Protein Functions

Proteins have more diverse functions than other macro-molecules. These include:

  • Structure. Keratin, a tough structural protein, gives strength to the nails, hair, and skin surface. Deeper layers of the skin, as well as bones, cartilage, and teeth, contain an abundance of the durable protein collagen.
  • Communication. Some hormones and other cell-to-cell signals are proteins, as are the receptors to which the signal molecules bind in the receiving cell. A hormone or other molecule that reversibly binds to a protein is called a ligand27 (LIG-and).
  • Membrane transport. Some proteins form channels in cell membranes that govern what passes through the membranes and when. Other proteins act as carriers that briefly bind to solute particles and transport them to the other side of the membrane. Among their other roles, such proteins turn nerve and muscle activity on and off.
  • Catalysis. Most metabolic pathways of the body are controlled by enzymes, which are globular proteins that function as catalysts.
  • Recognition and protection. The role of glycoproteins in immune recognition was mentioned earlier.

24tert = third 25quater = fourth

26prosthe = appendage, addition 27 lig = to bind

Saladin: Anatomy & Physiology: The Unity of Form and Function, Third Edition

2. The Chemistry of Life

Text

-»Amino acids

sheet

-»Amino acids

sheet

Primary Structure Hemoglobin

Primary structure

Peptide bonds Sequence of amino acids joined by peptide bonds

Heme groups a chain a chain

Figure 2.24 Four Levels of Protein Structure. The molecule shown for quaternary structure is hemoglobin, which is composed of four polypeptide chains. The heme groups are iron-containing nonprotein moieties.

Primary structure

Peptide bonds Sequence of amino acids joined by peptide bonds

Heme groups a chain

Secondary structure a helix or p sheet formed by hydrogen bonding

Tertiary structure

Folding and coiling due to interactions among R groups and between R groups and surrounding water a chain

Quaternary structure

Association of two or more polypeptide chains with each other

Figure 2.24 Four Levels of Protein Structure. The molecule shown for quaternary structure is hemoglobin, which is composed of four polypeptide chains. The heme groups are iron-containing nonprotein moieties.

Saladin: Anatomy & I 2. The Chemistry of Life I Text I I © The McGraw-Hill

Physiology: The Unity of Companies, 2003 Form and Function, Third Edition

82 Part One Organization of the Body

82 Part One Organization of the Body

Disulfide Bridges Hemoglobin
Figure 2.25 Primary Structure of Insulin. Insulin is composed of two polypeptide chains joined by disulfide bridges.

and trypsin. The modern system of naming enzymes, however, is more uniform and informative. It identifies the substance the enzyme acts upon, called its substrate; sometimes refers to the enzyme's action; and adds the suffix -ase. Thus, amylase digests starch (amyl- = starch) and carbonic anhydrase removes water (anhydr-) from carbonic acid. Enzyme names may be further modified to distinguish different forms of the same enzyme found in different tissues (see insight 2.4).

Insight 2.4 Clinical Application

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  • FERDINANDA
    Which structure in physiology contains peptide bonds?
    6 years ago

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