Chapter 2 A&P Lecture, the Chemistry of Life

Chemical Elements

·       Element-simplest form of matter to have unique chemical properties

·       Chemical symbols-letters that represent the element

·       91 naturally occurring elements

·       24 play a role in normal physiology in humans

·       6 account for 98.5% of the body’s weight (O-oxygen, C-carbon, H-hydrogen, N-nitrogen, Ca-calcium, P-phosphorus)

  Water

·       Polar covalent bonds

·       Your body is 50-75 % water

·       Water has properties of solvency, cohesion, adhesion, chemical reactivity, and thermal stability

·       Solvency is the ability to dissolve other chemicals, water is the universal solvent

o   Substances that dissolve in water are called hydrophilic

o   Substances that do not dissolve in water are called hydrophobic

·       Chemical reactivity is waters ability to participate in chemical reactions

o   Water ionizes many other chemicals like salts and acids

o   Water can also ionize itself into H⁺ and OH⁻

o   These ions can be incorporated into other molecules (hydrolysis) or released from them (condensation)

Acids, Bases, and pH

·       acid is a proton donor

·       base is a proton acceptor

·       pH is a measure of acidity derived from the molarity of H⁺ and is symbolized in brackets [H⁺]

·       solutions with pH of 7 are neutral

·       solutions with pH of 1-6 are acidic

·       solutions with pH of 8-14 are basic (alkaline)

·       pH scale is logarithmic, so a change in one number on the scale is actually a tenfold change

·       buffers are chemical solutions that resist changes in pH

Energy and Work

·       energy is the ability or capacity to do work

·       potential energy is the energy stored in an object

·       kinetic energy is the energy of motion

·       chemical energy is potential energy stored in the bonds of molecules

·       heat is the kinetic energy of molecular motion

·       electromagnetic energy is the kinetic energy of moving ‘packets’ of radiation called photons

o   the most familiar form of this is light

·       electrical energy has both potential and kinetic forms

o   it is potential when charged particles accumulate on one side of a cell membrane

o   it becomes kinetic when these particles move across and create an electrical current

·       free energy is the potential energy available in a system to do useful work.

o   In human physiology the most relevant free energy is the energy stored in chemical bonds or organic molecules

Classes of Chemical Reactions:

·       A chemical reaction is a process in which covalent or ionic bonds are formed or broken

·       Chemical equation shows reactants on the left and products on the right, with an arrow pointing from reactants to products

·       Reversible reactions have a double arrow indicting it can go in either direction (A + B↔ AB)

o   Typically follows the law of mass action and proceed from reactants in greater quantity to substances with the lesser quantity

·       Decomposition reactions occur when a large molecule is broken down into two or more smaller ones (A→A+B)

·       Synthesis reactions occur when two or more small molecules combine into a large one (A + B → AB)

Reaction Rates

·       Molecules are in constant motion

·       Rate of reaction depends on nature of reactants and the frequency and force of the collisions between molecules

·       Things that affect reaction rates are:

o   Concentration (more concentration will increase rate of reaction)

o   Temperature (higher temperature will increase the rate of reaction)

o   Catalysts (biological catalysts or enzymes speed up reactions)

Metabolism, Oxidation, Reduction

·       Metabolism is the sum of all chemical reactions

·       Anabolism  builds small molecules into larger ones, and store energy (endergonic reactions)

·       Catabolism breaks down large molecules into smaller ones, and release energy (exergonic reactions)

·       Oxidation-process where electrons are given up and energy is released (LEO)

o   Electron donor or reducing agent

·       Reduction-process where electrons are gained and energy is stored (GER)

o   Oxidizing agent or electron acceptor

·      Organic Compounds --substances that contain carbon

·       carbohydrates-provide energy for the cell

§  -these are necessary for cell structures (glycoprotein)

§  -carbohydrates are water soluble molecules containing carbon, hydrogen, and oxygen in a 1:2:1 ratio

§  -Carbs are classified by size

·       Simple sugars are monosaccharides with 3-7 carbons in a ring or a chain

-        pentoses have 5 carbons (ribose and deoxyribose)

-        hexoses have 6 carbons (the examples below are isomers)

§  These include glucose or dextrose (blood sugar), fructose (fruit sugar), and galactose (C₆H₁₂O₆)

·       Disaccharides are composed of two, six carbon units and include sucrose (table sugar) which is glucose and fructose, lactose (milk sugar)  which is glucose and galactose, and maltose (malt sugar) which is glucose and glucose

·       Complex carbohydrates are also known as polysaccharides

-        One is called cellulose is found in plants.  Humans need this for fiber, but can’t digest it

