1. The Chemistry of Living Things
Chapter 2:
The Chemistry of Living Things
OBJECTIVES
Define/describe an atom and its subatomic particles
Describe differences between atoms, isotopes, and ions
Understand how and why atoms form molecules
Know the attributes of water
Understand what is pH and what is a buffer
Describe the four organic molecules and their function

2. All Matter Consists of Elements
Chemistry: the study of matter
Matter
Anything that has mass and occupies space
Composed of elements
Elements
Cannot be broken down to a simpler form
Periodic table of elements—lists all known elements

3. Atoms—Smallest Functional Units of an Element
Atoms consist of
Nucleus (central core)
Protons
positive charge
have mass
Neutrons
no charge
Shells (surrounding nucleus)
Electrons
negative charge
no discernable mass

4. Hydrogen Oxygen Sodium Electron Proton 1 proton Shell 1 electron
Figure 2.3
Electron
Proton
Hydrogen
1 proton
1 electron
Shell
Neutron
Oxygen
8 protons
8 neutrons
8 electrons
in 2 shells
Nucleus
Figure 2.3 The structure of atoms.
Sodium
11 protons
11 neutrons
11 electrons
in 3 shells 4

5. More About Atoms Atomic symbol: one or two letters Atomic number
Na: sodium
O: oxygen
Atomic number
Number of protons, always the same number for any atom of a particular element
Atomic mass
Roughly equal to number of protons plus neutrons
In an electrically neutral atom
Number of protons  number of electrons

6. Isotopes Have a Different Number of Neutrons
Isotopes are atoms of the same element that have a different number of neutrons
They will have a different atomic mass
Unstable isotopes are called radioisotopes: they give off:
Energy in the form of radiation, particles
Some radioisotopes have scientific and medical uses
Diagnostic imaging
Cancer treatment
Power supply for implants such as cardiac pacemakers

7. Energy Fuels Life’s Activities
Energy: the capacity to do work
Potential energy: stored energy
Kinetic energy: energy in motion, doing work
Potential energy can be transformed into kinetic energy

8. Kinetic energy is energy in motion.
Figure 2.4
Potential energy is
locked up in the
chemical bonds of
energy-storage
molecules in Greg
Louganis’ tissues.
Figure 2.4 Energy.
Kinetic energy is energy
in motion. 8

9. Energy Fuels Life’s Activities
Electrons have potential energy
Each shell corresponds to a specific level of potential energy
Shells that are farther from the nucleus contain electrons with more potential energy
Atoms are most stable when their outermost shell is full
Atoms will interact with other atoms to fill their outermost shells (rule of eight)

10. Chemical Bonds Link Atoms to Form Molecules
Chemical bonds: attractive forces holding atoms together
Kinds of chemical bonds
Covalent bonds
Ionic bonds
Hydrogen bonds

11. Covalent Bonds Involve Sharing Electrons
Covalent bonds form when atoms share electrons
Very strong bonds
Nonpolar covalent bonds: electrons are shared equally H2 O2
Polar covalent bonds: electrons are NOT shared equally
H2O: The oxygen has a stronger pull on the shared electrons than the hydrogen does

12. Structural representation
Figure 2.5
Structural formula with covalent bond
Written formula
Structural representation
Hydrogen (H2) H H
Single covalent bond
Oxygen (O2) O O
Double covalent bond
Figure 2.5 Covalent bonds.
Water (H2O) O H
Two single covalent bonds H 12

13. Ionic Bonds Occur Between Oppositely Charged Ions
Ion: an electrically charged atom or molecule
Positively charged ion: forms if an atom or molecule loses electrons
Negatively charged ion: forms if an atom or molecule gains electrons
Ionic bond: attractive force between oppositely charged ions
Example: NaCl

14. Loss of electron: positive charge Gain of electron: negative charge
Figure 2.6
Loss of electron: positive charge
Gain of electron: negative charge + –  Na Cl Na Cl
Sodium atom (Na)
Figure 2.6 Ionic bonds.
Chlorine atom (Cl)
Sodium ion (Na+)
Chlorine ion (Cl–)
Sodium chloride molecule (NaCl) 14

