Transcript Chapter 2

Chapter 2:
The Chemistry of Living Things
OBJECTIVES
1. Define/describe an atom and its subatomic particles
2. Describe differences between atoms, isotopes, and
ions
3. Understand how and why atoms form molecules
4. Know the attributes of water
5. Understand what is pH and what is a buffer
6. Describe the four organic molecules and their
function
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All Matter Consists of Elements
 Chemistry: the study of matter
 Matter
– Anything that has mass and occupies space
– Composed of elements
 Elements
– Cannot be broken down to a simpler form
– Periodic table of elements—lists all known elements
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Atoms—Smallest Functional Units of an Element
 Atoms consist of
– Nucleus (central core)
– Protons
– positive charge
– have mass
– Neutrons
– no charge
– have mass
– Shells (surrounding nucleus)
– Electrons
– negative charge
– no discernable mass
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Figure 2.3
Electron
Proton
a) Hydrogen
Shell
1 proton
1 electron
Neutron
b) Oxygen
Nucleus
8 protons
8 neutrons
8 electrons
in 2 shells
c) Sodium
11 protons
11 neutrons
11 electrons
in 3 shells
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More About Atoms
 Atomic symbol: one or two letters
– Na: sodium
– O: oxygen
 Atomic number
– Number of protons, always the same number for any
atom of a particular element
 Atomic mass
– Roughly equal to number of protons plus neutrons
 In an electrically neutral atom
– Number of protons  number of electrons
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Isotopes Have a Different Number of Neutrons
 Isotopes are atoms of the same element that have a
different number of neutrons
– They will have a different atomic mass
 Unstable isotopes are called radioisotopes: they give
off:
– Energy in the form of radiation, particles
 Some radioisotopes have scientific and medical
uses
– Diagnostic imaging
– Cancer treatment
– Power supply for implants such as cardiac
pacemakers
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Energy Fuels Life’s Activities
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Energy: the capacity to do work
Potential energy: stored energy
Kinetic energy: energy in motion, doing work
Potential energy can be transformed into kinetic
energy
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Figure 2.4
Potential energy is
locked up in the
chemical bonds of
energy-storage
molecules in Greg
Louganis’ tissues.
Kinetic energy is energy
in motion.
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Energy Fuels Life’s Activities
 Electrons have potential energy
– Each shell corresponds to a specific level of potential
energy
– Shells that are farther from the nucleus contain
electrons with more potential energy
 Atoms are most stable when their outermost shell is
full
 Atoms will interact with other atoms to fill their
outermost shells (rule of eight)
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Chemical Bonds Link Atoms to Form Molecules
 Chemical bonds: attractive forces holding atoms
together
 Kinds of chemical bonds
– Covalent bonds
– Ionic bonds
– Hydrogen bonds
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Covalent Bonds Involve Sharing Electrons
 Covalent bonds form when atoms share electrons
 Very strong bonds
 Nonpolar covalent bonds: electrons are shared
equally
– H2
– O2
 Polar covalent bonds: electrons are NOT shared
equally
– H2O: The oxygen has a stronger pull on the shared
electrons than the hydrogen does
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Figure 2.5
Written
formula
Structural representation
Hydrogen
(H2)
H
H
Single covalent bond
Oxygen
(O2)
O
O
Double covalent bond
Water
(H2O)
O
H
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H
Two single
covalent bonds
Structural
formula with
covalent bond
Ionic Bonds Occur Between Oppositely Charged Ions
 Ion: an electrically charged atom or molecule
 Positively charged ion: forms if an atom or molecule
loses electrons
 Negatively charged ion: forms if an atom or molecule
gains electrons
 Ionic bond: attractive force between oppositely
charged ions
 Example: NaCl
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Figure 2.6
Loss of electron:
positive charge
+
Gain of electron:
negative charge
–

Na
Cl
Na
Cl
Sodium atom (Na)
Chlorine atom (Cl)
Sodium ion (Na+)
Chlorine ion (Cl–)
Sodium chloride molecule (NaCl)
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Hydrogen Bonds Form between Polar Molecules
 Hydrogen Bonds
 Weak hydrogen bonds form between oppositely
charged regions of polar molecules
–
–
–
–
Example:
weak forces between polar water molecules
In DNA
proteins
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Table 2.1
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Atoms Combine to Form Molecules
When atoms gain, lose, or share they stay close
together, held by attractions called chemical bonds
• When is a covalent bond formed?
