Comprehensive Protein Structure and Function in Biochemistry

Protein

A naturally occurring, unbranched polymer in which the monomer units are amino acids.

Protein

is a peptide in which at least 40 amino acid residues are present.

Monomeric protein

Only one peptide chain is present.

Multimeric protein

More than one peptide chain is present.

Protein Subunits

Peptide chains present in multimeric proteins.

Monomeric or multimeric

More than one peptide chain may be present in a protein.

Insulin

The small protein, which functions as a hormone in the human body, is a multimeric protein with two protein subunits; one subunit contains 21 amino acid residues and the other 30 amino acid residues.

Simple protein

Only amino acid residues are present. More than one protein subunit may be present in a simple protein, but all subunits contain only amino acids.

Conjugated protein

Has one or more non-amino acid entities present in its structure in addition to one or more peptide chains.

Lipoproteins

Contain lipid prosthetic groups.

Glycoproteins

Contain carbohydrate groups.

Metalloproteins

Contain specific metal ions.

Prosthetic group

Is a non-amino acid group present in a conjugated protein.

Primary protein structure

is the order in which amino acids are linked together in a protein.

Primary protein structure

always involves more than just the numbers and kinds of amino acids present; it also involves the order of attachment of the amino acids to each other through peptide bonds.

Insulin

the hormone that regulates blood-glucose levels, was the first protein for which primary structure was determined

Frederick Sanger

In insulin, the 'sequencing' of its 51 amino acids was completed in 1953, after eight years of work by this British biochemist.

Myoglobin

A protein involved in oxygen storage in muscles; it contains 153 amino acids assembled in the particular.

Diabetes mellitus

Insufficient insulin production or an inability to use insulin produced (insulin resistance) results in this condition.

Insulin analogs

They are not exact copies of human insulin but, rather, slightly modified copies of human insulin. The modifications are planned modifications. These insulin analogs affect glucose levels in the same manner as 'regular' insulin but often have better absorption rates and longer periods of bioactivity.

Peptide bond planarity

The net effect of this is the zigzag arrangement of atoms within a protein backbone.

Secondary protein structure

Is the arrangement in space adopted by the backbone portion of a protein.

alpha helix and beta pleated sheet

The two most common types of secondary structure.

Hydrogen Bonding

The type of interaction responsible for both of these types of secondary structure is between a carbonyl oxygen atom of a peptide linkage and the hydrogen atom of an amino group of another peptide linkage farther along the protein backbone.

alpha helix

This structure is a protein secondary structure in which a single protein chain adopts a shape that resembles a coiled spring (helix), with the coil configuration maintained by hydrogen bonds.

Beta pleated sheet

This structure is a protein secondary structure in which two fully extended protein chain segments in the same or different molecules are held together by hydrogen bonds.

U-turn structure

This is the most frequently encountered type of beta pleated sheet structure.

Unstructured Segments

The portions of a protein that have neither a helix nor beta pleated sheet structure.

Tertiary protein structure

Is the overall three-dimensional shape of a protein that results from the interactions between amino acid side chains (R groups) that are widely separated from each other within a peptide chain.

Covalent Disulfide Bonds

The strongest of the tertiary-structure interactions, result from the -SH groups of two cysteine residues reacting with each other to form a covalent disulfide bond.

Electrostatic Attractions

Also called salt bridges, always involve the interaction between an acidic side chain (R group) and a basic side chain (R group). The side chains of acidic and basic amino acids, at the appropriate pH, carry charges, with the acidic side chain being negatively charged and the basic side chain being positively charged.

Hydrogen bonds

Relatively weak bonds that are easily disrupted by changes in pH and temperature.

Hydrophobic interactions

Result when two nonpolar side chains are close to each other.

Intramolecular

The hydrogen bonding present in an alpha helix.

Intermolecular or Intramolecular

In a b pleated sheet, the hydrogen bonding can be (between two different chains) or (a single chain folding back on itself).

Myoglobin

In 1959, a protein tertiary structure was determined for the first time. A conjugated protein whose function is oxygen storage in muscle tissue.

Quaternary protein structure

The highest level of protein organization found only in multimeric proteins.

Hemoglobin

An example of a protein with quaternary structure, the oxygen-carrying protein in blood.

Primary protein structure

The sequence of amino acids present in a protein's peptide chain or chains

Secondary protein structure

The regularly repeating ordered spatial arrangements of amino acids near each other in the protein chain, which result from hydrogen bonds between carbonyl oxygen atoms and amino hydrogen atoms

Tertiary protein structure

The overall three-dimensional shape that results from the attractive forces between amino acid side chains (R groups) that are not near each other in the protein chain

Quaternary protein structure

The three-dimensional shape of a protein consisting of two or more independent peptide subunits, which results from noncovalent interactions between R groups

Alpha helix

Hydrogen bonds between every fourth amino acid

Beta pleated sheet

Hydrogen bonds between two side-by-side chains, or a single chain that is folded back on itself

Protein Hydrolysis

When a protein or smaller peptide in a solution of strong acid or strong base is heated, the peptide bonds of the amino acid chain are hydrolyzed and free amino acids are produced

Protein denaturation

Partial or complete disorganization of a protein's characteristic three-dimensional shape due to disruption of structural interactions.

