Study Set Content:
For example, for aspartic acid, the neutral form is dominant between pH 1.88 and 3.65, pI is halfway between these two values, i.e. pI = 1/2 (pKa1 + pKa3 ), so pI =
2.77
The pI will be at a (blank) pH because the basic side chain introduces an "extra" positive charge. So the neutral form exists under more basic conditions when the extra positive has been neutralized.
higher
For example, for histidine, the neutral form is dominant between pH
6.00 and 9.17
For example, for histidine, the neutral form is dominant between pH 6.00 and 9.17, pI is halfway between these two values, i.e. pI = 1/2 (pKa2 + pKa3), so pI =
7.59
Neutral side chains
pI= pKa1 + pKa2 / 2
Acidic side chains
pI= pKa1 + pKa3 / 2
Basic side chains
pI= pKa2 + pKa3 / 2
Formation of a peptide bond
hydrolysis and dehydration of amino acid 1 and 2 yields protein
• By far the most important of all biological compounds
PROTEINS
proteins comes from the Greek word
“proteios
comes from the Greek word “proteios”, which means
of first importance”.
• Proteins are naturally occurring, unbranched polymer in which the monomer units are amino acids linked together by
peptide bonds
All proteins contain the elements
Carbon, Hydrogen, Oxygen and Nitrogen; most also contain Sulfur
Functions of Proteins
structure
catalysis
movement
transport
hormones
protection
storage
regulation
collagen and keratin are the chief constituents of skin, bones, hair, and nails
Structure:
muscle proteins, actin and myosin
Movement
biological catalysts called Enzymes
Catalysis
Hemoglobin, a protein in the blood, carries oxygen from the lungs to the cells in which it is used and carbon dioxide from the cells to the lungs
Transport:
chemical messengers that control and coordinate activities throughout the body (insulin, erythropoietin, and human growth hormone)
Hormones
casein in milk and ovalbumin in eggs store nutrients for newborn mammals and birds, Ferritin, a protein in the liver, stores iron
Storage
