Peptides 1 & 2 Flashcards
What does it mean that amino acids are amphoteric?
Accept or donate H+
How many different R groups is there?
20
Describe non-polar, neutral amino acids?
No charge or electronegative atoms to form H bonds
Not soluble in H2O
Glycine unique = achiral
Proline unique = cyclic
Describe polar, neutral amino acids
Partial charges = form H bonds
Soluble in H2O
Describe charged amino acids
Charged side chains = form H bonds + ionic bonds
Very soluble in H2O
Describe chirality of amino acids
α-C in all amino acids = chiral
EXCEPT glycine
Where are L amino acids found?
Proteins
What do most L amino acids have?
Absolute configuration of S
What does zwitterionic character help to calculate?
pI
How do you calculate pI?
Draw out reaction charges Then find neutral species Then add pKa of molecule either side of species The divide by 2 = pI
How can amino acids be separated?
pI separation by electrophoresis
By polarity-chromatography
Ion exchange chromatography
How can amino acids be synthesised?
From α-halo acids
Strecker synthesis
Describe synthesise from α-halo acids
Carboxylic acid + Br2, Pbr3, H2O —-> RBrCHCOOH + excess NH3 —-> amino acid
Describe strecker synthesis
Aldehyde + trace acid, NH3 —-> imine + CN, HCl —-> RCHNH3CN + HCl, H2O —-> amino acid
Describe synthesis of peptide
Carboxyl group + amino group —-> Amino acid with peptide bond
Describe peptide bonds
Stabilised by resonance
e- shared unequally = greater density at O
Describe synthesis of Gly-Ala
Protect N in glycine
Activate carbonyl group
Solid phase synthesis
What happens in solid phase synthesis of Gly-Ala?
Use resin to attach to 1st amino acid
Deprotect N
Add to activated amino acid
Then cleave resin + BOC
What is a peptide?
Fewer than 50 amino acids
What is a protein?
One or more peptides arranged in biologically functional way
Describe primary structure
Determined by mRNA
Can use cleavage agents to determine sequence
Describe secondary structure
H bonding between peptide
Alpha helix or beta sheet
Describe alpha helix
Narrow tube coiled in right hand sequence
H bonds run parallel to helix
Proline interrupts helix = sharp kink
Describe beta sheets
2 or more lengths of polypeptide chains lie parallel to each other
R groups point above + below sheet
BUT C=O + NH point towards each other
H bonds between sections
What is the Ramachadron plot?
A way to visualise angles of amino acids in protein structure
Describe tertiary structure
Interactions between R groups of amino acids
Produce other folds/interactions to give final geometric shape
What are the 4 types of interactions that give rise to tertiary structure?
Ionic bonds
H bonds
Hydrophobic interactions
Disulphide bridges (covalent)
How is a disulphide formed?
1
Mild oxidation
Thiol —-> disulphide
How is a disulphide formed?
2
Reduction
Disulphide —-> thiol
Describe quaternary structure
Not present in all proteins 2 or more polypeptide chains interact with each other Can include inorganic groups Forces between chains = same as tertiary Fibrous or globular
Is denaturation irreversible or reversible?
Can be either
Why do proteins fold the way thy do?
Energetically favourable
What happens of you have a loss of structure?
Loss of activity
