1.2 Biochemistry as a Biological Science

Figure 1.6: Anatomy of an Animal Cell

As shown in figure 1.6, there are many organelles (and hence functions) in an animal cell.

Figure 1.7: Levels of Biochemistry

Nonetheless, biochemistry also comes in all shapes and sizes as displayed in figure 1.7!

1.2.1 Types of polymers

There are many types of natural polymers present in the Biology side of Biochemistry.

These polymers include:

1. Cellulose

   

   Figure 1.8: Structure of Cellulose

   This is made by joining many identical glucose units via \(\alpha\)(1, 4) glycosidic bonds.

2. Starch

   Like cellulose, starch is a homopolymer of glucose (i.e., a polymer made up of identical subunits). However, \(\alpha\)(1, 6) and \(\alpha\)(1, 4) glycosidic bonds are present in starch (i.e., the polymer is branched).

   Polysaccharides can also serve as structural components and as a form of energy storage (e.g., glycogen).

3. Proteins

   

   Figure 1.9: Structure of a Protein

   These are heteropolymers of amino acids - they are linked by peptide bonds. Proteins can serve as enzymes, hormones, receptors, and structural components (e.g., collagen).

   As an example, myoglobin (an oxygen-carrying protein in muscle) has a mass of 16.7 kDa. It is also distantly related to hemoglobin in red blood cells, contains iron, and binds to oxygen.

4. Nucleic acids

   

   Figure 1.10: Structure of DNA

   This is also a heteropolymer; it is made by combining different nucleotides: adenine, guanine, cytosine, thymine, or uracil. These polymers are responsible for the storage and the transmission of genetic information (i.e., the central dogma).

1.2.2 Lipids

Figure 1.11: Structure of Lipids

As witnessed in figure 1.11, lipids can take many forms.

Figure 1.12: Structure of a Phospholipid Bilayer

Lipids are generally used for energy storage purposes (e.g., body fat) and are the main constituents of the cell membrane.

1.2.3 Water in Biology

Figure 1.13: Structure and Intermolecular Bonding Water Molecules

As implied in figure 1.13, the oxygens in a water molecule have a greater partial negative charge (i.e., \(\delta-\)); the hydrogens have a greater partial positive charge (i.e., \(\delta+\)).

Water serves intracellular and extracellular roles due to its two properties:

1. Its ability to form hydrogen bonds.
2. Its polar character.

Substances that readily dissolve in water are termed hydrophilic or “water-loving.”

Figure 1.14: Hydration Shell Around an Anion

When ionic compounds are dissolved in water, the interactions of the negative ends of the water dipoles with cations and the positive ends with anions cause the ions to become hydrated. They become surrounded by water molecules and form a hydration shell (as depicted in figure 1.14).