An atom’s subatomic particles differ in mass, electrical charge, and position in the atom.
An atom has a central nucleus containing protons and neutrons tightly bound together.
Proton: A subatomic particle that bears a positive electrical charge.
Neutron: A subatomic particle that is neutral.
Electrons: A subatomic particle that bears a negative charge equal in strength to the positive charge of the proton.
Planetary Model: A simplified model of atomic structure.
Orbitals: Regions around the nucleus in which a given electron or electron pair is likely to be found most of the time.
Orbital Model: A more modern model of atomic structure, which is more useful for predicting the chemical behavior of atoms.
Element | % Body Mass | Function |
---|---|---|
Oxygen (O) | 65.0 % | Needed for the production of ATP |
Carbon (C) | 18.5 % | A primary component of all organic molecules. |
Hydrogen (H) | 9.5 % | As an ion, it influences the pH of body fluids. |
Nitrogen (N) | 3.2 % | A component of proteins and nucleic acids. |
Calcium (Ca) | 1.5 % | Its ion form is required for muscle contraction, conduction of nerve impulses, and blood clotting. |
Phosphorus (P) | 1.0 % | Part of calcium phosphate salts in bones and teeth. |
Potassium (K) | 0.4 % | Necessary for conduction of nerve impulses and muscle contraction. |
Sulfur (S) | 0.3 % | Component of proteins, particularly muscle proteins |
Sodium (Na) | 0.2 % | Important for water balance, conduction of nerve impulses, and muscle contraction. |
Chlorine (Cl) | 0.2 % | Its ion is the most abundant negative ion (anion) in extracellular fluids. |
Magnesium (Mg) | 0.1 % | Also an important cofactor in a number of metabolic reactions. |
Iodine (I) | 0.1 % | Needed to make functional thyroid hormones. |
Iron (Fe) | 0.1 % | Component of hemoglobin and some enzymes. |
Mixtures: These are substances composed of two or more components physically intermixed.
Solutions: These are homogeneous mixtures of components that may be gases, liquids, or solids.
Solvent: Substance present in greatest amounts.
Solute: Substance present in smaller amounts.
Water: The body’s chief solvent.
Most solutions in the body are true solutions containing gases, liquids, or solids dissolved in water. These solutions are usually transparent.
Solutions used in a college laboratory or a hospital are often described in terms of the percent of the solute in the total solution.
Milligrams per deciliter (mg/dl) is another common concentration measurement.
Molarity: A way to express the concentration of a solution — or moles per liter. A more complicated method but much more useful.
A mole of any element or compound is equal to its atomic weight or molecular weight weighed out in grams.
Avogadro’s number: One mole of any substance always contains exactly the same number of solute particles, that is, 6.02 x 10^23.
Colloid: Also called emulsion, — are heterogeneous mixtures, which means that their composition is dissimilar in different areas of the mixture.
Suspensions: These are heterogeneous mixtures with large, often visible solutes that tend to settle out.
Electrons forming the electron cloud around the nucleus of an atom occupy regions of space called electron shells that consecutively surround the atomic nucleus.
The attraction between the positively charged nucleus and negatively charged electrons is greatest when electrons are closest to the nucleus and falls off with increasing distance.
When we consider bonding behavior, the only electrons that are important are those in the atom’s outermost energy level. Inner electrons usually do not take part in bonding because they are more tightly held by the atomic nucleus.
When the outermost energy level of an atom is filled to capacity or contains eight electrons, the atom is stable.
Atoms in which the outermost energy level contains fewer than eight electrons tend to gain, lose, or share electrons with other atoms to achieve stability.
The number of electrons that can participate in bonding is still limited to a total of eight.
Valence Shell: It indicates an atom’s outermost energy level or that portion of it containing the electrons that are chemically reactive.
Ionic Bond: A chemical bond between atoms formed by the transfer of one or more electrons from one atom to the other.
Ions: An atom or molecule with a net electric charge due to the loss or gain of one or more electrons.
Electron acceptor: The atom that gains one or more electrons.
Electron donor: The atom that loses electrons.
Both anions and cations are formed whenever electron transfer between atoms occurs. Because opposite charges attract, these ions tend to stay close together, resulting in an ionic bond.
Ionic bonds are commonly formed between atoms with one or two valence shell electrons and atoms with seven valence shell electrons .
Crystals: Large arrays of cations and anions held together by ionic bonds.
Covalent Bond: Electron sharing produces molecules in which the shared electrons occupy a single orbital common to both atoms.
Hydrogen with its single electron can fill its only shell (shell 1) by sharing a pair of electrons with another atom.
When it shares with another hydrogen atom, a molecule of hydrogen gas is formed.
The shared electron pair orbits around the molecule as a whole, satisfying the stability needs of each atom.
When two atoms share one pair of electrons, a single covalent bond is formed (indicated by a single line connecting the atoms, such as H¬H).
