Hydrogen Bonds
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Transcript Hydrogen Bonds
2
The Chemical Level of
Organization
PowerPoint® Lecture Presentations prepared by
Jason LaPres
Lone Star College—North Harris
© 2012 Pearson Education, Inc.
An Introduction to the Chemical Level of
Organization
• Chemistry
• Is the science of change
• Topics of this chapter include:
• The structure of atoms
• The basic chemical building blocks
• How atoms combine to form increasingly complex
structures
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2-1 Atoms and Atomic Structure
• Matter
• Is made up of atoms
• Atoms join together to form chemicals with different
characteristics
• Chemical characteristics determine physiology at the
molecular and cellular levels
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2-1 Atoms and Atomic Structure
• Subatomic Particles
• Proton
• Positive charge, 1 mass unit
• Neutron
• Neutral, 1 mass unit
• Electron
• Negative charge, low mass
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2-1 Atoms and Atomic Structure
• Atomic Structure
• Atomic number
• Number of protons
• Nucleus
• Contains protons and neutrons
• Electron cloud
• Contains electrons
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Figure 2-1 The Structure of Hydrogen Atoms
Electron shell
Hydrogen-1
mass number: 1
A typical hydrogen
nucleus contains a
proton and no neutrons.
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Hydrogen-2,
deuterium
Hydrogen-3,
tritium
mass number: 2
mass number: 3
A deuterium (2H)
nucleus contains a
proton and a neutron.
A tritium (3H) nucleus
contains a pair of
neutrons in addition
to the proton.
Table 2-1 Principal Elements in the Human Body
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Table 2-1 Principal Elements in the Human Body
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2-1 Atoms and Atomic Structure
• Elements and Isotopes
• Elements are determined by the atomic number of an
atom
• Remember atomic number = number of protons
• Elements are the most basic chemicals
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2-1 Atoms and Atomic Structure
• Elements and Isotopes
• Isotopes are the specific version of an element based
on its mass number
• Mass number = number of protons plus the number of
neutrons
• Only neutrons are different because the number of
protons determines the element
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2-1 Atoms and Atomic Structure
• Atomic Weights
• Exact mass of all particles
• Measured in moles
• Average of the mass numbers of the isotopes
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2-1 Atoms and Atomic Structure
• Electrons and Energy Levels
• Electrons in the electron cloud determine the reactivity of an
atom
• The electron cloud contains shells, or energy levels that hold a
maximum number of electrons
• Lower shells fill first
• Outermost shell is the valence shell, and it determines
bonding
• The number of electrons per shell corresponds to the number
of atoms in that row of the periodic table
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Figure 2-2 The Arrangement of Electrons into Energy Levels
The first energy level
can hold a maximum of
two electrons.
Hydrogen, H
Atomic number: 1
Mass number: 1
1 electron
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Helium, He
Atomic number: 2
Mass number: 4
(2 protons 2 neutrons)
2 electrons
Figure 2-2 The Arrangement of Electrons into Energy Levels
The second and third
energy levels can
each contain up to 8
electrons.
Lithium, Li
Atomic number: 3
Mass number: 6
(3 protons 3 neutrons)
3 electrons
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Neon, Ne
Atomic number: 10
Mass number: 20
(10 protons 10 neutrons)
10 electrons
2-2 Molecules and Compounds
•
Chemical Bonds
•
Involve the sharing, gaining, and losing of electrons in the
valence shell
•
Three major types of chemical bonds
1. Ionic bonds
•
Attraction between cations (electron donor) and anions
(electron acceptor)
2. Covalent bonds
•
Strong electron bonds involving shared electrons
3. Hydrogen bonds
•
Weak polar bonds based on partial electrical attractions
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2-2 Molecules and Compounds
• Chemical Bonds
• Form molecules and/or compounds
• Molecules
• Two or more atoms joined by strong bonds
• Compounds
• Two or more atoms OF DIFFERENT ELEMENTS
joined by strong or weak bonds
• Compounds are all molecules, but not all molecules are
compounds
• H2 = molecule only
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H2O = molecule and compound
2-2 Molecules and Compounds
• Ionic Bonds
• One atom—the electron donor—loses one or more
electrons and becomes a cation, with a positive
charge
• Another atom—the electron acceptor—gains those
same electrons and becomes an anion, with a
negative charge
• Attraction between the opposite charges then draws
the two ions together
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Figure 2-3a The Formation of Ionic Bonds
Formation of ions
Sodium atom
Attraction between
opposite charges
Formation of an
ionic compound
Sodium ion (Na)
Sodium chloride (NaCl)
Chlorine atom
Chloride ion (Cl)
1 A sodium (Na) atom loses an
electron, which is accepted by a chlorine (Cl) atom. 2 Because the
sodium (Na) and chloride (Cl) ions have opposite charges, they are
attracted to one another. 3 The association of sodium and chloride
ions forms the ionic compound sodium chloride.
