides?

Answer 5

high ratio of energy storing carbon-hydrogen bonds to carbon atoms and therefore an excellent source of energy.
they have low mass to energy ratio, making them good storage molecules because much energy can be stored in small volume.

being large , non polar molecules, triglycerides are insoluble in water.As a result their storage does not affect osmosis in cells or the water potential of them.

due to the high ratio of hydrogen to oxygen atoms, triglycerides release water when oxidised and therefore provide an important source of water, especially for organisms living indry deserts.

Question 6

what are R-groups?

Answer 6

fatty acids (can be saturated or unsaturated)

Question 7

contrast the saturated and unsaturated fats?

Answer 7

saturated fats:
- contain only single bonds
-straight chain molecules
-higher MP = solid at room temperature
- found in animal fats

unsaturated fats:
- contain C=C double bonds
- lower melting point = liquid at room temperature
- found in plant oils

Question 8

describe the structure and function of phospholipids?

Answer 8

a glycerol backbone attached to 2 hydrophobic fatty acid tails and one hydrophilic polar phosphate head.

Question 9

what does ‘hydrophilic head’ mean?

Answer 9

attracted to water

Question 10

what does ‘hydrophobic tail’ mean?

Answer 10

repels water but mixes readily with fat

Question 11

what happens when phospholipid molecule is placed in water?

Answer 11

They position themselves so that the hydrophilic heads are close to the water as possible and the hydrophobic tails are as far away from the water as possible.

Question 12

how is the structure of phospholipids related to their properties?

Answer 12

• they are polar molecules, which means in an aqueous environment, phospholipid molecules form a bilayer within cell-surface membranes. As a result a hydrophilic barrier is formed between the inside and outside of the cell.
• the hydrophilic phosphate heads help to hold at the surface of the cell-surface membrane
• phospholipid structure allows them to form glycolipids combining with carbohydrates within the cell-surface membrane. glycolipids are important in cell recognition.

Question 13

what are the similarities of phospholipids and triglycerides?

Answer 13

• both have a glycerol backbone

-both may be attached to a mixture of saturated, monounsaturated, polyunsaturated fatty acids.

• both contain elements C,H,O
• both formed by condensation reactions.

Question 14

what are the differences between phospholipids and triglycerides?

Answer 14

PHOSPHOLIPIDS:
- 2 fatty acids + 1 phosphate group attached
- hydrophilic head and hydrophobic tail
- used primarily in membrane formation

TRIGLYCERIDES:
- 3 fatty acids attached
- entire molecule is hydrophobic
- used for storage ( oxidation releases energy)

Question 15

Are phospholipids and triglycerides polymers?

Answer 15

NO they are not made from small repeating units. They are macromolecules