Biological Molecules A2

Question 1

Define monomer

Answer 1

Smaller units that join together to form larger units

Question 2

Give some examples of a monomer

Answer 2

•Monosaccharides (glucose, fructose, galactose)
•Amino acids
•Nucleotides

Question 3

Define polymer

Answer 3

Molecules formed when many monomers join together

Question 4

Give some examples of a polymer

Answer 4

•Polysaccharides
•Proteins
•DNA/RNA

Question 5

What happens in a condensation reaction?

Answer 5

A chemical bond forms between 2 molecules & a molecule of water is produced

Question 6

What happens in a hydrolysis reaction?

Answer 6

A water molecule is used to break a chemical bond between 2 molecules

Question 7

Name the 3 hexose monosaccharides

Answer 7

•Glucose
•Fructose
•Galactose
All have the molecular formula C6H12O6

Question 8

Name the type of bond formed when monosaccharides react

Answer 8

(1,4 or 1,6) glycosidic bond
2 Monomers = 1 chemical bond = disaccharide
Multiple monomers = many chemical bonds = polysaccharide

Question 9

Name 3 disaccharides. Describe how they form

Answer 9

Condensation reaction forms glycosidic bond between 2 monosaccharides
•Maltose: glucose+glucose
•Sucrose: glucose+fructose
•Lactose: glucose+galactose
All have molecular formula C12H12O11

Question 10

Describe the structure of starch

Answer 10

Made from amylose & amylopectin
•Amylose:1,4 glycosidic bonds, helix with intermolecular H-bonds=compact
•Amylopectin:1,4&1,6 glycosidic bonds branched=many terminal ends for hydrolysis into glucose

Question 11

Describe the function of starch

Answer 11

Storage polymer of alpha glucose in plant cells
•insoluble=no osmotic effect on cells
•large=does not diffuse out of cells

Question 12

Describe the structure of glycogen

Answer 12

•1,4 and 1,6 glycosidic bonds
•Branched=many terminal ends for hydrolysis
•Insoluble=no osmotic effect & does not diffuse out of cells
•Compact

Question 13

Describe the function of glycogen

Answer 13

Main storage polymer of alpha glucose in animal cells (but also found in plant cells)

Question 14

Describe the structure of cellulose

Answer 14

•1,4 glycosidic bonds
•Straight-chain, unbranched molecule
•Alternate glucose molecules are rotated 180°
•H-bonds crosslinks between parallel strands from microfibrils=high tensile strength

Question 15

Describe the function of cellulose

Answer 15

Polymer of beta glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up)

Question 16

Describe the Benedict’s test for reducing sugars

Answer 16

1.Add an equal volume of Benedict’s reagent to a sample
2.Heat the mixture in an electric water bath at 100°C for 5 minutes
3.Positive result: colour change from blue to orange & brick red ppt forms

Question 17

Describe the Benedict’s test for non-reducing sugars

Answer 17

1.Negative result: Benedict’s reagent remains blue
2.Hydrolyse non-reducing sugars eg sucrose into their monomers by adding 1cm^3 of HCL.Heat in a boiling water bath for 5 minutes
3.Neutralise the mixture using sodium carbonate solution
4.Proceed with Benedict’s as usual

Question 18

Describe the test for starch

Answer 18

1.Add iodine solution
2.Positive result:Colour change from orange to blue-black

Question 19

Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch

Answer 19

1.Make standard solutions with known concentrations.Record absorbance or % transmission values
2.Plot calibration curve:Absorbance or % transmission values (y-axis), concentration (x-axis)
3.Record absorbance or % transmission values of unknown samples.Use calibration curve to read off concentration

Question 20

Describe how to test for lipids in a sample

Answer 20

1.Dissolve solid samples in ethanol
2.Add an equal volume of water and shake
3.Positive result:milky white emulsion forms

Question 21

How do triglycerides form?

Answer 21

Condensation reaction between 1 molecule of glycerol and 3 fatty acids form ester bonds

Question 22

Contrast saturated and unsaturated fatty acids

Answer 22

Saturated: •Contains only single bonds
•Straight-chain molecules have many contact points
•Higher melting point=solid at room temperature
•Found in animal fats

Unsaturated:•Contain C=C double bonds
•’Kinked’ molecules have fewer contact points
•Lower melting point=liquid at room temperature
•Found in plant cells

Question 23

Relate the structure of triglycerides to their functions

Answer 23

•High energy:Mass ratio=High calorific value from oxidation (energy storage)
•Insoluble hydrocarbon chain=No effect on water potential of cells and used for waterproofing
•Slow conductor of heat=Thermal insulation e.g adipose tissue
•Less dense than water=Buoyancy of aquatic animals

Question 24

Describe the structure of phospholipids

Answer 24

Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head

Question 25

Describe the function of phospholipids

Answer 25

•Forms phospholipid bilayer in water= component of membranes
•Tails can splay outwards = waterproofing