REVIEW
ELEMENTS, ATOMS, AND MOLECULES
Chapter 2
Chemistry of Life
• Living organisms are composed of about 25
chemical elements
– Everything an organism is and does depends on
chemistry
– Chemistry is in turn dependent on the arrangement
of atoms in molecules
– In order to understand the whole, biologists study
the parts (reductionism)
– About 25 different chemical elements
•
Are essential to life
Biology – Mrs. Stolipher
– Carbon, hydrogen, oxygen, and nitrogen
•
Make up the bulk of living matter
CONNECTION
• Trace elements are common additives to
food and water
– Dietary deficiencies in trace elements can
cause various physiological conditions
• Atoms consist of protons, neutrons, and
electrons
– The smallest particle of matter that still retains the
properties of an element is an atom
– Different elements have different types of atoms
–
–
2e–
+
+
Electron
cloud
• A compound is a
substance made of the
joined atoms of two or
more different elements.
+
+
Nucleus
2 +
Protons
2
Neutrons
2 –
Electrons
Mass
number = 4
1
– Atoms whose shells are not full
• Electron arrangement determines the
chemical properties of an atom
•
– Electrons in an atom are arranged in shells,
which may contain different numbers of
electrons
Tend to interact with other atoms and gain, lose, or
share electrons
– These interactions
•
Form chemical bonds
Outermost electron shell (can hold 8 electrons)
First electron shell (can hold 2 electrons)
Electron
Hydrogen (H)
Atomic number = 1
Figure 2.6
Nitrogen (N)
Atomic number = 7
Carbon (C)
Atomic number = 6
Oxygen (O)
Atomic number = 8
• Ionic bonds are attractions between ions of
opposite charge
– When atoms gain or lose electrons
• Charged atoms called ions are created
– An electrical attraction between ions with opposite
charges
•
• Covalent bonds join atoms into molecules
through electron sharing
– In covalent bonds
• Two atoms share one or more pairs of
outer shell electrons, forming molecules
Results in an ionic bond
–
–
+
Transfer of
electron
–
Na
Cl
Na
Sodium atom
Cl
Chlorine atom
Na
Cl
Na+
Sodium ion
Cl–
Chloride ion
Sodium chloride (NaCl)
• Unequal electron sharing creates polar
molecules
– A molecule is nonpolar when its covalently bonded
atoms share electrons equally
– In a polar covalent bond electrons are shared
unequally between atoms, creating a polar
(–)
molecule
(–)
O
Nonpolar molecules do not dissolve well in
water.
The inability of nonpolar molecules to dissolve
in polar molecules is important to organisms.
For example, the shape and function of cell
membranes depend on the interaction of
polar water with nonpolar membrane
molecules.
Example of a polar bond
H
(+)
H
(+)
2
• Polymer mean many monomers
•A monomer is a molecule that is able to bond in long
chains
H
OH
H
H
OH
OH
Unlinked monomer
Unlinked
Short Short
polymer
polymer
H2O
Dehydration
reaction
monomer
– Hydrocarbons are composed of only hydrogen
and carbon
– Organic compounds are composed of H+ & C and
found in living organisms
• May have others elements such as N, O, P, S
– Some carbon compounds are isomers
• Molecules with the same molecular formula
but different structures
OH
OH
H
H
Longer polymer
H
H
H
C
C
H
H
H
H
C
H
H
Ethane
H
H
C
C
H
H
Functional groups help determine the properties of
organic compounds
H
• Functional groups are the groups of atoms that
participate in chemical reactions
Propane
Carbon skeletons vary in length.
H
C
H
H
H
H
H
H
C
C
C
C
H
H
H
H
H
H
H
H
H
C
C
C
H
H
H
Butane
• They are polar, & therefore the molecules they are
attached to are also polar
H
Isobutane
Skeletons may be unbranched or branched.
H
H
H
C
C
C
H
H
H
H
C
H
H
H
H
H
H
C
C
C
C
H
H
H
1-Butene
2-Butene
Skeletons may have double bonds, which can vary in location.