15. Hydrogen Bonds Form between Polar Molecules
Weak hydrogen bonds form between oppositely charged regions of polar molecules
Example:
weak forces between polar water molecules
In DNA
proteins

16. Table 2.1
Table 2.1 Summary of the three types of chemical bonds. 16

17. Atoms Combine to Form Molecules
When atoms gain, lose, or share they stay close together, held by attractions called chemical bonds
When is a covalent bond formed?
When is an ionic bond formed?
What is a hydrogen bond? H
H2O + – O
© 2011 Pearson Education, Inc.

18. Living Organisms Contain Only Certain Elements
Over 100 different elements
99% of body weight consists of 6 elements
Oxygen
Carbon
Hydrogen
Nitrogen
Calcium
Phosphorus

19. Life Depends on Water Key properties of water:
Water is an excellent solvent
Water is liquid at body temperature
Water can absorb and hold heat energy
Evaporation of water uses up heat energy
Water participates in essential chemical reactions

20. Water Is the Biological Solvent
Solvent: liquid in which other substances dissolve
Solute: any dissolved substance
Hydrophilic: polar molecules that are attracted to water and interact easily with water
Hydrophobic: nonpolar neutral molecules that do not interact with or dissolve in water

21. Water Is a Liquid at Body Temperature
Water serves an important transport function in the blood, which is 90% water
Water is the main constituent of:
Intracellular spaces
Extracellular spaces
60% of body weight is water

22. Water Helps Regulate Body Temperature
Water absorbs and holds a large amount of heat energy with only a modest increase in temperature
Prevents rapid changes in body temperature
Evaporative cooling enables body to lose excess heat quickly

23. Water Participates In Chemical Reactions
Synthesis of carbohydrates, proteins, and lipids produces water molecules
Breakdown of carbohydrates, proteins and lipids consumes water molecules

24. The Importance of Hydrogen Ions
Acids
Donate hydrogen ions (H)
Increase hydrogen ion concentration in solutions
Bases
Accept hydrogen ions
Decrease hydrogen ion concentration in solutions
pH Scale
A measure of hydrogen ion concentration

25. The pH Scale Expresses Hydrogen Ion Concentration
Measure of hydrogen ion concentration in solution
Ranges from 0 to 14
Acids: pH  7
Neutral: pH  7
Basic: pH  7

26. Concentrated nitric acid
Figure 2.10
Drain opener
Bleach
Ammonia cleanser
More alkaline
Soapy water
Baking soda
Neutral pH
Human blood, tears
Saliva, urine
Figure 2.10 The pH scale.
Black coffee
Tomatoes
More acidic
Vinegar, cola
Lemon juice
Hydrochloric acid
Concentrated nitric acid 26

27. Buffers Minimize Changes in pH
Minimize pH change
Help maintain stable pH in body fluids
Carbonic acid and bicarbonate act as one of the body’s most important buffer pairs
HCO3 + H H2CO (reversible reaction)
If blood is too acidic: HCO3 + H H2CO3
If blood is too alkaline: H2CO HCO3  H

28. The Organic Molecules of Life-
What are organic molecules?
Contain carbon
forms 4 covalent bonds
The backbone of biological molecules
Some are called macromolecules
Built by dehydration synthesis reactions
Broken down by hydrolysis reaction
4 major groups of macromolecules:

29. Carbohydrates: Used for Energy and Structural Support
General formula: Cn(H20)n
Monosaccharides: simple sugars
Glucose
Fructose
Galactose
Ribose
Deoxyribose
Disaccharides: two monosaccharides linked together
Sucrose: glucose  fructose
Maltose: glucose  glucose
Lactose: glucose  galactose

