Transcript Understanding Our Environment

The Chemistry of Life
Chapter 3
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Outline
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Atoms
 Electrons
 Isotopes
 Radioactive Decay
Molecules
Chemical Bonds
Macromolecules
Origin of Life
How Cells Arose
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Atoms
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Atom - Smallest particle a substance can be
divided into and still retain its chemical
properties.
 Mass - Amount of a substance
 Weight - Force exerted by gravity
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Atoms
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Nucleus - Center of atom
 Protons - Positive charge
 Neutrons - Neutral

Electrons - Negative Charge
- Circles nucleus
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Atoms
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Ions - Atoms in which number of electrons
does not equal number of protons.
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Electrons
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Energy is the ability to perform work.
 Electrons have energy due to their relative
position (potential energy).
When an electron is transferred between
atoms, it retains its energy of position.
Each energy level has a specific number of
orbitals, with each orbital holding up to two
electrons.
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Electrons

In living organisms, chemical energy is
stored by using it to move electrons to
more distant orbits.
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Electrons
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Oxidation - Loss of electron
Reduction - Gain of electron
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Isotopes
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Atomic Number - Number of protons.
Atomic Mass - Number of protons and
neutrons.
Isotopes - Atoms with the same number of
protons but different number of neutrons.
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Radioactive Decay
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Some isotopes are termed radioactive as
they spontaneously decay at a constant rate.
14C.
 Radioisotopic dating uses
- Gradually decays losing neutrons to
form 14N.
 Half-Life is the length of time it takes
to decay half of the substance.
14C = 5,600 yrs.
 Half-Life of
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Radioactive Isotope Dating
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Molecules
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Molecule - Group of atoms held together by
energy.
 Binding force is a chemical bond.
- Ionic Bonds - Form when atoms are
attracted by opposite charges.
 Strong and not directional.
- Covalent Bonds - Formed when atoms
share electrons.
 Strong and very directional.
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Sodium Chloride
(Ionic Bond)
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Water
(Covalent Bond)
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Hydrogen Bonds
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Form in water because shared electrons are
more attracted to oxygen than hydrogen.
 Polar molecule - Positive and negative
poles attracting each other.
- Weak and highly directional.
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Hydrogen Bonds and Water
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Weak hydrogen bonds produce a lattice of
hydrogen bonds within liquid water.
 Requires large input of thermal energy to
disrupt the lattice and raise temperature.
- Evaporating one gram of water from skin
requires 586 calories of heat.
 At low temperatures, few bonds break and
the lattice assumes a crystal-like solid
structure (ice).
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Hydrogen Bonds and Water
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Water molecules are very polar thus are
attracted to other polar molecules.
 Same polar molecule - cohesion.
 Different polar molecule - adhesion.
- Surface tension of water is created by
cohesion.
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Hydrogen Bonds and Water
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Polar molecules are termed hydrophilic
(water-loving).
 All polar molecules that dissolve in water
are termed soluble.
Nonpolar molecules are termed hydrophobic
(water-hating).
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Water
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Covalent bonds within a water molecule
occasionally break spontaneously.
 One proton dissociates and lacks negative
electrons thus becomes a positively
charged ion H+.
- pH scale is a convenient method of
expressing hydrogen ion concentration
of a solution.
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pH
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pH scale defined as negative logarithm of
hydrogen ion concentration.
 Value of seven indicates neutrality (balance
between H+ and OH-).
- Acid - Dissociates in water to increase H+
concentration (pH values below 7).
+
- Base - Combines with H when dissolved
in water (pH values above 7).
 Buffer - Hydrogen ion reservoir that donates
or removes H+ as necessary.