Formation of an ionic bond.
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Figure 2-3b The Formation of Ionic Bonds
Chloride ions
(Cl)
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Sodium ions
(Na)
Sodium chloride
crystal. Large
numbers of sodium and
chloride ions form a
crystal of sodium
chloride (table salt).
2-2 Molecules and Compounds
• Covalent Bonds
• Involve the sharing of pairs of electrons between
atoms
• One electron is donated by each atom to make the pair
of electrons
• Sharing one pair of electrons is a single covalent
bond
• Sharing two pairs of electrons is a double covalent
bond
• Sharing three pairs of electrons is a triple covalent
bond
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Figure 2-4 Covalent Bonds in Four Common Molecules
Molecule
Electron Shell Model and
Structural Formula
Hydrogen
(H2)
HH
Oxygen
(O2)
OO
Carbon
dioxide
(CO2)
Nitric
oxide
(NO)
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OCO
NO
2-2 Molecules and Compounds
• Covalent Bonds
• Nonpolar covalent bonds
• Involve equal sharing of electrons because atoms
involved in the bond have equal pull for the electrons
• Polar covalent bonds
• Involve the unequal sharing of electrons because one
of the atoms involved in the bond has a
disproportionately strong pull on the electrons
• Form polar molecules — like water
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Figure 2-5 Polar Covalent Bonds and the Structure of Water
Hydrogen
atom
Hydrogen
atom
Oxygen atom
Hydrogen
atom
Oxygen
atom
2
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2-2 Molecules and Compounds
• Hydrogen Bonds
• Bonds between adjacent molecules, not atoms
• Involve slightly positive and slightly negative portions
of polar molecules being attracted to one another
• Hydrogen bonds between H2O molecules cause
surface tension
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Figure 2-6 Hydrogen Bonds between Water Molecules
2
2
2
2
2
2
KEY
Hydrogen
Oxygen
Hydrogen bond
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2
2-2 Molecules and Compounds
• States of Matter
• Solid
• Constant volume and shape
• Liquid
• Constant volume but changes shape
• Gas
• Changes volume and shape
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2-2 Molecules and Compounds
• Molecular Weights
• The molecular weight of a molecule is the sum of
the atomic weights of its component atoms
• H = approximately 1
• O = approximately 16
• H2 = approximately 2
• H2O = approximately 18
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2-3 Chemical Reactions
• In a Chemical Reaction
• Either new bonds are formed or existing bonds are broken
• Reactants
• Materials going into a reaction
• Products
• Materials coming out of a reaction
• Metabolism
• All of the reactions that are occurring at one time
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Figure 2-7 Chemical Notation
Atoms
The symbol of an element indicates one atom of that element. A number preceding the symbol of an
element indicates more than one atom of that element.
VISUAL REPRESENTATION
CHEMICAL NOTATION
one atom
of hydrogen
one atom
of oxygen
one atom one atom
of hydrogen of oxygen
two atoms
of hydrogen
two atoms
of oxygen
two atoms two atoms
of hydrogen of oxygen
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Figure 2-7 Chemical Notation
Molecules
A subscript following the symbol of an element indicates a molecule with that number of atoms of
that element.
