Essay about The Functions of Proteins
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The Functions of Proteins
Protein accounts for about three-fourths of the dry matter in human tissues other than fat and bone. It is a major structural component of hair, skin, nails, connective tissues, and body organs. It is required for practically every essential function in the body. Proteins are made from the following elements; carbon, hydrogen, oxygen, nitrogen and often sulphur and phosphorus. Proteins cannot be stored except in eggs and seeds and they form the body's main structural elements and are found in every cell and tissue. The human body uses proteins for growth and to build and repair bones, muscles, tissue, skin, internal organs and blood. Hormones, antibodies…show more content…
They serve as enzymatic catalysts that speed up biochemical reactions while remaining unchanged in the process. Without these biological catalysts, chemical reactions would occur so slowly that life as we know it could not exist. With them, chemical reactions can occur at rates as much as 10 billion times faster than would be possible without enzymes. Enzymes are critical to digestion and metabolism, they are required to release nutrients from foods so they can be absorbed and utilized by the body. If enzymes are not present in sufficient quantities, complete digestion cannot take place. Enzymes also keep the body's metabolic "machinery" running smoothly. In turn, vitamins and minerals are essential for proper enzyme functioning.
Proteins are also used as transport molecules, such protein is haemoglobin which transports oxygen in red blood cells all around the body. The main haemoglobin in adult humans is Haemoglobin A and it contains two alpha and two beta subunits. Haemoglobin also transports carbon dioxide away from the tissues to the lungs where it is exhaled.
Haemoglobins are a chain of polypeptide which is held in position by three types of bonds; disulphide bond, ionic bond and hydrogen bond. Haemoglobins are formed when four Globin molecules link together.
Proteins are the most versatile macromolecules in living systems and serve crucial functions in essentially all biological processes. They function as catalysts, they transport and store other molecules such as oxygen, they provide mechanical support and immune protection, they generate movement, they transmit nerve impulses, and they control growth and differentiation. Indeed, much of this text will focus on understanding what proteins do and how they perform these functions.
Several key properties enable proteins to participate in such a wide range of functions.
Proteins are linear polymers built of monomer units called amino acids. The construction of a vast array of macromolecules from a limited number of monomer building blocks is a recurring theme in biochemistry. Does protein function depend on the linear sequence of amino acids? The function of a protein is directly dependent on its threedimensional structure (Figure 3.1). Remarkably, proteins spontaneously fold up into three-dimensional structures that are determined by the sequence of amino acids in the protein polymer. Thus, proteins are the embodiment of the transition from the one-dimensional world of sequences to the three-dimensional world of molecules capable of diverse activities.
Proteins contain a wide range of functional groups. These functional groups include alcohols, thiols, thioethers, carboxylic acids, carboxamides, and a variety of basic groups. When combined in various sequences, this array of functional groups accounts for the broad spectrum of protein function. For instance, the chemical reactivity associated with these groups is essential to the function of enzymes, the proteins that catalyze specific chemical reactions in biological systems (see Chapters 8–10).
Proteins can interact with one another and with other biological macromolecules to form complex assemblies. The proteins within these assemblies can act synergistically to generate capabilities not afforded by the individual component proteins (Figure 3.2). These assemblies include macro-molecular machines that carry out the accurate replication of DNA, the transmission of signals within cells, and many other essential processes.
Some proteins are quite rigid, whereas others display limited flexibility. Rigid units can function as structural elements in the cytoskeleton (the internal scaffolding within cells) or in connective tissue. Parts of proteins with limited flexibility may act as hinges, springs, and levers that are crucial to protein function, to the assembly of proteins with one another and with other molecules into complex units, and to the transmission of information within and between cells (Figure 3.3).
Crystals of human insulin. Insulin is a protein hormone, crucial for maintaining blood sugar at appropriate levels. (Below) Chains of amino acids in a specific sequence (the primary structure) define a protein like insulin. These chains fold into well-defined (more...)
Structure Dictates Function. A protein component of the DNA replication machinery surrounds a section of DNA double helix. The structure of the protein allows large segments of DNA to be copied without the replication machinery dissociating from the (more...)
A Complex Protein Assembly. An electron micrograph of insect flight tissue in cross section shows a hexagonal array of two kinds of protein filaments. [Courtesy of Dr. Michael Reedy.]
Flexibility and Function. Upon binding iron, the protein lactoferrin undergoes conformational changes that allow other molecules to distinguish between the iron-free and the iron-bound forms.
3.1 Proteins Are Built from a Repertoire of 20 Amino Acids
3.2 Primary Structure: Amino Acids Are Linked by Peptide Bonds to Form Polypeptide Chains
3.3 Secondary Structure: Polypeptide Chains Can Fold Into Regular Structures Such as the Alpha Helix, the Beta Sheet, and Turns and Loops
3.4 Tertiary Structure: Water-Soluble Proteins Fold Into Compact Structures with Nonpolar Cores
3.5 Quaternary Structure: Polypeptide Chains Can Assemble Into Multisubunit Structures
3.6 The Amino Acid Sequence of a Protein Determines Its Three-Dimensional Structure
Appendix: Acid-Base Concepts