Concept 5.4: Proteins include a diversity of structures, resulting in a wide range of functions

Flashcards from Concept 5.4 of Pearson's Campbell Biology, Twelfth Edition.

Proteins

Biological molecules that account for more than 50% of the dry mass of most cells, serving in a variety of functions

• Contain one or more polypeptides

• Functions result from their structure of polypeptides twosted, foiled, and coiled to bind to other molecules

Enzymatic proteins

Proteins that selectively accelerate chemical reactions

• Digestive enzymes catalyze the hydrolysis of bonds in food molecules

Defensive proteins

Proteins that protect against disease

• Antibodies activate and help destroy virsues and bacteria

Storage proteins

Proteins that store amino acids

• Casein in milk is the major source of amino acids for baby mammals

• Plants have storage proteins in their seeds

• Ovalbumin is the protein of egg white, used as an amino acid source for the developing embryo

Transport proteins

Proteins that transport substances

• Hemoglobin is the iron-containing protein of vertebrate blood, transporting oxygen from the lungs to other parts of the body

• Transport proteins exist in cell membranes for molecular passage

Hormonal proteins

Proteins that coordinate an organism’s activities

• Insulin (a hormone secreted by the pancreas) causes glucose uptake in cells, regulating blood sugar concentration

Receptor proteins

Proteins that aid cellular responses to chemical stimuli

• Receptors in nerve cell membranes detect signaling molecules released by other nerve cells

Contractile proteins (motor proteins)

Proteins that function in movement

• Motor proteins aid the movement of cilia and flagella

• Actin and myosin proteins are responsible for the contraction of muscles

Structural proteins

Proteins that support cellular structures

• Keratin is the protein of hair, horns, feathers, and other skin appendages

• Insects and spiders use silk fibers to make their cocoons and webs

• Collagen and elastin proteins provide a fibrous framework in animal connective tissues

Amino acids

Organic molecules with amino and carboxyl groups that serve as the monomers in proteins

• Have differing properties due to differing side chains called R groups

Polypeptides

Unbranched polymers built from amino acids joined by peptide bonds

Peptide bonds

Bonds that join amino acids in polypeptides

Primary structure

A protein’s first structure defined by its unique sequence of amino acids

• Like the order of letters in a long word

• Determined by inherited genetic information

Secondary structure

A protein’s second structure defined by its coils and folds in its polypeptide chains

Tertiary structure

A protein’s third structure defined by its interactions among various side chains (R groups)

Quaternary structure

A protein’s fourth and final structure when a protein consists of multiple polypeptide chains to form one macromolecule

• Collagen consists of three polypeptides like a rope

Sickle-cell disease

An inherited blood disorder that results from a single amino acid substitution in the protein hemoglobin, causing an abnormal sickle shape in the red blood cell

Denaturation

The loss of a protein’s native structure caused by physical or chemical conditions

• pH, salt concentration, and temperature are some factors

• Extremely high fevers can be fatal because of this