– Hydroxyl groups are characteristic of alcohols
– Carbonyl groups are characteristic of some sugars
– The carboxyl group acts as an acid
– Amino group characteristic of amino acids & proteins
H
H
H
H
C
H
C
H
H
C
C
C
C
H
H
H
C
H
C
C
H
H
C
H
C
C
H
H
H
Cyclohexane
H
Benzene
Skeletons may be arranged in rings.
– Examples of functional groups
Table 3.2
3
CARBOHYDRATES
• Carbo: carbon (C)
• Hydrate: water (H2O)
• Class of organic molecules
– Range in size from small sugars (monosaccharides)
to large polysaccharides
• Are a key source of energy, and they are
found in most foods—especially fruits,
vegetables, and grains.
• Suffix “-ose” indicates that the molecule is a
sugar
– Some polymers are the exception to this rule
(ex. Starch & glycogen)
Monosaccharides are the simplest
carbohydrates
◦ The carbohydrate monomers are
monosaccharides
◦ A monosaccharide has a formula that is a
multiple of CH2O
◦ It also contains hydroxyl groups and a carbonyl
group
◦ Basic function: fuels for cellular work & to make
disaccharides & polysaccharides
◦ Ex. C6H12O6
or
C12H24O12
Watch Carbohydrate video (vc00)
Disaccharides
Polysaccharides
• Monosaccharides can join to form
disaccharides, such as sucrose (table sugar)
and maltose (brewing sugar)
Glucose
Glucose
• Are polymers of monosaccharides
• Just using glucose, organisms can build starch,
glycogen, & cellulose – all of which store sugar for
later use
– Glycogen: used for long term energy storage only
in animals, which can later break it down to get
glucose
– Starch: used for long term energy storage only in
plants
– animals can break it down to obtain glucose
– Cellulose: makes up cell walls of plants & algae
Sucrose
– animals cannot break it down, that’s why it is called fiber
Figure 3.5
Maltose
LIPIDS
Starch granules in
potato tuber cells
Glycogen granules in
muscle tissue
Cellulose fibrils in
a plant cell wall
Cellulose
molecules
Figure 3.7
Glucose
monomer
STARCH
GLYCOGEN
• Are nonpolar molecules that are not soluble in
water. They include fats, phospholipids,
steroids, and waxes.
• Fats are lipids that are mostly energy-storage
molecules
• Are diverse compounds
CELLULOSE
– Consist mainly of C and H atoms linked by nonpolar
covalent bonds
– Have very little oxygen
– General formula: (CH2)n
4
A typical fat (aka triglyceride) contains three fatty
acids bonded to a glycerol molecule backbone.
Fatty
acids
Glycerol
In a saturated fat, all of the carbon atoms in the
chain are bonded to two hydrogen atoms (except
the carbon atom on the end, which is bonded to
three hydrogen atoms).
•
•
•
•
Have only single bonds between the carbons
They are solid at room temperature
Are very flexible
Found in animal products
In an unsaturated fat, some of the carbon atoms are
linked by a “double” covalent bond, each with only one
hydrogen atom, producing kinks in the molecule.
– Double bonds prevent them from solidifying at room
temperature
– Causes molecules to be less flexible
– They don’t pack into solid globules
SATURATED FAT
Saturated and Unsaturated Fatty Acids
UNSATURATED FAT
Double
bond
Why are unsaturated fats healthier
than saturated fats?
• The lack of double bonds in the fatty acid tails of
saturated fats result in long, straight carbon chains.
Unsaturated fats are healthier because…
• the double bonds of unsaturated fats
result in “kinks” in the fatty acid tails.
• Long straight carbon chains can clump together
and attach to the walls of blood vessels.
• these kinks in the molecule reduce
“clumping” of fat molecules in blood vessels.
These cause the buildup of atheroschlerotic
plaque which can lead to disease such as…
• this minimizes the buildup of atheroschlerotic
plaques
•
Arteriosclerosis
Hypertension
Heart attack
Stroke
5
Types of lipids & their functions
PROTEIN
• Fats are used for energy storage, insulation, &
protection
• Phospholipids are a major component of cell &
organelle membranes
– Have both a hydrophobic & a hydrophilic region
• Waxes form waterproof coatings on some animals
to ward off water
General chemical composition: contains C, H, O & N
Is a large molecule formed by linked smaller
molecules called amino acids.
