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The Life of a Cell
The Chemistry of Life
Atoms and Their Interactions
Elements
• Everything – whether it is a rock, frog, or
flower – is made of substances called elements.
• Element: a substance that can’t be broken
down into simpler chemical substances. It is
made of one type of atom.
Natural elements in living things
• Of the naturally occurring elements on Earth,
only about 25 are essential to living
organisms.
• Carbon, hydrogen, oxygen, and nitrogen
make up more than 96 percent of the mass of
a human body.
Trace elements
• Trace elements such as iron and copper, play
a vital role in maintaining healthy cells in all
organisms.
• Plants obtain trace elements by absorbing
them through their roots; animals get them
from the foods they eat.
Table 6.1 Some Elements That Make Up the Human Body
Percent By
Percent By
Element
Element
Symbol Mass in
Symbol Mass in
Human Body
Human Body
Oxygen
Fe
O
65.0
Iron
trace
Zn
Zinc
Carbon
C
18.5
trace
Hydrogen
Cu
H
9.5
Copper
trace
I
Iodine
Nitrogen
N
3.3
trace
Calcium
Ca
1.5
trace
Manganese Mn
Boron
B
1.0
Phosphorus P
trace
Cr
K
Potassium
0.4
Chromium
trace
trace
Molybdenum Mo
Sulfur
S
0.3
Cobalt
Sodium
Co
trace
Na
0.2
Se
Chlorine
0.2
Selenium
trace
Cl
Fluorine
F
Magnesium Mg
0.1
trace
Atoms: The Building Blocks of Elements
• Atom: the smallest particle of an element
that has the characteristics of that element.
• Atoms are the basic building blocks of all
matter.
The structure of an atom
• Nucleus: the center of an atom
• contain positively charged particles called protons
(p+)
• particles with no charge, called neutrons (n0).
• Space surrounding the nucleus contains
negatively charged particles called electrons
(e-)
The Structure of an atom
Nucleus
Electron
energy
levels
The Structure of an atom
• Protons and neutrons are approximately the
same size and mass, however electrons are far
smaller
• Because opposites attract, the negatively
charged electrons are held in the electron cloud
by the positively charged nucleus.
Electron energy levels
• Electrons exist around
the nucleus in regions
known as energy
levels.
Nucleus
8 protons (p+)
8 neutrons (n0)
Oxygen atom
• First energy level can hold two e-.
• Second level can hold a maximum of eight e-.
• Third level can hold up to 18 e-.
Electron energy levels
• An atom of fluorine has nine electrons.
How many electrons are in its second
energy level?
Electron energy levels
• Atoms contain equal numbers of electrons
and protons; therefore, they have no net
charge.
• If an atom of fluorine has nine electrons,
how many protons are in an atom of
fluorine?
•How many e- does phosphorous (P) have?
•How many p+ does P have?
•How do you know?
Isotopes of an Element
• Atoms of the same element always have the
same number of protons but may contain
different numbers of neutrons.
• Isotopes: atoms of the same element that have
different numbers of neutrons
• Carbon-12, carbon-13 and carbon-14 are
examples of isotopes.
Compounds and Bonding
• Compound: a substance that is composed two
or more different elements that are chemically
combined.
• Table salt (NaCl) Chemical
formula
is a compound
composed of the
elements sodium and
chlorine.
•Water (H20)
Hydrogen and
Oxygen by
themselves are
flammable –
together they are
stable…
Bonds: Types and how they form
• Atoms combine with other atoms to become
more stable.
• For many elements, an atom becomes stable
when its outermost energy level is full.
• Sharing electrons with other atoms is
one way for elements to become stable.
• Bonding is how they “share”
• Covalent bond : an
attractive force between
two atoms that share
electrons.
• Molecule : a
group of atoms
held together by
covalent bonds.
It has no overall
charge.
Water
molecule
How covalent bonds form
• Two hydrogen
atoms can combine
with each other
by sharing their
electrons.
• Each atom
becomes stable
by sharing its
electron with
the other atom.
Hydrogen molecule
•Think: full outer shell
Ionic bonds
• An atom (or group of atoms) that gains or
loses electrons and has an electrical charge
and is called an ion.
• Ionic bond : attractive force between two
ions of opposite charge
• Example: A chlorine atom becomes a
chloride ion when it gains an electron.
Hydrogen Bonds
• biological bonds
• Weak bonds (think magnet) between
hydrogen (H+) and oxygen (O-).
– Unequal sharing of electrons making it a polar
molecule
• Hydrogen bonds give water unique properties
Hydrogen Bonds
• Unique properties of water due to H bonds:
• Universal solvent
– Can bond with other water molecules and
molecules of other substances
• Water has a greater resists to changes in
temperature (boiling and feezing)
• Found in all 3 states: gas, a liquid, and a solid
– Less dense when in a solid state
• Helps in temperature regulation of all organisms on
earth
Bonds and Chemical Reactions
• How are bonds and chemical reactions “related” ?
