Protein Structure Flashcards
Definition of primary
Sequence of AA in peptide chain
Definition of secondary
Folding of chain into a helix/b pleated sheets
Definition of tertiary
Peptide chain folds upon itself
Definition of quaternary
Folded peptide chains joined together
Functional groups on amino acids
Amino
Carboxyl
Reactions between amino acids and dipeptides
Dehydration/synthesis
Acid hydrolysis
Properties of peptide bonds
Has characteristics of C=C However, C-N bond length shorter than expected, no rotation, trans groups Partial -ve on O Partial +ve on N HB can form between 2 polar AA
Direction of polypetides
NH3+ = N terminal COO- = C terminal
Covalent linkages, post translation modification
Disulphide bridges Cys-Cys
Glycosylation
Phosphorylation
Methylation via NH2 groups
How does glycosylation work
Sugars bind to OH of Thr, Her
Sugars bind tp NH2 of Asn
How does phosphorylation affect proteins
Cell signal transduction
Change in enzyme activity
How does methylation via NH2 groups affect proteins
Histones and gene expression
Properties of a helices
HB in same PP chain, not between side chains
HB formed between COOH, NH2 of every 4th peptide
RH helix
Turn stabilized by HB
R groups on outside
Rigid cylinder, support for protein
Properties of b pleated sheets
Linear peptide chains
HB between chains holds strands in B sheet
Side chains in each strand alternately lie above and below sheet plane
Properties of collagen triple helix
3 chains with HB between chains
LH helix
Gly, Pro, hydroxypro, repeated sections
Forces that stabilize protein structure
Covalent (disulphide bridges) HB IB LF Hydrophobic effects
How do HB work
2 delta -ve atoms compete for the same H atom
Between H and lone electron pair on O, N
How do IB work
Between charged side chains
Asp, Glu COO-
Arg, Lys NH3+
How do LF work
Sum of attractive/repulsive forces between molecules
Unequal distribution of electrons results in instantaneous dipoles
How do hydrophobic effects work
Fold in a way to minimize contact with water
Cannot form HB due to hydrophobic R groups
How to disrupt protein structure and function
pH
Temperature
Ionic strength
How are proteins folded
All proteins have different structures but only 1 is functional
Primary structure encodes pathway that leads to final structure which is most stable
What can misfiled proteins result in
Mutations can cause a protein to fold incorrectly
If not folded properly, stable protein aggregates can form
Neurological symptoms in Creutzfeldt Jakob disease
Walking difficulties Slurred speech Numbness Dizziness Visual problems
Psychological symptoms of Creutzfeldt Jakob disease
Severe depression Withdrawal Anxiety Irritability Insomnia
What happens to the normal prion proteins
Normal cellular prion proteins become pathogenic prion proteins
Pathogenic prions can form fibril aggregates
Compare the structures of prion proteins
PrPc
a helix, no b sheets
Susceptible to proteolysis
PrPsc
less a helix, b sheet present
Protease resistant
Both have the same AA sequence