Amino acids are the building blocks of proteins.
– Ex. Insects, plants & humans
• Steroids are hydrophobic
– Cholesterol - important component of cell membranes & helps
maintain membrane fluidity; also functions in the digestion of
fats
– Hormones - signaling molecules of the endocrine system
ex. Male & female sex hormones
– Anabolic steroids - increase muscle mass
An amino group
A carboxyl group
An R group, which distinguishes each of
the 20 different amino acids
H
O
H
N
• Diversity is based on different arrangements of amino
acids
Twenty different amino acids are found in proteins.
Proteins are essential to the structures and activities of
life
– Each amino acid contains
•
•
•
Proteins are the most structurally and functionally
diverse of life’s molecules
C
C
H
•
Types of Proteins
1. Structural: hair, cell’s
cytoskeleton
2. Contractile: part of muscle
&
other motile cells, produces movement
3. Storage: sources of amino acids
4. Defense: antibodies, membrane proteins
5. Transport: hemoglobin, membrane proteins
6. Signaling: hormones, membrane proteins
7. Catalyst: enzymes regulate chemical reactions
OH
R
Amino
group
Carboxyl (acid)
group
NUCLEIC ACIDS
Is a long chain of smaller molecules called
nucleotides.
A nucleotide has three parts: a sugar, a base, and a
phosphate group, which contains phosphorus and
oxygen atoms.
There are two types of nucleic acids—DNA and RNA—
and each type contains four kinds of nucleotides.
DNA, or deoxyribonucleic acid, consists of two strands
of nucleotides that spiral around each other.
RNA, or ribonucleic acid, consists of a single strand of
nucleotides.
Class
Monomer(s)
Carbohydrates
monosaccharides
Proteins
Lipids
Nucleic acids
amino acids
fatty acids
and glycerol
nucleotides
Polymer(s)
polysaccharides
polypeptides
fats, phospholipids,
steroids
polynucleotides
6
Chapter 2
Section 4 Energy and Chemical
Reactions
2
Energy for Life Processes
• Energy is the ability to move or change
matter.
• Energy exists in many forms—including light,
heat, chemical energy, mechanical energy,
and electrical energy—and it can be
converted from one form to another.
• Energy can be stored or released by
chemical reactions.
Chapter 2
Energy and Chemical Reactions
Energy in Chemical Reactions
• In chemical reactions, energy is
absorbed or released when
chemical bonds are broken and
new ones are formed.
• Metabolism is the term used to
describe all of the chemical
reactions that occur within an
organism.
Activation Energy
• The energy needed to start a chemical
reaction is called activation energy.
• Activation energy is simply a chemical
“push” that starts a chemical reaction.
• Even in a chemical reaction that releases
energy, activation energy must be supplied
before the reaction can occur.
Watch video Sec 4 (v01)
Enzymes
Enzyme Specificity
• Enzymes are substances that increase the
speed of chemical reactions.
• A substance on which an enzyme acts during a
chemical reaction is called a substrate.
• Most enzymes are proteins.
• Enzymes act only on specific substrates.
• Enzymes are catalysts, which are substances
that reduce the activation energy of a
chemical reaction.
• An enzyme’s shape determines its activity.
Typically, an enzyme is a large protein with one
or more deep folds on its surface. These folds
form pockets called active sites.
• An enzyme increases the speed of a
chemical reaction by reducing the
activation energy of the reaction.
• The enzyme is NOT changed by the reaction
Watch video Sec 4 (v02)
7
Enzyme Specificity – con’t
• An enzyme acts only on a specific substrate because only that
substrate fits into its active site.
Step 1 When an enzyme first attaches to a substrate, the enzyme’s
shape changes slightly.
Step 2 At an active site, an enzyme and a substrate interact, reducing
the reaction’s activation energy.
Factors in Enzyme Activity
• Any factor that changes the shape of an
enzyme can affect the enzyme’s activity.
• Temperature and pH value can alter an
enzymes effectiveness.
Step 3 The reaction is complete when products have formed.
• The enzymes that are active at any one
time in a cell determine what happens in
that cell.
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