3 The Chemistry of Life: Organic Compounds

Lecture Outline

I. Carbon atoms form an enormous variety of structures, including hydrocarbons, composed of carbon and hydrogen only

A. Carbon has 4 valence electrons in the outer shell, and therefore may form up to 4 covalent bonds

B. Carbon tends to bond to carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus

C. Single bonds between carbon molecules allow rotation and flexibility of the molecule

II. Isomers have the same molecular formula but different structures

A. Structural isomers differ in the arrangement of the covalent bonds

B. Geometric isomers vary in the arrangement of groups around the double bond

C. Enantiomers are mirror images of each other

D. Single bonds allow rotation and flexibility of the molecule

III. Functional groups change the properties of organic molecules

A. Hydrocarbons are hydrophobic and cluster together

B. Polar and ionic functional groups are hydrophilic and associate with polar water molecules

C. A hydroxyl group (RC OH) is polar

D. A carbonyl group (C=O) is polar and characterizes aldehydes and ketones

E. A carboxyl group (RC COOH) is weakly acidic and is an important part of amino acids

F. Amino groups (RC NH2) are weakly basic and are an important part of amino acids

G. Phosphate groups (RC PO4H2) are parts of phospholipids and nucleic acids

H. Sulfhydryl groups (RC SH) are important in some amino acids

I. Methyl groups (RC CH3) are nonpolar

IV. Many biological molecules are polymers

A. Macromolecules are large polymers

B. Polymers are based on repeating subunits (monomers)

C. Monomers are linked by condensation reactions

D. Polymers are degraded by hydrolysis reactions

V. Carbohydrates include sugars, starches, and cellulose

A. Monosaccharides are simple sugars

1. Glucose, fructose, and galactose are hexoses

a) Glucose is extremely abundant and important, particularly as an energy source

b) The hexoses form ring structures

2. Deoxyribose and ribose are pentoses

B. Disaccharides consist of two monosaccharide units

1. Maltose, lactose, and sucrose are disaccharides

C. Polysaccharides can store energy or provide structure

1. Starch is the main storage carbohydrate of plants

a) Starch is a polymer of alpha-glucose

b) Amylose is an unbranched starch

c) Amylopectin is a branched chain and is more common

d) Plants store starch in plastids

2. Glycogen is the main storage carbohydrate of animals

a) Glycogen is primarily stored in liver and muscle cells

3. Cellulose is a structural carbohydrate

a) Cellulose is a glucose polymer that composes cell walls

4. Most organisms cannot digest cellulose

D. Some modified and complex carbohydrates have special roles

1. Glucosamine makes up chitinC important in arthropod exoskeletons and fungal cell walls

2. Galactosamine is a component of cartilage

3. Glycoproteins and glycolipids are important molecules of the plasma membrane

VI. Lipids are fats or fatlike substances

A. Fats are hydrophobic and are composed primarily of hydrogen and oxygen

B. Triacylglycerols (=triglycerides = triglycerols) contain glycerol and fatty acids

1. Triacylglycerols are the most abundant lipids

2. Fats are an important source of energy

3. Triacylglycerols are composed of a glycerol head with up to 3 fatty acid chains attached

a) Saturated fats have the maximum number of hydrogen atoms in the fatty acid chains

(1) Saturated fats are typically solid at room temperature

(2) Saturated fats are often from animal sources

b) Unsaturated fats have one or more double bonds in the fatty acid chains

(1) Unsaturated fats are typically liquid at room temperature

(2) Unsaturated fats are healthier than saturated fats

(3) Hydrogenation changes an unsaturated fatty acid to a saturated fatty acid

C. Phospholipids are components of cell membranes

1. Phospholipids are amphipathic

D. Carotenoid plant pigments are derived from isoprene units

E. Steroids contain 4 rings of carbon atoms

1. Steroids include cholesterol, bile salts, and hormones such as testosterone

F. Some chemical mediators are lipids

1. Prostaglandins (in vertebrates) and juvenile hormone in insects are examples

VII. Proteins are the most versatile cell components

A. Amino acids are the subunits of proteins

1. Amino acids contain an amino group, a carboxyl group, an alpha carbon, and a unique R group

2. There are 20 commonly occurring amino acids

3. Essential amino acids are those that must be ingested in the diet of an animal

B. Peptide bonds join amino acids

1. 2 amino acids form a dipeptide

2. Polypeptides are formed from more than 2 amino acids

C. Proteins have 4 levels of organization

1. Primary structure is the amino acid sequence

2. Secondary structure results from hydrogen bonding

a) The alpha helix is a coiled secondary structure

b) The beta-pleated sheet is formed by folding

c) A single polypeptide may have portions with both types of structure

3. Tertiary structure depends on interactions among side chains

a) R-groups interact in various ways

4. Quaternary structure results from interactions among polypeptides

a) Hemoglobin is composed of 4 polypeptide chains

D. The amino acid sequence of a protein determines its conformation

1. Molecular chaperones may aid in the folding process in vivo

E. Protein conformation determines function

1. Regions of a protein, called domains, are important in the function of the protein

2. Denaturation results in disruption of the secondary, tertiary, or quaternary structure of a protein

3. Denaturation may be due to changes in pH, temperature, or various chemicals

F. Protein conformation is studied through a variety of methods

1. Methods using computer technology and biotechnology allow determination of protein structure

VIII. DNA and RNA are nucleic acids

A. Nucleic acids consist of nucleotide subunits

1. Nucleotides are composed of a pentose, a phosphate group, and a nitrogenous base

2. The nitrogenous base may be a double ringed purine or a single ringed pyrimidine

B. Some nucleotides are important in energy transfers and other cellular function

1. ATP is the energy A currency@ of the cell

2. GPT transfers energy and is important in cell signaling

3. cAMP is important in cellular functioning

4. cGMP is important in cell signaling

5. Other dinucleotides are important in electron transfers

6. DNA and RNA are large nucleic acids important in genetics and protein synthesis