The Chemistry of Life

1
The Chemistry of Life

• Unit III
• Chapter 2

2
Atoms

• The study of chemistry begins with the basic unit
  of matter, the atom
• Very small (1 million atoms 1cm)
• Atoms are made up of subatomic particles called
  protons, neutrons, and electrons
• Protons are charged
• Neutrons are neutral
• Electrons are charged
• Together, protons and neutrons make up the
  nucleus of an atom (at the center of the atom)
• Electrons are in constant motion in the space
  surrounding the nucleus (much smaller than
  protons neutrons)

3
Elements

• A chemical element is a pure substance that
  consists entirely of one type of atom
• Represented by 1 or 2 letter symbols such as C,
  H, Na
• The number of protons in an atom of an element is
  the elements atomic number
• Example Carbons atomic is 6, meaning that an
  atom of carbon has 6 protons and 6 electrons

4
Isotopes

• Atoms of an element can have different numbers of
  neutrons
• These atoms of the same element that differ in
  the number of neutrons they contain are known as
  isotopes
• The sum of the protons and neutrons in the
  nucleus of an atom is called its mass number
• Because they have the same number of electrons,
  all isotopes of an element have the same chemical
  properties

5
Radioactive Isotopes

• Some isotopes are radioactive, meaning that their
  nuclei are unstable and break down at a constant
  rate over time
• Can be dangerous but useful
• Geologists can determine ages of fossils by
  analyzing the isotopes found in them
• Radioactive isotopes can be used to treat cancers

6
Chemical Compounds

• In nature, most elements are found combined with
  other elements in compounds.
• A chemical compound is a substance formed by the
  chemical combination of two or more elements in
  definite proportions
• Chemical formulas are used to show what elements
  make up a compound
• Example H2O, NaCl

7
Chemical Bonds

• The atoms in compounds are held together by
  chemical bonds
• Bond formation involves the electrons that
  surround each atomic nucleus
• Electrons that are available to form bonds are
  called valence electrons
• The main types of chemical bonds are ionic bonds
  and covalent bonds

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Ionic Bonds

• An ionic bond is formed when one or more
  electrons are transferred from one atom to
  another
• An atom that loses electrons is no longer
  neutral, instead it becomes positively charged
• An atom that gains an electron is no longer
  neutral, instead it becomes negatively charged
• These positively and negatively charged atoms are
  called ions

9
Covalent Bonds

• Sometimes electrons are shared by atoms instead
  of being transferred
• These electrons are located in a region between
  the atoms
• A covalent bond forms when electrons are shared
  between atoms
• The structure that results when atoms are joined
  together by covalent bonds is called a molecule
  (this is the smallest unit of most compounds)

10
Properties of Water

• Water is the most abundant compound in living
  things
• A water molecule is polar because there is an
  uneven distribution of electrons between the
  oxygen and hydrogen atoms
• Because of there partial positive and negative
  charges, polar molecules such as water can
  attract to each other (this is an example of a
  hydrogen bond)
• Cohesion is an attraction between molecules of
  the same substance as a result of hydrogen
  bonding
• Example as water flows through a leaf, the
  water molecules stick to each other because of
  their cohesive properties
• This cohesive property produces high surface
  tension

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Properties of Water

• Adhesion is an attraction between molecules of
  different substances water molecules often
  adhere to other substances
• Example as water flows through a leaf, it
  sticks to the walls of the leaf vein because of
  its adhesive properties this demonstrates
  capillary action by rising up the vein in the
  plant
• Water is an excellent solvent many ionic
  substances are easily dissolved in water
• Water has a high heat capacity the temperature
  of water changes very slowly compared to the
  surrounding air
• Results in evaporative cooling when sweat
  evaporates from your skin, a large amount of heat
  is taken with it and you are cooled
• Ice floats water expands and becomes less dense
  as it freezes

12
The pH Scale

• Chemists have devised a measurement system called
  the pH scale to indicate the concentration of H
  ions in solution
• Ranges from 0 to 14
• At a pH of 7, the concentration of H ions and
  OH- ions is equal (pure water has a pH of 7)
• Solutions with a pH below 7 are called acidic
  because they have more H ions than OH- ions (the
  lower the pH, the greater the acidity)
• Solutions with a pH above 7 are called basic
  because they have more OH- ions than H ions (the
  higher the pH, the more basic the solution)

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Acids

• An acid is any compound that forms H ions in
  solution
• Acidic solutions contain higher concentrations of
  H ions than pure water and have pH values below
  7
• Stomach acid
• Lemon juice
• Tomato juice
• Acid rain
• Normal rainfall
• milk

14
Bases

• A base is a compound that produces hydroxide ions
  (OH- ions) in solution
• Basic, or alkaline, solutions contain lower
  concentrations of H ions than pure water and
  have pH values above 7
• Human blood
• Sea water
• Soap
• Ammonia solution
• Bleach
• Oven cleaner

