Amino Acids and proteins/ Protein Structure Flashcards
What are the special properties of a peptide bond?
The C-N bond is shorter than expected.
There is no rotation around the C-N bond
+ trans arrangement
Partial positive charge on the N and a partial negative charge on the O.
What groups are found at either end of a polypeptide chain?
-NH3+ or COO-
What amino acid allows disulphide bridges to develop?
Cysteine.
What are the two types of glycosylation?
O-linked glycosylation of the -OH group in thr and ser; and N-linked glycosylation of the -NH2 of asn.
What are the levels of protein structure?
Primary = sequence of aa's Secondary = helices + sheets Tertiary = peptide folds back on and bonds with itself Quaternary = more than one peptide chain bonding together
Describe a-helices
Formed by H-bonds between the O in the carbonyl group and the H of the amino group of every fourth peptide.
Helices are regular right handed helices with 3.6 residues per turn.
R groups face to the outside of the helix.
Describe B-pleated sheets
Linear polypeptide chains bonded together by H-bonds, R groups alternate between being on top of and below to plane.
Can be parallel or antiparallel;
proteins with a large proportion of sheets have a good tensile strength but poor elasticity.
What is a supersecondary structure?
A combination of helices and sheets
What are the forces/bonds that give rise to the structure of a protein?
Disulphide bridges; H-bonds; electrostatic attractions; hydrophobic interactions; van der Waals forces
In which aa’s can side groups be ionised, so that electrostatic attractions can be formed between their charged side groups?
Carboxyl group ionised to COO- in asp and glu
Amino group ionised to NH3+ in lys and arg
What are 3 diseases that are caused by the misfolding of proteins?
Sickle cell anaemia; v.CJD; Alzheimers.
What happens in the formation of the prions that cause v.CJD?
Some a-helices are removed, and some B-sheets are added; this forms a prion which is protease resistant (can’t be hydrolysed/broken down) which then builds up in nervous tissue.
What amino acids can by methylated?
Arg lys