Renaturation

A process where denaturation effects can be reversed, possible for limited denaturation changes.

Coagulation

Extensive denaturation resulting in loss of water solubility.

Disulfide

Linkages that occur in the tertiary structure of hair, where 16%-18% of hair is the amino acid cysteine.

Ammonium thioglycolate

A reducing agent used when administering a permanent to hair.

Potassium bromate

An oxidizing agent used after hair has been reduced and rearranged.

Fibrous protein

A protein whose molecules have an elongated shape with one dimension much longer than the others.

Globular protein

A protein whose molecules have peptide chains folded into spherical or globular shapes.

Membrane protein

A protein found associated with a membrane system of a cell.

Alpha keratin

A fibrous protein abundant in nature, found in protective coatings for organisms.

Alpha keratin

It is the major protein constituent of hair, feathers, wool, fingernails and toenails, claws, scales, horns, turtle shells, quills, and hooves.

Protofilament

In hair, two of the coiled coils twist together to form this.

Collagen

The most abundant protein in humans, major structural material in tendons, ligaments, blood vessels, and skin.

Collagen

The predominant structural feature within collagen molecules, a triple helix formed by three chains of amino acids.

Hemoglobin

It is a tetramer (four peptide subunits) with each subunit also containing a heme group, the entity that binds oxygen

Myoglobin

a monomer, has a higher affinity for oxygen than does hemoglobin. Oxygen stored in myoglobin molecules serves as a reserve oxygen source for working muscles when their demand for oxygen exceeds that which can be supplied by hemoglobin.

Myosin

Structurally, this consists of a rodlike coil of two alpha helices (fibrous protein) with two globular protein heads.

Actin

Has the appearance of two filaments spiraling about one another.

Fetal Hemoglobin

This hemoglobin has a greater affinity for oxygen than the mother's hemoglobin. This ensures a steady flow of oxygen to the fetus. Shortly after birth, a baby's body ceases to produce this.

Catalytic Proteins

Proteins with the role of biochemical catalyst are called enzymes.

Enzymes

The chemistry of human genetics is very dependent on the presence of Catalytic Proteins.

Defense Proteins

These proteins, also called immunoglobulins or antibodies, are central to the functioning of the body's immune system.

Immunoglobulins or antibodies

Defense proteins. These proteins, also called immunoglobulins or antibodies, are central to the functioning of the body's immune system. They bind to foreign substances, such as bacteria and viruses, to help combat invasion of the body by foreign particles.

Transferrin

In transport proteins, this carries iron from the liver to the bone marrow.

Transport Proteins

These proteins bind to particular small biomolecules and transport them to other locations in the body and then release the small molecules as needed at the destination location.

Messenger proteins

These proteins transmit signals to coordinate biochemical processes between different cells, tissues, and organs. A number of hormones that regulate body processes are messenger proteins, including insulin and glucagon.

Contractile proteins

These proteins are necessary for all forms of movement. Muscles are composed of filament-like contractile proteins that, in response to nerve stimuli, undergo conformation changes that involve contraction and extension. Actin and myosin are examples of such proteins.

Structural Proteins

These proteins confer stiffness and rigidity to otherwise fluid-like biochemical systems.

Transmembrane proteins

These proteins, which span a cell membrane, help control the movement of small molecules and ions through the cell membrane.

Storage proteins

These proteins bind (and store) small molecules for future use.

Regulatory proteins

These proteins are often found 'embedded' in the exterior surface of cell membranes.

Nutrient proteins

These proteins are particularly important in the early stages of life, from embryo to infant.

Buffer proteins

These proteins are part of the system by which the acid-base balance within body fluids is maintained.

Fluid-balance proteins

These proteins help maintain fluid balance between blood and surrounding tissue.

Glycoprotein

Is a protein that contains carbohydrates or carbohydrate derivatives in addition to amino acids.

Collagen

The fibrous protein, whose structure qualifies as a glycoprotein because carbohydrate units are present in its structure.

Immunoglobulins

Are among the most important and interesting of the soluble proteins in the human body. It is a glycoprotein produced by an organism as a protective response to the invasion of microorganisms or foreign molecules.

Antigen

Is a foreign substance, such as a bacterium or virus, that invades the human body.

Antibody

Is a biochemical molecule that counteracts a specific antigen.

Cyclosporine

Is a compound that was initially isolated from a soil fungus; it is a fungal peptide.

Colostrum

This substance, secreted in low-volume amounts, is a thick yellow secretion that is rich in maternal antibodies (immunoglobulins) and carbohydrates and low in fat.

Lipoprotein

Is a conjugated protein that contains lipids in addition to amino acids.

Plasma lipoprotein

Is a lipoprotein that is involved in the transport system for lipids in the bloodstream.

Chylomicrons

Their function is to transport dietary triacylglycerols from the intestine to the liver and to adipose tissue.

Very-low-density lipoproteins

Their function is to transport triacylglycerols synthesized in the liver to adipose tissue.

Low-density lipoproteins

Their function is to transport cholesterol synthesized in the liver to cells throughout the body.

High-density lipoproteins

Their function is to collect excess cholesterol from body tissues and transport it back to the liver for degradation to bile acids.