Transcript proteins - SD57 Mail

PROTEINS
Learning Outcomes:
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B4 - describe the chemical structure of proteins
List functions of proteins
Draw and describe the structure of an amino acid
Describe the formation of peptide bonds
Describe the 4 levels of protein structure
ELEMENTS
• All contain C, H, O, N
• Some contain S
MONOMERS
• Amino Acids consist of an acid (carboxyl) group, an
amino group, and a variable R group (R for
“remainder”)
• There are 20 amino acids, each with a unique R
group
• some of these are known as “essential amino
acids” because our bodies can’t synthesize
them
• Examples: (see p. 37, note different R groups)
POLYMERS
• Proteins consist of
chains of amino
acids
• A single protein
may contain
several hundred
amino acids
• A dipeptide contains two amino acids joined
by a peptide bond
Condenstation Synthesis
• A molecule of H2O
is removed to form
a peptide bond
between two
amino acids
Hydrolysis
• Proteins can be
broken down into
amino acids
• A molecule of H2O
is added when a
peptide bond is
broken
• A polypeptide is a chain of many amino acids
joined by peptide bonds
LEVELS OF
STRUCTURE
• Proteins have four
levels of structure,
resulting in large
complex
molecules with
definite 3D shapes
Primary structure
• The sequence of amino acids in the polypeptide
chain
Secondary structure
• The chain forms a
shape such as a
helix (coil) or
pleated sheet
• Held together by
hydrogen bonds
between R groups
Amino acid basics
Tertiary structure
• The coil or sheet folds
into a 3-dimensional
shape • may be due to
hydrogen, ionic or
covalent bonding
• Hydrophobic parts on
the inside, hydrophilic
parts on the outside
Quaternary structure
• Two or more polypetide chains combine to form a
complex molecule
• Ex. Hemoglobin contains 4 polypeptide chains
• The 3 dimensional shape of a protein is important
to its function
FUNCTIONS
1. Structural proteins in all parts of the body
• Ex. Keratin in hair and nails; collagen in skin; actin
and myosin in muscle
• Muscle proteins form long fibers
2. Blood proteins such as hemoglobin, clotting
proteins, antibodies
• Hemoglobin is the oxygen carrying protein in red
blood cells
• consists of four polypeptide chains and an ironcontaining heme group
3. Enzymes - very important!
• Enzymes catalyze chemical reactions in all parts
of the body (we have over 2000 different ones)
• All enzymes are proteins
• The specific shape of the enzyme molecule
allows it to bind to reactants
4. Cell membranes
• proteins are found in cell membranes, where
they have various functions
(along with phospholipids - more on this later!)