Presentation is loading. Please wait.

Presentation is loading. Please wait.

Chapter 2: The Chemical Basis of Life

Similar presentations


Presentation on theme: "Chapter 2: The Chemical Basis of Life"— Presentation transcript:

1 Chapter 2: The Chemical Basis of Life

2 BASIC CHEMISTRY Elements and compounds (Figure 2-1)
Matter: anything that has mass and occupies space Element: simple form of matter; a substance that cannot be broken down into two or more different substances 26 elements are present in the human body Includes 11 major elements, four of which (carbon, oxygen, hydrogen, and nitrogen) make up 96% of the human body (Figure 2-2) 15 trace elements make up less than 2% of body weight Compound: atoms of two or more elements joined to form chemical combinations

3

4

5 BASIC CHEMISTRY: ATOMS
Atoms (Figure 2-3) The concept of the atom was proposed by the English chemist John Dalton Atomic structure: atoms contain several different kinds of subatomic particles; the most important are: Protons: positively charged subatomic particles found in the nucleus Neutrons: neutral subatomic particles found in the nucleus Electrons: negatively charged subatomic particles found in the electron cloud (Figure 2-4)

6

7

8 BASIC CHEMISTRY: ATOMS (cont.)
Atomic number and atomic weight Atomic number (Table 2-1) Number of protons in an atom’s nucleus Atomic number is critically important; identifies the kind of element Atomic weight Mass of a single atom Equal to the number of protons plus the number of neutrons in the nucleus

9 BASIC CHEMISTRY: ATOMS (cont.)
Energy levels (Figures 2-5 and 2-6) Total number of electrons in an atom equals the number of protons in the nucleus (in a stable atom) Electrons form a “cloud” around the nucleus

10

11

12 BASIC CHEMISTRY: ATOMS (cont.)
Bohr model: a model resembling planets revolving around the sun; useful in visualizing the structure of atoms Exhibits electrons in concentric circles, showing relative distances of the electrons from the nucleus Each ring or shell represents a specific energy level and can hold only a certain number of electrons Number and arrangement of electrons determine whether an atom is chemically stable An atom with eight electrons, or four pairs, in the outermost energy level is chemically inert An atom without a full outermost energy level is chemically active

13 BASIC CHEMISTRY: ATOMS (cont.)
Octet rule: atoms with fewer than eight or more than eight electrons in the outer energy level will attempt to lose, gain, or share electrons with other atoms to achieve stability

14 BASIC CHEMISTRY: ATOMS (cont.)
Isotopes (Figure 2-7) Isotopes of an element contain the same number of protons but different numbers of neutrons Isotopes have the same atomic number and therefore the same basic chemical properties as any other atom of the same element, but they have a different atomic weight Radioactive isotope (radioisotope): an unstable isotope that undergoes nuclear breakdown and emits nuclear particles and radiation

15

16 BASIC CHEMISTRY: CHEMICAL BONDS
Attractions between atoms: chemical bonds Chemical reaction: interaction between two or more atoms that occurs as a result of activity between electrons in their outermost energy levels Molecule: two or more atoms joined together Compound: consists of molecules formed by atoms of two or more elements Chemical bonds: two types unite atoms into molecules Ionic, or electrovalent, bond: formed by transfer of electrons; strong electrostatic force that binds positively and negatively charged ions together (Figure 2-8) Covalent bond: formed by sharing electron pairs between atoms (Figure 2-9)

17

18

19 BASIC CHEMISTRY: CHEMICAL BONDS (cont.)
Hydrogen bond (Figures 2-10 and 2-11) Much weaker than ionic or covalent bonds Results from unequal charge distribution on molecules

20

21

22 BASIC CHEMISTRY: CHEMICAL BONDS (cont.)
Attractions between molecules Hydrogen bonds Form when electrons are unequally shared Example: water molecule Polar molecules have regions with partial electrical charges resulting from unequal sharing of electrons among atoms Areas of different partial charges attract one another and form hydrogen bonds Other weak attractions attract molecules to each other through differences in electrical charge

23 BASIC CHEMISTRY: CHEMICAL BONDS (cont.)
Chemical reactions Involve the formation or breaking of chemical bonds Three basic types of chemical reactions are involved in physiology: Synthesis reaction: combination of two or more substances to form a more complex substance; formation of new chemical bonds: A + B  AB Decomposition reaction: breakdown of a substance into two or more simpler substances; breaking of chemical bonds: AB  A + B Exchange reaction: decomposition of two substances and, in exchange, synthesis of two new compounds from them: AB + CD  AD + CB Reversible reactions: occur in both directions

