Functional Roles of Proteins in Humans

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Polyacrylamide Gel Electrophoresis in the Presence of a Detergent
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HPLC Chromatographic Techniques Separate Amino Acids, Peptides, and Proteins
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Affinity Chromatography
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General Approach to Protein Purification
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Determination of Amino Acid Composition of a Protein
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Techniques to Determine Amino Acid Sequence of a Protein
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X­Ray Diffraction Techniques Are Used to Determine the Three­
Dimensional Structure of Proteins
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Various Spectroscopic Methods Are Employed in Evaluating Protein Structure and Function
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Ultraviolet Light Spectroscopy
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Fluorescence Spectroscopy
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Optical Rotatory Dispersion and Circular Dichroism Spectroscopy
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Nuclear Magnetic Resonance
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Bibliography
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Questions and Answers
Clinical Correlations
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2.1 Plasma Proteins in Diagnosis of Disease
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2.2 Differences in Primary Structure of Insulins used in Treatment of Diabetes Mellitus
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2.3 A Nonconservative Mutation Occurs in Sickle Cell Anemia
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2.4 Symptoms of Diseases of Abnormal Collagen Synthesis
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2.5 Hyperlipidemias
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2.6 Hypolipoproteinemias
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2.7 Glycosylated Hemoglobin, HbA1c
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2.8 Use of Amino Acid Analysis in Diagnosis of Disease
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2.1— Functional Roles of Proteins in Humans
Proteins perform a surprising variety of essential functions in mammalian organisms. These may be grouped into dynamic and structural. Dynamic functions include transport, metabolic control, contraction, and catalysis of chemical transformations. In their structural functions, proteins provide the matrix for bone and connective tissue, giving structure and form to the human organism.
An important class of dynamic proteins are the enzymes. They catalyze chemical reactions, converting a substrate to a product at the enzyme's active site. Almost all of the thousands of chemical reactions that occur in living organisms require a specific enzyme catalyst to ensure that reactions occur at a rate compatible with life. The character of any cell is based on its particular chemistry, which is determined by its specific enzyme composition. Genetic traits are expressed through synthesis of enzymes, which catalyze reactions that establish the phenotype. Many genetic diseases result from altered levels of enzyme production or specific alterations to their amino acid sequence. Transport is another major function for proteins. Particular examples discussed in greater detail in this text are hemoglobin and myoglobin, which transport oxygen in blood and in muscle, respectively. Transferrin transports iron in blood. Transport proteins bind and carry steroid hormones in blood from their site of synthesis to their site of action. Many drugs and toxic compounds are transported bound to proteins. Proteins participate in contractile mechanisms. Myosin and actin function in muscle contraction.
Proteins have a protective role through a combination of dynamic functions. Immunoglobulins and interferon are proteins that protect the human against bacterial or viral infection. Fibrin stops the loss of blood on injury to the vascular system.
Many hormones are proteins or peptides. Protein hormones include insulin, thyrotropin, somatotropin (growth hormone), luteinizing hormone, and follicle­stimulating hormone. Many diverse polypeptide hormones have a low molecular weight (<5000) and are referred to as peptides. In general, the term protein is used for molecules composed of over 50 amino acids and the term peptide is used for molecules of less than 50 amino acids. Important peptide hormones include adrenocorticotropin hormone, antidiuretic hormone, glucagon, and calcitonin.
Proteins control and regulate gene transcription and translation. These include histones that are closely associated with DNA, repressor and enhancer transcription factors that control gene transcription, and proteins that form a part of the heteronuclear RNA particles and ribosomes.