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Macromolecules
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Organisms largely made of four kinds of
molecules:
 Carbohydrates, Lipids, Proteins, and
Nucleic Acids.
 Can be very large - building blocks of cells.
- Polymer - Long chains of similar subunits.
- Organic molecule - Long molecule with
carbon-based core and attached
functional groups.
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Making and Breaking Macromolecules
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Dehydration Synthesis - removal of hydroxyl
group (OH) and hydrogen (H).
 Requires help of enzymes (specialized
proteins) to facilitate positioning.
Hydrolsis - breaking a polymer by adding a
water molecule.
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Carbohydrates
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Any molecule that contains carbon, hydrogen
and oxygen in a 1:2:1 ratio
 Simple carbohydrates - Small molecules
- Simple sugars - monsaccharides
 Complex carbohydrates - Long molecules
- Polysaccharides - sugars liked together
into long polymer chains.
 Starch - Energy storage in plants
 Glycogen - Energy storage in animals
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Lipids
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Oil soluble biological molecules.
 Fat composed of fatty acid and glycerol.
- Fatty acid - long hyrdocarbon chain
ending in carboxyl group (COOH).
 Saturated - all internal carbons contain
maximum number of hydrogen atoms.
 Unsaturated - contain fewer than
maximum number of hydrogen atoms.
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Lipids
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Phospholipid - Modified fat molecule having a
polar group at one end and two long, strongly
nonpolar, ends.
 Forms lipid bilayer in water.
Steroid - Composed of four carbon rings.
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Proteins
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Polymer chains made of amino acid subunits.
 Amino acids - Made of central carbon atom,
with an amino group (-NH2), carboxyl group
(-COOH), hydrogen atom (H), and functional
group.
Peptide bond - Covalent bond linking two
amino acids.
 Polypeptide - Long chain of amino acids
linked by peptide bonds.
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Protein Structure
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Primary - Sequence of amino acids.
Secondary - Initial folding of protein chains.
Tertiary - Final, three-dimensional shape.
Quaternary - Arrangement of multiple chains.
 Denaturation - Process of unfolding chains
(changing shape).
 Catalysis - Enhancing chemical reactions.
- Proteins are catalytic agents of cells.
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Nucleic Acids
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Long polymers of repeating nucleotides.
 Five-carbon sugar, phosphate group, and a
organic nitrogen-containing base.
Deoxyribonucleic Acid (DNA)  Double helix shape due to large bases
bonding with small bases (Adenine Thymine and Guanine - Cytosine)
Ribonucleic Acid (RNA)
 Single Stranded
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Nucleotide
Structure of DNA
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Origin of Life
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Three possibilities for the appearance of first
living organisms on earth:
 Extraterrestrial origin
 Special creation
 Evolution
Bubble model proposes key chemical
processes generating the building blocks of
life took place within bubbles on ocean’s
surface.
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How Cells Arose
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Scientists suspect first macromolecules were
RNA molecules.
First cells may have aggregated
spontaneously.
Before 1.7 billion years ago, only prokaryotes
found in fossil record.
 First microfossils (eukaryotes) appear in
fossil record 1.7 billion years ago.
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How Cells Arose
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Endosymbiotic Theory
 Energy-producing bacteria formed
symbiotic relationship with early eukaryotic
cells. Eventually evolved into mitochondria.
Sexual Reproduction
 Allowed genetic recombination.
Multicellularity
 Assumption of different duties.
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Kingdoms of Life
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Archaebacteria
Eubacteria
Protista
Fungi
Plantae
Animalia
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Evolutions Critics
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Evolution is just a theory…..
There are no fossil intermediates….
Intelligent design….
Violates Second Law of Thermodynamics….
Proteins are too improbable….
Natural Selection does not imply evolution….
Irreducible complexity….
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Review
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Atoms
 Electrons
 Isotopes
 Radioactive Decay
Molecules
Chemical Bonds
Macromolecules
Origin of Life
How Cells Arose
Johnson - The Living World: 3rd Ed. - All Rights Reserved - McGraw Hill Companies
Copyright © McGraw-Hill Companies Permission required for reproduction or display
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