Download Chapter 11 Protein

Chapter 11 Protein
• Proteins are mainly composed of the
elements carbon, hydrogen, oxygen, and
nitrogen
• Proteins are made up of subunits called
organic acids which contain carboxyl
groups (-COOH)
• Organic acids in proteins are called amino
acids
Amino Acids
• Amino acids have three parts to their
structure; a side chain of carbon and
hydrogen atoms, a carboxyl group, and an
amine group.
• An amine group contains one nitrogen and
two hydrogen atoms, (-NH2)
• When two amino acids join together the
bond is called a peptide bond
Amino Acids
• There are 20 amino acids that are
necessary for the body to remain healthy,
grow, and maintain body functions
• Eight of these amino acids cannot be
produced in the body and are classified as
essential amino acids
• Essential amino acids- amino acids that
must be supplied by foods in the diet
Complete vs. Incomplete Proteins
• Complete proteins- foods that contain all 8
essential amino acids
• Most come from animal sources and are high
quality proteins, ex. eggs, milk, fish, poultry,
meats
• Incomplete proteins- foods that are short of one
or more of the 8 essential amino acids needed
for human growth
• Most come from grains, nuts, vegetables, and
legumes
Protein Structures
• There are infinite numbers of protein
structures but they can be classified in
three ways.
• 1. Primary structure
• 2. Secondary structure
• 3. Tertiary structure
Primary Structure
• Primary structure of a protein molecule is
the order the amino acids occur in the
chain
• A result of the chain of peptide bonds
formed in making the protein molecule
Secondary Structure
• Secondary structure of a protein molecule
refers to the shape of sections of the
amino acid chain
• The three patterns of secondary structures
are the helix, random coil, and the pleated
sheet
Tertiary Structure
• Tertiary structure of a protein molecule refers to
the three-dimensional structure of an entire
amino acid chain
• The two main tertiary structures are globular
(balled up) and fibrous (strands)
• Globular proteins- hemoglobin, lipoprotein,
casein, and albumin
• Fibrous proteins- helix shaped strands,ex.
collagen, elastin, keratin, myosin are all found in
muscle fibers, ligaments, tendons, hair and
fingernails
Hydrophobic Interactions
• A common interaction between protein
molecules is a hydrophobic, or water
repelling, interaction that occurs between
nonpolar side chains with carbon rings
• Casein, found in milk, is an example of a
hydrophobic protein and is vital to the
formation of curds in cheese making
Oxidation and Reduction
• The reversible process of adding and
removing oxygen to a compound is called
oxidation and reduction
• Oxidation adds oxygen to a compound
• Reduction removes oxygen from a
compound
Denaturation of Proteins
• Denaturation- Any change of the shape of
a protein molecule without breaking
peptide bonds and usually results in a
loosening or unfolding of the protein
molecule
• Denaturation is occasionally reversible but
it is not when disulfide cross-links are
broken
Causes of Denaturation
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Hot and cold temperatures
Mechanical actions
Sound waves
Pressure
Irradiation
pH changes
Mineral salts
Heat and Denaturation
• The rate of increase for protein
denaturation is 600 times for every 10ºC
increase in temperature
Coagulation
• Coagulation- a type of permanent
denaturation when a liquid or semiliquid
protein forms solid or semisoft clots.
• Example- milk curdling to form cheese