Proteins, Enzymes, and Nucleic Acids
Proteins
Proteins are organic compounds composed of C, H, O, N, and S. They are large polymers made of smaller units called amino acids, which are joined by peptide bonds. The union of 1 to 12 amino acids gives rise to an oligopeptide, 12-100 forms a polypeptide, and more than 100, or if their molecular weight exceeds 5000 g/mol, constitutes a protein.
Biological Importance: Proteins are the most abundant organic compounds in cells. Their importance lies in the enormous quantity of functions they perform:
- Enzymatic function: Enzymes are proteins that regulate cell metabolism by increasing the speed of reactions.
- Regulatory or hormonal function: Some proteins are hormones.
- Defensive and immunological functions: They protect the organism.
- Transport: For example, hemoglobin transports oxygen through the blood.
- Structural: Some glycoproteins are part of cell membranes.
- Homeostatic: Intracellular proteins participate in the maintenance of osmotic equilibrium.
- Contractile: Actin and myosin are constituents of muscle myofibrils, responsible for muscle contractions.
- Reserve.
Amino Acids
These are the basic units of polypeptide chains. They have one carboxyl group and one amino group attached to a carbon atom. Also attached to this carbon is a hydrogen atom and a side chain (R), whose characteristics distinguish one amino acid from others.
Classification:
- Acidic amino acids: Negatively charged at pH 7 (aspartic acid and glutamic acid).
- Basic amino acids: Positively charged at pH 7 (lysine and arginine).
- Amino acids with nonpolar R group: Uncharged at pH 7. R has hydrophobic groups that interact with other hydrophobic groups (alanine and valine).
- Amino acids with uncharged polar R group at pH 7: R contains polar groups that can form hydrogen bonds with other polar groups (glycine and serine).
Properties of Amino Acids:
- Spatial Isomerism: Due to the presence of asymmetric carbons.
- Optical Isomerism: Almost all amino acids have an asymmetric carbon; because of this, they can divert the plane of polarized light.
- Acid-Base Properties: Amino acids can act as acids or bases in biological media.
Peptide Bond:
Peptide bonds are covalent links established between amino acids to form peptides and proteins. It is a very stable link established between the carboxyl group of one amino acid and the amino group of the next, releasing a water molecule for each bond formed. The resulting molecule is a dipeptide. This bond is very strong and has a partial double bond character, maintaining the atoms at a set distance of 1.
Enzymes
Biocatalysis Concept: A catalyst is a substance that accelerates or retards a chemical reaction while remaining unchanged. Biocatalysts regulate and coordinate the functions of living things. There are three types: enzymes, vitamins, and hormones.
Nucleic Acids
Concept and Biological Significance: Nucleic acids are biopolymers formed by nucleotides, compounds containing C, H, O, N, and P. They are giant, unbranched fibrillar molecules that contain the necessary information for life and detailed instructions to be read.
Nucleotides: are molecules formed by a nucleoside and phosphoric acid. Nucleosides are molecules formed by the union of a sugar and a nitrogenous base through an N-glycosidic bond. This bond involves the release of a water molecule. The sugar is a pentose and may be ribose or deoxyribose.
The nitrogenous bases are:
- Purines: Adenine, Guanine
- Pyrimidines: Cytosine, Thymine, and Uracil