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2_Chemical_Basis.ppt

Chemical basis of life

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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 2
The Chemical
Basis of Life
Collagen and Elastic Fibers
Matter
• The “stuff” of the universe
• Anything that has mass and takes up
space
• States of matter
– Solid: has definite shape and volume
– Liquid: has definite volume, changeable
shape
– Gas: has changeable shape and volume
Composition of Matter
• Elements: unique substances that cannot
be broken down by ordinary chemical
means
• Atoms: more-or-less identical building
blocks for each element
• Atomic symbol: one- or two-letter
chemical shorthand for each element
Properties of Elements
• Each element has unique physical and
chemical properties
– Physical properties: those detected with our
senses
– Chemical properties: pertain to the way
atoms interact with one another
Major Elements of the Human Body
• About 96% of body weight results from the
following elements:
Oxygen (O) Hydrogen (H)
Carbon (C) Nitrogen (N)
• Lesser elements make up 3.9% of the body:
Phosphorus (P) Potassium (K) Calcium (Ca)
Sulfur (S) Sodium (Na) Chlorine (Cl)
Magnesium (Mg) Iodine (I) Iron (Fe)
• Trace elements make up < 0.01% of the body:
– Required in minute amounts
– Found as part of enzymes
Atomic Structure
• The nucleus consists of
neutrons and protons
– Neutrons:
• No charge
• Mass= one atomic mass unit (amu)
– Protons:
• Positive charge
• Mass of 1 amu
• Electrons are found orbiting
the nucleus
– Electrons:
• Negative charge
• Mass of 1/2000 amu
Fig. 2.1

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2_Chemical_Basis.ppt

  • 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 2 The Chemical Basis of Life Collagen and Elastic Fibers
  • 2. Matter • The “stuff” of the universe • Anything that has mass and takes up space • States of matter – Solid: has definite shape and volume – Liquid: has definite volume, changeable shape – Gas: has changeable shape and volume
  • 3. Composition of Matter • Elements: unique substances that cannot be broken down by ordinary chemical means • Atoms: more-or-less identical building blocks for each element • Atomic symbol: one- or two-letter chemical shorthand for each element
  • 4. Properties of Elements • Each element has unique physical and chemical properties – Physical properties: those detected with our senses – Chemical properties: pertain to the way atoms interact with one another
  • 5. Major Elements of the Human Body • About 96% of body weight results from the following elements: Oxygen (O) Hydrogen (H) Carbon (C) Nitrogen (N) • Lesser elements make up 3.9% of the body: Phosphorus (P) Potassium (K) Calcium (Ca) Sulfur (S) Sodium (Na) Chlorine (Cl) Magnesium (Mg) Iodine (I) Iron (Fe) • Trace elements make up < 0.01% of the body: – Required in minute amounts – Found as part of enzymes
  • 6. Atomic Structure • The nucleus consists of neutrons and protons – Neutrons: • No charge • Mass= one atomic mass unit (amu) – Protons: • Positive charge • Mass of 1 amu • Electrons are found orbiting the nucleus – Electrons: • Negative charge • Mass of 1/2000 amu Fig. 2.1
  • 7. Atomic Structure • Atoms are electrically neutral because the number of protons in atoms equals the number of electrons Fig. 2.2
  • 8. Identification of Elements • Atomic number: equal to the number of protons • Mass number: equal to the mass of the protons and neutrons • Atomic weight: average of the mass numbers of all isotopes • Isotope: atoms with same number of protons but a different number of neutrons
  • 9. Chemical Bonds • Electron shells (energy levels) surround the nucleus of an atom – Bonds are formed using the electrons in the outermost electron shell • Valence shell: outermost energy level containing chemically active electrons • Octet rule: except for the first shell, which is full with two electrons, atoms interact in a manner to have eight electrons in their valence shell
  • 10. Types of Chemical Bonds • Ionic bond: formed when one atom loses an electron and another accepts that electron • Covalent bond: the sharing of electrons • Hydrogen bond: hydrogen atoms (bound covalently to either N or O atoms) have a small positive charge that is weakly attracted to the small negative charge of other atoms
  • 11. Ionic Bonds • Ionic bonds form between atoms by the transfer of one or more electrons • Ions: charged atoms resulting from the gain or loss of electrons – Anions: negatively charged ions due to gaining one or more electrons – Cations: positively charged ions due to losing one or more electrons • Ionic compounds form crystals instead of individual molecules Example: NaCl (sodium chloride)
  • 14. Covalent Bonds • Covalent bonds are formed by the sharing of two or more electrons • Electron sharing produces molecules – single covalent bond: sharing of a pair of electrons (H — H) – double covalent bond: sharing of two pairs of electrons (O ═ C ═ O) Fig. 2.4
  • 16. Polar and Nonpolar Molecules • Electrons shared equally between atoms produce nonpolar molecules • Unequal sharing of electrons produces polar molecules Fig. 2.5
