Ch. 2 The Chemistry of Life
The Chemical Context of Life
Image by Riedell
KEY CONCEPTS:
2.1 Matter consists of chemical elements in pure form
and in combinations called compounds.
2.2 An elements properties depend on the structure of
its atoms
2.3 The formation and function of molecules depend on
chemical bonding between atoms
2.4 Chemical reactions make and break chemical bonds.
NOTES
Atoms
• Atom - the basic unit of matter
• The three particles that make up atoms are
protons, neutrons, & electrons
NOTES
Atoms
• The space surrounding the nucleus of an atom
contains electrons.
• Electron - a negatively charged particle
NOTES
•The nucleus is made up of
protons and neutrons
•Most of the mass of an
atom is concentrated in the
nucleus
Electrons ( - charge)
Protons ( + charge)
Neutrons ( no charge)
Atoms differ in __________
of
NUMBERS
PROTONS
_______, NEUTRONS
________,&ELECTRONS
_______
Image from: http://www.uic.edu/classes/bios/bios100/summer2004/lect02.htm
NOTES
Elements & Isotopes
• Element - a pure substance that consists
entirely of one type of atom
• Isotopes - atoms of the same element with
the same number of protons and electrons
with a different number of neutrons
NOTES
ATOMIC NUMBER & MASS
• The atomic number is determined by the
number of protons.
• The mass number is the sum of the protons
and neutrons.
Questions
If an atom contains 11 protons and 12 neutrons
11
it atomic number is _________
If an atom contains 15 protons, it must contain
15 electrons
15 _______
Isotopes of Carbon
1
2
The mass number of carbon for 1 is _______ for 2
is ________
NOTES
Chemical Compounds
• Compound - a substance formed by the
chemical combination of 2 or more elements
– Ex.) NaCl
NOTES
Chemical Bonds
• The 2 main types of chemical bonds are ionic
bonds & covalent bonds
• Ionic bond - formed when 1 or more electrons
are transferred from 1 atom to another
• Ions - positively & negatively charged atoms
NOTES
Atoms that have gained or
lost electrons are called
ions
- Na
Cl
+
Ions are written
with a + or –
next to their
symbol
NOTES
IONS
Questions
• What type of ion forms when an atom loses
electrons ? ______
Positive
• A chemical bond formed by the transfer of
ionic
electrons is a ___________
bond
Sodium Chloride - An Ionic Bond
NOTES
The types of electrons available to form bonds are
called valence electrons
NOTES
Chemical Bonds
• Covalent bond – formed as a result of sharing
an electron pair.
• Molecule - the smallest unit of most
compounds
What atoms make up a water
molecule?
Two atoms of
hydrogen and one
atom of oxygen
NOTES
The Water Molecule
• A water molecule is polar because there is an
uneven distribution of electrons between the
oxygen & hydrogen atoms
• The most abundant compound in most living
things is water
MOLECULES CAN BE SHOWN
IN DIFFERENT WAYS
Water molecule: http://www.lsbu.ac.uk/water/molecule.html
Electron
configuration
H 2O
Other Images by: Riedell
Chemical
Formula
The Water Molecule
• Cohesion - an attraction between molecules of
the same substance
– Ex.) Water
NOTES
HYDROGEN BONDS
Water molecules are polar because there is an uneven
distribution of electrons between the oxygen and the
hydrogen, with the oxygen side being slightly negative and
the hydrogen side being slightly positive.
EX: water molecules
are held together
by Hydrogen bonds
Hydrogen bond animation
Images from: http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookCHEM2.html
NOTES
CHEMICAL BOND ATTRACTION
Chemical bond attraction in order of
increasing attraction.
Low------------------------------------------high
Hydrogen-------- covalent------- ionic
NOTES
The Water Molecule
• Adhesion - an attraction between molecules
of different substances
– Ex.) Water molecules to glass
NOTES
Solutions & Suspensions
• Mixture - a material composed of 2 or more
elements or compounds that are physically
mixed together, but not chemically combined
• Suspensions- mixtures of water and
undissolved materials.
NOTES
Solutions & Suspensions
• Solution – Evenly distributed mixture of two
or more substances.
• Solute - the substance that is dissolved
• Solvent - the substance in which the solute
dissolves
– Ex.) In a saltwater solution, salt is the solute &
water is the solvent
NOTES
Acids, Bases, and pH
• pH scale - measurement system to indicate
the concentration of H+ ions in solution,
ranges from 0-14
NOTES
Hydrogen Ions
+
(H )
http://www.guardiantrader.com/images/ph_scale.gif
The pH scale
measurement
system
indicates the
concentration
of H+ ions to
determine how
acidic a solution
will be.