• When is an ionic bond formed?
• What is a hydrogen bond?
•
–
O
+
H
H2O
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H +
Living Organisms Contain Only Certain Elements
 Over 100 different elements
 99% of body weight consists of 6 elements
–
–
–
–
–
–
Oxygen
Carbon
Hydrogen
Nitrogen
Calcium
Phosphorus
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Life Depends on Water
Key properties of water:
–
–
–
–
–
Water is an excellent solvent
Water is liquid at body temperature
Water can absorb and hold heat energy
Evaporation of water uses up heat energy
Water participates in essential chemical reactions
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Water Is the Biological Solvent
 Solvent: liquid in which other substances dissolve
 Solute: any dissolved substance
 Hydrophilic: polar molecules that are attracted to
water and interact easily with water
 Hydrophobic: nonpolar neutral molecules that do
not interact with or dissolve in water
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Water Is a Liquid at Body Temperature
 Water serves an important transport function in the
blood, which is 90% water
 Water is the main constituent of:
– Intracellular spaces
– Extracellular spaces
 60% of body weight is water
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Water Helps Regulate Body Temperature
 Water absorbs and holds a large amount of heat
energy with only a modest increase in temperature
– Prevents rapid changes in body temperature
 Evaporative cooling enables body to lose excess
heat quickly
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Water Participates In Chemical Reactions
 Synthesis of carbohydrates, proteins, and lipids
produces water molecules
 Breakdown of carbohydrates, proteins and lipids
consumes water molecules
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The Importance of Hydrogen Ions
 Acids
– Donate hydrogen ions (H)
– Increase hydrogen ion concentration in solutions
 Bases
– Accept hydrogen ions
– Decrease hydrogen ion concentration in solutions
 pH Scale
– A measure of hydrogen ion concentration
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The pH Scale Expresses Hydrogen Ion Concentration
 Measure of hydrogen ion concentration in solution
 Ranges from 0 to 14
– Acids: pH  7
– Neutral: pH  7
– Basic: pH  7
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Figure 2.10
More alkaline
Drain opener
More acidic
Neutral pH
Bleach
Ammonia cleanser
Soapy water
Baking soda
Human blood, tears
Saliva, urine
Black coffee
Tomatoes
Vinegar, cola
Lemon juice
Hydrochloric acid
Concentrated nitric acid
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Buffers Minimize Changes in pH
 Minimize pH change
 Help maintain stable pH in body fluids
 Carbonic acid and bicarbonate act as one of the
body’s most important buffer pairs
 HCO3 + H
H2CO3
(reversible reaction)
If blood is too acidic: HCO3 + H
If blood is too alkaline: H2CO3
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H2CO3
HCO3  H
The Organic Molecules of Life
What are organic molecules?