VISUAL REPRESENTATION
hydrogen molecule
composed of two
hydrogen atoms
oxygen molecule
composed of two
oxygen atoms
water molecule composed
of two hydrogen atoms
and one oxygen atom
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CHEMICAL NOTATION
hydrogen oxygen
molecule molecule
water
molecule
Figure 2-7 Chemical Notation
Reactions
In a description of a chemical reaction, the participants at the start of the reaction are called
reactants, and the reaction generates one or more products. An arrow indicates the direction of
the reaction, from reactants (usually on the left) to products (usually on the right). In the following
reaction, two atoms of hydrogen combine with one atom of oxygen to produce a single molecule
of water.
VISUAL REPRESENTATION
Chemical reactions neither create nor destroy
atoms; they merely rearrange atoms into new
combinations. Therefore, the numbers of atoms
of each element must always be the same on
both sides of the equation for a chemical
reaction. When this is the case, the
equation is balanced.
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CHEMICAL NOTATION
Balanced equation
Unbalanced equation
Figure 2-7 Chemical Notation
Ions
A superscript plus or minus sign following the symbol of an element indicates an ion. A single plus
sign indicates a cation with a charge of 1. (The original atom has lost one electron.) A single minus
sign indicates an anion with a charge of 1. (The original atom has gained one electron.) If more than
one electron has been lost or gained, the charge on the ion is indicated by a number preceding the
plus or minus sign.
VISUAL REPRESENTATION
sodium ion
chloride ion
the sodium
the chlorine
atom has lost atom has gained
one electron
one electron
A sodium atom
becomes a sodium ion
Electron lost
Sodium
atom (Na)
Sodium
ion (Na)
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calcium ion
the calcium
atom has lost
two electrons
CHEMICAL NOTATION
sodium
ion
chloride
ion
calcium
ion
2-3 Chemical Reactions
• Basic Energy Concepts
• Energy
• The power to do work
• Work
• A change in mass or distance
• Kinetic energy
• Energy of motion
• Potential energy
• Stored energy
• Chemical energy
• Potential energy stored in chemical bonds
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2-3 Chemical Reactions
•
Types of Chemical Reactions
1. Decomposition reaction (catabolism)
2. Synthesis reaction (anabolism)
3. Exchange reaction
4. Reversible reaction
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2-3 Chemical Reactions
• Decomposition Reaction (Catabolism)
• Breaks chemical bonds
• AB A + B
• Hydrolysis A-B + H2O A-H + HO-B
• Synthesis Reaction (Anabolism)
• Forms chemical bonds
• A + B AB
• Dehydration synthesis (condensation reaction)
A-H + HO-B A-B + H2O
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2-3 Chemical Reactions
• Exchange Reaction
• Involves decomposition first, then synthesis
• AB + CD AD + CB
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2-3 Chemical Reactions
• Reversible Reaction
• A + B AB
• At equilibrium the amounts of chemicals do not change
even though the reactions are still occurring
• Reversible reactions seek equilibrium, balancing opposing
reaction rates
• Add or remove reactants
• Reaction rates adjust to reach a new equilibrium
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2-4 Enzymes
• Chemical Reactions
• In cells cannot start without help
• Activation energy is the amount of energy needed to
get a reaction started
• Enzymes are protein catalysts that lower the
activation energy of reactions
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Figure 2-8 The Effect of Enzymes on Activation Energy
Activation energy
required
Energy
Without
enzyme
With enzyme
Reactants
Stable
product
Progress of reaction
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2-4 Enzymes
• Exergonic (Exothermic) Reactions
• Produce more energy than they use
• Endergonic (Endothermic) Reactions
• Use more energy than they produce
ANIMATION Chemical Reactions: Enzymes
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2-5 Organic and Inorganic Compounds
• Nutrients
• Essential molecules obtained from food
• Metabolites
• Molecules made or broken down in the body
• Inorganic Compounds
• Molecules not based on carbon and hydrogen
• Carbon dioxide, oxygen, water, and inorganic acids, bases, and salts
• Organic Compounds
• Molecules based on carbon and hydrogen
• Carbohydrates, proteins, lipids, and nucleic acids
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2-6 Properties of Water
• Water
• Accounts for up to two-thirds of your total body weight
• A solution is a uniform mixture of two or more
substances
• It consists of a solvent, or medium, in which atoms,
ions, or molecules of another substance, called a
solute, are individually dispersed
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2-6 Properties of Water
• Solubility
• Water’s ability to dissolve a solute in a solvent to
make a solution
• Reactivity
• Most body chemistry occurs in water
• High Heat Capacity
• Water’s ability to absorb and retain heat
• Lubrication
• To moisten and reduce friction
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2-6 Properties of Water
• The Properties of Aqueous Solutions
• Ions and polar compounds undergo ionization, or
dissociation in water
• Polar water molecules form hydration spheres around
ions and small polar molecules to keep them in
solution
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Figure 2-9 The Activities of Water Molecules in Aqueous Solutions
Hydration
spheres
Negative
pole
H
Cl
Positive
pole
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Na
Glucose
molecule
Figure 2-9a The Activities of Water Molecules in Aqueous Solutions
Negative
pole
H
Positive
pole
Water molecule. In a
water molecule, oxygen
forms polar covalent
bonds with two
hydrogen atoms.
