Download Acids and Bases (cont.)

Chapter 2 – Part B
Chemistry Comes Alive-REVIEW from previous chemistry courses.
IMPORTANT
Part 2 – Biochemistry
 Biochemistry is the study of chemical composition and reactions of living matter
 All chemicals either organic or inorganic
– Inorganic compounds
 Water, salts, and many acids and bases
 Do not contain carbon
– Organic compounds
 Carbohydrates, fats, proteins, and nucleic acids
 Contain carbon, are usually large, and are covalently bonded
 Both equally essential for life
2.6 Inorganic Compounds
Water
 Most abundant inorganic compound
– Accounts for 60%–80% of the volume of living cells
 Most important inorganic compound because of its properties
– High heat capacity
– High heat of vaporization
– Polar solvent properties
– Reactivity
– Cushioning
Water
 High heat capacity
– Ability to absorb and release heat with little temperature change
– Prevents sudden changes in temperature
 High heat of vaporization
– Evaporation requires large amounts of heat
– Useful cooling mechanism
Water (cont.)
 Polar solvent properties
– Dissolves and dissociates ionic substances
– Forms hydration (water) layers around large charged molecules
 Example: proteins
– Body’s major transport medium
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Water (cont.)
 Reactivity
– Necessary part of hydrolysis and dehydration synthesis reactions
 Cushioning
– Protects certain organs from physical trauma
 Example: cerebrospinal fluid cushions nervous system organs
Salts
 Salts are ionic compounds that dissociate into separate ions in water
– Separate into cations (positively charged molecules) and anions (negatively
charged)
 Not including H+ and OH– ions
Salts (cont.)
 Salts (cont.)
– All ions are called electrolytes because they can conduct electrical currents in
solution
– Ions play specialized roles in body functions
 Example: sodium, potassium, calcium, and iron
– Ionic balance is vital for homeostasis
– Common salts in body
 NaCl, CaCO3, KCl, calcium phosphates
Clinical – Homeostatic Imbalance 2.1
 Ionic balance is vital for homeostasis
 Kidneys play a big role in maintaining proper balance of electrolytes
 If electrolyte balance is disrupted, virtually all organ systems cease to function
Acids and Bases

Acids and bases are both electrolytes
– Ionize and dissociate in water
 Acids
– Are proton donors: they release hydrogen ions (H+), bare protons (have no
electrons) in solution
 Example: HCl → H+ + Cl–
– Important acids
 HCl (hydrochloric acid), HC2H3O2 (acetic acid, abbreviated HAc), and H2CO3
(carbonic acid)
Acids and Bases (cont.)
 Bases
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– Are proton acceptors: they pick up H+ ions in solution
 Example: NaOH → Na+ + OH–
– When a base dissolves in solution, it releases a hydroxyl ion (OH –)
– Important bases
 Bicarbonate ion (HCO3–) and ammonia (NH3)
Acids and Bases (cont.)
 pH: Acid-base concentration
– pH scale is measurement of concentration of hydrogen ions [H+] in a solution
– The more hydrogen ions in a solution, the more acidic that solution is
– pH is negative logarithm of [H+] in moles per liter that ranges from 0–14
– pH scale is logarithmic, so each pH unit represents a 10-fold difference
 Example: a pH 5 solution is 10 times more acidic than a pH 6 solution
Acids and Bases (cont.)
 pH: Acid-base concentration (cont.)
– Acidic solutions have high [H+] but low pH
 Acidic pH range is 0–6.99
– Neutral solutions have equal numbers of H+ and OH– ions
 All neutral solutions are pH 7
 Pure water is pH neutral
– pH of pure water  pH 7: [H+]  10–7 m
– Alkaline (basic) solutions have low [H+] but high pH
 Alkaline pH range is 7.01–14
Acids and Bases (cont.)
 Neutralization
– Neutralization reaction: acids and bases are mixed together
 Displacement reactions occur, forming water and a salt
NaOH + HCl →
NaCl + H2O
Acids and Bases (cont.)