24 METABOLISM Metabolism: all the chemical reactions that occur in body cells (Figure 2-12) Catabolism Chemical reactions that break down complex compounds into simpler ones and release energy; hydrolysis is a common catabolic reaction Ultimately, the end products of catabolism are carbon dioxide, water, and other waste products More than half the energy released is transferred to adenosine triphosphate, which is then used to perform cellular work (Figure 2-33)

25

26 METABOLISM (cont.) Anabolism
Chemical reactions that join simple molecules together to form more complex molecules Chemical reaction responsible for anabolism is dehydration synthesis

27 ORGANIC AND INORGANIC COMPOUNDS
Inorganic compounds: few have carbon atoms and none have C–C or C–H bonds Organic molecules Have at least one carbon atom and at least one C–C or C–H bond in each molecule Often have functional groups attached to the carbon-containing core of the molecule (Figure 2-13)

28

29 INORGANIC MOLECULES Water
The body’s most abundant and important compound Properties of water (Table 2-2) Polarity: allows water to act as an effective solvent; ionizes substances in solution (Figure 2-10) The solvent allows transportation of essential materials throughout the body (Figure 2-14) High specific heat: water can lose and gain large amounts of heat with little change in its own temperature; enables the body to maintain a relatively constant temperature High heat of vaporization: water requires the absorption of significant amounts of heat to change it from a liquid to a gas; allows the body to dissipate excess heat

30

31 INORGANIC MOLECULES (cont.)
Oxygen and carbon dioxide: closely related to cellular respiration Oxygen: required to complete decomposition reactions necessary for the release of energy in the body Carbon dioxide: produced as a waste product and helps maintain the appropriate acid-base balance in the body

32 INORGANIC MOLECULES: ELECTROLYTES
Large group of inorganic compounds that includes acids, bases, and salts Substances that dissociate in solution to form ions (resulting ions are sometimes called electrolytes) Positively charged ions are cations; negatively charged ions are anions

33 INORGANIC MOLECULES: ELECTROLYTES (cont.)
Acids and bases: common and important chemical substances that are chemical opposites Acids Any substance that releases a hydrogen ion (H+) when in solution; “proton donor” Level of acidity depends on the number of H+ a particular acid will release Bases Electrolytes that dissociate to yield hydroxide ions (OH) or other electrolytes that combine with H+ Described as “proton acceptors” pH scale: assigns a value to measures of acidity and alkalinity (Figure 2-15) pH indicates the degree of acidity or alkalinity of a solution pH of 7 indicates neutrality (equal amounts of H+ and OH); a pH less than 7 indicates acidity; a pH higher than 7 indicates alkalinity

34

35 INORGANIC MOLECULES: ELECTROLYTES (cont.)
Buffers Maintain the constancy of pH Minimize changes in the concentrations of H+ and OH Act as a “reservoir” for hydrogen ions Salts (Table 2-3) Compound that results from chemical interaction of an acid and a base Reaction between an acid and a base to form a salt and water is called a neutralization reaction

36 ORGANIC MOLECULES “Organic” describes compounds that contain C–C or C–H bonds (Figure 2-16; Table 2-4)

37

38 ORGANIC MOLECULES: CARBOHYDRATES
Carbohydrates: organic compounds containing carbon, hydrogen, and oxygen; commonly called sugars and starches Monosaccharides: simple sugars with short carbon chains; those with six carbons are hexoses (e.g., glucose); those with five are pentoses (e.g., ribose, deoxyribose) (Figure 2-17) Disaccharides and polysaccharides: two (di-) or more (poly-) simple sugars bonded together through a synthesis reaction (Figure 2-18)

39

40

41 ORGANIC MOLECULES: LIPIDS
Lipids (Table 2-5) Water-insoluble organic molecules that are critically important biological compounds Major roles: Energy source Structural role Integral parts of cell membranes

42 ORGANIC MOLECULES: LIPIDS (cont.)
Triglycerides or fats (Figures 2-19 and 2-20) Most abundant lipids and most concentrated source of energy Building blocks of triglycerides are glycerol (the same for each fat molecule) and fatty acids (different for each fat and determine the chemical nature) Types of fatty acids: saturated fatty acid (all available bonds are filled) and unsaturated fatty acid (has one or more double bonds) Triglycerides are formed by dehydration synthesis

43

44

45 ORGANIC MOLECULES: LIPIDS (cont.)
Phospholipids (Figure 2-21) Fat compounds similar to triglyceride One end of the phospholipid is water soluble (hydrophilic); the other end is fat soluble (hydrophobic) Phospholipids can join two different chemical environments Phospholipids may form double layers called bilayers that make up cell membranes (Figure 2-22)

46

47

48 ORGANIC MOLECULES: LIPIDS (cont.)
Steroids (Figure 2-23) Main component is steroid nucleus Involved in many structural and functional roles Prostaglandins (Figure 2-24) Commonly called tissue hormones; produced by cell membranes throughout the body Effects are many and varied; however, they are released in response to a specific stimulus and are then inactivated

