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protein
Table of Contents
Introduction & Top Questions
General structure and properties of proteins
The amino acid composition of proteins
Structures of common amino acids
Physicochemical properties of the amino acids
Amino acid sequence in protein molecules
Levels of structural organization in proteins
Primary structure
Secondary structure
Tertiary structure
Quaternary structure
The isolation and determination of proteins
Physicochemical properties of proteins
The molecular weight of proteins
The shape of protein molecules
Hydration of proteins
Electrochemistry of proteins
Electrometric titration
Electrophoresis
Conformation of globular proteins
Results of X-ray diffraction studies
Other approaches to the determination of protein structure
Spectrophotometric behavior
Optical activity
Chemical reactivity of proteins
Association of protein subunits
Protein denaturation
Conformation of proteins in interfaces
Classification of proteins
Classification by solubility
Classification by biological functions
Special structure and function of proteins
Structural proteins
Scleroproteins
Collagen
Keratin
Others
The muscle proteins
Fibrinogen and fibrin
Albumins, globulins, and other soluble proteins
Proteins of the blood serum
Milk proteins
Egg proteins
Protamines and histones
Plant proteins
Conjugated proteins
Combination of proteins with prosthetic groups
Mucoproteins and glycoproteins
Lipoproteins and proteolipids
Metalloproteins
Heme proteins and other chromoproteins
Nucleoproteins
Respiratory proteins
Hemoglobin
Other respiratory proteins
Protein hormones
Hormones of the thyroid gland
Hormones of the pancreas
Peptides with hormonelike activity
Immunoglobulins and antibodies
Enzymes
Role of enzymes in metabolism
Other functions
General properties
Classification and nomenclature
Chemical nature
Cofactors
The nature of enzyme-catalyzed reactions
The nature of catalysis
The role of the active site
The specificity of enzymes
The mechanism of enzymatic action
The rate of enzymatic reactions
The Michaelis-Menten hypothesis
Inhibition of enzymes
Effects of temperature
Enzyme flexibility and allosteric control
The induced-fit theory
Types of allosteric control
References & Edit History
Quick Facts & Related Topics
Images & Videos
For Students
protein summary
Quizzes
Medical Terms and Pioneers Quiz
Related Questions
Where is protein stored?
What do proteins do?
Read Next
What Is the Difference Between a Peptide and a Protein?
Why Is Eating Protein Important?
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Contents
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Health & Medicine
Anatomy & Physiology
protein: Media
biochemistry
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https://www.britannica.com/science/protein/images-videos
Videos
How does protein help build muscles?
How proteins build muscle.
Video: © American Chemical Society (
A Britannica Publishing Partner
)
protein engineering
How protein engineering helps scientists battle diseases.
Video: AbbVie (
A Britannica Publishing Partner
)
Why do lobsters change color when cooked?
Using chemistry to understand the colors and diseases of lobster shells.
Video: © American Chemical Society (
A Britannica Publishing Partner
)
Why is blood red?
Are you “red-y” to find out?
Video: Encyclopædia Britannica, Inc.
The chemistry of digestion: How food is broken down
Using chemistry to explain how humans digest carbohydrates, proteins, and fats.
Video: © American Chemical Society (
A Britannica Publishing Partner
)
Large biological molecules: Carbs, lipids, proteins, and nucleic acids
Overview of large biological molecules.
Video: Encyclopædia Britannica, Inc.
Why our bodies need proteins
The structure and function of amino acids.
Video: Encyclopædia Britannica, Inc.
The science behind dyeing Easter eggs
Successful Easter egg dyeing requires the interaction of calcium carbonate, protein,...
Video: © American Chemical Society (
A Britannica Publishing Partner
)
What really makes a nutritious and complete breakfast?
Discover what constitutes a complete breakfast.
Video: © American Chemical Society (
A Britannica Publishing Partner
)
Images
peptide
The molecular structure of a peptide (a small protein) consists of a sequence of...