-        Plant starch is easily digested (potatoes for example)

-        Animals have starch too, but it is called glycogen and it is stored in the muscles and liver

·       Lipids-fatty acids, triglycerides, phospholipids, eiconsanoids, and  steroids

§  -organic chemicals that are insoluble in water so are hydrophobic (won’t dissolve)

§  -these are vital for homeostasis, but should be limited to 30% of the diet

§  -most common type of lipid is fat, which is used for energy (at least twice the energy from sugar)

§  -fat is composed of carbon, hydrogen, and oxygen, but in different proportions than sugar

§  -the building block of fat is the fatty acid molecule and the glycerol molecule

§  -all fats have a carboxyl group (COOH) at the end of a chain of carbons

·       -saturated fatty acids are linked by a single carbon-carbon bond and are saturated with hydrogen molecules

-        these are solid at room temperature and come from animals

-        limit consumption of this type of fatty acid to <10% of your total fat intake per day.

·       -unsaturated fats (like linoleic acid) have some double covalent bonds in between carbons, so they are not completely saturated with hydrogens

-        -these are liquid at room temperature and come from plants, and are more healthy

-        -polyunsaturated fats have two or more double bonds

-        monounsaturated fats have one double bond

-        -triglycerides have a glycerol and 3 fatty acid chains

§  formed by dehydration synthesis (lose water)

§  stored in adipose

-        essential fatty acids must be obtained from the diet

·       trans fats and cardiovascular health (read Deeper insight 2.3)

-        trans fats can pack together and are solid at room temperature

-        cis fats can’t pack closely together and are oils

·       -phospholipids have 2 fatty acid chains and a portion containing a phosphate group

·       -the phosphate group is hydrophilic (water loving) and is called the head

·       -the fatty acid portion is hydrophobic (water fearing) and is called the tail

o   Because of this they are called amphipathic

·       -phospholipids are important in cell membrane construction

·       Eicosanoids are modified 20 carbon fatty acids that are synthesized as needed from arachidonic acid

-        classes include prostaglandins, and leukotrienes

·       prostaglandins play a role in inflammation, blood clotting, hormone action, labor contractions, control of blood vessel diameter, etc

·       steroids are complex rings of carbon and include cholesterol, sex hormones, and adrenal hormones

-        medical condition:  hypercholesterolemia, not enough LDL receptors

-        see Deeper insight 2.4 (good and bad cholesterol)

·       Glycolipids are associated with plasma membranes and serve as cellular binding sites

·       fat soluble vitamins (A, D, E, and K) are also lipids

Proteins

·       -there are both structural and functional proteins

·       -proteins may function as antibody, as receptors on cell surfaces, as energy sources, as chemical messengers, membrane transport, etc

·       -one type of protein is an enzyme

-        -enzymes are modified proteins that act as catalysts and speed up metabolic reactions

-        Enyzmes bind to substrate at the active site and form an enzyme-substrate complex

-        Enzymes usually end in the suffix ‘ase’

-        Factors that change the shape of the enzyme (temperature and pH can alter or destroy the enzymes ability to bind to its substrate

-        Cofactors-enzymes need ‘helpers’ that are nonprotein (inorganic like minerals)

-        If the cofactor is organic and derived from a vitamin like riboflavin they are called coenzymes

-        NAD, FAD, CoA are all coenzymes that are necessary for cellular respiration

·         -proteins are made of building blocks called amino acids (20 different kinds)

-all proteins have an amino group (NH₂), a central carbon (C), a carboxyl group (COOH), and an ‘R’ group

·       peptide bond links amino acids

·       an oligopeptide is a chain of fewer than 10 or 15 amino acids

·       a polypeptide is a chain of 16- or more amino acids

·       protein is a chain of 50 or more amino acids

·       -we have primary, secondary, tertiary, and quaternary structures (see figure 2.24)

·       -proteins can be denatured (destroyed) by high temperatures, radiation, extremes in pH, and some types of chemicals

ATP and other Nucleotides

·      Adenosine triphosphate is the body’s most important energy transfer molecule

·      Require enzymes called ATPases to hydrolyze the 3^rd phosphate

·      ATP↔ADP + P

·      GTP is another nucleotide involved in energy reactions

·      cAMP is a nucleotide formed by the removal both the 2^nd and 3^rd phosphate groups from ATP

Nucleic Acids

·       -these are necessary to give instruction to cells, form genes, and protein synthesis

·       -includes DNA or deoxyribonucleic acid and RNA or ribonucleic acid