Because both hydrogen
atoms are at one end of
the molecule, it has an
uneven distribution of
charges, creating
positive and negative
poles.
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Figure 2-9b The Activities of Water Molecules in Aqueous Solutions
Hydration
spheres
Cl
Na
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Sodium chloride in
solution. Ionic compounds,
such as sodium chloride,
dissociate in water as the
polar water molecules break
the ionic bonds in the large
crystal structure. Each ion in
solution is surrounded by
water molecules, creating
hydration spheres.
Figure 2-9c The Activities of Water Molecules in Aqueous Solutions
Glucose
molecule
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Glucose in solution.
Hydration spheres also
form around an organic
molecule containing
polar covalent bonds. If
the molecule binds
water strongly, as does
glucose, it will be
carried into solution—in
other words, it will
dissolve. Note that the
molecule does not
dissociate, as occurs
for ionic compounds.
Table 2-2 Important Electrolytes that Dissociate in Body Fluids
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2-6 Properties of Water
• The Properties of Aqueous Solutions
• Electrolytes and body fluids
• Electrolytes are inorganic ions that conduct electricity
in solution
• Electrolyte imbalance seriously disturbs vital body
functions
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2-6 Properties of Water
• The Properties of Aqueous Solutions
• Hydrophilic and hydrophobic compounds
• Hydrophilic
• hydro- = water, philos = loving
• Interacts with water
• Includes ions and polar molecules
• Hydrophobic
• phobos = fear
• Does NOT interact with water
• Includes nonpolar molecules, fats, and oils
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2-6 Properties of Water
• Colloids and Suspensions
• Colloid
• A solution of very large organic molecules
• For example, blood plasma
• Suspension
• A solution in which particles settle (sediment)
• For example, whole blood
• Concentration
• The amount of solute in a solvent (mol/L, mg/mL)
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2-7 pH and Homeostasis
• pH
• The concentration of hydrogen ions (H+) in a solution
• Neutral pH
• A balance of H+ and OH
• Pure water = 7.0
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2-7 pH and Homeostasis
• Acidic pH Lower Than 7.0
• High H+ concentration
• Low OH concentration
• Basic (or alkaline) pH Higher Than 7.0
• Low H+ concentration
• High OH concentration
• pH of Human Blood
• Ranges from 7.35 to 7.45
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2-7 pH and Homeostasis
• pH Scale
• Has an inverse relationship with H+ concentration
• More H+ ions mean lower pH, less H+ ions mean higher
pH
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Figure 2-10 pH and Hydrogen Ion Concentration
1 mol/L
hydrochloric
acid
Beer,
vinegar,
wine, Tomatoes,
pickles grapes
Stomach
acid
Extremely
acidic
pH 0
[H] 100
(mol/L)
1
101
Urine
Saliva,
milk
Increasing concentration of H
2
102
3
103
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4
104
5
105
1 mol/L
sodium
hydroxide
6
106
Blood Ocean Household
Pure Eggswater
bleach
water
Neutral
7
107
Household
ammonia
Increasing concentration of OH
8
108
9
109
10
1010
11
1011
12
1012
Oven
cleaner
Extremely
basic
13
1013
14
1014
2-8 Inorganic Compounds
• Acid
• A solute that adds hydrogen ions to a solution
• Proton donor
• Strong acids dissociate completely in solution
• Base
• A solute that removes hydrogen ions from a solution
• Proton acceptor
• Strong bases dissociate completely in solution
• Weak Acids and Weak Bases
• Fail to dissociate completely
• Help to balance the pH
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2-8 Inorganic Compounds
• Salts
• Solutes that dissociate into cations and anions other
than hydrogen ions and hydroxide ions
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2-8 Inorganic Compounds
• Buffers and pH Control
• Buffers
• Weak acid/salt compounds
• Neutralize either strong acid or strong base
• Sodium bicarbonate is very important in humans
• Antacids
• Basic compounds that neutralize acid and form a salt
• Alka-Seltzer, Tums, Rolaids, etc.
