polypeptides Flashcards
is amide linkage formed by the reaction between α-carboxyl group of one amino acid and α-amino group of another amino acid with the elimination of water molecule
Peptide (peptide bond)
two amino acids are combined
Dipeptide
3 to 10 amino acids combined
Oligopeptide
> 10 amino acids combined
Polypeptide
300-1000 amino acids combined
Proteins
There are four levels of protein structure:
primary
secondary
tertiary
quarternary
linear sequence of amino acids
primary
regular patterns formed by primary structure folding
secondary
completely folded polypeptide with one or more domains
tertiary
association of multiple polypeptides; not found in all proteins
quaternary
The simplest level of protein structure is simply the amino acid sequence within a polypeptide chain.
the primary structure
Understanding the ??? is important because many genetic diseases results in protein with abnormal amino acid sequences
primary structure of proteins
is local interactions between stretches of a polypeptide chain and includes α-helix and β-pleated sheets structures.
Secondary structure
is primarily due to interactions between the R groups of amino acid which make up the protein.
The tertiary structure
R group interactions (4)
§ hydrogen bonding
§ ionic bonding
§ dipole-dipole interactions
§ London dispersion forces
are also important for the tertiary structure, in which amino acids with non-polar, hydrophobic R groups cluster together within the protein, leaving hydrophilic amino acids outside to interact with surrounding water molecules.
Hydrophobic interactions
One specific form of covalent bond may contribute to tertiary structure: the
disulfide bond
Many proteins however consist of several polypeptide chains, also known as ???
subunits
They give the protein its quaternary form, as these subunits come together.
subunits
One example of a ???
is hemoglobin.
quaternary-structured protein
In general, the same types of interactions that lead to tertiary structure also hold the
subunits together to give ???
quaternary structure
interactions that lead to tertiary structures are mostly ???
weak interactions,
such as hydrogen bonding and dispersion forces in London
??? protein structure;
??? bonding of the peptide backbone causes amino acids to fold into a ??? pattern
secondary;
hydrogen;
repeating
tertiary protein structure:
3-D folding pattern of a protein due to ??? interactions
side chain interactions
quaternary protein structure:
protein consisting of ?
more than one amino acid chain
refers to any disruption in the secondary, tertiary and quaternary levels of protein structure.
denaturation
in what protein structure does denaturation not occur?
primary protein structure
denaturation does not cleave the peptide bonds, therefore the ??? of structure is not altered.
primary level
The physical signs of protein denaturation are ??? and ???
precipitation and coagulation;
the most significant consequence of denaturation is ???
the loss of biological activity.
happens in many cases when denatured protein goes back to its native biologically active form.
Renaturation
Heat and UV radiation
this breaks the ??? bonds causing the folded structures of protein to ???
H-bonds;
uncoil or unwind into random loops
agent of denaturation:
form intermolecular H- bonds
with the protein
Organic solvents
agent of denaturation:
??? and ??? break salt linkages by altering the pH causing a change in the ionization pf ??? and ??? groups
Acids and bases;
-COOH and -NH2 groups.
agent of denaturation:
Prolonged contact with ??? and ??? will also cleave peptide bonds
acids and bases
agent of denaturation:
??? like Hg+2, Ag+, Pb2+ and their salts form stronger bonds with ??? of acidic amino acids.
It also cleaves the ??? bonds (ex. The use of egg albumin as antidote for heavy metal poisoning)
Heavy metals;
carboxylate ions;
-SH
agent of denaturation:
??? precipitate proteins by combining with ??? and disrupting ??? (ex. Use of tannic acid for tanningleather; picric acid and tea for treating burns)
Alkaloid reagents;
positively charged groups;
salt linkages
alkaloid reagents examples
picric acid and tannic acid
