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Chemical bonds play an important role in the world of biology. Chemical bonds hold your computer together, the cells in your body together, and connect almost everything around us on the atomic level. A chemical bond is an attraction between atoms due to sharing of electrons between atoms or a complete transfer of electrons from one atom to another. There are three types of chemical bonds. They are ionic, covalent, and polar covalent. Separate from chemical bonds are also hydrogen bonds, which deal with hydrogen atoms.
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A Review of the Types of Chemical Bonds
Ionic Bonds - An ionic bond is a complete transfer of electrons from one atom to another. This generally happens between atoms that have opposite electronegativity. This means one has very few atoms in their outer shell, while the other has many. A common example of an ionic bond is that of salt, with Na and Cl. Sodium has one electron in its outer shell, in which it transfers to chloride to make an ionic bond.
Covalent Bonds - Covalent bonds involve a complete sharing of electrons between two atoms. It occurs most commonly between atoms that have outer shells that are only partially filled. If the two atoms have similar electronegativity, then the electrons can be shared between them. Carbon forms covalent bonds.
Polar Covalent Bonds - A polar covalent bond is much like a covalent bond, except that it occurs between atoms that have differing electronegativity. When this happens, the electrons are still shared, but they tend to spend more time around the more electronegative atom versus the other. Such an example is with water. Oxygen is very electronegative, while hydrogen is not. The electrons tend to favor oxygen and spend more time around it.
Hydrogen Bonds - Hydrogen bonds are less of chemical bonds and are more of a static attraction. They involve the reaction between a hydrogen atom and an electronegative atom. The strength of a hydrogen bond is less than a tenth of a covalent bond.
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Ionic Bonds in Biology
Ionic bonds are usually found in dry forms such as salts and are found in compounds throughout the human body. Ionic compounds are generally water soluble.
Protein Shapes - Ionic bonds play an important role in shaping tertiary and quaternary proteins. As a protein undergoes its folding process, certain atoms on the protein will be attracted to one another and will from ionic bonds that hold the general shape of a protein together.
Chromosome Shapes - Much like protein shapes, ionic bonds help determine the shapes of chromosomes depending on what atoms bond to each other.
Muscle Contraction - There are many different ionic compounds (salts) in cells. Ions are used to maintain cell potentials and are important in cell signaling and muscle contraction. As ions move in and out of cells, they can build up positive and negative charges on different sides of those cells. Once these charges build up, they can trigger a reaction such as muscle or nerve contraction.
Ionic bonds are also involved in determining cell shapes, catalytic reactions, and neuron functions.
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Covalent & Polar Covalent Bonds in Biology
Covalent bonds can be found as gasses, liquids, or solids and are all around us. They are not soluble in water. The atoms of materials with covalent bonds are bound tightly to each other in stable molecules, yet, they are generally not very attracted to other molecules in or around the material. Carbon-Carbon bonds (C-C) are covalent bonds and form the basis of most biomolecules.
Sugars - Monosaccharides such as glucose, fructose and galactose are held together by a type of covalent bond known as a glycosidic bond. When they are connected together, they can form larger carbohydrates. Two monosaccharides linked together form a disaccharide. Such an example is sucrose, which is composed of two monosaccharides, glucose and fructose.
Polar covalent bonds link together amino acids in chains, creating peptides. They can also be found holding together amines.
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Hydrogen Bonds In Biology
Hydrogen bonds are considerably weak when compared to others, but these weak chemical interactions are very important in the world of biology, dues to the fact that the molecules they form can be easily taken apart and put back together again. Some of these hydrogen bonds are significant in the survival of organisms.
Water - The hydrogen on a water molecule has a positive charge, while oxygen has a negative one. The opposite ends of water molecules attract each other simply with negative and positive attraction. This is why water droplets are attracted to each other when they are in a small distance of each other. Water can form this type of bond with other polar molecules or ions such as sodium ions or hydrogen ions.
Ice - When water freezes and turns to ice, hydrogen bonds space water molecules further apart than they would normally be in the liquid form. Because of the extra space now created, water is less dense when it freezes, and it enables ice to float on top of the liquid form of water.
Water Striders - The water strider is an insect that hunts for its food on the surface of still water, such as a pond or swamp. It has widely spaced feet that depress the surface of the water when they are spread out, creating a weight light enough to be held up by the surface tension created from the hydrogen bonding in the water. This essentially helps it to walk on water.
DNA - As you recall, DNA is formed in the shape of a double helix. The double strands of DNA are held together by hydrogen bonds. Each single strand has a backbone made of sugar and phosphate, as well as either a purine (adenine or guanine) or pyrimidine (cytosine or thymine). Each purine is connected to a pyrimidine through a hydrogen bond, giving the double DNA strand strength, and flexibility. This bond holds the two sides of DNA together, each bond contributing to the overall strength of DNA. When DNA is replicated, special enzymes known as DNA helicase "unzip" DNA and these bonds are broken so the two strands can be individually replicated.
After studying chemical bonds and their applications in biology, it becomes clear to us that the world around us is connected at so many levels, and it makes sense that all sciences are linked in some way.
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Virtual Biology. Chemical Bonds, http://staff.jccc.edu/PDECELL/chemistry/bonds.html
Georgia State University. Chemical Bonding, http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/bond.html
Exploratorium - Sticky Water, http://www.exploratorium.edu/ronh/bubbles/sticky_water.html
City University of New York. Ionic Bonds, http://academic.brooklyn.cuny.edu/biology/bio4fv/page/ionic_b.htm
Dr Walt Volland. Polar Bonds and ELectronegativity, http://www.800mainstreet.com/5/0005-008-negativity.htm
The Biology Project: Chemistry Tutorial, http://www.biology.arizona.edu/biochemistry/tutorials/chemistry/main.html
Ohio State University. The Chemical Context of Life, http://www.mansfield.ohio-state.edu/~sabedon/campbl02.htm