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2-9 Carbohydrates
• Organic Molecules
• Contain H, C, and usually O
• Are covalently bonded
• Contain functional groups that determine chemistry
• Carbohydrates
• Lipids
• Proteins (or amino acids)
• Nucleic acids
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Table 2-3 Important Functional Groups of Organic Compounds
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2-9 Carbohydrates
• Carbohydrates
• Contain carbon, hydrogen, and oxygen in a 1:2:1 ratio
• Monosaccharide — simple sugar
• Disaccharide — two sugars
• Polysaccharide — many sugars
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2-9 Carbohydrates
• Monosaccharides
• Simple sugars with 3 to 7 carbon atoms
• Glucose, fructose, galactose
• Disaccharides
• Two simple sugars condensed by dehydration
synthesis
• Sucrose, maltose
• Polysaccharides
• Many monosaccharides condensed by dehydration
synthesis
• Glycogen, starch, cellulose
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Figure 2-12a The Formation and Breakdown of Complex Sugars
DEHYDRATION
SYNTHESIS
Glucose
Fructose
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Sucrose
Figure 2-12a The Formation and Breakdown of Complex Sugars
DEHYDRATION
SYNTHESIS
Glucose
Fructose
Formation of the disaccharide sucrose through
dehydration synthesis.
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Figure 2-12a The Formation and Breakdown of Complex Sugars
DEHYDRATION
SYNTHESIS
Sucrose
During dehydration synthesis, two molecules are joined
by the removal of a water molecule.
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Figure 2-12b The Formation and Breakdown of Complex Sugars
HYDROLYSIS
Sucrose
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Glucose
Fructose
Figure 2-12b The Formation and Breakdown of Complex Sugars
HYDROLYSIS
Sucrose
Breakdown of sucrose into simple sugars by hydrolysis.
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Figure 2-12b The Formation and Breakdown of Complex Sugars
HYDROLYSIS
Glucose
Fructose
Hydrolysis reverses the steps of dehydration
synthesis; a complex molecule is broken down by the
addition of a water molecule.
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Figure 2-13 The Structure of the Polysaccharide Glycogen
Glucose
molecules
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Table 2-4 Carbohydrates in the Body
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2-10 Lipids
• Lipids
• Mainly hydrophobic molecules such as fats, oils, and waxes
• Made mostly of carbon and hydrogen atoms
• Include:
• Fatty acids
• Eicosanoids
• Glycerides
• Steroids
• Phospholipids and glycolipids
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2-10 Lipids
• Fatty Acids
• Long chains of carbon and hydrogen with a carboxyl
group (COOH) at one end
• Are relatively nonpolar, except the carboxyl group
• Fatty acids may be:
• Saturated with hydrogen (no covalent bonds)
• Unsaturated (one or more double bonds)
• Monounsaturated = one double bond
• Polyunsaturated = two or more double bonds
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Figure 2-14a Fatty Acids
Lauric acid (C12H24O2)
Lauric acid demonstrates two structural
characteristics common to all fatty acids: a
long chain of carbon atoms and a carboxyl
group (—COOH) at one end.
