Download Chemical Basis of Life Chapter 2

Chemical Basis of Life
Chapter 2
Chemistry - study of matter
Biochemistry-chemistry of
organisms
2.1: Introduction
Why study chemistry in an
Anatomy and Physiology class?
- Body functions depend on cellular functions
- Cellular functions result from chemical changes
- Biochemistry helps to explain physiological processes
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2.2: Structure of Matter
Matter – anything that takes up space and has mass (weight).
It is
composed of elements.
Elements – composed of chemically identical atoms:
• Bulk elements – required by the body in large amounts
• Trace elements - required by the body in small amounts
• Ultratrace elements – required by the body in very minute amounts
Atoms – smallest particle of an element
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Structure of Matter
A. Atoms-basic unit
1. Nucleus
a. proton- “+”, 1 amu
b. neutron- no charge, 1 amu
2. Energy Levels/Shells
a. electron- “-”, 0 amu
2,8,8
• All atoms are electrically neutral
because the # of p+ = # of e-.
• Atomic number = # of protons.
• Atomic weight = # of protons +
neutrons.
• Isotopes-atoms of the same element
having different atomic masses.
• Radioactive isotopes-an isotope which
easily loses subatomic particles.
Molecules and Compounds
Molecule – particle formed when two or more atoms chemically
combine
Compound – particle formed when two or more atoms of different
elements chemically combine
Molecular formulas – depict the elements present and the
number of each atom present in the molecule
H2
C6H12O6
H2O
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Bonding of Atoms: Ions
Ion
• An atom that gains or loses electrons to become stable
• An electrically charged atom
Cation
• A positively charged ion
• Formed when an atom loses
electrons
11p+
12n0
17p+
18n0
Anion
• A negatively charged ion
• Formed when an atom gains
electrons
Sodium atom (Na)
Chlorine atom (Cl)
(a) Separate atoms
If a sodium atom loses an electron to a chlorine atom, the sodium
atom becomes a sodium ion (Na+), and the chlorine atom becomes
a chloride ion (Cl–).
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Covalent Bonding
• occurs when the atoms forming the
bond SHARE one or more pairs of
electrons
• this results in MOLECULES
• Each “dash” represents a pair of shared
electrons (single covalent bond)
Bonding of Atoms:
Structural Formula
• Structural formulas show how atoms bond and are arranged in various
molecules
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H
H
H
H2
O
O
O2
H
O
H2O
O
C
CO2
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O
Bonding of Atoms:
Polar Molecules
Polar Molecules
• Molecule
with a slightly negative end and a slightly positive
end
• Results when electrons are not shared equally in covalent
bonds
Slightly negative end
• Water is an important polar molecule
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(a)
Slightly positive ends
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Hydrogen Bonds
Hydrogen Bonds
• A weak attraction between the positive end of one polar molecule and
the negative end of another polar molecule
• Formed between water molecules
• Important for protein and nucleic acid structure
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H
H
O
H
O
H
O
H
O
H
H
O
(b)
Hydrogen bonds
H
H
H
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Chemical Reactions
Chemical reactions occur when chemical bonds form or break among
atoms, ions, or molecules
Reactants are the starting materials of the reaction - the atoms, ions, or
molecules
Products are substances formed at the end of the chemical reaction
NaCl  Na+ + ClReactant
Products
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Chemical Reactions
• SYNTHESIS - “A + B---> AB”
Ex: H2 + O2---> H2O
• DECOMPOSITION - “AB ---> A + B”
Ex: 2H2O ---> 2H2 + O2
• EXCHANGE - “AB + CD ---> AD + CB”
Ex: HCl + NaOH ---> NaCl + H2O
• Many reactions are reversible
Ex: A + B <---> AB
Acids, Bases, and Salts
Electrolytes – substances that release ions in water
NaCl  Na+ + ClAcids – electrolytes that dissociate to release hydrogen ions
in water
HCl  H+ + ClBases – substances that release ions that can combine with hydrogen
ions
NaOH  Na+ + OHSalts – electrolytes formed by the reaction between an acid and a
base
HCl + NaOH  H2O + NaCl
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+
H
pH-measurement of the
concentration of a solution
0<---------7---------->14
acidic alkaline
(basic)
distilled water is
neutral, having a pH
of 7.0
blood pH = 7.4
if below--->acidosis
if above--->alkalosis
pH scale ranges from
0 - 14
Figure 02.10
Chemistry of Cells
Organic -contain C & H
Inorganic-don’t contain both C & H
2.3: Chemical Constituents
of Cells
Organic v. Inorganic Molecules
Organic molecules
• Contain C and H
• Usually larger than inorganic molecules
• Dissolve in water and organic liquids
• Carbohydrates, proteins, lipids, and nucleic acids
Inorganic molecules
• Generally do not contain C
• Usually smaller than organic molecules
• Usually dissociate in water, forming ions
• Water, oxygen, carbon dioxide, and inorganic salts
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Inorganic substances
(usually electrolytes)
Water
2/3 of wt.
Oxygen
Carbon
dioxide
Inorganic
Salts
(electrolyte
balance)
Organic Compounds
Organic compounds almost always
have covalent bonds.
The four types we will discuss are:
1. Carbohydrates
• contain C, H, O---H:O ratio is 2:1
Ex: C6H12O6 C12H22O11
• provide immediate energy source
• short-term energy storage
• carbon is in short chains or RINGS
• Monosaccharides (simple sugars) examples
are: glucose, fructose, galactose, ribose,
deoxyribose
• Disaccharides (double sugars): examples
are sucrose, lactose, maltose. These are
each made of 2 rings of carbons (2 simple
sugars joined together.
• Polysaccharides: examples are starch,
glycogen (animal starch), and cellulose.
These are made of many rings of carbon
(many simple sugars joined together).
Figure 02.12
2. Lipids
• provide long-term energy storage
• water insoluble (either the entire molecule
or part of the molecule)
• cell structure, vitamins, hormones
• types: fats, phospholipids, cholesterol
Fats (animal fats, oils)
• made of C,H,&O, but H:O ratio is MUCH
greater than 2:1 (C57H110O6)
• Each molecule is called a triglyceride, and
is made of 1 glycerol and 3 fatty acids.
• An unsaturated fat has at least one carbon to
carbon double or triple bond in its fatty
acids, and it is usually liquid--good.
• A saturated fat has no C=C or triple, usually
solid--bad.
Phospholipids
• major component of cell membranes
• Each molecule is made of 1 glycerol, 2 fatty
acids, and 1 phosphoric acid
• partially water insoluble
Cholesterol
• important in cell membranes and as source
of steroid hormones
• partially water insoluble
3. Proteins
• structural component of cells, some
hormones, transporters, enzymes
• Each molecule is made of a LONG chain of
amino acids. This chain takes on a 3dimensional shape due to hydrogen bonding
between the amino acids.
• Denaturization-results from the breaking of
H-bonds---alters shape--destroys function
Animation:
Protein Denaturation
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4. Nucleic Acids
• DNA, RNA
• made of chains of nucleotides--each
nucleotide is made of: 5-C sugar,
phosphate, and nitrogenous base
• DNA-found in chromosomes-provides code
for protein production (genes)
• RNA-helps in protein production
Figure 02.21