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EXAM I Powerpoint II A Little Chemistry. Chemical elements. Elements are substances that cannot be broken down to other particles by ordinary means. Chemical elements are composed of atoms, which are the smallest units of elements that retain the element’s properties.
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Chemical elements Elements are substances that cannot be broken down to other particles by ordinary means. Chemical elements are composed of atoms, which are the smallest units of elements that retain the element’s properties. There are over 100 known elements but four of them: oxygen (O), hydrogen (H), carbon (C), and nitrogen (N) make up most of your body
Subatomic particles • protons have a positive charge and are found in the nucleus of the atom • electrons have a negative charge and are found orbiting the nucleus in orbits called electron shells • neutrons have no charge and are also found in the nucleus of the atoms
Ionic Bonds An ionic bond is an association between a positive ion (an atom that has lost one or more electrons) and a negative ion (an atom that has gained one or more electrons). These ions are bonded together when one atoms transfers one or more electrons to another, instead of a sharing of electrons. Example Na+Cl-
Covalent Bonds Part I A Covalent bond is an association between two or more atoms involving the sharing of electrons. One, two or three pairs of electrons may be shared between atoms. This ability to share electrons is related to the position of the electrons in the shells
Covalent Bonds Part II 1. Nonpolar covalent bonds occur when both atoms exert the same pull on the shared electrons 2. Polar covalent bonds occur when the atoms do not exert the same pull on the shared electrons. The most attractive atom is slightly negative and the other is slightly positive.
Hydrogen Bonds A Hydrogen bond is a weak association between an atom of a molecule with a neighboring hydrogen atom that is already involved in a polar covalent bond
Water is a special molecule because:
Cohesion, Adhesion, and Surface Tension Cohesion occurs when like substances hold together and adhesion occurs due to the attachment of different substances to each other. Surface tension is the result of cohesion of water molecules
High specific heat water heats up slowly and then holds that heat (it acts as a heat sink)
Thermal conductivity heat spreads rapidly when applied to one part of a body of water
High boiling point water requires a great deal of heat energy to break the hydrogen bonds (holding the water molecules together) and change the liquid water into a gas
Evaporative cooling for example sweating or panting.
High Freezing Point High freezing point and it is less dense as a solid. Ice floats
Part of Chemical Reactions Many substances dissolve in water and it is a part of many chemical reactions
pH A. When water partially dissociates (comes apart) it forms hydrogen ions (H+) and hydroxide ions (OH-) These ions can change the pH (acidity or alkalinity) of a substance depending on the relative concentrations of the types of ions.
pH continued An acid contains more H+ ions A base (or alkaline substance) contains more OH- ions Substances with a pH below 7 are acidic, substances with a pH above 7 are basic or alkaline, and substances with a pH of approximately 7 are neutral
pH Buffers Both acids and bases are very caustic and in general damage proteins, cells, and tissues. Thus pH is under homeostatic control. Buffers are substances that help stabilize pH by combining with and/or releasing H+. For example HCO3- + H+ - H2CO3 (bicarbonate + hydrogen ion carbonic acid)
Organic compounds Compounds are substances that are composed of atoms or two or more different elements. There are four very important types of biological compounds and all of these are organic (they contain C)
Lipids organic compounds that are not soluble in water (they are nonpolar). They contain mostly C and H, and are involved in energy storage and cellular structures
Fatty acids are components of cell membranes that are made of a long hydrocarbon chain (the backbone - which is hydrophobic or water hating) with an attached carboxyl group (which is polar and hydrophilic or water loving). Some of these are trans fats (unhealthy) and others are cis fats (less unhealthy in moderation). A saturated fat contains all single bonds and is solid (e.g., Crisco shortening) and an unsaturated fat (oil) contains one or more double bonds is more liquid (e.g., Crisco cooking oil) depending on the number of double bonds
Glycerides (neutral fats) are storage lipids (they also function in insulation against cold temperatures) which consist of fatty acid tails attached to a backbone of glycerol
Phospholipids also have a back bone of glycerol, two (not three as in triglycerides) fatty acid tails and one or more phosphate groups. They are important components of cell membranes due to their structure with both hydrophilic and hydrophobic parts.
Steroids are insoluble in water and contain carbon rings (they have no fatty acid tails). Examples include sex hormones and the cholesterols found in cell membranes
Waxes possess long-chain fatty acids and long-chain alcohols or carbon rings. They repel water.
Carbohydrates carbon compounds involved in energy storage (e.g., glucose) or structural molecules (e.g., cellulose found in plant cell walls)
Monosaccharides are simple sugars that contain energy storing bonds (e.g., glucose)
Disaccharides (and other oligosaccharides) are compounds consisting of two monosaccharides that are bonded together. Examples include table sugar (sucrose), and milk sugar (lactose).
Polysaccharides are large compounds often called complex carbohydrates that are composed of many monosaccharides bonded together. Examples: glycogen (energy storage for animals), starch (energy storage for plants ), cellulose (plant cell walls), chitin (exoskeletons of insects)
Proteins Amino acids are the building blocks of proteins
These amino acids are linked together by special bonds called peptide bonds to form proteins or polypeptides
Protein structure involves four levels a. primary structure - the sequence of the amino acids b. secondary structure - the shape of these chains of amino acids (e.g., alpha helix) c. tertiary structure - the three-dimensional shape d. quaternary structure or associations between the individual chains of proteins that are made up of more than one polypeptide
Enzymes are special proteins (with few exceptions all enzymes are proteins), that act as catalysts (they speed up reactions). Each enzyme is specific in that it reacts with a particular substrate in what is called a “lock and key” mechanism. Enzymes are greatly affected by the concentrations of the substrate, inhibitors, pH changes, and temperature changes.
Nucleic acids Nucleotides are the building blocks of DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). DNA is the heritable material that codes for proteins. It exists are a double helix and is generally double stranded, and contains the sugar deoxyribose RNA (usually single stranded and contains the sugar ribose) is the compound that directs the information encoded in DNA in the formation of proteins. Thus we have • DNA > RNA > proteins