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Figure 2-14b Fatty Acids
Saturated
Unsaturated
A fatty acid is either saturated (has single
covalent bonds only) or unsaturated (has
one or more double covalent bonds). The
presence of a double bond causes a
sharp bend in the molecule.
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2-10 Lipids
• Eicosanoids
• Derived from the fatty acid called arachidonic acid
• Leukotrienes
• Active in immune system
• Prostaglandins
• Local hormones, short-chain fatty acids
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Figure 2-15 Prostaglandins
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2-10 Lipids
•
Glycerides
•
Fatty acids attached to a glycerol molecule
•
Triglycerides are the three fatty-acid tails
•
Also called triacylglycerols or neutral fats
•
Have three important functions
1. Energy source
2. Insulation
3. Protection
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Figure 2-16 Triglyceride Formation
Glycerol
Fatty acids
Fatty Acid 1
Saturated
Fatty Acid 2
Saturated
Fatty Acid 3
Unsaturated
DEHYDRATION
SYNTHESIS
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HYDROLYSIS
Triglyceride
2-10 Lipids
• Steroids
• Four rings of carbon and hydrogen with an
assortment of functional groups
• Types of steroids:
• Cholesterol
• Component of plasma (cell) membranes
• Estrogens and testosterone
• Sex hormones
• Corticosteroids and calcitriol
• Metabolic regulation
• Bile salts
• Derived from steroids
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Figure 2-17 Steroids
Cholesterol
Estrogen
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Testosterone
2-10 Lipids
• Phospholipids and Glycolipids
• Diglycerides attached to either a phosphate group
(phospholipid) or a sugar (glycolipid)
• Generally, both have hydrophilic heads and
hydrophobic tails and are structural lipids,
components of plasma (cell) membranes
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Figure 2-18a Phospholipids and Glycolipids
Nonlipid
group
Phosphate
group
Glycerol
Fatty
acids
The phospholipid lecithin. In a phospholipid, a phosphate
group links a nonlipid molecule to a diglyceride.
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Figure 2-18b Phospholipids and Glycolipids
Carbohydrate
Fatty
acids
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In a glycolipid, a carbohydrate
is attached to a diglyceride.
Figure 2-18c Phospholipids and Glycolipids
Hydrophilic
heads
In large numbers,
phospholipids and
glycolipids form micelles,
Hydrophobic
with the hydrophilic
tails
heads facing the water
molecules, and the
hydrophobic tails on the
Phospholipid
Glycolipid
inside of each droplet.
WATER
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Table 2-5 Representative Lipids and Their Functions in the Body
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2-11 Proteins
• Proteins
• Are the most abundant and important organic
molecules
• Contain basic elements
• Carbon (C), hydrogen (H), oxygen (O), and nitrogen (N)
• Basic building blocks
• 20 amino acids
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2-11 Proteins
• Seven Major Protein Functions
1. Support
•
Structural proteins
2. Movement
•
Contractile proteins
3. Transport
•
Transport (carrier)
proteins
4. Buffering
•
Regulation of pH
5. Metabolic Regulation
•
Enzymes
6. Coordination and
Control
•
Hormones
7. Defense
•
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Antibodies
2-11 Proteins
•
Protein Structure
•
Long chains of amino acids
•
Five components of amino acid structure
1. Central carbon atom
2. Hydrogen atom
3. Amino group (—NH2)
4. Carboxyl group (—COOH)
5. Variable side chain or R group
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Figure 2-19 Amino Acids
Structure of an Amino Acid
Amino group
Central carbon
Carboxyl group
R group (variable side chain
of one or more atoms)
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2-11 Proteins
• Hooking Amino Acids Together
• Requires a dehydration synthesis between:
• The amino group of one amino acid and the
carboxyl group of another amino acid
• Forms a peptide bond
• Resulting molecule is a peptide
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Figure 2-20 The Fomation of Peptide Bonds
Peptide Bond Formation