Nonpolar molecules: The molecules formed are electrically balanced. There has no separation of charge, so no positive or negative poles are formed.
Polar molecule: A molecule containing polar bonds where the sum of all the bond's dipole moments is not zero.
Electronegativity: The tendency for an atom of a given chemical element to attract shared electrons (or electron density) when forming a chemical bond.
Electropositivity: A measure of an element's ability to donate electrons, and therefore form positive ions; thus, it is antipode to electronegativity.
Dipole: Any molecule or radical that has delocalised positive and negative charges
Hydrogen bonds: It is formed when a hydrogen atom, already covalently linked to one electronegative atom (usually nitrogen or oxygen), is attracted by another electron-hungry atom, so that a “bridge” forms between them.
Hydrogen bonding is common between dipoles such as water molecules, because the slightly negative oxygen atoms of one molecule attract the slightly positive hydrogen atoms of other molecules.
Hydrogen bonding is responsible for the tendency of water molecules to cling together and form films, referred to as surface tension.
Although hydrogen bonds are too weak to bind atoms together to form molecules, they are important intramolecular bonds (literally, bonds within molecules), which hold different parts of a single large molecule in a specific three-dimensional shape.
H + H → H2 (hydrogen gas)
4H + C → CH4 (methane)
Synthesis Reaction: Also known as a Combination reaction, it occurs when atoms or molecules combine to form a larger, more complex molecule.
Decomposition Reaction: This occurs when a molecule is broken down into smaller molecules or its constituent atoms.
Exchange Reaction: Also known as the displacement reaction, it involve both synthesis and decomposition.
Oxidation-Reduction Reaction: Also known as a redox reaction.
Cellular Respiration: A series of chemical reactions that break down glucose to produce ATP, which may be used as energy to power many reactions throughout the body.
A + B ⥂ AB
A + B ⇌ AB
}}Maintaining proper ionic balance in our body fluids is one of the most crucial homeostatic roles of the kidneys. When this balance is severely disturbed, virtually nothing in the body works. All the physiological activities listed above and thousands of others are disrupted and grind to a stop.}}
Organic molecules are very large molecules, but their interactions with other molecules typically involve only small, reactive parts of their structure called functional groups.
Polymers: Chainlike molecules made of many similar or repeating units which are joined together by dehydration synthesis.
Carbohydrates: A group of molecules that includes sugars and starches, represent 1–2% of cell mass.
Monosaccharides: Simple sugars.
(CH2O)n
— where n is the number of carbons in the sugar.Disaccharides: Double sugar.
Polysaccharides: Polymers of simple sugars linked together by dehydration synthesis.
Lipids: These are insoluble in water but dissolve readily in other lipids and in organic solvents such as alcohol and ether.
Triglycerides: Neutral fats.
Phospholipids: Modified triglycerides.
Steroids: Flat molecules made of four interlocking hydrocarbon rings.
Fat-soluble vitamins
Eicosanoids: Group of molecules derived from fatty acids found in all cell membranes.
Lipoproteins: Lipoid and protein-based substances that transport fatty acids and cholesterol in the bloodstream.
Protein: Composes 10–30% of cell mass and is the basic structural material of the body.
Amino acids: Building blocks of proteins.
Fibrous proteins: Extended and strandlike proteins.
Globular proteins: Compact, spherical proteins that have at least tertiary structure.
Protein Denaturation: Occurs when hydrogen bonds begin to break when the pH drops or the temperature rises above normal (physiological) levels, causing proteins to unfold and lose their specific three-dimensional shape.
Molecular Chaperones: Helps proteins to achieve their functional threedimensional structure.
Enzymes: Globular proteins that act as biological catalysts.
Primary structure of a protein — the linear sequence of amino acids composing the polypeptide chain.
Secondary structure of a protein — the primary chain twist or bend upon themselves to form this.
Tertiary structure of a protein — Achieved when α-helical or β-pleated regions of the polypeptide chain fold upon one another to produce a compact ball-like, or globular, molecule.
Quaternary structure of a protein — When two or more polypeptide chains aggregate in a regular manner to form a complex protein.
CHARACTERISTIC | DNA | RNA |
---|---|---|
Major cellular site | Nucleus | Cytoplasm |
Major functions | Is the genetic material; directs protein synthesis; replicates itself before cell division | Carries out the genetic instructions for protein synthesis |
Sugar | Deoxyribose | Ribose |
Bases | Adenine, guanine, cytosine, thymine | Adenine, guanine, cytosine, uracil |
Structure | Double strand coiled into a double helix | Single strand, straight or folded |
Glucose: The most important cellular fuel, but none of the chemical energy contained in its bonds is used directly to power cellular work.
Adenosine Triphosphate (ATP): The primary energy-transferring molecule in cells and it provides a form of energy that is immediately usable by all body cells.
Adenosine Diphosphate: A compound consisting of an adenosine molecule bonded to three phosphate groups, present in all living tissue.