Download Chapter 3 Everyday Chemistry of Life Chemistry is crucial Biology

Chapter 3
Everyday Chemistry of Life
Chemistry is crucial
 Biology, like our entire universe, is dependent upon the laws of chemistry
 The chemistry of life observes the basic laws of chemistry
o
The important chemicals in biology are carbon, hydrogen, oxygen, and
nitrogen
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Chemically, humans also contain small quantities of calcium, phosphorus,
sulfur, sodium, chlorine, and magnesium
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Crucial trace elements include iron, iodine, and selenium
Atomic structure
 Matter is anything that has weight and takes up space
 Elements are the basic building blocks of matter that cannot be broken down by
chemical means
 Atoms are the smallest units of an element that retain the element’s physical and
chemical properties
 Atoms bond together to form molecules
 Subatomic particles of atoms
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Neutrons have a neutral charge
o
Protons are positively charged
o
Neutrons and protons make up the nucleus
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Electrons are negatively charged and orbit the nucleus
 The atomic number equals the number of protons
 The mass number equals the number of protons plus the number of neutrons
Isotopes
o Isotopes are atoms that have the same atomic number (number of protons) but a
different atomic mass because the number of neutrons differ
o Isotopes of an element have the same chemical properties but may have different
physical properties
Molecules
o They are made of atoms that are bonded together
o They can be made up of atoms of the same elements or atoms of different elements
o It’s all about the electrons
o Actually, it’s all about the electrons in the valence shell, the outermost shell
o It’s all about filling the valence shell
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Atoms with filled valence shells are usually unreactive
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Atoms with unfilled valence shells are reactive
 The first (innermost) valence shell fills first and can accommodate
up to 2 electrons
 The second shell can accommodate up to 8 electrons
 The third shell can also accommodate up to 8 electrons
 2, 8, 8, 18*
Chemical bonds
o Atoms form chemical bonds by trying to fill their valence shells
Ionic bonds
o Atoms that give up or take on electrons become ions
o Since these ions have unequal numbers of protons and electrons, they are charged
o Ionic bonds occur between oppositely-charged ions
o
Many ions in the human body can form ionic bonds including calcium
(Ca++), sodium (Na+), potassium (K+), hydrogen (H+), phosphate (PO4---),
bicarbonate (HCO3-), chloride (Cl-), and hydroxyl (OH-)
o
These are all important for maintaining homeostasis
Covalent bonds
o Atoms in this type of bond share electrons
o This results in stable outer valence shells for all atoms involved
o Covalent bonds are very important for biology
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Most covalent bonds in humans involve C, H, O, N
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In most of these bonds, the atoms share the electrons evenly ... except
when hydrogen atoms are involved
What are the properties of water?
o The water molecule is polar
o Liquid at room temperature
o Liquid water does not change temperature quickly
o High heat of vaporization
o Frozen water is less dense than liquid water
o Molecules of water cling together
o A solvent for polar molecules
o Water freezes top down
o Hydrogen bonds make water unique
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Hydrogen bonds occur between the slight positive charge at the hydrogen
end of a molecule and
a molecule with a negative charge
o
These are relatively weak bonds
Chemical bonds can also store energy
o Some chemical reactions release energy
o Other reactions require energy to form bonds
o Energy can be stored in these bonds
o That stored energy will be released when the bonds are broken
Acids and bases
o Acids are substances that dissociate and release hydrogen ions
o Bases are substances that take up hydrogen ions or release hydroxyl ions
The pH scale
o A measure of hydrogen ion concentration
o The working scale is between 0 and 14 with 7 being neutral
o A pH below 7 is acidic and above 7 is basic
o The concentration of ions between each whole number on the scale is a factor of 10
The proper pH
o Hydrogen ion concentration is crucial for the proper function of our cells and body
o Blood pH must be maintained within a precise pH range of 7.4-7.5
Building up and breaking down organic macromolecules
o Dehydration reaction – the removal of water that allows subunits to link together
into larger molecules
o Hydrolysis reaction – the addition of water that breaks larger molecules into their
subunits
The four main forms of organic molecules
1. Carbohydrates
2. Lipids
3. Proteins
4. Nucleic acids
Carbohydrates
o Made of subunits called monosaccharides
o Made of C, H and O in which the C, H and O atoms are usually close to a 1:2:1 ratio
o Function as short and long-term energy storage molecules
o Found as simple and complex forms
Lipids
o Molecules that do not dissolve in water - hydrophobic
o Used as energy molecules
o A major component of cell membranes
o Found as fats and oils, phospholipids and steroids
o Fats
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Usually of animal origin
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Solid at room temperature
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Function as long-term energy storage, insulation from heat loss, and
cushioning for organs
o Oils
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Usually of plant origin
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Liquid at room temperature
o Phospholipids are a specialized form of lipid
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All biological membranes are based on phospholipids
o Steroids
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They are a type of lipid
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They have a structure with four fused carbon rings
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Examples are cholesterol and the sex hormones
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Anabolic steroids mimic testosterone spurring muscle growth
Proteins
o Made of subunits called amino acids
o They are important for a wide variety of functions in the body including hormones,
structure, enzymes, communication, and transport
o All of the huge variety of proteins are composed of the same 20 amino acids
o They can denature, changing in shape, causing loss of function
Amino acids
o All amino acids share a common basic structure
o Their 20 different side chains or R groups give us the 20 different amino acids
o The R group determines the properties of the amino acid
o When two amino acids are joined together via a peptide covalent bond, they form a
dipeptide
o As more amino acids are added to the chain, they form a polypeptide
A protein is functional
Levels of protein organization
o Primary – the linear order of amino acids
o Secondary – localized folding into pleated sheets and helices
o Tertiary – the 3-D shape of the entire protein
o Quaternary – combination of more than one polypeptide
o All proteins have primary, secondary and tertiary structure, while only a few have
quaternary structure
Protein function
o The 3-D shape of a protein is crucial to its function
o The shape is dependent on the primary sequence of amino acids
o Sometimes, changing even one amino acid can destroy the function of a protein
o Other times, changing one amino acid can have no effect
Enzymes
o Enzymes are specialized forms of proteins
o They catalyze chemical reactions
o They are highly specific for their particular substrates
Nucleic acids
o They are made of nucleotide subunits
o They function in the cell to store and convey genetic information
o They include DNA and RNA
The energy currency of the cell
o To perform cellular work, there has to be a form of currency capable of providing a
convenient unit of energy
o Long-term energy storage
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Glycogen in muscle and liver cells
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Fat molecules stored in adipocytes
o Short-term energy storage
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Mainly ATP (adenosine triphosphate)