Glycine (gly)
DEHYDRATION
SYNTHESIS
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Alanine (ala)
HYDROLYSIS
Peptide bond
2-11 Proteins
• Protein Shape
• Primary structure
• The sequence of amino acids along a polypeptide
• Secondary structure
• Hydrogen bonds form spirals or pleats
• Tertiary structure
• Secondary structure folds into a unique shape
• Quaternary structure
• Final protein shape — several tertiary structures together
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Figure 2-21 Protein Structure
A1
A3
A2
A5
A4
A7
A6
A8
A9
Linear chain of amino acids
A1
A1
A6
A3
A3
A4
Hydrogen bond
Hydrogen
bond
A2
A2
A5
A5
A9
A8
A7
A6
A11
A12
A13
A14
A10
A7
A9
Alpha-helix
OR
Pleated sheet
OR
Heme units
Hemoglobin
(globular protein)
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Keratin or collagen
(fibrous protein)
Figure 2-21ab Protein Structure
A1
A2
A3
A5
A4
A6
A7
A8
Linear chain of amino acids
Primary structure. The
primary structure of a
polypeptide is the
sequence of amino acids
(A1, A2, A3, and
Hydrogen
so on) along
bond
its length.
A2
A1
A6
A3
A5
A7
A9
Alpha-helix
Secondary structure. Secondary structure is primarily the result of
hydrogen bonding along the length of the polypeptide chain. Such
bonding often produces a simple spiral (an alpha-helix) or a flattened
arrangement known as a pleated sheet.
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A9
Figure 2-21ab Protein Structure
A1
A2
A3
A4
A7
A6
A5
A9
A8
Linear chain of amino acids
Primary structure. The primary structure of a polypeptide is the
sequence of amino acids (A1, A2, A3, and so on) along its length.
A1
A2
A3
A4
Hydrogen bond
A5
A9
A8
A7
A6
A11
A12
A13
A14
A10
Pleated sheet
Secondary structure. Secondary structure is primarily the result of
hydrogen bonding along the length of the polypeptide chain. Such
bonding often produces a simple spiral (an alpha-helix) or a flattened
arrangement known as a pleated sheet.
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Figure 2-21cd Protein Structure
Heme units
Tertiary structure. Tertiary
structure is the coiling and folding
of a polypeptide.
Hemoglobin
(globular protein)
Quaternary structure.
Quaternary structure develops
when separate polypeptide
subunits interact to form a larger
molecule. A single hemoglobin
molecule contains four globular
subunits.
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Figure 2-21cd Protein Structure
Heme units
Tertiary structure. Tertiary
structure is the coiling and folding
of a polypeptide.
Keratin or collagen
(fibrous protein)
Quaternary structure. Quaternary structure develops
when separate polypeptide subunits interact to form a larger
molecule.
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2-11 Proteins
• Fibrous Proteins
• Structural sheets or strands
• Globular Proteins
• Soluble spheres with active functions
• Protein function is based on shape
• Shape is based on sequence of amino acids
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Figure 2-21d Protein Structure
OR
Heme units
Hemoglobin
(globular protein)
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Keratin or collagen
(fibrous protein)
2-11 Proteins
• Enzyme Function
• Enzymes are catalysts
• Proteins that lower the activation energy of a chemical
reaction
• Are not changed or used up in the reaction
• Enzymes also exhibit:
1. Specificity — will only work on limited types of
substrates
2. Saturation Limits — by their concentration
3. Regulation — by other cellular chemicals
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Figure 2-22 A Simplified View of Enzyme Structure and Function
Substrates bind to active
site of enzyme
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Figure 2-22 A Simplified View of Enzyme Structure and Function
Once bound to the
active site, the
substrates are held
together and their
interaction facilitated
Enzyme-substrate
complex
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Figure 2-22 A Simplified View of Enzyme Structure and Function
Substrate binding
alters the shape
of the enzyme, and
this change promotes
product formation
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Figure 2-22 A Simplified View of Enzyme Structure and Function
Product detaches from
enzyme; entire process can
now be repeated