49

50

51 ORGANIC MOLECULES: PROTEINS
Proteins (Table 2-6) Most abundant organic compounds Chainlike polymers Amino acids: building blocks of proteins (Figures 2-25 to 2-27) Essential amino acids: eight amino acids that cannot be produced by the human body Nonessential amino acids: 12 amino acids that can be produced from molecules available in the human body Amino acids consist of a carbon atom, an amino group, a carboxyl group, a hydrogen atom, and a side chain

52

53

54

55 ORGANIC MOLECULES: PROTEINS (cont.)
Levels of protein structure (Figure 2-28) Protein molecules are highly organized and show a definite relation between structure and function Protein organization is defined by four levels: Primary structure: the number, kind, and sequence of amino acids that make up the polypeptide chain Secondary structure: polypeptide is coiled or bent into pleated sheets stabilized by hydrogen bonds Tertiary structure: a secondary structure can be further twisted and converted to a globular shape; the coils touch in many places and are “welded” by covalent and hydrogen bonds Quaternary structure: highest level of organization; occurs when protein contains more than one polypeptide chain

56

57 ORGANIC MOLECULES: PROTEINS (cont.)
Importance of protein shape: shape of protein molecules determines their function (Figure 2-29) Final, functional shape of the protein molecule is called its native state Structural proteins form the structures of the body Functional proteins cause chemical changes in the molecules Denatured proteins have lost their shape and therefore their function (Figure 2-30) Proteins can be denatured by changes in pH, temperature, radiation, and other chemicals If the chemical environment is restored, proteins may be renatured and function normally

58

59

60 ORGANIC MOLECULES: NUCLEIC ACIDS AND RELATED MOLECULES
DNA (deoxyribonucleic acid) Composed of deoxyribonucleotides: structural units consist of the pentose sugar (deoxyribose), phosphate group, and nitrogenous base (cytosine, thymine, guanine, or adenine) DNA molecule consists of two long chains of deoxyribonucleotides coiled into a double-helix shape (Figure 2-31) Alternating deoxyribose and phosphate units form the backbone of the chains Base pairs hold the two chains of DNA molecule together Specific sequence of more than 100 million base pairs constitutes one human DNA molecule; all DNA molecules in one individual are identical and different from those of all other individuals DNA functions as the molecule of heredity

61

62 ORGANIC MOLECULES: NUCLEIC ACIDS AND RELATED MOLECULES (cont.)
RNA (ribonucleic acid) (Figure 2-32; Table 2-7) Composed of the pentose sugar (ribose), phosphate group, and a nitrogenous base Nitrogenous bases for RNA are adenine, uracil, guanine, or cytosine (uracil replaces thymine) Some RNA molecules are temporary copies of segments (genes) of the DNA code and are involved in synthesizing proteins Some RNA molecules are regulatory and act as enzymes (ribozymes) or silence gene expression (RNA interference)

63

64 ORGANIC MOLECULES: NUCLEIC ACIDS AND RELATED MOLECULES (cont.)
Nucleotides Nucleotides have other important roles in the body Adenosine triphosphate (ATP) (Figure 2-33) Composed of: Adenosine Ribose, a pentose sugar Adenine, a nitrogen-containing molecule Three phosphate subunits High-energy bonds present between phosphate groups Cleavage of high-energy bonds releases energy during catabolic reactions

65

66 ORGANIC MOLECULES: NUCLEIC ACIDS AND RELATED MOLECULES (cont.)
Adenosine triphosphate (ATP) (cont.) Energy stored in ATP is used to do the body’s work ATP often called the energy currency of cells ATP is split into adenosine diphosphate (ADP) and an inorganic phosphate group by a special enzyme If ATP is depleted during prolonged exercise, creatine phosphate or ADP can be used for energy

67 ORGANIC MOLECULES: NUCLEIC ACIDS AND RELATED MOLECULES (cont.)
Nicotinamide adenine dinucleotide and flavin adenine dinucleotide (Figure 2-34) Used as coenzymes to transfer energy-carrying molecules from one chemical pathway to another Cyclic adenosine monophosphate Made from ATP by removing two phosphate groups to form a monophosphate Used as an intracellular signal

68

69 ORGANIC MOLECULES: COMBINED FORMS
Combined forms: large molecules can be joined together to form even larger molecules Gives the molecules a completely different function Names of combined molecules identify what they are made of Base word tells which component is dominant Prefix is the component found in a lesser amount Examples (Table 2-4) Adenosine triphosphate: two extra phosphate groups to a nucleotide Lipoproteins: lipid and protein groups combined into a single molecule Glycoproteins: carbohydrate (glyco, meaning sweet) and protein


Download ppt "Chapter 2: The Chemical Basis of Life"

Similar presentations


Ads by Google