30. Polysaccharides Store Energy
Polysaccharides: thousands of monosaccharides joined in linear and/or branched chains
Starch: made in plants; stores energy
Glycogen: made in animals; stores energy
Cellulose: indigestible polysaccharide made in plants for structural support

31. Lipids: Insoluble in Water
Three important classes of lipids
Triglycerides: energy storage molecules
Phospholipids: primary component of cell membranes
Steroids: carbon-based ring structures

32. Stored in adipose tissue as energy-storage molecules
Triglycerides:
Stored in adipose tissue as energy-storage molecules
Composed of glycerol and three fatty acids
Fatty acids may be saturated or unsaturated (in oils)
Steroids:
Composed of four carbon rings
Examples: Cholesterol, hormones e.g. estrogen, testosterone
Phospholipids: primary component of cell membranes

33. Proteins: Complex Structures Constructed of Amino Acids
Long chains (polymers) of subunits called amino acids
Amino acids are joined by peptide bonds, which are produced by dehydration synthesis reactions
Polypeptide: a polymer of 3–100 amino acids
Protein: a polypeptide longer than 100 amino acids that has a complex structure and function

34. Enzymes Facilitate Biochemical Reactions
Are proteins
Function as biological catalysts
Speed up chemical reactions
Are not altered or consumed by the reaction
Without enzymes, many biochemical reactions would not proceed quickly enough to sustain life

35. Enzyme Reactants Product Reactants approach enzyme Reactants
Figure 2.22
Enzyme
Reactants
Product
Reactants
approach enzyme
Reactants
bind to enzyme
Enzyme
changes shape
Products
are released
Figure 2.22 Enzymes facilitate chemical reactions. 35

36. Nucleic Acids Store Genetic Information
Nucleic acids are long chains containing subunits known as nucleotides
Two types of nucleic acids
DNA: deoxyribonucleic acid
RNA: ribonucleic acid
DNA contains the instructions for producing RNA
RNA contains the instructions for producing proteins
Proteins direct most of life processes
DNA  RNA  Proteins

37. Nucleic Acids Store Genetic Information
Nucleotides: building blocks (monomers) of nucleic acids
Each nucleotide contains
5 carbon sugar
Phosphate group
Nitrogenous base
Adenine
Guanine
Cytosine
Thymine in DNA & Uracil in RNA

38. Nucleic Acids Store Genetic Information
Structure of DNA (deoxyribonucleic acid)
Double–stranded
Nucleotides contain
Deoxyribose (sugar)
Nitrogenous bases
Adenine
Guanine
Cytosine
Thymine
Complementary base pairing:
Adenine - Thymine
Guanine - Cytosine

39. Base pair Phosphate Sugar Nucleotide Figure 2.24
Figure 2.24 The double helical structure of DNA. T P P A T P P G C P 39

40. Nucleic Acids Store Genetic Information
Structure of RNA (ribonucleic acid)
Single–stranded
Nucleotides contain
Ribose (sugar)
Nitrogenous bases
Adenine
Guanine
Cytosine
Uracil

41. Phosphate Ribose Uracil Figure 2.25 P C P A P
Figure 2.25 The structure of RNA. G P
Uracil
(U) P 41

42. ATP Carries Energy
Structure and function of adenosine triphosphate (ATP)
Universal energy source
Bonds between phosphate groups contain potential energy
Breaking the bonds releases energy
ATP  ADP  P  energy

43. The breakdown and synthesis of ATP.
Figure 2.26
Hydrolysis of ATP
produces useful energy
for the cell
Adenosine
H2O
Adenine (A)
Triphosphate
Adenosine P P P
Adenosine P P P
(ATP)
(ADP)
Energy for ATP synthesis
comes from food or body
stores of glycogen or fat
H2O
Figure 2.26 Adenosine triphosphate (ATP).
Ribose
The structure of ATP.
The breakdown and synthesis of ATP.
The breakdown (hydrolysis) of ATP yields
energy for the cell. The reaction is reversible,
meaning that ATP may be resynthesized
using energy from other sources. 43