Molecules of Life

1
Molecules of Life

• Chapter 2
• Part 1

2
2.1 Impacts/IssuesFear of Frying

• All living things consist of the same kinds of
  molecules, but small differences in the ways they
  are put together have big effects on health
• Artificial trans fats found in manufactured and
  fast foods raise cholesterol and increase risk of
  atherosclerosis, heart attack, and diabetes

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Video Fear of frying
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Fear of Frying

• Trans fats are made by adding hydrogen atoms to
  liquid vegetable oils

5
trans fatty acid
Fig. 2-1, p. 20
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2.2 Start With Atoms

• All substances consist of atoms
• Atom
• Fundamental building-block particle of matter
• Lifes unique characteristics start with the
  properties of different atoms

7
Subatomic Particles and Their Charge

• Atoms consist of electrons moving around a
  nucleus of protons and neutrons
• Electron (e-)
• Negatively charged subatomic particle that
  occupies orbitals around the atomic nucleus
• Charge
• Electrical property of some subatomic particles
• Opposite charges attract like charges repel

8
Subatomic Particles in the Nucleus

• Nucleus
• Core of an atom, occupied by protons and neutrons
• Proton (p)
• Positively charged subatomic particle found in
  the nucleus of all atoms
• Neutron
• Uncharged subatomic particle found in the atomic
  nucleus

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An Atom
10
an atom
Fig. 2-2a, p. 21
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Elements Different Types of Atoms

• Atoms differ in numbers of subatomic particles
• Element
• A pure substance that consists only of atoms with
  the same number of protons
• Atomic number
• Number of protons in the atomic nucleus
• Determines the element

12
Elements in Living Things

• The proportions of different elements differ
  between living and nonliving things
• Some atoms, such as carbon, are found in greater
  proportions in molecules made only by living
  things the molecules of life

13
Same Elements, Different Forms

• Isotopes
• Forms of an element that differ in the number of
  neutrons their atoms carry
• Changes the mass number, but not the charge
• Mass number
• Total number of protons and neutrons in the
  nucleus of an elements atoms

14
Radioactive Isotopes

• Radioisotope
• Isotope with an unstable nucleus, such as carbon
  14 (14C)
• Radioactive decay
• Process by which atoms of a radioisotope
  spontaneously emit energy and subatomic particles
  when their nucleus disintegrates

15
Carbon 14 A Radioisotope

• Most carbon atoms have 6 protons and 6 neutrons
  (12C)
• Carbon 14 (14C) is a radioisotope with six
  protons and eight neutrons
• When 14C decays, one neutron splits into a proton
  and an electron, and the atom becomes a different
  element nitrogen 14 (14N)

16
Radioactive Tracers

• Researchers introduce radioisotope tracers into
  living organisms to study the way they move
  through a system
• Tracers
• Molecules with a detectable substance attached,
  often a radioisotope
• Used in research and clinical testing

17
Why Electrons Matter

• Electrons travel around the nucleus in different
  orbitals (shells) atoms with vacancies in their
  outer shells tend to interact with other atoms
• Atoms get rid of vacancies by gaining or losing
  electrons, or sharing electrons with other atoms
• Shell model
• Model of electron distribution in an atom

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Shell Models
19
Fig. 2-3 (top), p. 22
20
Fig. 2-3 (a-c), p. 22
21
1 proton
1
2
1 electron
first shell
hydrogen (H)
helium (He)
8
10
6
second shell
carbon (C)
oxygen (O)
neon (Ne)
11
17
18
third shell
sodium (Na)
chlorine (Cl)
argon (Ar)
Fig. 2-3 (a-c), p. 22
22
Stepped Art
Fig. 2-3 (a-c), p. 22
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Animation Shell models of common elements
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Ions

• The negative charge of an electron balances the
  positive charge of a proton in the nucleus
• Changing the number of electrons may fill its
  outer shell, but changes the charge of the atom
• Ion
• Atom that carries a charge because it has an
  unequal number of protons and electrons

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Ion Formation
26
electron gain
Chlorine atom
17p
17
17e
charge 0
Chloride ion
17
17p
18e
charge 1
Sodium atom
electron loss
11p
11
11e
charge 0
Sodium ion
11
11p
10e
charge 1
Fig. 2-4, p. 23
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Fig. 2-4a, p. 23
28
electron gain
Chlorine atom
17p
17
17e
charge 0
Chloride ion
17p
17
18e
charge 1
Fig. 2-4a, p. 23
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Fig. 2-4b, p. 23
30
electron loss
Sodium atom
11p
11
11e
charge 0
Sodium ion
11
11p
10e
charge 1
Fig. 2-4b, p. 23
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Stepped Art
Fig. 2-4, p. 23
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Animation How atoms bond
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Animation PET scan
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Animation The shell model of electron
distribution
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Animation Subatomic particles
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Animation Atomic number, mass number
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Animation Electron arrangements in atoms
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Animation Isotopes of hydrogen
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Video ABC News Nuclear Energy
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Animation Electron distribution
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2.3 From Atoms to Molecules

• Atoms can also fill their vacancies by sharing
  electrons with other atoms
• A chemical bond forms when the electrons of two
  atoms interact
• Chemical bond
• An attractive force that arises between two atoms
  when their electrons interact

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From Atoms to Molecules

• Molecule
• Group of two or more atoms joined by chemical
  bonds
• Compound
• Type of molecule that has atoms of more than one
  element

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Referring to a Molecule
44
Same Materials, Different Results
45
Animation Building blocks of life
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Ionic Bonds and Covalent Bonds