  • 17. Hydrogen Bonds • Too weak to bind atoms together • Common in dipoles such as water • Responsible for surface tension in water • Important as intramolecular bonds, giving the molecule a three-dimensional shape
  • 19. Molecules and Compounds • Molecule: two or more atoms held together by chemical bonds to form a structure that behaves as an independent unit • Compound: two or more different kinds of atoms chemically combined – covalent compound: a molecule – ionic compound: organized array of ions
  • 20. Dissociation • Separation of ions in an ionic compound by polar water molecules – Dissociated ions are called electrolytes because they can conduct electricity – Molecules that do not dissociate in water are called nonelectrolytes
  • 22. Chemical Reactions • Occur when chemical bonds are formed, rearranged, or broken – Reactants: substances that enter a chemical reaction – Products: substances that result from the chemical reaction • Written in symbolic form using chemical equations – Chemical equations contain: • Number and type of reacting substances • Products produced • Relative amounts of reactants and products
  • 23. Synthesis Reaction • Combination of reactants to form a new larger product – Dehydration reaction: a synthesis reaction in which water is a product Fig. 2.8
  • 24. Decomposition Reaction • Breakdown of larger reactants into smaller products – Hydrolysis reaction: a decomposition reaction that uses water Fig. 2.8
  • 25. Reversible Reactions • All chemical reactions are theoretically reversible A + B  AB AB  A + B • If neither a forward nor reverse reaction is dominant, chemical equilibrium is reached
  • 26. Energy • The capacity to do work (put matter into motion) • Types of energy – Potential: stored (inactive) energy that could do work – Kinetic: energy that does work by causing the movement of an object
  • 27. Energy • Can be neither created nor destroyed • Easily converted from one form to another – Mechanical: directly involved in moving matter – Chemical: stored in the bonds of chemical substances – Electrical: results from the movement of charged particles – Radiant or electromagnetic: travels in waves (i.e., visible light, ultraviolet light, and X-rays)
  • 28. Energy • Exists in chemical bonds as potential energy • Released when the products contain less potential energy than the reactants – Energy can be “lost” as heat, can be used to synthesize molecules, or can do work. • Absorbed in reactions when the products contain more potential energy than the reactants
  • 29. Adenosine Triphosphate (ATP) • ATP stores and provides energy • Source of immediately usable energy for the cell Fig. 2.9
  • 31. Factors Influencing Rate of Chemical Reactions • Concentration: higher reacting particle concentrations produce faster reactions • Temperature: chemical reactions proceed quicker at higher temperatures • Catalysts: increase the rate of a reaction without being chemically changed – Enzymes are biological catalysts • Particle size: the smaller the particle the faster the chemical reaction
  • 32. Acids and Bases • Acids release H+ and are therefore proton donors HCl  H+ + Cl – • Bases release OH– and are proton acceptors NaOH  Na+ + OH– • Acid-Base concentration is measured using a pH scale
  • 33. pH Scale • Ranges from 0 to 14 • Indicates the H+ concentration of a solution – Neutral solutions have an equal number of H+ and OH– and a pH of 7.0 – Acidic solutions have more H+ than OH– and a pH of less than 7.0 – Basic (alkaline) solutions have fewer H+ than OH– and a pH greater than 7.0
  • 34. pH Scale • Neutral: pH 7.00 • Acidic: pH 0–6.99 • Basic: pH 7.01–14.00 Fig. 2.11
  • 35. Acids and Bases • Salts are formed by the reaction of an acid and a base HCl + NaOH → NaCl + H2O (acid) (base) (salt) (water) • Buffers are chemicals that resist changes in pH when acids or bases are added – Example: Carbonic acid-bicarbonate system • Carbonic acid dissociates, reversibly releasing bicarbonate ions and protons • The chemical equilibrium between carbonic acid and bicarbonate resists pH changes in the blood
  • 36. Buffers a) Addition of an acid to a nonbuffered solution results in an increase of H+ and a decrease in pH b) In a buffered solution the added H+ is bound by the buffer and the pH change is much smaller Fig. 2.12
  • 37. Biochemistry • Inorganic chemistry – Mostly concerned with non-carbon-containing substances but does include such carbon- containing substances as CO, CO2, and HCO3 - • Organic chemistry – Substances contain carbon, are covalently bonded, and are often large – Usually have carbon-carbon or carbon- hydrogen bonding
  • 38. Inorganic Compounds • Oxygen (O2) is involved with the extraction of energy from food molecules to make ATP • Carbon Dioxide (CO2) is a by-product of the breakdown of food molecules • Water (H2O) has many important properties for living organisms and is essential for life
  • 39. Properties of Water • Stabilizes body temperature – The high heat capacity of water allows it to absorb and release large amounts of heat before changing temperature • Protection – acts as a lubricant or cushion • Chemical reactions – Most of the chemical reactions necessary for life do not take place unless the reacting molecules are dissolved in water – Water also directly participates in many chemical reactions • Transport – Polar solvent properties: dissolves ionic substances, forms hydration layers around large charged molecules, and serves as the body’s major transport medium
