Proteins

quaternary structure

The structural level of a protein composed of more than one polypeptide chain, each of which has its own tertiary structure; the individual chains are called subunits. ----the interfaces where the subunits touch one another are often nonpolar, and they play a key role in transmitting information between the subunits about individual subunit activities

Proteins

leaner polymers made up of 20 amino acids -amino group (-NH2) & acidic carboxyl group (-COOH) -A protein is composed of one or more long unbranched chains(polypeptide)

essential amino acids

20 commonly occur in proteins. Of these 20, 8 are called essential amino acids because humans cannot synthesize them and thus must get them from their diets.

chaperone protein

A class of enzymes that help proteins fold into the correct configuration and can refold proteins that have been misfolded or denatured. Many are heat shock proteins, produced in greatly increased amounts when cells are exposed to elevated temperature. High temperatures cause proteins to unfold, and heat shock chaperone proteins help the cell's proteins to refold properly.

amino acid are chiral

amino acids are chiral and can exist as two enantiomeric forms: d or l. In living systems, only the l-amino acids are found in proteins, and d-amino acids are rare.

sickle cell hemoglobin

change of glutamate acid with valine in the beta globin chain his change substitutes a charged amino acid for a nonpolar one on the surface of the protein, leading the protein to become sticky and form clumps

R group

determines the chemistry of amino acids Five chemical classes based on there r group ---Non polar amino acid ---Polar uncharged amino acids, such as threonine, have R groups that contain oxygen (or —OH). ---Charged amino acids, such as glutamic acid, have R groups that contain acids or bases that can ionize. --Aromatic amino acids, such as phenylalanine, have R groups that contain an organic (carbon) ring with alternating single and double bonds. These are also non polar. ---Amino acids that have special functions have unique properties. Some examples are methionine, which is often the first amino acid in a chain of amino acids; proline, which causes kinks in chains; and cysteine, which links chains together.

polypeptide

A molecule consisting of many joined amino acids; not usually as complex as a protein.

Motif

A substructure in proteins that confers function and can be found in multiple proteins. One example is the helix-turn-helix motif found in a number of proteins that is used to bind to DNA. One very common protein motif is the β-α-β motif, which creates a fold or crease; the so-called "Rossmann fold" at the core of nucleotide-binding sites in a wide variety of proteins Motifs have been useful in determining the function of unknown proteins. Databases of protein motifs are used to search new unknown proteins. Finding motifs with known functions may allow an investigator to infer the function of a new protein.

dissociation

In proteins, the reversible separation of protein subunits from a quaternary structure without altering their tertiary structure. Also refers to the dissolving of ionic compounds in water.

Functions of proteins

Proteins are the most diverse group of biological macromolecules, both chemically and functionally. 1)Enzyme catalysis. Enzymes are biological catalysts that facilitate specific chemical reactions. Enzymes are three-dimensional globular proteins This fit facilitates chemical reactions by stressing particular chemical bonds. 2) Defense. Other globular proteins use their shapes to "recognize" foreign microbes and cancer cells. These cell-surface receptors form the core of the body's endocrine and immune systems. 3) Transport. A variety of globular proteins transport small molecules and ions. The transport protein hemoglobin, for example, transports oxygen in the blood. Membrane transport proteins help move ions and molecules across the membrane. 4) Support. Protein fibers play structural roles. These fibers include keratin in hair, fibrin in blood clots, and collagen. The last one, collagen, forms the matrix of skin, ligaments, tendons, and bones and is the most abundant protein in a vertebrate body. 5) motion -Muscles contract through the sliding motion of two kinds of protein filaments: actin and myosin cell's cytoskeleton and in moving materials within cells. 6)Regulation. turning on and shutting off genes during development, for example. In addition, proteins receive information, acting as cell-surface receptors. 7)Storage. Calcium and iron are stored in the body by binding as ions to storage proteins.

secondary structure

Secondary structure-In a protein, hydrogen-bonding interactions between —CO and —NH groups of the primary structure. results from hydrogen bonds forming between nearby amino acids.This produces two different kinds of structures: beta (β) pleated sheets, and coils called alpha (α) helices. alpha helices --A form of secondary structure in proteins where the polypeptide chain is wound into a spiral due to interactions between amino and carboxyl groups in the peptide backbone. beta pleated sheets ---A form of secondary structure in proteins where the polypeptide folds back on itself one or more times to form a planar structure stabilized by hydrogen bonding between amino and carboxyl groups in the peptide backbone. Also known as a β-pleated sheet.

tertiary structure

The folded shape of a protein, produced by hydrophobic interactions with water, ionic and covalent bonding between side chains of different amino acids, and van der Waal's forces; may be changed by denaturation so that the protein becomes inactive.

denature

The loss of the native configuration of a protein or nucleic acid as a result of excessive heat, extremes of pH, chemical modification, or changes in solvent ionic strength or polarity that disrupt hydrophobic interactions; usually accompanied by loss of biological activity. Blood-borne enzymes that course through a human body at a pH of about 7.4 would rapidly become denatured in the highly acidic environment of the stomach.

primary structure

amino acid sequence

domains

functional units within a larger structure. They can be thought of as substructure within the tertiary structure of a protein To continue the metaphor: Amino acids are letters in the protein language, motifs are words or phrases, and domains are paragraphs. A single polypeptide chain connects the domains of a protein, like a rope tied into several adjacent knots. Often the domains of a protein have quite separate functions—one domain of an enzyme might bind a cofactor, for example, and another the enzyme's substrate.

Amino acid

he subunit structure from which proteins are produced, consisting of a central carbon atom with a carboxyl group (—COOH), an amino group (—NH2), a hydrogen, and a side group (R group); only the side group differs from one amino acid to another.

Peptide bond

the type of bond that links amino acids together in proteins through a dehydration reaction.(covalent bond) The two amino acids linked by such a bond are not free to rotate around the N—C linkage because the peptide bond has a partial double-bond character A peptide bond forms when the amino end of one amino acid joins to the carboxyl end of another