© raimund14/Fotolia
legume; amino acid
Legumes—such as beans, lentils, and peas—are high in protein and contain many essential...
© Elenathewise/Fotolia
hemoglobin
Hemoglobin is a protein made up of four polypeptide chains (α1, α2,...
Encyclopædia Britannica, Inc.
protein synthesis
Ribosomes are key components of protein synthesis in cells.
Encyclopædia Britannica, Inc.
X-ray diffraction
X-ray diffraction pattern of a crystallized enzyme.
Jeff Dahl
macromolecules
Flow birefringence
. Orientation of elongated, rodlike macromolecules (A)...
Encyclopædia Britannica, Inc.
electrometric titration of glycine
Electrometric titration of glycine.
Encyclopædia Britannica, Inc.
Two-dimensional gel electrophoresis
In the biological sciences, gel electrophoresis represents a separation process,...
J.E. Celis, Danish Centre for Human Genome Research
protein structure; α-helix
The α-helix in the structural arrangement of a protein.
Encyclopædia Britannica, Inc.
lysozyme; protein conformation
The simplified structure of lysozyme from hen's egg white has a single peptide chain...
Encyclopædia Britannica, Inc.
collagen
Collagen molecule.
© ynse/Shutterstock.com
keratin
Scanning electron micrograph showing strands of keratin in a feather, magnified 186×.
Janice Carr/Centers for Disease Control and Prevention (CDC) (Image Number: 8673)
collagenous fibres
Randomly oriented collagenous fibres of varying size in a thin spread of loose areolar...
Don W. Fawcett, M.D.
muscle: actin and myosin
The structure of actin and myosin filaments.
Encyclopædia Britannica, Inc.
fibrin in blood clotting
Red blood cells (erythrocytes) trapped in a mesh of fibrin threads. Fibrin, a tough,...
BSIP/age fotostock
antibody structure
The four-chain structure of an antibody, or immunoglobulin, molecule. The basic unit...
Encyclopædia Britannica, Inc.
blue-green algae
Blue-green algae in Morning Glory Pool, Yellowstone National Park, Wyoming.
© Yoyo_slc/Shutterstock.com
tobacco mosaic virus
Schematic structure of the tobacco mosaic virus. The cutaway section shows the helical...
Encyclopædia Britannica, Inc.
IgG immunoglobulin
Diagram of an IgG immunoglobulin.
Encyclopædia Britannica, Inc.
B-vitamin coenzymes in metabolism
Functions of B-vitamin coenzymes in metabolism.
Encyclopædia Britannica, Inc.
enzyme; active site
The role of the active site in the lock-and-key fit of a substrate (the key) to an...
Encyclopædia Britannica, Inc.
mechanisms of enzymatic action
Mechanisms of enzymatic action (see text).
Encyclopædia Britannica, Inc.
diagram of enzyme action
Curves representing enzyme action (see text).
Encyclopædia Britannica, Inc.
induced-fit theory
Induced-fit binding of a substrate to an enzyme surface and allosteric effects.
Encyclopædia Britannica, Inc.
schematic representation of proteins of the immunoglobulin superfamily
Schematic representation of some proteins of the immunoglobulin (Ig) superfamily....
Encyclopædia Britannica, Inc.
endoplasmic reticulum in protein biosynthesis
The endoplasmic reticulum (ER) plays a major role in the biosynthesis of proteins....
Encyclopædia Britannica, Inc.
DNA and protein synthesis
DNA in the cell nucleus carries a genetic code, which consists of sequences of adenine...
Encyclopædia Britannica, Inc.
major histocompatibility complex
Protein images comparing the MHC I (left) and MHC II (right) molecules. The orange...
David S. Goodsell/Protein Data Bank/Research Collaboratory for Structural Bioinformatics (RCSB)
protein and amino acid metabolism
General scheme of protein and amino acid metabolism.
Encyclopædia Britannica, Inc.
gene; intron and exon
Genes are made up of promoter regions and alternating regions of introns (noncoding...
Encyclopædia Britannica, Inc.
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