Biological Molecules A2 Flashcards
(25 cards)
Define monomer
Smaller units that join together to form larger units
Give some examples of a monomer
•Monosaccharides (glucose, fructose, galactose)
•Amino acids
•Nucleotides
Define polymer
Molecules formed when many monomers join together
Give some examples of a polymer
•Polysaccharides
•Proteins
•DNA/RNA
What happens in a condensation reaction?
A chemical bond forms between 2 molecules & a molecule of water is produced
What happens in a hydrolysis reaction?
A water molecule is used to break a chemical bond between 2 molecules
Name the 3 hexose monosaccharides
•Glucose
•Fructose
•Galactose
All have the molecular formula C6H12O6
Name the type of bond formed when monosaccharides react
(1,4 or 1,6) glycosidic bond
2 Monomers = 1 chemical bond = disaccharide
Multiple monomers = many chemical bonds = polysaccharide
Name 3 disaccharides. Describe how they form
Condensation reaction forms glycosidic bond between 2 monosaccharides
•Maltose: glucose+glucose
•Sucrose: glucose+fructose
•Lactose: glucose+galactose
All have molecular formula C12H12O11
Describe the structure of starch
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
Describe the function of starch
Storage polymer of alpha glucose in plant cells
•insoluble=no osmotic effect on cells
•large=does not diffuse out of cells
Describe the structure of glycogen
•1,4 and 1,6 glycosidic bonds
•Branched=many terminal ends for hydrolysis
•Insoluble=no osmotic effect & does not diffuse out of cells
•Compact
Describe the function of glycogen
Main storage polymer of alpha glucose in animal cells (but also found in plant cells)
Describe the structure of cellulose
•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
Describe the function of cellulose
Polymer of beta glucose gives rigidity to plant cell walls (prevents bursting under turgor pressure, holds stem up)
Describe the Benedict’s test for reducing sugars
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
Describe the Benedict’s test for non-reducing sugars
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
Describe the test for starch
1.Add iodine solution
2.Positive result:Colour change from orange to blue-black
Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch
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
Describe how to test for lipids in a sample
1.Dissolve solid samples in ethanol
2.Add an equal volume of water and shake
3.Positive result:milky white emulsion forms
How do triglycerides form?
Condensation reaction between 1 molecule of glycerol and 3 fatty acids form ester bonds
Contrast saturated and unsaturated fatty acids
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
Relate the structure of triglycerides to their functions
•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
Describe the structure of phospholipids
Amphipathic molecule: glycerol backbone attached to 2 hydrophobic fatty acid tails and 1 hydrophilic polar phosphate head
