Chemical Composition and Functions of Living Beings

Chemistry of Life

The universe is mainly composed of Hydrogen (H) and Helium (He). The Earth's crust is composed of Silicon (Si), Iron (Fe), Magnesium (Mg), and carbon (C). Living organisms form organic macromolecules. Oxygen and Hydrogen constitute 68-70% of living matter (Water = H₂O). Nitrogen (N) is part of proteins.

Properties of Living Beings

Living beings are complex materials that can interact with the world around them and reproduce.

Features

• Made mostly of Carbon and H₂O
• Their reactions inside cells are governed by the laws of physics and chemistry.
• They reproduce

Interaction with the Environment

Living beings evolve and react to external or internal stimuli, creating responses through the nervous and endocrine systems (hormones).

Nutrition

Living beings exchange energy and matter with the outside.

• Autotrophs create organic matter from inorganic matter.
• Photosynthesis: Photosynthetic organisms capture the sun's energy for conversion into chemical energy and produce power from organic matter of the inorganic.
• Heterotrophs take food directly from the outside because they cannot synthesize it.
• Cellular Respiration is a process common to all living beings, by which, through a series of reactions, they oxidize organic matter for energy.

Chemical Composition of Living Things

Living things are comprised of both inorganic and organic molecules.

• Inorganic molecules are part of both living and inert material. These are mainly salt and water.
• Organic molecules are exclusively in living matter. They are carbohydrates, lipids, proteins, and nucleic acids.

Biomolecules

Carbohydrates

Composed of Carbon, Hydrogen, and Oxygen.

• Simple or monosaccharides: Single chain of 5 or 6 carbons, usually have a sweet taste (e.g., lactose, glucose, fructose).
• Compounds or polysaccharides: (e.g., pasta, rice).

Starch has an energetic function. Cellulose has a structural function. Glycogen has an energy function.

Lipids

A group of organic molecules that are not soluble in water.

• Fats: Reserve substance par excellence of animals. They are formed by triglycerides (the union of 3 fatty acids and glycerol).
• Saturated fats: No double bonds.
• Unsaturated fats: With double and triple bonds.
• Phospholipids form the structure of the cell membrane of all cells.
• Cholesterol forms bile and hormones.

Proteins

Macromolecules formed by the joining of amino acids. There are only 20 amino acids in living matter. Humans can synthesize 11, and 9 have to be taken from outside. Depending on the content of essential amino acids, proteins can be:

• Complete proteins: Animal origin.
• Incomplete proteins: Vegetable origin.

Functions:

• Structural
• Enzymatic (regulatory)
• Transportation
• Defensive (antibodies)
• Hormonal

Nucleic Acids

Macromolecules comprising the nucleotide binding. Each nucleotide consists of a pentose, a nitrogenous base, and phosphoric acid. DNA consists of a double helix consisting of nucleotides, whereas RNA is a single chain.

Nitrogenous bases:

• Adenine
• Thymine
• Cytosine
• Guanine

DNA contains our genetic information, which is shown by protein synthesis. The order of the amino acids that form proteins depends on the sequence of nitrogenous bases of DNA. The relationship established between 3 nucleobases dictates a particular amino acid. This is the code used by living things to display their characters. This code is called the genetic code.