Chapter 2 - The Chemical Basis of Life
Chapter 2 - The Chemical Basis of Life
Chapter 2 - The Chemical Basis of Life
The Chemical
Basis of Life
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Matter
• Elements:
– unique substances, cannot be broken down
by ordinary chemical means
• Atoms:
– more-or-less identical building blocks for each
element
• Atomic symbol:
– 1-2 letter chemical abbrev. for each element
Properties of Elements
Fig. 2.2
Identification of Elements
• Atomic number:
• number of p
• Mass number:
• mass of p and n
• Atomic weight:
• average of mass #s of all isotopes
• Isotope:
• atoms with same # of p but a different # of
n
Chemical Bonds
• Ionic bond:
• formed when 1 atom loses an e and
another accepts that e
• Covalent bond:
• the sharing of e
• Hydrogen bond:
• H atoms (bound covalently to either N or O
atoms) have a small + charge that is
weakly attracted to the small - charge of
other atoms
Ionic Bonds
Fig. 2.4
Polar and Nonpolar Molecules
• Electrons shared
equally between
atoms produce
nonpolar molecules
• Unequal sharing of
electrons produces
polar molecules
Fig. 2.5
Hydrogen Bonds
Figure 2.10a
Molecules and Compounds
Fig. 2.8
Decomposition Reaction
• Breakdown of larger reactants into smaller
products
– Hydrolysis reaction: a decomposition reaction that
uses water
Fig. 2.8
Reversible Reactions
Fig. 2.9
Fig. 2.10
Factors Influencing Rate of Chemical Reactions
• Ranges from 0 to 14
• Indicates the H+ concentration of a
solution
– Neutral solutions have an equal number of H+
and OH– and a pH of 7.0
– Acidic solutions have more H+ than OH– and a
pH of less than 7.0
– Basic (alkaline) solutions have fewer H+ than
OH– and a pH greater than 7.0
pH Scale
• Neutral: pH 7.00
• Acidic: pH 0–6.99
• Basic: pH 7.01–14.00
Fig.
2.11
Acids and Bases
• Salts are formed by the reaction of an acid and a
base
HCl + NaOH → NaCl + H2O
b) In a buffered solution
the added H+ is bound
by the buffer and the
pH change is much
smaller
Fig.
2.12
Blood Buffers
2 H2O + CO2 ↔ H2CO3 + H2O ↔ H3O+ + HCO3-
Biochemistry
• Inorganic chemistry
– Mostly non-C-containing substances
– BUT includes CO, CO2, and HCO3-
• Organic chemistry
– Substances contain C, covalently bonded,
often large
– Usually have C-C or C-H bonding
Inorganic Compounds
• Contain C, H, O
– 1:2:1 (C:H:O)
• major function: supply a source of cellular
food
• Examples
– Monosaccharides – glucose and fructose
– Disaccharides – sucrose and lactose
– Polysaccharides – starch and glycogen
Figure 2.14a
Fig. 2.13
2. Lipids
• Dissolve in nonpolar solvents, such as alcohol or
acetone, but not in polar solvents, such as water
• C, H, and O, but less oxygen in lipids than in
carbohydrates (ratio)
• Examples:
– Fats or triglycerides: energy
– Phospholipids: structural components of cell
membranes
– Eicosanoids: regulate physiological processes
– Steroids: regulate physiological processes
Examples of Lipids Found in the Body
Fig. 2.14
Fatty Acids
• Saturated: only single covalent bonds between carbons
• Unsaturated: one or more double covalent bonds
between carbons
Fig. 2.15
Other Lipids
• Phospholipids: modified triglycerides with 2 fatty
acid groups and a phosphorus group
Fig. 2.16
Other Lipids
• Eicosanoids: 20-C fatty acids found in cell membranes
• Steroids: flat molecules with 4 interlocking HC rings
Fig. 2.17
3. Proteins
• Macromolecules
• C, H, O, N, some S
• 20 basic types of amino acids bound
together with peptide bonds
– Dipeptide: 2 amino acids
– Tripeptide: 3 amino acids
– Polypeptide: Many amino acids
• Proteins are polypeptides of hundreds of
amino acids
Amino Acids (AA)
• Building blocks of
proteins
• Organic acids containing
4 parts:
– amino group (-NH2)
– a carboxyl group (COOH)
– a hydrogen atom
– a side chain designated by the
symbol R attached to the same
carbon atom as the hydrogen
4 Structural Levels of Proteins
• Primary: determined by the # , kind, &
arrangement of amino acids
• Secondary: folding or bending of polypeptide
chain caused by the H bonds between amino
acids (helices and pleated sheets)
• Tertiary: folding of helices or pleated sheets and
the H bonds formed with water
• Quaternary: spatial relationships between 2 or
more proteins that associate to form a functional
unit
Fig.
2.19ab
Fig.
2.19cd
Proteins
• 3 Main Functions
– regulate chemical reactions (enzymes)
– structural - provide framework for many of body’s tissues
– responsible for muscle contraction
• 2 Types
– Fibrous proteins
• Extended and strand-like proteins
• Examples: keratin, elastin, collagen, and certain contractile fibers
– Globular proteins
• Compact, spherical proteins with tertiary and quaternary structures
• Examples: antibodies, hormones, and enzymes
• Denaturation
– Disruption of H bonds, changes shape of proteins and
makes them nonfunctional
Characteristics of Enzymes
• Speed up chemical reactions by lowering the
activation energy
• Most are globular proteins that act as biological
catalysts
• Are chemically specific
• Frequently named for the type of reaction they
catalyze
• Names usually end in -ase
• Chemical events of the body are regulated
primarily by mechanisms that control
– concentration of enzymes
– activity of enzymes
Fig. 2.20
Enzymes
• Enzymes bind to
reactants according to the
lock-and-key model
– shape of both enzyme and
reactants are critical to
function of enzyme
– By bringing the reactants
close to each other it reduces
activation energy for reaction
– Each enzyme catalyzes only
one type of chemical
reaction
– After each reaction the
enzyme is released and can
be used again
Fig. 2.21
4. Nucleic Acids
• C, O, H, N, and P
• basic unit of nucleic acids: nucleotide
– a monosaccharide, phosphate, organic base
• 5 nitrogenous bases contribute to nucleotide
structure:
– adenine (A)
– guanine (G)
– cytosine (C)
– thymine (T)
– uracil (U)
• Two major classes: DNA and RNA
Deoxyribonucleic Acid (DNA)
• Double-stranded helical molecule found in the
nucleus of the cell
• Genetic material of cell
• Replicates itself before cell divides, ensuring
genetic continuity
• Provides instructions for protein synthesis
• Contains the monosaccharide deoxyribose and
the organic bases
– adenine
– thymine
– guanine
– cytosine
Fig. 2.22
Ribonucleic Acid (RNA)