lecture 4 - proteins Flashcards
Which polypeptide helix is more common? right-handed or left handed?
Right - handed
Why do polypeptide helices have a dipole moment?
C terminus = negative
N terminus = positive
Why don’t peptide bonds liked to be lined up with a 0 degree angle?
Don’t want a steric clash
What is the minimum number of polypeptide chains needed for a Beta pleated sheet?
2
Which Beta sheet is stronger? Anti - parallel or parallel?
Anti- Parallel
Do Beta sheets have a dipole moment ?
NO - due to the alternating planes which cancel each other out.
What are two very rare polypeptide chains?
Beta helices and Allpha - pleated sheets
What is a Beta turn?
Antiparallel sheets connected via a Beta turn
Primary structure
Amino acid sequence
Secondary structure
Regular, arrangement of the polypeptide chain
Tertiary structure
Complete fading of a single chain
Quaternary structure
association of multiple chains
How is the conformation stabilised?
Non - covalent interactions;
- Hydrogen bond
- Ionic interactions
- Hydrophobic interaction
- Van der Waals interaction
What are the roles of disulphide bonds (form of covalent bonds)
- covalent bonds between cysteine side chains
- ## no all proteins have cys residues
What environment can disulphide bonds form in?
Can only happen In an oxidising environment
What do disulphide bridges do in hair?
Cause a curl
What reducing agent is used to straighten hair/
ammonium thioglycolate
What oxidising agent is used to permanently curly hair?
Hydrogen peroxide
Do covalent bonds break under heat?
NO
The synthesis of insulin
- Synthesised as inactive precursor prepreinsulin
- pre - sequence removed
- proinsulin folds and and disulphides form - forms inactive precursor
- Activation involves removal of pro sequence
What are the experimental methods for study of proteins?
- purification
- determine amino acid sequence
- determine conformation
how to determine conformation
- X-ray crystallography / NMR
- Homology model if there is a closely related protein of a known structure
Column chromatography
- separations of soluble proteins based on differences in molecular characteristics
Gel filtration
separation depends on molecular charge
ion exchange
separation depends on molecular charge
Affinity chromatography
separation depends on specific binding interaction
