Lipids and Proteins Flashcards
Proteins
Formed from the monomer Amino Acid
Amino Acids contain An Amine Group (NH2), Carboxylic Group (-COOH) and a variable R group
There are 20 different amino acids. The type of amino acid is determined by the R group.
Forming a Dipeptide
A dipeptide forms when 2 or more amino acids join together in a condensation reaction. A peptide bond forms between the amino acids. Water is produced/released.
Primary structure of a protein
The primary structure of a protein is the order and number of amino acids in a protein
The secondary structure of a protein
The secondary structure is the shape that the chain of amino acids makes - either an alpha helix or beta pleated sheet
The hydrogen in the -NH has a slight positive charge whilst the oxygen in the -C-O has a slight negative charge. As a result weak hydrogen bonds can form.
The tertiary structure of a protein
The tertiary structure of a protein is the 3D shape which is formed from further twisting and folding
There are different bonds:
Disulphide Bonds - Interactions between the sulphur in the R group of amino acid “cystine” - strong and not easily broken
Ionic Bonds - Form between the carboxyl and amine groups that are not involved in the peptide bond. Easily broken by pH
Hydrogen bonds - hydrophobic, weak bonds between non-polar R groups
Biuret Test - Test for proteins
Place a small amount of extract in a labelled test tube
Add a few drops of sodium hydroxide to make it alkaline, add a few drops of copper sulphate
The colour change is blue to violet if protein is present
Tryclicerides
Made of one molecule of glycerol and three fatty acids, joined by ester bonds in a condensation reaction
Can be either saturated/unsaturated
Triglycerides are not a polymer - They are not made up of the same repeating unit
Fatty acids contain between 14-22 C atoms
Phospholipids
One of the fatty acids replaced by a phosphate group
The phosphate group has a negative charge (polar) whereas the fatty acid and tails are non-polar
This makes the phospho-glycerol head hydrophilic and the fatty acid tails hydrophobic
Difference between hydrophobic and hydrophilic
Hydrophylic - Attracts water, soluble
Hydrophobic - Repels water, soluble
Difference between hydrophobic and hydrophilic
Hydrophylic - Attracts water, soluble
Hydrophobic - Repels water, soluble
Emulsion test for a lipid
Place a small amount of a sample in a test tube with 2cm^3 of ethanol
Shake mixture so fat dissolves
Water added dropwise, shaken again
A white or cloudy emulsion indicates a positive result