 Buffers
– Acidity involves only free H+ in solution, not H+ bound to anions
– Buffers resist abrupt and large swings in pH
 Can release hydrogen ions if pH rises
 Can bind hydrogen ions if pH falls
– Convert strong acids or bases (completely dissociated) into weak ones (slightly
dissociated)
 Carbonic acid–bicarbonate system (important buffer system of blood):
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2.7 Organic Compounds: Synthesis and Hydrolysis
 Organic molecules contain carbon
– Exceptions: CO2 and CO, which are inorganic
 Carbon is electroneutral
– Shares electrons; never gains or loses them
– Forms four covalent bonds with other elements
– Carbon is unique to living systems
 Major organic compounds: carbohydrates, lipids, proteins, and nucleic acids
2.7 Organic Compounds: Synthesis and Hydrolysis
 Many are polymers
– Chains of similar units called monomers (building blocks)
 Synthesized by dehydration synthesis
 Broken down by hydrolysis reactions
2.8 Carbohydrates
 Carbohydrates include sugars and starches
 Contain C, H, and O
– Hydrogen and oxygen are in 2:1 ratio
 Three classes
– Monosaccharides: one single sugar
 Monomers: smallest unit of carbohydrate
– Disaccharides: two sugars
– Polysaccharides: many sugars
 Polymers are made up of monomers of monosaccharides
2.8 Carbohydrates
 Monosaccharides
– Simple sugars containing three to seven carbon atoms
– (CH2O)n — general formula
 n  number of carbon atoms
– Monomers of carbohydrates
– Important monosaccharides
 Pentose sugars
– Ribose and deoxyribose
 Hexose sugars
– Glucose (blood sugar)
Carbohydrates (cont.)
 Disaccharides
– Double sugars
– Too large to pass through cell membranes
– Important disaccharides
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 Sucrose, maltose, lactose
– Formed by dehydration synthesis of two monosaccharides
 glucose + fructose → sucrose + water
Carbohydrates (cont.)
 Polysaccharides
– Polymers of monosaccharides
 Formed by dehydration synthesis of many monomers
– Important polysaccharides
 Starch: carbohydrate storage form used by plants
 Glycogen: carbohydrate storage form used by animals
– Not very soluble
2.9 Lipids
 Contain C, H, O, but less than in carbohydrates, and sometimes contain P
 Insoluble in water
 Main types:
– Triglycerides or neutral fats
– Phospholipids
– Steroids
– Eicosanoids
Lipids (cont.)
 Triglycerides or neutral fats
– Called fats when solid and oils when liquid
– Composed of three fatty acids bonded to a glycerol molecule
– Main functions
 Energy storage
 Insulation
 Protection
Lipids (cont.)
 Triglycerides can be constructed of:
– Saturated fatty acids
 All carbons are linked via single covalent bonds, resulting in a molecule with
the maximum number of H atoms (saturated with H)
 Solid at room temperature (Example: animal fats, butter)
Lipids (cont.)
– Unsaturated fatty acids
 One or more carbons are linked via double bonds, resulting in reduced H
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


atoms (unsaturated)
Liquid at room temperature (Example: plant oils, such as olive oil)
Trans fats – modified oils; unhealthy
Omega-3 fatty acids – “heart healthy”
Lipids (cont.)
 Phospholipids
– Modified triglycerides
 Glycerol and two fatty acids plus a phosphorus-containing group
– “Head” and “tail” regions have different properties
 Head is a polar region and is attracted to water
 Tails are nonpolar and are repelled by water
– Important in cell membrane structure
Lipids (cont.)
 Steroids
– Consist of four interlocking ring structures
– Common steroids: cholesterol, vitamin D, steroid hormones, and bile salts
– Most important steroid is cholesterol
 Is building block for vitamin D, steroid synthesis, and bile salt synthesis
 Important in cell plasma membrane structure
Lipids (cont.)
 Eicosanoids
– Many different ones
– Derived from a fatty acid (arachidonic acid) found in cell membranes
– Most important eicosanoids are prostaglandins
 Play a role in blood clotting, control of blood pressure, inflammation, and labor
contractions
2.10 Proteins
 Comprise 20–30% of cell mass
 Have most varied functions of any molecules
– Structural, chemical (enzymes), contraction (muscles)
 Contain C, H, O, N, and sometimes S and P
 Polymers of amino acid monomers held together by peptide bonds
 Shape and function due to four structural levels
Amino Acids and Peptide Bonds
 All proteins are made from 20 types of amino acids
– Joined by covalent bonds called peptide bonds
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– Contain both an amine group and acid group
– Can act as either acid or base
– Differ by which of 20 different “R groups” is present
Structural Levels of Proteins
 Four levels of protein structure determine shape and function
1. Primary: linear sequence of amino acids (order)
2. Secondary: how primary amino acids interact with each other
 Alpha () helix coils resemble a spring
 Beta () pleated sheets resemble accordion ribbons
3. Tertiary: how secondary structures interact
4. Quaternary: how 2 or more different polypeptides interact with each other
Fibrous and Globular Proteins
 Shapes of proteins fall into one of two categories: fibrous or globular
1. Fibrous (structural) proteins
 Strandlike, water-insoluble, and stable
 Most have tertiary or quaternary structure (3-D)
 Provide mechanical support and tensile strength
 Examples: keratin, elastin, collagen (single most abundant protein in body),
and certain contractile fibers
Fibrous and Globular Proteins (cont.)
