(03) ST: Protein Structure Flashcards
what is different about the 20 amino acids?
different side chains
determines properties and shapes
–> hydrophobic/hydrophilic
main functional groups on amino acids
amino group (-NH2)
carbonyl group (-COOH)
attached to central C called alpha carbon
chemistry of polymerisation
dehydration reaction: -COOH loses OH and NH2 loses an H, expelled as water
forms a peptide bond
what is the polymerisation reaction of amino acids to proteins catalysed by?
ribosomes (in the process of translation)
what is a primary structure
the sequence of an amino acid as encoded by the DNA
when it comes out of the ribosome as a linear polypeptide
what are the N and C-terminus of primary proteins?
N-terminus - the side of the primary structure that ends with the amino group
C-terminus - the side with the carboxyl group
usually read from N to C terminus
what is a “residue” on a polypeptide chain?
each monomeric unit is a residue because it is what is left over after the dehydration reaction
what are secondary protein structures
localised folding
alpha helix - backbone forms spiral shape with 3-4 amino acids per turn
beta sheets - the backbone extends one way and do a U-turn toward opposite directions and line up
what are alpha helices and beta sheets held together by?
multiple Hydrogen bonds
define tertiary protein structure
complete folding of the entire polypeptide
brings together sequences that are far apart
describe the hydrophobic effect in tertiary folding
the interaction of hydrophobic side chains with aq envrionment, burial in the interior of the protein
so the hydrophobic residues go inside while hydrophilic residues go on the outside
a key driver of protein folding!
name, describe and give examples of the two types of tertiary protein
Globular protein = compact, round blob (eg. alpha amylase in saliva)
Fibrous protein = long and spindly (eg. collagen, actin filaments)
describe quaternary structure
two or more polypeptide chains form a larger structure
each different chain = “subunit” - completely separate
not a required step
what forces maintain protein structures?
MULTIPLE WEAK BONDS:
Hydrogen bonds
ionic / electrostatic interactions (oppositely charged groups), forms salt bridge
hydrophobic interaction - the hydrophobic effect, can form a hydrophobic core (the weakest, but large numbers)
covalent: disulfate bond
processes and protein involved in the formation of a disulphate bridge
a strong covalent bond
CYSTEINE (Cys / C) = -CH2SH
under mild oxidising conditions, two Cys side chains are close together to form disulphide bridge
-CH2-S-S-CH2-
