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