• Contain carbon
•forms 4 covalent bonds
•The backbone of biological molecules
• Some are called macromolecules
• Built by dehydration synthesis reactions
• Broken down by hydrolysis reaction
• 4 major groups of macromolecules:
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Carbohydrates: Used for Energy and Structural
Support
 General formula: Cn(H20)n
 Monosaccharides: simple sugars
–
–
–
–
–
Glucose
Fructose
Galactose
Ribose
Deoxyribose
 Disaccharides: two monosaccharides linked together
– Sucrose: glucose  fructose
– Maltose: glucose  glucose
– Lactose: glucose  galactose
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Polysaccharides Store Energy
 Polysaccharides: thousands of monosaccharides
joined in linear and/or branched chains
– Starch: made in plants; stores energy
– Glycogen: made in animals; stores energy
– Cellulose: indigestible polysaccharide made in plants
for structural support
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Lipids: Insoluble in Water
 Three important classes of lipids
– Triglycerides: energy storage molecules
– Phospholipids: primary component of cell
membranes
– Steroids: carbon-based ring structures
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 Triglycerides:
 Stored in adipose tissue as energy-storage
molecules
 Composed of glycerol and three fatty acids
– Fatty acids may be saturated or unsaturated (in oils)
 Steroids:
 Composed of four carbon rings
 Examples: Cholesterol, hormones e.g. estrogen,
testosterone
 Phospholipids: primary component of cell membranes
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Proteins: Complex Structures Constructed of Amino
Acids
 Long chains (polymers) of subunits called amino
acids
 Amino acids are joined by peptide bonds, which are
produced by dehydration synthesis reactions
 Polypeptide: a polymer of 3–100 amino acids
 Protein: a polypeptide longer than 100 amino acids
that has a complex structure and function
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Enzymes Facilitate Biochemical Reactions
 Enzymes
– Are proteins
– Function as biological catalysts
– Speed up chemical reactions
– Are not altered or consumed by the reaction
– Without enzymes, many biochemical reactions would
not proceed quickly enough to sustain life
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Figure 2.22
Enzyme Reactants
Product
Reactants
approach enzyme
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Reactants
bind to enzyme
Enzyme
changes shape
Products
are released
Nucleic Acids Store Genetic Information
 Nucleic acids are long chains containing subunits
known as nucleotides
 Two types of nucleic acids
– DNA: deoxyribonucleic acid
– RNA: ribonucleic acid
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DNA contains the instructions for producing RNA
RNA contains the instructions for producing proteins
Proteins direct most of life processes
DNA  RNA  Proteins
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Nucleic Acids Store Genetic Information
 Nucleotides: building blocks (monomers) of nucleic
acids
 Each nucleotide contains
– 5 carbon sugar
– Phosphate group
– Nitrogenous base
– Adenine
– Guanine
– Cytosine
– Thymine in DNA & Uracil in RNA
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Nucleic Acids Store Genetic Information
 Structure of DNA (deoxyribonucleic acid)
– Double–stranded
– Nucleotides contain
– Deoxyribose (sugar)
– Nitrogenous bases
– Adenine
– Guanine
– Cytosine
– Thymine
– Complementary base pairing:
– Adenine - Thymine
– Guanine - Cytosine
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Figure 2.24
C
A
G
T
G
Phosphate
Sugar
Nucleotide
A
T
T
A
P
Base pair
C
G
P
G
C
P
P
A
P
T
P
A
T
P
P
G
C
P
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Nucleic Acids Store Genetic Information
 Structure of RNA (ribonucleic acid)
– Single–stranded
– Nucleotides contain
– Ribose (sugar)
– Nitrogenous bases
– Adenine
– Guanine
– Cytosine
– Uracil
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Figure 2.25
Phosphate
Ribose
P
C
P
A
P
G
P
Uracil
(U)
P
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ATP Carries Energy
 Structure and function of adenosine triphosphate
(ATP)
– Universal energy source
– Bonds between phosphate groups contain potential
energy
– Breaking the bonds releases energy
– ATP  ADP  P  energy
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Figure 2.26
Adenosine
H2O
Hydrolysis of ATP
produces useful energy
for the cell
Adenine (A)
Adenosine
P P P
(ATP)
Triphosphate
H2O
Adenosine
P P
(ADP)
Energy for ATP synthesis
comes from food or body
stores of glycogen or fat
Ribose
The structure of ATP.
The breakdown and synthesis of ATP.
The breakdown (hydrolysis) of ATP yields
energy for the cell. The reaction is reversible,
meaning that ATP may be resynthesized
using energy from other sources.
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P