Testing for biological molecules
Carbohydrates
Triglycerides
Phospholipids and Water
Proteins
100

Why is Benedicts test on reducing sugars called "semi quanititative?"

  • This test is semi-quantitative as the degree of the colour change can give an indication of how much (the concentration of) reducing sugar present
100

What are the three main types of carbohydrate?

Monosaccharide, disaccharide, polysaccharide

100

What are common properties of all lipids?

Non polar and hydrophobic

100

Describe the structure of a phospholipid

  •  monomer: glycerol and fatty acids
  • Two fatty acids bonded to a glycerol molecule in a phospholipid as one has been replaced by a phosphate ion (PO43-)
100

What sort of bond, in what sort of reaction, joins protein monomers into a polymer?

Amino acids are joined by peptide bonds in a condensation reaction. 

200

How do we test for non reducing sugars?

Add dilute HCl to the sample and heat in a water bath which has been bought to boiling.
Neutralise the solution with sodium hydrogencarbonate
Use an indicator to find the neutralisation point then add slightly more sodium hydrogen carbonate to create alkaline conditions
Add benedicts reagent
Put solution in a water bath, boiling, for 5 minutes
If a colour change to orange or red - non reducing sugar present

200

What are the two most common forms of the main monomer of carbohydrates? Describe their difference

Alpha and Beta glucose

In alpha - OH on C1 is below the ring
In beta - OH on C1 is above the ring

200

What are the monomers of triglyceride?
Describe their structure

Fatty acid and glycerol

  • Glycerol is an alcohol (an organic molecule that contains a hydroxyl group bonded to a carbon atom)
  • Fatty acids contain a methyl group at one end of a hydrocarbon chain (chains of hydrogens bonded to carbon atoms, typically 4 to 24 carbons long) and at the other is a carboxyl group
200

Phospholipids are amphipathic, what does this mean?

  • As the phosphate is polar it is soluble in water (hydrophilic)
  • The fatty acid ‘tails’ are non-polar and therefore insoluble in water (hydrophobic)
200

What is the primary level of protein structure?

  • The sequence of amino acids bonded by covalent peptide bonds is the primary structure of a protein
300

Which common sugars are non reducing?

sucrose

300

Which isomers of glucose are found in starch, glycogen and cellulose?

Alpha - starch and glycogen
Beta - cellulose

300

What sort of reaction creates a triglyceride and what sort of bond is formed?

Esterification, ester bond

300

What sort of bonding is found WITHIN a water molecule?

covalent bonding

300

What sort of interactions are found in the tertiary level of protein structure?

Weak hydrophobic interaction, disulphide bond, hydrogen bonds, ionic bonds

400

Describe the ethanol emulsion test for lipids

Add ethanol to the food sample.

Shake

Decant mixture into a test tube of water

If a cloudy layer forms on top, lipids are present

400

What is the bond found in polysaccharides and disaccharides, and what sort of reaction forms it?
Where is it found in cellulose?

Glycosidic
Condensation reaction 

1,4 glycosidic bond 

Carbon 1- carbon 4 of next molecule

400

Give 4 functions of triglycerides

Energy storage, insulation, protection, buoyancy 

400

What are the key properties of water which make it essential for life?

  • An excellent solvent – many substances can dissolve in water
  • A relatively high specific heat capacity
  • A relatively high latent heat of vaporisation
  • Water is less dense when a solid
  • Water has high surface tension and cohesion
  • It acts as a reagent
400

What is the general formula for an amino acid?

  • The general structure of all amino acids is a central carbon atom bonded to:
    • An amine group -NH2
    • A carboxylic acid group -COOH
    • A hydrogen atom
    • An R group (which is how each amino acid differs and why amino acid properties differ e.g. whether they are acidic or basic or whether they are polar or non-polar)
500

What reduction reaction happens in the benedicts test?

Copper sulfate (II) is reduced to copper oxide (I)

500

Describe the bonding and shape in amylose
How does its shape aid its function?

  • Amylose (10 - 30% of starch)
    • Unbranched helix-shaped chain with 1,4 glycosidic bonds between α-glucose molecules
    • The helix shape enables it to be more compact and thus it is more resistant to digestion
500

Why are triglycerides suitable for energy storage?

  • The long hydrocarbon chains contain many carbon-hydrogen bonds with little oxygen (triglycerides are highly reduced)
    • So when triglycerides are oxidised during cellular respiration this causes these bonds to break releasing energy used to produce ATP
500

Where do the hydrogen bonds form between water molecules?

oxygen of one water molecule to the hydrogen atom of another).

500

Compare globular and fibrous proteins, with an example for each

Globular - Heamoglobin, 

Spherical, irregular amino acid sequence, physiological/functional, soluble in water

Fibrous - collagen,
Long strands, repetitive amino acid sequence, structural, insoluble in water

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