2. Globular (functional) proteins
 Compact, spherical, water-soluble, and sensitive to environmental changes
 Tertiary or quaternary structure (3-D)
 Specific functional regions (active sites)
 Examples: antibodies, hormones, molecular chaperones, and enzymes
Protein Denaturation
 Denaturation: globular proteins unfold and lose their functional 3-D shape
– Fibrous proteins are more stable
– Active sites become deactivated
 Can be caused by decreased pH (increased acidity) or increased temperature
 Usually reversible if normal conditions restored
 Irreversible if changes are extreme
– Example: cannot undo cooking an egg
Enzymes and Enzyme Activity
 Enzymes: globular proteins that act as biological catalysts
– Catalysts regulate and increase speed of chemical reactions without getting used
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up in the process
– Lower the energy needed to initiate a chemical reaction
 Leads to an increase in the speed of a reaction
 Allows for millions of reactions per minute!
Enzymes and Enzyme Activity (cont.)
 Characteristics of enzymes
– Most functional enzymes, referred to as holoenzymes, consist of two parts
 Apoenzyme (protein portion)
 Cofactor (metal ion) or coenzyme (organic molecule, often a vitamin)
– Enzymes are specific
 Act on a very specific substrate
– Names usually end in –ase and are often named for the reaction they catalyze
 Example: hydrolases, oxidases
Enzymes and Enzyme Activity (cont.)
 Enzyme action
– Enzymes lower activation energy, which is the energy needed to initiate a
chemical reaction
 Enzymes “prime” the reaction
– Enzymes allow chemical reactions to proceed quickly at body temperatures
– Three steps are involved in enzyme action:
1. Substrate binds to enzyme’s active site, temporarily forming enzyme-substrate
complex
2. Complex undergoes rearrangement of substrate, resulting in final product
3. Product is released from enzyme
2.11 Nucleic Acids
 Nucleic acids, composed of C, H, O, N, and P, are the largest molecules in the body
 Nucleic acid polymers are made up of monomers called nucleotides
– Composed of nitrogen base, a pentose sugar, and a phosphate group
 Two major classes:
– Deoxyribonucleic acid (DNA)
– Ribonucleic acid (RNA)
2.11 Nucleic Acids
 DNA holds the genetic blueprint for the synthesis of all proteins
– Double-stranded helical molecule (double helix) located in cell nucleus
– Nucleotides contain a deoxyribose sugar, phosphate group, and one of four
nitrogen bases:
 Purines: adenine (A), guanine (G)
 Pyrimidines: cytosine (C) and thymine (T)
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2.11 Nucleic Acids
 DNA holds the genetic blueprint for the synthesis of all proteins (cont.)
– Bonding of nitrogen base from strand to opposite strand is very specific
 Follows complementary base-pairing rules:
– A always pairs with T
– G always pairs with C
2.11 Nucleic Acids
 RNA links DNA to protein synthesis and is slightly different from DNA
– Single-stranded linear molecule is active mostly outside nucleus
– Contains a ribose sugar (not deoxyribose)
– Thymine is replaced with uracil
– Three varieties of RNA carry out the DNA orders for protein synthesis
 Messenger RNA (mRNA), transfer RNA (tRNA), and ribosomal RNA (rRNA)
2.12 ATP
 Chemical energy released when glucose is broken down is captured in ATP
(adenosine triphosphate)
 ATP directly powers chemical reactions in cells
– Offers immediate, usable energy needed by body cells
 Structure of ATP
– Adenine-containing RNA nucleotide with two additional phosphate groups
2.12 ATP
 Terminal phosphate group of ATP can be transferred to other compounds that can
use energy stored in phosphate bond to do work
– Loss of phosphate group converts ATP to ADP
– Loss of second phosphate group converts ADP to AMP
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