山口県宇部市から情報発信 Information from Ube City, Japan



Water and living body constituents



1. Basic molecules that make up the living body

 The basic molecules that make up the living body are amino acids, nucleic acids, sugars, etc., and these molecules have hydrophilic groups such as amino group-NH2, carboxyl group-COOH, and hydroxyl group-OH, and serve as proton acceptors/donors. It has the ability to ionize and hydrogen bond. These molecular groups combine with hydrophobic molecules to form larger biomolecules, and exert various functions by interacting with water.




図1 DNAの構造

2. Three-dimensional structure of water and bio-polymer

(1) Gene

 The long chain of DNA is made up of alternating sugars and phosphates. Since sugar and phosphoric acid are hydrophilic and base is hydrophobic, two chains are entangled in water so that the sugar and phosphoric acid face outward and the base faces inward, and the two bases are connected by a hydrogen bond. The sugar and phosphate exposed on the outside are hydrated to maintain a stable double helix structure. When dried, the double helix structure is lost.

Fig.1 Structure of DNA



図2 タンパク質の構造

(2) Protein

 Amino acids are hydrophilic and hydrophobic. In water, hydrophobic amino acids work by gathering together hydrophobic amino acids, and bend as if the hydrophobic groups are folded inside. Water is eliminated from inside the protein, and atoms are packed as densely as crystals. On the surface of a protein, many hydrophilic groups are aligned and hydrogen bonds with water molecules to maintain a three-dimensional structure, and various functional groups for performing biological functions are appropriately arranged.

Fig.2 Structure of protein



図3 細胞膜の構造

3. Water and cell membrane

 The membrane covering the surface of cells is composed of two layers of phospholipids (phospholipid bilayer). Therefore, gases such as oxygen and carbon dioxide and fat-soluble substances can freely pass through the cell membrane, but water and electrolytes (ions such as Na+, K+, Ca2+) are almost impermeable. In this way, the cell membrane controls the uptake of electrolytes and nutrients (glucose, amino acids, etc.) and the release of metabolites that are essential for life support.
 Special proteins (Fig.2) are embedded in various forms in the phospholipid bilayer, and each has a unique function. Such proteins include enzymes that are involved in special chemical reactions, chemical mediators and hormones that are involved in the transmission of information, and receptors that transmit information into cells, water-soluble substances, especially water and electrolytes. Tiny pores (channels) are carriers that transport substances into and out of cells by binding to certain substances, and glycoproteins (sugars attached to saccharides on proteins with heads protruding outside the cell membrane) have various roles such as determining blood group and acting as a receptor that binds to bacteria, viruses and toxins in immune system cells.

Fig.3 Structure of cell membrane


Posted: July 03, 2017
Update: July 04, 2020 (English version added)
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