Lewis/Life - Review of Key Concepts

Review of Key Concepts - Chapter 3

All life consists of chemicals. Chemicals affect our lives in many ways.
Organisms obtain energy from the environment and convert it to a usable form. Matter can be broken down into pure substances called elements. Elements are organized in the periodic table according to their number of subatomic particles. Bulk elements, those essential to life in large quantities, include carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus.
An atom is the smallest unit of an element. Subatomic particles include the positively charged protons and neutral neutrons that form the nucleus and the negatively charged, much smaller electrons that circle the nucleus.
Atomic number is an element's characteristic number of protons, and the atomic weight is the weight of its protons and neutrons. Isotopes of an element differ by the number of neutrons.
Compounds are built of bonded atoms of different elements, in a consistent ratio. A molecule is the smallest unit of a compound that retains the characteristics of that compound. A compound's characteristics differ from those of its constituent elements.
Chemical shorthand indicates the numbers of atoms and molecules in a compound. In a chemical reaction, different compounds are broken down and form, but the total number of atoms of each element remains the same.
Electrons move constantly; they occupy volumes of space called electron orbitals, which form levels of energy called energy shells.
An atom's tendency to fill its outermost shell with valence electrons drives atoms to bond and form molecules.
Covalent bonds share electrons and form between atoms that have three, four, or five valence electrons. Carbon atoms form up to four covalent bonds and build hydrocarbons. A nonpolar covalent bond shares all electrons equally. In a polar covalent bond, the nucleus of one type of atom attracts electrons more than the nucleus of another type of atom, resulting in opposite charges in different parts of the molecule.
In an ionic bond, an atom with one, two, or three valence electrons loses them to an atom with seven, six, or five valence electrons, respectively; the resulting bonds form a lattice of positively and negatively charged ions. Ionic bonds in organisms are weak.
Hydrogen bonds form when a hydrogen in one molecule is drawn to part of a neighboring molecule because of unequal electrical charge distribution.
van der Waals attractions occur between parts of molecules that are temporarily oppositely charged.
Most biochemical reactions occur in an aqueous environment. Water is cohesive and adhesive, enabling many substances to dissolve in it. Water helps regulate temperature in organisms because of its high heat capacity and high heat of vaporization. pH is a measure of H{pos} concentration, or how acidic or basic a solution is. Water has a pH of 7, which means that the numbers of H{pos} and OH{neg} in water are equal.
An acid adds H{pos} to a solution, lowering the pH below 7. A base adds OH{neg}, raising pH to between 7 and 14. Buffer systems consisting of weak acid-and-base pairs maintain the pH ranges of body fluids.
The hydrogen bonds that keep water fluid are constantly forming and breaking. Water is a solvent for salts and for polar covalent bonds. Freezing water expands and becomes less dense.
Carbohydrates provide energy and support. They consist of carbon, hydrogen, and oxygen in the ratio 1:2:1. Monosaccharides contain three to seven carbons and differ from each other by how their atoms are bonded. Oligosaccharides consist of 2 to 100 monomers and include the disaccharides. Two monosaccharides combine to form a disaccharide by dehydration synthesis. Polysaccharides are long polymers of monosaccharides (sugars) linked by dehydration synthesis.
Lipids are a diverse group of organic compounds that provide energy, slow digestion, waterproof the outsides of organisms, cushion organs, and preserve body heat. Lipids include fats and oils, do not dissolve in water, and contain carbon, hydrogen, and oxygen but have less oxygen than carbohydrates. Triglycerides consist of glycerol and three fatty acids, which may be saturated (no double bonds), unsaturated (at least one double bond), or polyunsaturated (more than one double bond). Double bonds make a lipid oily at room temperature, whereas saturated fats are more solid. Unsaturated fats and omega-3 fatty acids are more healthful to eat than are saturated fats and omega-6 fatty acids. Sterols are lipids containing four carbon rings.
Proteins have many functions and a great diversity of structures. They consist of 20 types of amino acids, each of which includes a hydrogen, an amino group, an acid or carboxyl group, and an R group bonded to a central carbon. Amino acids join by forming peptide bonds through dehydration synthesis. A protein's conformation, or three-dimensional shape, is vital to its function and is determined by the amino acid sequence (primary structure) and interactions between amino acids close together (secondary structure) and far apart (tertiary structure) in the sequence. Water molecules and chaperone proteins also contribute to conformation. A protein with more than one polypeptide has a quaternary structure.
Nucleic acid sequences encode amino acid sequences. DNA and RNA are polymers consisting of a sugar-phosphate backbone and sequences of nitrogenous bases. DNA includes deoxyribose and the bases adenine, cytosine, guanine, and thymine. RNA contains ribose and has uracil instead of thymine. A nucleotide, a nucleic acid monomer, consists of a phosphate, a base, and a sugar. DNA can replicate. DNA carries genetic information. RNA translates the information to enable the cell to synthesize proteins.