15
What Life is Made Of

• Living things are composed of
• SULFUR
• PHOSPHORUS
• OXYGEN
• NITROGEN
• CARBON
• HYDROGEN
• REMEMBER SPONCH

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Macromolecules

• Many of the molecules in living cells are so
  large that they are known as macromolecules
• Formed by a process called polymerization (making
  large compounds by joining smaller compounds
  together)
• Smaller unit known as monomer join together to
  form polymers
• Four groups of organic compounds found in living
  things are
• Carbohydrates
• Lipids
• Nucleic acids
• proteins

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Carbohydrates

• Carbohydrates are compounds made up of carbon,
  hydrogen, and oxygen atoms
• Usually found in a ratio of 121
• Living things use carbohydrates as their main
  source of energy
• Plants and some animals also use carbohydrates
  for structural purposes
• The breakdown of sugars, such as glucose,
  supplies immediate energy for all cell activities
• Extra sugar is stored by living things as starch
  (composed of glucose)

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Lipids

• Lipids are a group of molecules that are
  generally not soluble (do not dissolve) in water
• They are made mostly from carbon and hydrogen
  atoms
• Common categories include fats, oils, steroids,
  and waxes
• Lipids can be used to store energy and some
  lipids are important parts of biological
  membranes and waterproof coverings
• Lipids are also used to cushion and insulate the
  body
• Lipids are formed when a glycerol molecule
  combines with 3 fatty acids
• If each carbon atom in a lipids fatty acid chain
  is joined to another carbon atom by a single
  bond, the lipid is said to be saturated
• If there is at least one carbon-carbon double
  bond in a fatty acid, the fatty acid is said to
  be unsaturated

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Nucleic Acids

• Nucleic acids are macromolecules containing
  hydrogen, oxygen, nitrogen, carbon, and
  phosphorus
• They are polymers assembled from individual
  monomers called nucleotides
• Nucleotides consist of 3 parts a 5-carbon
  sugar, a phosphate group, and a nitrogenous base
• Nucleic acids store and transmit hereditary
  (genetic) information
• There are 2 kinds of nucleic acids
• RNA (ribonucleic acid)
• DNA (deoxyribonucleic acid)

20
Proteins

• Proteins are macromolecules that contain nitrogen
  as well as carbon, hydrogen, and oxygen
• They are polymers of molecules called amino acids
• Amino acids are compounds with an amino group
  (-NH2) on one end and a carboxyl group (-COOH) on
  the other end
• Each protein has a specific role
• Some control the rate of reactions and regulate
  cell processes
• Others transport substances into or out of cells
  or help to fight disease
• Others are used to build and repair body tissues
  such as muscles

21
Chemical Reactions

• Everything that happens in an organism its
  growth, its interaction with the environment, its
  reproduction, and even its movement is based on
  chemical reactions
• A chemical reaction is a process that changes one
  set of chemicals into another set of chemicals
• Can occur slowly or very quickly
• The elements that enter into a chemical reaction
  are known as reactants
• The elements or compounds produced by a chemical
  reaction are known as products
• Chemical reactions always involve the breaking of
  bonds in reactants and the formation of new bonds
  in products

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Energy in Reactions

• Energy is released or absorbed whenever chemical
  bonds form or are broken
• Therefore, all chemical reactions involve changes
  in energy
• Some chemical reactions release energy and some
  absorb energy
• Chemical reactions that release energy often
  occur spontaneously
• Chemical reactions that absorb energy will not
  occur without a source of energy

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Activation Energy

• Even chemical reactions that release energy do
  not always occur spontaneously
• Chemists call the energy that is needed to get a
  reaction started the activation energy
• Activation energy is a factor in whether the
  overall chemical reaction releases energy or
  absorbs energy

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Enzymes

• Some chemical reactions that make life possible
  are too slow or have activation energies that are
  too high to make them practical for living tissue
• These chemical reactions are made possible by
  catalysts
• A catalysts is a substance that speeds up the
  rate of a chemical reaction
• Catalysts work by lowering the activation energy
  needed to make the reaction occur

25
Enzymes

• Enzymes are proteins that act as biological
  catalysts
• Cells use enzymes to speed up chemical reactions
  that take place in cells
• Enzymes act by lowering the activation energies
• Enzymes are very specific, generally catalyzing
  only one chemical reaction

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Enzyme Action

• For a chemical reaction to take place, the
  reactants must collide with enough energy so that
  existing bonds will be broken and new bonds will
  be formed
• Enzymes speed up chemical reactions by providing
  a site where reactants can be brought together to
  react
• Such a site reduces the energy needed for the
  reaction by placing the reactants in a position
  favorable for the reaction to occur
• The reactants of enzyme-catalyzed reactions are
  known as substrates
• Enzymes can be affected by changes in pH, changes
  in temperature and can be turned on or off at
  critical stages in the life of a cell