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2-11 Proteins
• Cofactors and Enzyme Function
• Cofactor
• An ion or molecule that binds to an enzyme before
substrates can bind
• Coenzyme
• Nonprotein organic cofactors (vitamins)
• Isozymes
• Two enzymes that can catalyze the same reaction
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2-11 Proteins
• Effects of Temperature and pH on Enzyme
Function
• Denaturation
• Loss of shape and function due to heat or pH
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2-11 Proteins
• Glycoproteins and Proteoglycans
• Glycoproteins
• Large protein + small carbohydrate
• Includes enzymes, antibodies, hormones, and mucus
production
• Proteoglycans
• Large polysaccharides + polypeptides
• Promote viscosity
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2-12 Nucleic Acids
• Nucleic Acids
• Are large organic molecules, found in the nucleus, which store and
process information at the molecular level
• Deoxyribonucleic acid (DNA)
• Determines inherited characteristics
• Directs protein synthesis
• Controls enzyme production
• Controls metabolism
• Ribonucleic acid (RNA)
• Controls intermediate steps in protein synthesis
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2-12 Nucleic Acids
•
Structure of Nucleic Acids
•
DNA and RNA are strings of nucleotides
•
Nucleotides
•
Are the building blocks of DNA and RNA
•
Have three molecular parts
1. A pentose sugar (deoxyribose or ribose)
2. Phosphate group
3. Nitrogenous base (A, G, T, C, or U)
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Figure 2-23a Nucleotides and Nitrogenous Bases
Generic nucleotide
The nitrogenous base may be a purine or a pyrimidine.
Sugar
Phosphate
group
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Nitrogenous
base
Figure 2-23b Nucleotides and Nitrogenous Bases
Purines
Adenine
Guanine
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Figure 2-23c Nucleotides and Nitrogenous Bases
Pyrimidines
Cytosine
Thymine
(DNA only)
Uracil
(RNA only)
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2-12 Nucleic Acids
• DNA and RNA
• DNA is double stranded, and the bases form hydrogen bonds to hold
the DNA together
• Sometimes RNA can bind to itself but is usually a single strand
• DNA forms a twisting double helix
• Complementary base pairs
• Purines pair with pyrimidines
• DNA
• Adenine (A) and thymine (T)
• Cytosine (C) and guanine (G)
• RNA
• Uracil (U) replaces thymine (T)
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Figure 2-24 The Structure of Nucleic Acids
Phosphate
group
Deoxyribose
Adenine
Thymine
Hydrogen bond
DNA strand 1
DNA strand 2
RNA molecule.
Cytosine
DNA molecule.
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Guanine
2-12 Nucleic Acids
• Types of RNA
• Messenger RNA (mRNA)
• Transfer RNA (tRNA)
• Ribosomal RNA (rRNA)
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Table 2-6 Comparison of RNA with DNA
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2-13 High-Energy Compounds
• Nucleotides Can Be Used to Store Energy
• Adenosine diphosphate (ADP)
• Two phosphate groups; di- = 2
• Adenosine triphosphate (ATP)
• Three phosphate groups; tri- = 3
• Phosphorylation
• Adding a phosphate group to ADP with a high-energy bond to
form the high-energy compound ATP
• Adenosine triphosphatase (ATPase)
• The enzyme that catalyzes the conversion of ATP to ADP
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Figure 2-25 The Structure of ATP
Adenine
Ribose
Phosphate
Phosphate
Phosphate
High-energy bonds
Adenosine
Adenosine monophosphate (AMP)
Adenosine diphosphate (ADP)
Adenosine triphosphate (ATP)
Adenine
Phosphate groups
Ribose
Adenosine
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2-14 Chemicals and Cells
• Chemicals and Cells
• Biochemical building blocks form functional units
called cells
• Metabolic turnover lets your body grow, change, and
adapt to new conditions and activities
• Your body recycles and renews all of its chemical
components at intervals ranging from minutes to
years
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Table 2-7 Classes of Inorganic and Organic Compounds
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Table 2-8 Turnover Times
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