1. The Chemical Building Blocks of Life
Chapter 2
The Chemical Building Blocks of Life

2. 2.1 Organisms Are Composed of Atoms
Matter is Composed of Atoms
An atom is the smallest unit of an element having the properties of that element
Atoms are made of a nucleus containing protons and neutrons, surrounded by a negatively charged cloud of electrons
Figure 02.02AB: Atomic Structure and the Electron Configurations for Four Biologically Important Elements.

3. Figure 02.03: Formation of an Ion.
Atoms Can Vary in the Number of Neutrons or Electrons
Isotopes are atoms of the same element that have different numbers of neutrons
An ion is an atom with a charge
Electron Placement Determines Chemical Reactivity
An atom with an unfilled outer electron shell is unstable.
It can become stable by interacting with another unstable atom
Figure 02.03: Formation of an Ion.

4. 2.2 Chemical Bonds Form Between Reactive Atoms
Ionic Bonds Form between Oppositely Charged Ions
In forming an ionic bond, one atom gives up its outermost electrons to another atom

5. Figure 02.06A: Chemical Bonding and Hydrocarbons.
Covalent Bonds Share Electrons
Covalent bonds are formed when atoms share outer shell electron pairs.
Carbon frequently forms covalent bonds with other atoms.
Covalent bonds can be nonpolar (no electrical charges) or polar (has electrical charges).
Figure 02.06A: Chemical Bonding and Hydrocarbons.

6. Hydrogen Bonds Form between Polar Groups or Molecules
Hydrogen bonding is the electrostatic attraction between a partially positive hydrogen atom that is covalently bonded to a partially negative polar molecule
Figure 02.07A: Chemical Bonding and Water.

7. Chemical Reactions Change Bonding Partners Chemical reactions can
break larger compounds into smaller ones (e.g., hydrolysis), or
C6H12O6 + C6H12O6 → C12H22O11 + H2O
Glucose Glucose Maltose Water
add smaller reactants together to form a larger product (e.g., dehydration synthesis or condensation)
C12H22O11 + H2O → C6H12O6 + C6H12O6
Maltose Water Glucose Glucose

8. 2.3 All Living Organisms Depend on Water
Water Has Several Unique Properties
All cellular chemical reactions occur in water
Water is an excellent solvent for other polar molecules
Figure 02.08: Solutes Dissolve in Water.

9. Figure 02.09: A Sample of pH Values for Some Common Substances.
Acids and Bases Affect a Solution’s pH
An acid is a chemical substance that donates a H+ to a solution; a base accepts the H+
The pH scale indicates the acidity or alkalinity of a solution
Every time the pH changes by 1 unit, the H+ ions change by 10 times
Figure 02.09: A Sample of pH Values for Some Common Substances.

10. Figure 02.10AB: Hypothetical Example of pH Shifts.
Cell chemistry is Sensitive to pH Changes
Buffers Are a Combination of a Weak Acid and Base
Buffers prevent pH shifts
Figure 02.10AB: Hypothetical Example of pH Shifts.

11. 2.4 Living Organisms Are Composed of Four Types of Organic Compounds
Figure 02.11: Organic Compounds in Bacterial Cells.

12. Functional Groups Define Molecular Behavior
Functional groups are groups of atoms projecting from biological molecules
Chemical reactions can occur with functional groups if facilitated by an enzyme
Table 02.03: Common Functional Groups on Organic Compounds.

13. Figure 02.12ABC: Carbohydrate Monomers Are Built into Polymers.
Carbohydrates Consist of Sugars and Sugar Polymers.
Monosaccharides are simple sugars like glucose and fructose.
Disaccharides are composed of two monosaccharides.
Polysaccharides are complex carbohydrates made of many thousands of monosaccharides.
For example, starch
Carbohydrates provide structure and energy .
Figure 02.12ABC: Carbohydrate Monomers Are Built into Polymers.

14. Lipids Are Water-Insoluble Compounds
Lipids are hydrophobic; they don’t dissolve in water
Saturated fatty acids are filled with H, with single bonds
Unsaturated fatty acids have at least one double bond
Figure 02.13A: Lipid and Lipid-Related Compounds.

15. Figure 02.13B: Lipid and Lipid-Related Compounds.
Phospholipids make up cell membranes
Sterols are hydrophobic molecules that stabilize some membranes
Figure 02.13B: Lipid and Lipid-Related Compounds.
Figure 02.13C: Sterol.

16. Nucleic Acids Are Large, Information-Containing Polymers
Deoxyribonucleic acid (DNA) and Ribonucleic acid (RNA) are both composed of nucleotides.
Nucleotides are composed of a sugar molecule, a phosphate group, and a nitrogenous base.

17. Figure 02.14C: DNA Double Helix.
In DNA, complementary base pairs hold the double-stranded molecule together.
The double strand twists to form a double helix.
Figure 02.14C: DNA Double Helix.

18. Microinquiry 02.02: The Hershey-Chase experiment.
DNA is the genetic material in all organisms
The genetic information is contained in thousands of genes
Genes are located in chromosomes
Microinquiry 02.02: The Hershey-Chase experiment.

19. Nucleic Acids Are Large, Information-Containing Polymers (Cont.)
RNA is a single-stranded molecule that copies gene information for use in protein synthesis
Many viruses carry their genetic information as RNA instead of DNA
Damage to nucleic acids inevitably injures or kills the organism

20. Figure 02.15A: Amino Acids and Their Assembly into Polypeptides.
Proteins Are the Workhorse Polymers in Cells.
They are built from amino acids joined together by a (covalent) peptide bond.
Each of the 20 amino acids has a unique R group (side chain).
Figure 02.15A: Amino Acids and Their Assembly into Polypeptides.

21. Amino acids are joined through dehydration synthesis

22. Figure 02.15CDE: Amino Acids and Their Assembly into Polypeptides.
Proteins have several structural levels:
Primary structure: sequence of amino acids in the polypeptide
Secondary structure: regions form an alpha helix, pleated sheet, or random coil
Tertiary structure: part of the polypeptide folds back on itself and sulfur atoms join through disulfide bridges
Quaternary structure: occurs when two or more polypeptides join together
Figure 02.15CDE: Amino Acids and Their Assembly into Polypeptides.

23. Protein shape is held using ionic and hydrogen bonds.
When these relatively weak bonds are disrupted, the protein is denatured.
Figure 02.15D: The whole polypeptide folds into a tertiary structure through bonding between R groups.