KEY CONCEPT Carbon-based molecules are the foundation of life.

Carbon atoms have unique bonding properties. Carbon forms covalent bonds with up to four other atoms, including other carbon atoms. Carbon-based molecules have three general types of structures. straight chain/linear branched chain ring

Linear and ring forms

Functional groups

Many carbon-based molecules are made of many small subunits bonded together. Monomers are the individual subunits. Polymers are made of many monomers.

Dehydration/condensation reaction

Hydrolysis reaction

Four main types of carbon-based molecules are found in living things. Carbohydrates are made of carbon, hydrogen, and oxygen. All carbohydrates exist in a ratio of 1 carbon: 2 hydrogen: 1 oxygen or CH2O.

Four main types of carbon-based molecules are found in living things. Carbohydrates are made of carbon, hydrogen, and oxygen. Carbohydrates include sugars and starches. Monosaccharides are simple sugars. Polysaccharides include starches, cellulose, and glycogen.

Carbohydrates can be broken down to provide energy for cells. Some carbohydrates are part of cell structure. Polymer (starch) Starch is a polymer of glucose monomers that often has a branched structure. Polymer (cellulose) Cellulose is a polymer of glucose monomers that has a straight, rigid structure monomer

The polysaccharide cellulose is a major component of the tough wall of plant cells Like starch, cellulose is a polymer of glucose, but the glycosidic linkages differ The difference is based on two ring forms for glucose: alpha () and beta () Cellulose in human food passes through the digestive tract as insoluble fiber Some microbes use enzymes to digest cellulose Many herbivores, from cows to termites, have symbiotic relationships with these microbes

Glycogen

Glycogen is a storage polysaccharide in animals Humans and other vertebrates store glycogen mainly in liver and muscle cells

1 m 0.5 m Chloroplast Starch granules Amylopectin Amylose Figure 5.6 Chloroplast Starch granules Amylopectin Amylose (a) Starch: a plant polysaccharide 1 m Mitochondria Glycogen granules Figure 5.6 Storage polysaccharides of plants and animals. Glycogen (b) Glycogen: an animal polysaccharide 0.5 m

Chitin, another structural polysaccharide, is found in the exoskeleton of arthropods Chitin also provides structural support for the cell walls of many fungi

The structure of the chitin monomer Figure 5.9 The structure of the chitin monomer Chitin forms the exoskeleton of arthropods. Figure 5.9 Chitin, a structural polysaccharide. Chitin is used to make a strong and flexible surgical thread that decomposes after the wound or incision heals.

Many contain carbon chains called fatty acids. Lipids are nonpolar molecules that include fats, oils, and cholesterol. Many contain carbon chains called fatty acids. Fats and oils contain fatty acids bonded to glycerol. Triglyceride

Fats and oils have different types of fatty acids. saturated fatty acids unsaturated fatty acids

Saturated fatty acids

Unsaturated fatty acids

Phospholipids make up all cell membranes. Polar phosphate “head” Nonpolar fatty acid “tails”/two fatty acid tails Arranged in bilayer in forming the cell membrane, with the hydrophilic heads pointing toward the watery cytosol or extra-cellular environment, and they hydrophobic tails sandwiched in between. Phospholipid

Phospholipids

Lipids have several different functions. broken down as a source of energy make up cell membranes/Phospholipids used to make hormones/steroids

Proteins are polymers of amino acid monomers. Twenty different amino acids are used to build proteins in organisms.

Proteins differ in the number and order of amino acids. Amino acids interact to give a protein its shape. hydrogen bond Hemoglobin Incorrect amino acids change a protein’s structure and function. Denaturation occurs when a protein A protein is denatured when it loses its shape and ability to function due to heat, a change in pH, or some other disturbance.

Enzymatic proteins Defensive proteins Storage proteins Figure 5.15-a Enzymatic proteins Defensive proteins Function: Selective acceleration of chemical reactions Function: Protection against disease Example: Digestive enzymes catalyze the hydrolysis of bonds in food molecules. Example: Antibodies inactivate and help destroy viruses and bacteria. Antibodies Enzyme Virus Bacterium Storage proteins Transport proteins Function: Storage of amino acids Function: Transport of substances Examples: Casein, the protein of milk, is the major source of amino acids for baby mammals. Plants have storage proteins in their seeds. Ovalbumin is the protein of egg white, used as an amino acid source for the developing embryo. Examples: Hemoglobin, the iron-containing protein of vertebrate blood, transports oxygen from the lungs to other parts of the body. Other proteins transport molecules across cell membranes. Figure 5.15 An overview of protein functions. Transport protein Ovalbumin Amino acids for embryo Cell membrane

Nucleic acids are polymers of monomers called nucleotides.

Nucleic acids are polymers of monomers called nucleotides. Nucleotides are made of a sugar, phosphate group, and a nitrogen base. A phosphate group nitrogen-containing molecule, called a base deoxyribose (sugar)

Nucleic acids are polymers of monomers called nucleotides. Nucleotides are made of a sugar, phosphate group, and a nitrogen base. DNA DNA stores genetic information. RNA RNA builds proteins. RNA is single-stranded. (for the most part) Its nucleotides are adenine, uracil, cytosine, and guanine. Note that uracil replaces thymine in RNA.

Base pair joined by hydrogen bonding Figure 5.27 5 3 Sugar-phosphate backbones Hydrogen bonds Base pair joined by hydrogen bonding Figure 5.27 The structures of DNA and tRNA molecules. Base pair joined by hydrogen bonding 3 5 (a) DNA (b) Transfer RNA

DNA and Proteins as Tape Measures of Evolution The linear sequences of nucleotides in DNA molecules are passed from parents to offspring Two closely related species are more similar in DNA than are more distantly related species Molecular biology can be used to assess evolutionary kinship © 2011 Pearson Education, Inc.