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© 2014 Pearson Education, Inc.
OBJECTIVESOBJECTIVES
1.1. Define/describe an atom and its subatomic particlesDefine/describe an atom and its subatomic particles
2.2. Describe differences between atoms, isotopes, and Describe differences between atoms, isotopes, and ionsions
3.3. Understand how and why atoms form moleculesUnderstand how and why atoms form molecules
4.4. Know the attributes of waterKnow the attributes of water
5.5. Understand what is pH and what is a bufferUnderstand what is pH and what is a buffer
6.6. Describe the four organic molecules and their Describe the four organic molecules and their functionfunction
Chapter 2:Chapter 2:The Chemistry of Living ThThe Chemistry of Living Thingsings
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Figure 2.3Electron
a) Hydrogen1 proton
1 electron
Proton
Shell
Neutron
Nucleus
b) Oxygen8 protons8 neutrons8 electrons in 2 shells
c) Sodium11 protons11 neutrons11 electrons
in 3 shells
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Energy Fuels Life’s Activities
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
© 2014 Pearson Education, Inc.
Figure 2.4
Potential energy islocked up in the chemical bonds ofenergy-storagemolecules in GregLouganis’ tissues.
Kinetic energy is energy in motion.
© 2014 Pearson Education, Inc.
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)
© 2014 Pearson Education, Inc.
Chemical Bonds Link Atoms to Form Molecules
Chemical bonds: attractive forces holding atoms together
Kinds of chemical bonds– Covalent bonds
– Ionic bonds
– Hydrogen bonds
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Figure 2.5
Hydrogen(H2)
Oxygen(O2)
Water(H2O)
Single covalent bond
Double covalent bond
Two single covalent bonds
Structural representationStructural formula with covalent bond
Written formula
H H
H
H
O O
O
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Figure 2.6
Loss of electron:positive charge
Sodium atom (Na)
+ –
Chlorine atom (Cl) Sodium ion (Na+) Chlorine ion (Cl–)
Sodium chloride molecule (NaCl)
Gain of electron: negative charge
Na NaCl Cl
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Table 2.1
© 2014 Pearson Education, Inc.
When atoms gain, lose, or share they stay close When atoms gain, lose, or share they stay close together, held by attractions called together, held by attractions called chemical bonds chemical bonds
• When is a covalent bond formed?When is a covalent bond formed?
• When is an ionic bond formed?When is an ionic bond formed?
• What is a hydrogen bond?What is a hydrogen bond?
•
© 2011 Pearson Education, Inc.
H HH2O
+ +
–
O
Atoms Combine to Form MoleculesAtoms Combine to Form Molecules
© 2014 Pearson Education, Inc.
Living Organisms Contain Only Certain Elements
Over 100 different elements 99% of body weight consists of 6 elements
– Oxygen
– Carbon
– Hydrogen
– Nitrogen
– Calcium
– Phosphorus
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Water Participates In Chemical Reactions
Synthesis of carbohydrates, proteins, and lipids produces water molecules
Breakdown of carbohydrates, proteins and lipids consumes water molecules
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Figure 2.10
Drain opener
Bleach
Ammonia cleanser
Soapy water
Baking soda
Human blood, tears
Saliva, urine
Black coffee
Tomatoes
Vinegar, cola
Lemon juice
Hydrochloric acid
Concentrated nitric acid
Mo
re a
lkal
ine
Mo
re a
cid
ic
Neutral pH
© 2014 Pearson Education, Inc.
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 H2CO3
If blood is too alkaline: H2CO3 HCO3 H
© 2014 Pearson Education, Inc.
The Organic Molecules of LifeThe Organic Molecules of Life--
--
--What are organic molecules?What are organic molecules?• Contain Contain carboncarbon
•forms 4 covalent bondsforms 4 covalent bonds•The backbone of biological moleculesThe backbone of biological molecules
• Some are called Some are called macromoleculesmacromolecules• Built by Built by dehydration synthesis dehydration synthesis reactionsreactions• Broken down by Broken down by hydrolysishydrolysis reaction reaction• 4 major groups of macromolecules: 4 major groups of macromolecules:
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Lipids: Insoluble in Water
Three important classes of lipids– Triglycerides: energy storage molecules
– Phospholipids: primary component of cell membranes
– Steroids: carbon-based ring structures
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Figure 2.22
Enzyme changes shape
Reactants
Product
Products are released
Reactants approach enzyme
Reactants bind to enzyme
Enzyme
© 2014 Pearson Education, Inc.
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 DNA contains the instructions for producing RNA RNA contains the instructions for producing proteins Proteins direct most of life processes DNA RNA Proteins
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Figure 2.24
Base pair
Phosphate
Sugar
Nucleotide
C
C
G
G
A
A
A
C
G
G
G C
A
T
T
T
T
P
P
P
P
P
P
P
P
P
T
A
© 2014 Pearson Education, Inc.
Nucleic Acids Store Genetic Information
Structure of RNA (ribonucleic acid)– Single–stranded
– Nucleotides contain– Ribose (sugar)– Nitrogenous bases
– Adenine
– Guanine
– Cytosine
– Uracil
© 2014 Pearson Education, Inc.
Figure 2.25
Phosphate
Ribose
Uracil
P
P
P
P
P
C
G
A
(U)
© 2014 Pearson Education, Inc.
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
© 2014 Pearson Education, Inc.
Figure 2.26
Adenosine
Adenosine Adenosine
Adenine (A)
Triphosphate
Ribose
H2O
(ATP) (ADP)
Hydrolysis of ATP produces useful energy for the cell
P P P P P P
H2O
Energy for ATP synthesis comes from food or body stores of glycogen or fat
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.
The structure of ATP.