More H+ = more acidic
NOTES
Acids, Bases, and pH
• Acid - any compound that forms H+ ions in
solution
• Acidic solutions have higher concentration of
H+ ions than pure water & have pH values
below 7
• The greater the concentration of H+ ions, the
lower the pH number
NOTES
Acids, Bases, and pH
• Base - a compound that produces hydroxide
ions in solution
• Basic, or alkaline, solutions have lower
concentrations of H+ ions than pure water &
have pH values above 7
• The lower the concentration of H+ ions, the
higher the pH value (up to 14)
NOTES
Acids, Bases, and pH
• Buffers - weak acids or
bases that can react
with strong acids or
bases to prevent
sharp, sudden
changes in pH
NOTES
QUESTIONS
If pH of stomach acid and of oven cleaner were measured
where would you find each item on the pH scale using 7
neutral? (above or below 7)
pH stomach acid below 7
pH oven cleaner above 7
A map in New Jersey shows rainfall in South and
North Jersey with pH levels of 4.22 in South Jersey
and 4.40 in North Jersey. According to these
figures, the most acidic rainfall is where?
North Jersey
NOTES
QUESTIONS
A substance with pH of 6 is called
acid
____________
Solutions that contain concentrations of
H+ ions lower than pure water are
Base
____________
NOTES
The Chemistry of Carbon
• Organic compounds - compounds created by
organisms
• 4 groups of organic compounds found in living
things are carbohydrates, lipids, nucleic acids,
& proteins
NOTES
Carbohydrates
• Carbohydrates - compounds made up of
carbon, hydrogen, & oxygen atoms
• Main source of energy for living things
– Ex.) Starches & sugars
– Ex.) Monosaccharides
NOTES
Lipids
• Lipids - made mostly from carbon & hydrogen
atoms
• They can be used to store energy
– Ex.) fats, oils, waxes
NOTES
Nucleic Acids
• Nucleic acids - molecules that store & transmit
genetic information, made up of nucleotides
• Nucleotide - has 3 parts: a 5-carbon sugar, a
phosphate group, & a nitrogenous base
NOTES
Nucleic Acids
• There are 2 kinds of nucleic acids: RNA
(ribonucleic acid) & DNA (deoxyribonucleic
acid)
• RNA contains the sugar ribose, DNA contains
the sugar deoxyribose
NOTES
Proteins
• Proteins - molecules that contain nitrogen,
carbon, hydrogen, & oxygen
• Proteins are made up of chains of amino acids
NOTES
Proteins
• Amino acids - compounds with an amino
group on one end & a carboxyl group on the
other end, there are more than 20 in nature
NOTES
Proteins
- Proteins help to carry out chemical reactions,
transport small molecules in & out of cells, &
fight diseases
NOTES
Chemical Reactions
• Chemical reaction - process that changes, or
transforms, 1 set of chemicals into another
• Reactants - the elements or compounds that enter
into a chemical reaction
• Products - elements or compounds produced by a
chemical reaction
• Chemical reactions always involve changes in the
chemical bonds that join atoms in compounds
NOTES
Energy in Reactions
• Energy is released when chemical bonds are
broken, & absorbed when chemical bonds are
formed
• When energy is released during a chemical
reaction they are usually in the form of heat,
sound or light.
NOTES
Energy Changes
• Chemical reactions that release energy often
occur spontaneously
• Reactions that absorb energy will not occur
without a source of energy
NOTES
Energy Changes
• Organisms need to carry out reactions that
require energy in order to stay alive
• Humans release the energy needed to grow,
breathe, think, & even dream through
chemical reactions
• Chemical reactions occur when humans
metabolize, or break down (digest) food
NOTES
Activation Energy
• Activation energy needed to get a reaction
started.
• If a reaction in one
direction releases
energy, the reaction in
the opposite direction
absorbs energy.
the energy
NOTES
Questions
• When hydrogen and oxygen combine to form
water, water is the product, reactant or both
Product
product and reactant?
• Identify the reactants in the chemical equation
CO2 + H2O -- H2CO3
CO2 + H2O
• Describe the general chemical equation
X + Y - XY in words
X + Y = Reactants
XY = Product
NOTES
Enzymes
• Catalyst - a substance that speeds up the rate
of a chemical reaction
• Enzymes - proteins
that act
as biological
catalysts
– Enzymes speed up
reactions
cells
chemical
that take place in
NOTES
Enzymes
• Enzymes are specific, they catalyze only 1
chemical reaction
• Enzymes provide a site where reactants can be
brought together to react
• Enzymes affect the reactions in living cells by
changing the speed of reaction
• Substrates - the reactants of enzyme-catalyzed
reactions
NOTES
The Enzyme-Substrate Complex
• The enzyme-substrate
is a site
reactants can
together
complex
where
be brought
to react
NOTES
Regulation of Enzyme Activity
• Enzymes may be affected by a change in pH,
temperature, or a change in shape
• pH & temperature cause enzymes to change
their shape, preventing them from fitting
together in the enzyme-substrate complex