Download 2. Intro to Proteins

PROTEINS
INTRODUCTION
Useful Proteins
• There are thousands and thousands of different
combinations of amino acids that can make up
proteins and that would increase if each one had
multiple shapes
• Proteins usually have only one useful
conformation
• Natural selection has eliminated proteins that do
not perform a specific function in the cell
Functions / importance of Proteins
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Type
Structural
Contractile
Transport
Storage
Hormonal
Enzyme
Protection
Energy
Signalling
Receptors
Motor proteins
Examples
tendons, cartilage, hair, nails
muscles
hemoglobin, albumin
ferritin
eg. insulin, growth hormone
eg. hydroxylases
immunoglobulins
4.1 k.cal/gm Motor
kinesin
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Protein
Families
Enzymes
• Have similarities in amino acid sequence and 3-D
structure
• Have similar functions such as breakdown
proteins but do it differently
Proteins at Work
• The conformation of a protein gives it a unique
function
• To work proteins must interact with other
molecules, usually 1 or a few molecules from the
thousands to 1 protein
• Ligand – the molecule that a protein can bind
• Binding site – part of the protein that interacts
with the ligand
– Consists of a cavity formed by a specific arrangement
of amino acids
Ligand Binding
Enzymes as Catalysts
• Enzymes are proteins that bind to their ligand as
the 1st step in a process
• An enzyme’s ligand is called a substrate
– May be 1 or more molecules
• Output of the reaction is called the product
• Enzymes can repeat these steps many times and
rapidly, called catalysts
Enzymes at Work
• Lysozyme is an important enzyme that protects us
from bacteria by making holes in the bacterial cell
wall and causing it to break
• Lysozyme adds H2O to the glycosidic bond in the
cell wall
• Active site is a special binding site in enzymes
where the chemical reaction takes place
Antibodies
• Y-shaped molecules with 2 binding sites at the
upper ends of the Y
• The loops of polypeptides on the end of the
binding site are what imparts the recognition
of the antigen
• Changes in the sequence of the loops make
the antibody recognize different antigens specificity
Antibodies
Antibody Family
• A family of proteins that can be created to
bind to almost any molecule
• Antibodies (immunoglobulins) are made in
response to a foreign molecule ie. bacteria,
virus, pollen… called the antigen
• Bind together tightly and therefore
inactivates the antigen or marks it for
destruction
Motor Proteins
• Proteins can move in the cell,
say up and down a DNA strand
but with very little uniformity
• The hydrolysis of ATP can direct
the the movement as well as
make it unidirectional
– The motor proteins that move
things along the actin
filaments or myosin
Protein Machines
• Complexes of 10 or more
proteins that work
together such as DNA
replication, RNA or
protein synthesis, transmembrane signaling etc.
• Usually driven by ATP or
GTP hydrolysis