Peptides 1+2 Flashcards
Describe features of amino acids.
- They are amphoteric
- They can accept or donate a proton (act as an acid or base) - depends on the pH of its surroundings
- Its charge will change at different pH
How do the 20 different R groups vary?
- size
- shape
- hydrogen bonding capacity
- Hydrophobic character
- Chemical reactivity
Describe non-polar, neutral amino acids.
- No charge or electronegative atoms to form hydrogen bonds
- Not soluble in water
Describe polar, neutral amino acids.
- Partial charges so can form hydrogen bonds
- Soluble in water
Describe charged amino acids.
- Charged side chains so can form hydrogen and ionic bonds
- Very soluble in water
Describe the properties of amino acids.
- Chirality: the alpha-carbon in all amino acids apart from glycine is chiral
- Zwitterionic character
Which amino acids are found in proteins?
- L amino acids
- Most L amino acids have an absolute configuration of S
How can we separate amino acids?
- pH separation by electrophoresis
- By polarity: chromatography
- Ion exchange chromatography
How are peptide bonds formed?
- Condensation reaction between a carboxyl group and an amino group forming a peptide bond
- Peptide bonds are resonance stabilised;
- Electrons are shared unequally, greater electron density on the oxygen
- With orbital overlap imparting partial double bond character to the amide bond
Describe the difference between peptides and proteins.
- Peptides have fewer than 50 amino acid residues
- Proteins consist of one or more peptides arranged in a biologically functional way e..g insulin
What is the primary structure?
Sequence of amino acids
What is the secondary structure?
Hydrogen bonding between peptide groups leads to organised structures within the peptide chain - alpha-helix and beta pleated sheets.
Describe alpha helix.
A narrow tube, coiled in a right hand spiral
Hydrogen bonds between the C=O of one peptide and the NH of another peptide group 4 units ahead in the primary structure
H bonds run parallel to the helix, within one polypeptide chain.
Proline group will interrupt the helix producing a sharp kink due to its cyclic structure.
Describe beta-sheets.
2 or more lengths of the polypeptide chain lie parallel to each other
R groups of the amino acids point above and below the sheets, while the NH and C=O parts of the peptide bond point towards each other
H-bonds between these sections
Describe tertiary structure.
Interactions between the R-groups of the amino acids.
Produce other folds/interactions to give a final geometric shape = tertiary structure
