Polypeptides (proteins) Flashcards
label an amino acid.
Carboxylic group (-COOH)
Amino group (-NH2)
One of 20 different ‘R groups’
Many amino acid (monomers) can be bonded together to form a polypeptide (polymer)
Explain the formation of a dipeptide.
2 amino acid molecules.
Condensation reaction.
Between the -COOH group of one amino acid and the -NH2 group of another.
A water molecule is released.
Forming PEPTIDE bond.
Name the four types of amino acid R-groups.
Ionic (+ or -)
Cysteine (-S)
Hydrogen bonding (-OH ….)
Hydrophobic (-CH3)
Primary structure
the sequence / order of amino acids in a polypeptide chain
Secondary structure
localised folding forming alpha helix / beta pleated sheet, stabilised be hydrogen bonding between the peptide bonds in the chain
Tertiary structure
precise 3D shape of a single polypeptide, stabilised by R-group interactions (i.e. hydrogen bonding, disulphide links, ionic interactions, hydrophobic interactions)
Quaternary structure
2 or more polypeptides bonded together (R - group interaction)
Explain the formation of a disulphide bond.
STRONG, COVALENT bond.
Between the R-groups…
… of 2 CYSTEINE amino acids
the food test for proteins.
Add Biuret reagent I (copper sulfate solution)
Add Biuret II (dilute sodium hydroxide solution)
Colour change from light blue to purple
What are the key features of globular proteins like haemoglobin
- Polypeptide chains form a - spherical shape.
- Often soluble
- Hydrophilic R groups on the outside, hydrophobic on the inside
- Sensitive to temperature and pH changes
What are the key features of fibrous proteins like collagen
Polypeptide chains are parallel
Tensile with a structural role