•Chemical reactions occur when bonds are
formed or broken.
• causing substances to recombine into different
substances (ex. burning paper).
•What do you think “Drives” all the breaking
and forming of bonds?
•ENERGY!!!
chemical reactions
• In a chemical reaction there are two parts:
Reactants and Products
Chemical Reactions as Chemical Equations
• 2H + O2 = H2O - chemical equation of Water
•Chemical equations
– Show bonds being broken and formed
– They show the Law of Conservation of
Mass (atoms are neither created nor
destroyed in chemical reactions. They are
simply rearranged.)
Mixtures and Solutions
• Mixture : a combination of substances in
which the individual components retain their
own properties.
• Neither component of the mixture changes.
– Salad, chex mix, sand and water
Mixtures and Solutions
• Solution : a mixture in which one or more
substances (solutes) are distributed evenly in
another substance (solvent).
• Kool-aid, hot coco
Acids and bases
• Chemical reactions can occur only when
conditions are right.
• A reaction may depend on:
- energy availability
- temperature
- concentration of a substance
- pH of the surrounding environment
Acids and bases
• pH : a measure of how acidic or basic a
solution is.
• A scale with values ranging from below 0 to
above 14 is used to measure pH.
More acidic
Neutral
More basic
Acids and bases
•pH below 7 are acidic.
•Acid : any substance that forms hydrogen
ions (H+) in water
More acidic
Neutral
More basic
Acids and bases
• Substances with a
pH above 7 are
basic.
•Base : any
substance that forms
hydroxide ions (OH-)
in water.
pH 11
The Life of a Cell
The Chemistry of Life
Organic Compounds: Macromolecules
The Role of Carbon in Organisms
• Carbon compounds that come from living
organisms are called organic compounds.
• Two carbon atoms can form various types of
covalent bonds—single, double or triple.
Molecular chains
• The small molecules, monomers, bond
together to form large chains called polymers.
• Polymer : a large molecule formed when
many smaller molecules bond together.
• Polymers usually form by covalent bonding.
• There are 4 main organic compounds
– Charbohydrates
– Poteins
– Lipids
– Nucleic Acids
The structure of carbohydrates
• Carbohydrate : composed of carbon, hydrogen,
and oxygen with a ratio of about two hydrogen
atoms and one oxygen atom for every carbon
atom.
The structure of carbohydrates
• Monosaccharide : the simplest type of
carbohydrate; a simple sugar (ie. glucose,
fructose)
• Glucose and fructose combine in a
condensation reaction to form sucrose (table
sugar)
• Which is the reactant and which is the
product?
The structure of carbohydrates
• The largest carbohydrate molecules are
polysaccharides, composed of many
monosaccharide subunits. (ie. potatoes,
liver)
• Which is the monomer?
• Which is the polymer?
The structure of lipids
• Lipids : large biomolecules that are made
mostly of carbon and hydrogen with a small
amount of oxygen. (ie. fats, oils, waxes)
The structure of lipids
• They are insoluble
in water because
their molecules are
nonpolar and
hydrophobic
• (hydro) (phobic)
The structure of lipids
• A fatty acid with single bonds is saturated; with
double bonds is unsaturated
The structure of proteins
• Protein : a large, complex polymer composed of
carbon, hydrogen, oxygen, nitrogen, and
sometimes sulfur.
The structure of proteins
• Amino acids : the basic building blocks of
proteins
• There are about 20 common amino acids that
can make literally thousands of proteins.
The structure of proteins
• Peptide bonds : covalent bonds formed between
amino acids.
The structure of proteins
• Proteins are the building blocks of many
structural components of organisms.
• Enzymes are important proteins found in
living things.
• They speed the reactions in digestion of food.
The structure of proteins
• Enzyme : a protein that changes the rate of a
chemical reaction.
• The sum of all the chemical reactions
occurring in an organism is Metabolism
The structure of nucleic acids
• Nucleic acid : a complex biomolecule that
stores cellular information in the form of a
code.
• Nucleotides : small subunits that make up
nuclei acids
The structure of nucleic acids
• Nucleotides are arranged in three groups—a
nitrogenous base, a simple sugar, and a
phosphate group.
Phosphate
Sugar
Nitrogenous
base
The structure of nucleic acids
• DNA, which stands for deoxyribonucleic acid
is a nucleic acid.
Phosphate
Sugar
Nitrogenous
base
The structure of nucleic acids
• The information coded in DNA contains the
instructions used to form all of an organism’s
enzymes and structural proteins.
• Another important nucleic acid is RNA, which
stands for ribonucleic acid. RNA is a nucleic
acid that forms a copy of DNA for use in
making proteins.