Chemistry of a Body

Chemistry of a Body : Biochemistry Review

Energy : the capacity to do work. Kinetic energy is in action, while potential energy is stored or inactive. Potential energy becomes kinetic when it is released.

Forms of energy : the body uses energy in several forms.

Chemical : energy stored in chemical bonds. When the bonds are broken, the energy is released. Ex. ATP

Electrical : the movement of charged particles. The particles can be ions or electrons. Ex. nerve impulse

Mechanical : energy directly involved in moving matter. Ex. energy provided by your muscles to move your fingers to move your pen.

Radiant : (also called electromagnetic) energy that travels in waves. Ex. visible light.

Energy can be converted from one form to another, but it can not be destroyed.

Composition of Matter : atoms, molecules and compounds

Atomic number : the number of protons in an atom

Atomic weight : roughly the number of protons and neutrons

Isotope : atom of the same element with different numbers of neutrons

Radioisotope : isotope of an element with an unstable, decaying nucleus (usually heavy elements). Radioisotopes give off particles, which are the essence of radioactivity.
Molecules and compounds are composed of more than one atom. Molecule usually refers to two or more atoms of the same element (H₂, O₃) while compounds have different elements (CO, CH₄)

Bonding

Covalent bonds between atoms that are sharing electrons are the strongest.

Ionic bonds form between atoms that actually give and taken electrons.

Hydrogen bonds form between a hydrogen atom and an "electron-hungry" particle (such as oxygen). This is the weakest type of bond.
Atoms bond for stability – most have an incomplete outer electron shell. With the exception of hydrogen and helium, eight electrons will fill the shell. If an atom naturally has 8 in the outer shell (2, in the case of helium), it is called an inert or noble gas, and does not react except in extremely rare cases. Besides helium, neon, argon, krypton, xenon, and radon are noble. Any other atoms with 8 electrons in their outer shell are ions, or are in the process of sharing electrons in a covalent bond.

Na⁺ ß has one missing electron, but has eight in its outer shell

Cl^- ß has one extra electron, but has eight in its outer shell

If sodium is missing an electron because it has given it to chlorine, an ionic bond is formed between them, as the now positively charged sodium is attracted to the negatively charged chlorine. This will make the familiar NaCl.

Covalent bonds usually form between non-metallic elements, and are represented in line drawings. Each line represents the shared electron pairs, and double and triple bonds are represented by the appropriate number of lines. Dots indicate unbonded electron pairs. 8 electrons should be accounted for, except in the case of hydrogen.

H—C==C==CH₂

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H

Bonds can be formed and broken in chemical reactions.

There are several kinds of reactions :

Synthesis : A + B à AB (anabolic)

Decomposition : AB à A + B (catabolic)

Single Displacement : AB + C à AC + B

Double Displacement : AB + CD à AD + CB

When a compound dissolves in water and releases ions when it does so, it is called an electrolyte. Electrolytes make solutions that will conduct an electric current.

NaCl à Na⁺ + Cl^-

Electrolytes that release H⁺ (hydrogen ions) are acids.

HCl à H⁺ + Cl^-

Electrolytes that release ions that will combine with H⁺ are called bases. The most commonly released ion is a hydroxyl ion (OH^-)

NaOH à Na⁺ + OH^-

Hydroxyl will combine with hydrogen to form water.
pH measures the amount of H⁺. The more H⁺, the lower the pH (it is the –log of the concentration of hydrogen ions), and the less OH^-. The less H⁺, the higher the pH, and the more OH^- . If the concentrations of H⁺ and OH^- are equal, the pH=7.0.

Chemical Constituents of Cells

Inorganic compounds (do not contain C—C or C—H bonds)

Generally, these are electrolytic

Water : H₂O, the most abundant compound in a living creature. The major ingredient of all body fluids. Most metabolic reactions occur in water, and it also plays an important role in transporting chemicals in the body. Water’s high heat capacity and high specific heat helps to maintain body temperature.

Oxygen : O₂, is needed in the process of cellular respiration, which liberates energy from glucose.

Carbon dioxide : CO₂, is a waste product of cellular respiration, but also needed as a vasodilator.

Inorganic salts : are the sources of many necessary ions, including Na⁺, Cl^-, K⁺, Ca⁺⁺, Mg⁺⁺, PO₄^-3, CO₃^-2, HCO₃^-, SO₄^-2

Organic compounds (contain C—C and/or C—H bonds)

There are four important groups of organic compounds.

Carbohydrates : as the name implies, these are composed of C, H, and O. Short chain carbohydrates are called sugars, or saccharides. The "simple sugars" or monosaccharides have 6-carbon chains or rings.

A disaccharide is a combination of two monosaccharides strung together. Starches are polysaccharides, which are long chains of monosaccharides strung together. Glycogen is similar to starch and is synthesized by animals.

Lipids : are insoluble in water, but will dissolve in organic solvents. Types of lipids include fats, phospholipids and steroids.

Fats : used to build cell parts and to supply energy. They are composed of C, H, and O, but in different proportions than in carbohydrates. Building blocks of fats are fatty acids and glycerol. Three fatty acids unite with one glycerol to form a triglyceride. Different kinds of fatty acids make different kinds of fats.

Phospholipids : are similar to a triglyceride, except one of the fatty acids is replaced with a phosphate group. These are the main structural components of cell membranes.

Steroids : are composed of four interconnected carbon rings. They have a variety of functions and examples include : cholesterol, adrenal cortex hormones, sex hormones, bile acids and vitamin D.

Proteins : are structural, sources of energy, hormones, and cell membrane receptors. Some are antibodies, some are enzymes. They contain C, H, O, N, and sometimes S.

Building blocks of proteins are amino acids. There are 20 amino acids found in living organisms, and different proteins arise from different combinations of amino acids.
Proteins have specific shapes, dictated by the amino acid sequences. A denatured protein is one that has lost this special shape, usually due to heating. Denaturation is permanent destruction of a protein.

Nucleic Acids : fundamental compounds. There are generally very large and very complex, containing C, H, O, N and P in building blocks called nucleotides. A nucleotide consists of a pentose sugar, a phophate group, and a nitrogenous base. A nucleic acid includes many of these nucleotides linked together in one or two chains.

RNA : ribonucleic acid. Ribose is the pentose sugar. It is single stranded.

DNA: deoxyribonucleic acid. Deoxyribose is the pentose sugar. It is a double helix.
DNA stores genetic information, which codes for proteins, which as enzymes, control all metabolic processes in the body.

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