  • 40. Organic Compounds • Molecules unique to living systems • They include: – Carbohydrates – Lipids – Proteins – Nucleic Acids
  • 41. Carbohydrates • Contain carbon, hydrogen, and oxygen – Ratio of 1:2:1 (C:H:O) • Their major function is to supply a source of cellular food • Examples – Monosaccharides – glucose and fructose – Disaccharides – sucrose and lactose – Polysaccharides – starch and glycogen Figure 2.14a
  • 43. Lipids • Dissolve in nonpolar solvents, such as alcohol or acetone, but not in polar solvents, such as water • Contain C, H, and O, but the proportion of oxygen in lipids is less than in carbohydrates • Examples: – Fats or triglycerides: energy – Phospholipids: structural components of cell membranes – Eicosanoids: regulate physiological processes – Steroids: regulate physiological processes
  • 44. Examples of Lipids Found in the Body • Fats: found in subcutaneous tissue and around organs • Phospholipids: chief component of cell membranes • Steroids: cholesterol, bile salts, vitamin D, sex hormones, and adrenal cortical hormones • Eicosanoids: prostaglandins, leukotrienes, and thromboxanes • Fat-soluble vitamins: vitamins A, D, E, and K • Lipoproteins: transport fatty acids and cholesterol in the bloodstream
  • 45. Fats (Triglycerides) • Composed of three fatty acids bonded to a glycerol molecule Fig. 2.14
  • 46. Fatty Acids • Saturated: only single covalent bonds between carbons • Unsaturated: one or more double covalent bonds between carbons Fig. 2.15
  • 47. Other Lipids • Phospholipids: modified triglycerides with two fatty acid groups and a phosphorus group Fig. 2.16
  • 48. Other Lipids • Eicosanoids: 20-carbon fatty acids found in cell membranes • Steroids: flat molecules with four interlocking hydrocarbon rings Fig. 2.17
  • 49. Proteins • Macromolecules • Contain C, H, O, N, and some S • Composed of 20 basic types of amino acids bound together with peptide bonds – Dipeptide: Two amino acids – Tripeptide: Three amino acids – Polypeptide: Many amino acids • Proteins are polypeptides of hundreds of amino acids
  • 50. Amino Acids (AA) • Building blocks of proteins • Organic acids containing – amino group (-NH2) – a carboxyl group (COOH) – a hydrogen atom – a side chain designated by the symbol R attached to the same carbon atom as the hydrogen
  • 51. Structural Levels of Proteins • Primary: determined by the number, kind, and arrangement of amino acids • Secondary: results from folding or bending of the polypeptide chain caused by the hydrogen bonds between amino acids (helices and pleated sheets) • Tertiary: results from the folding of the helices or pleated sheets and the hydrogen bonds formed with water • Quaternary: spatial relationships between two or more proteins that associate to form a functional unit
  • 55. Proteins • Functions – regulate chemical reactions (enzymes) – structural proteins provide the framework for many of the body’s tissues – responsible for muscle contraction – Fibrous proteins • Extended and strand-like proteins • Examples: keratin, elastin, collagen, and certain contractile fibers – Globular proteins • Compact, spherical proteins with tertiary and quaternary structures • Examples: antibodies, hormones, and enzymes • Denaturation – Disruption of hydrogen bonds, which changes the shape of proteins and makes them nonfunctional
  • 56. Characteristics of Enzymes • Speed up chemical reactions by lowering the activation energy • Most are globular proteins that act as biological catalysts • Are chemically specific • Frequently named for the type of reaction they catalyze • Names usually end in -ase • Chemical events of the body are regulated primarily by mechanisms that control – concentration of enzymes – activity of enzymes
  • 58. Enzymes • Enzymes bind to reactants according to the lock-and-key model – The shape of both the enzyme and reactants are critical to the function of the enzyme – By bringing the two reactants close to each other it reduces the activation energy for the reaction – Each enzyme catalyzes only one type of chemical reaction – After each reaction the enzyme is released and can be used again Fig. 2.21
  • 60. Nucleic Acids • Composed of C, O, H, N, and P • The basic unit of nucleic acids is the nucleotide, which is a monosaccharide with an attached phosphate and organic base • Five nitrogenous bases contribute to nucleotide structure: – adenine (A) – guanine (G) – cytosine (C) – thymine (T) – uracil (U) • Two major classes: DNA and RNA
  • 61. Deoxyribonucleic Acid (DNA) • Double-stranded helical molecule found in the nucleus of the cell • Genetic material of the cell • Replicates itself before the cell divides, ensuring genetic continuity • Provides instructions for protein synthesis • Contains the monosaccharide deoxyribose and the organic bases – adenine – thymine – guanine – cytosine
  • 63. Ribonucleic Acid (RNA) • Single-stranded molecule found in both the nucleus and the cytoplasm of a cell • Composed of the monosaccharide ribose and uses the organic base uracil instead of thymine • Three varieties of RNA: – messenger RNA – transfer RNA – ribosomal RNA