• Depending on the atoms, a chemical bond may be
  ionic or covalent
• Ionic bond
• A strong mutual attraction formed between ions of
  opposite charge
• Covalent bond
• Two atoms sharing a pair of electrons

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An Ionic Bond Sodium Chloride
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ionic bond
11
17
sodium ion (Na)
chloride ion (Cl)
p. 24
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Covalent Bonds

• Molecular hydrogen (HH) and molecular oxygen
  (OO)

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1
1
molecular hydrogen (H2)
8
8
molecular oxygen (O2)
p. 24
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Polarity

• A covalent bond is nonpolar if electrons are
  shared equally, and polar if the sharing is
  unequal
• Polarity
• Any separation of charge into distinct positive
  and negative regions

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Polar and Nonpolar Covalent Bonds

• Nonpolar
• Having an even distribution of charge
• When atoms in a covalent bond share electrons
  equally, the bond is nonpolar
• Polar
• Having an uneven distribution of charge
• When the atoms share electrons unequally, the
  bond is polar

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Importance of Polar Molecules

• A water molecule (H-O-H) has two polar covalent
  bonds the oxygen is slightly negative and the
  hydrogens are slightly positive which allows
  water to form hydrogen bonds

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p. 25
55
1
8
1
water (H2O)
p. 25
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Hydrogen Bonds

• Hydrogen bond
• Attraction that forms between a covalently bonded
  hydrogen atom and another atom taking part in a
  separate covalent bond

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hydrogen bond
p. 25
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Importance of Hydrogen Bonds

• Hydrogen bonds form and break more easily than
  covalent or ionic bonds they do not form
  molecules
• Hydrogen bonds impart unique properties to
  substances such as water, and hold molecules such
  as DNA in their characteristic shapes

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Animation Ionic bonding
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Animation Examples of hydrogen bonds
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Video ABC News Fuel Cell Vehicles
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Animation Sucrose synthesis
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Animation Covalent bonds
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2.4 Water

• All living organisms are mostly water, and all
  chemical reactions of life are carried out in
  water
• Hydrogen bonds between water molecules give water
  unique properties that make life possible
• Capacity to dissolve many substances
• Cohesion (surface tension)
• Temperature stability

65
Polarity and theUnique Properties of Water
66
Fig. 2-7a, p. 26
67
slight negative charge
slight positive charge
slight positive charge
Fig. 2-7a, p. 26
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Fig. 2-7b, p. 26
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Fig. 2-7c, p. 26
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Animation Structure of water
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Water and Solutions

• Polar water molecules hydrogen-bond to other
  polar (hydrophilic) substances, and repel
  nonpolar (hydrophobic) substances
• Hydrophilic (water-loving)
• A substance that dissolves easily in water
• Hydrophobic (water-dreading)
• A substance that resists dissolving in water

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Water and Solutions

• Water is an excellent solvent
• Solvent
• Liquid that can dissolve other substances
• Solute
• A dissolved substance

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Water and Solutions

• Salts, sugars, and many polar molecules dissolve
  easily in water
• Salt
• Compound that dissolves easily in water and
  releases ions other than H and OH-
• Example sodium chloride (NaCl)

74
Water and Solutions

• Water molecules surround the atoms of an ionic
  solid and pull them apart, dissolving it

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Animation Spheres of hydration
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Temperature Stability

• Temperature stability is an important part of
  homeostasis
• Water absorbs more heat than other liquids before
  temperature rises
• Hydrogen bonds hold ice together in a rigid
  pattern that makes ice float
• Temperature
• Measure of molecular motion

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Cohesion

• Cohesion helps sustain multicelled bodies and
  resists evaporation
• Cohesion
• Tendency of water molecules to stick together
• Evaporation
• Transition of liquid to gas
• Absorbs heat energy (cooling effect)

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2.5 Acids and Bases

• Water molecules separate into hydrogen ions (H)
  and hydroxide ions (OH-)
• pH
• A measure of the number of hydrogen ions (H) in
  a solution
• The more hydrogen ions, the lower the pH
• Pure water has neutral pH (pH7)
• Number of H ions OH- ions

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Acids and Bases

• Acid
• Substance that releases hydrogen ions in water
• pH less than 7
• Base
• Substance that releases hydroxide ions (accepts
  hydrogen ions) in water
• pH greater than 7

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A pH Scale
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0
battery acid
1
gastric fluid
acid rain
2
lemon juice
cola
vinegar
more acidic
3
orange juice
tomatoes, wine
4
bananas
beer
bread
5
black coffee
urine, tea, typical rain
corn
6
butter
milk
pure water
7
blood, tears
egg white
8
seawater
baking soda
detergents
9
Tums
toothpaste
10
hand soap
milk of magnesia
more basic
11
household ammonia
12
hair remover
bleach
13
oven cleaner
14
drain cleaner
Fig. 2-9, p. 27
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Animation The pH scale
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Acid Rain

• Sulfur dioxide and other airborne pollutants
  dissolve in water vapor to form acid rain

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Buffer Systems

• Most molecules of life work only within a narrow
  range of pH essential for homeostasis
• Buffers keep solutions in cells and tissues
  within a consistent range of pH
• Buffer
• Set of chemicals that can keep the pH of a
  solution stable by alternately donating and
  accepting ions that contribute to pH

85
CO2 and the Bicarbonate Buffer System

• CO2 forms carbonic acid in water
• CO2 H2O ? H2CO3 (carbonic acid)
• Bicarbonate buffer system
• Excess H combines with bicarbonate
• H HCO3- (bicarbonate) ? H2CO3

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Video ABC News Bottle Backlash
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Video ABC News Water Use
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Video ABC News Water Wars
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3D Animation Dissolution