Chapter 3: Biological Molecules
I. Why is Carbon so Important in Biological Molecules?
A. Organic Chemistry refers to chemistry dealing with chemicals that have a carbon skeleton and some hydrogen atoms.
B. Inorganic Chemistry refers to chemistry dealings with chemicals that do not have carbon or only carbon and oxygen.
C. The beauty of organic chemistry lies in the ability of carbon to bond with a significant number of other atoms.
D. A number of subunits can be seen that will bind to the carbon skeleton, these subunits are called functional groups (generically designated –R).
E. The chemistry of organic compounds is mainly dictated by the chemistry of the functional groups
II. How are Organic Molecules Synthesized?
A. Some organic molecules are composed of very unique and complex patterns of atoms; but, the vast majority of biological organic molecules are made from combining smaller, less complex subunits.
1. The small subunits are called monomers
2. The larger complex structures are called polymers
B. Biological molecules are joined together or broken apart by adding or removing water.
1. The chemical reaction that combines to monomers into a polymer, by removing water is called a dehydration synthesis.
III. What are Carbohydrates?
A. Carbohydrates are biological molecules composed of carbon, hydrogen, and oxygen in approximately 1:2:1.
B. Carbohydrates are either simple sugars or complex polymers.
C. Definition
1. Monosaccharide – single sugar
2. Disaccharide – Complex sugars composed of two monosaccharides
3. Polysaccharide – Complex polymers of monosaccharides
D. Carbohydrates serve important energy storage and structural roles.
E. There are many monosaccharides of slightly different structures
1. Monosaccharides are usually composed of three (3) to seven (7) carbon atoms.
2. Common Sugars
a. Glucose
b. Fructose
c. Ribose
d. Deoxyribose
F. Disaccharides consist of two sugars linked by a dehydration synthesis
1. Examples of Disaccharides
a. Lactose
b. Sucrose
c. Maltose
G. Polysaccharides are chains of single sugars
1. Examples of Polysaccharides
a. Chitin
b. Cellulose
c. Starch
IV. What are Lipids?
A. There are large regions of hydrophobic carbon-carbon and carbon-hydrogen bonds.
B. Three major groups
1. Oils, fats, and waxes
a. Contain only carbon, hydrogen, and oxygen
b. Contain one or more fatty acid (a long hydrocarbon chain terminated by a carboxyl group)
c. Fats and oils (triglycerides) are made by fusing three fatty acids to a molecule of glycerol.
i. Saturated triglycerides have no double bonds in their fatty acids, leading to tight packing and room temperature solidity. (animal fats)
ii. Unsaturated triglycerides have multiple double bonds in their fatty acids, leading to loose packing and room temperature fluidity. (plant oils)
iii. Waxes are triglycerides with highly saturated fatty acids that do not serve as food sources, but rather as structural material with high structural stability at room temperature.
2. Phospholipids
a. Phospholipids contain two distinct areas
i. Similar to triglycerides, two of the attachments on the glycerol molecule are bound to fatty acids that are typically highly saturated. (Hydrophobic)
ii. One glycerol binding site is connected to a phosphate group linked to a functional group (typically containing nitrogen, hydrophilic)
b. The dual chemical nature of the molecule has implications for its interactions with water.
3. Steroids
a. Fused rings structure that is adapted by protruding functional groups.
b. This is the basis for everything from cholesterol, to estrogen, to cortisol.
V. What are Proteins?
A. Proteins are polymers that are composed of monomers called amino acids.
B. Amino Acids
1. Small organic molecules that are composed of a central carbon atom bonded to an amino, carboxyl, and functional group.
2. Amino acids polymerize with a dehydration synthesis between the amino group of one amino acid and the carboxyl group of another amino acid.
3. Amino acids have a diverse set of functional groups that provide a variety of chemical activities.
4. Amino Acids are joined together with a peptide bond.
C. Proteins have up to four levels of structure
1. Primary Structure – The linear sequence of amino acids encoded in the genetic code.
2. Secondary Structure – The interactions of neighboring amino acids to form complex folds such as helices and β-pleated sheets.
3. Tertiary Structure – The complex three dimensional interactions of distant amino acids to give a final shape.
4. Quaternary Structure – Some proteins interact with other protein chains to form a complex multi-chain form (i.e. hemoglobin)
5. The complex structure of a protein can be destroyed, this is denaturation.
D. The function of a protein is linked to the three-dimensional shape of the protein.
E. Biochemically active proteins are referred to as enzymes.
VI. What are Nucleic Acids?
A. A nucleic acid is a polymer of similar monomers called nucleotides.
B. Nucleotides
1. Nucleotides are composed of three subunits
a. Phosphate – an inorganic phosphate group allows for polymerization through dehydration synthesis.
b. Carbohydrate – Each nucleotide ha at its base either a ribose or deoxyribose sugar
c. Base – There are five possible nitrogen-containing, organic bases
i. Adenine
ii. Guanine
iii. Cytosine
iv. Thymine
v. Uracil
2. DNA – Deoxyribonucleic acid – A nucleic acid composed of nucleotides made from deoxyribose.
3. RNA – Ribonucleic acid – A nucleic acid composed of nucleotides made from ribose.
4. DNA and RNA serve as the molecules of heredity
5. Other chemical modifications of nucleotides can result in energy carriers, intracellular messengers, and coenzymes.