Bioelements and Biomolecules: Composition and Properties of Living Matter

Posted on Nov 25, 2024 in Biology

Bioelements

Bioelements are the chemical elements that constitute living matter.

  • Primary (95%): C, H, O, N
  • Secondary (4.5%): P, S, Ca, Na, K, Mg, Cl
  • Trace (0.5%): Mn, Cu, Zn, Fe

Biomolecules

  • Inorganic: Water and mineral salts
  • Organic: Carbohydrates, lipids, proteins, nucleic acids, biocatalysts (enzymes, vitamins, and hormones)

Water

Characteristics

Water is formed by two hydrogen atoms and one oxygen atom, linked by single covalent bonds. It is electrically neutral. Water molecules can interact with each other, building hydrogen bonds. The stability of hydrogen bonds decreases with increasing temperature. In the case of water, hydrogen bonds are present up to 100°C.

Properties

  • High molecular cohesion: Liquid water is incompressible and can maintain a constant volume even when pressure is applied.
  • High surface tension: Surface molecules experience attractive forces to form a surface film that acts as a membrane.
  • High latent heat: Water molecules absorb a large amount of heat to change state.
  • High specific heat: Water can absorb much heat without changing temperature.
  • High heat of vaporization: Water absorbs much heat to break hydrogen bonds.
  • High dielectric constant: Water molecules oppose the electrostatic attraction between positive and negative ions.

Biological Significance

  • Principal biological solvent
  • Metabolic function
  • Structural function
  • Mechanical/shock-absorbing function
  • Thermoregulatory function
  • Transport function
  • Allows aquatic life in cold weather

Mineral Salts

Functions

  • Maintaining the salinity of the body
  • Regulating enzyme activity: The presence of certain ions activates or inhibits biochemical reactions.
  • Regulating osmotic pressure and cell volume: Media with high salt concentration are hypertonic, and those with low concentration are hypotonic. Water enters hypertonic solutions and leaves hypotonic solutions.
  • Stabilizing colloidal dispersions: Salts retain their degree of hydration, and their dissociation into ions contributes to maintaining colloidal particles in suspension.
  • Generating electrical potential
  • Regulating pH: Buffered solutions, such as bicarbonate and phosphate buffers, maintain the pH of biological fluids.

Osmosis

Osmosis is the diffusion of a solvent through a semipermeable membrane from a more dilute solution to a more concentrated one. Water molecules diffuse from the hypotonic medium to the hypertonic medium, increasing the pressure on the hypotonic side of the membrane. This pressure is called osmotic pressure.

Carbohydrates

Carbohydrates are chemically aldehydes or ketones with multiple hydroxyl groups. More complex carbohydrates also contain other organic functional groups. The simplest carbohydrates are monosaccharides.

Monosaccharides

Monosaccharides are white, crystalline solids, soluble in water, and have a sweet taste, hence they are also known as sugars. Asymmetric carbons are carbon atoms bonded to four different radicals. Epimers are two sugars that differ only in the configuration around one carbon atom. The anomeric carbon is the carbon in a cyclic sugar that is bonded to a hydroxyl group.

  • Trioses: Glyceraldehyde and dihydroxyacetone exist as phosphate esters within cells, participating in glucose metabolism.
  • Pentoses: Ribose is a structural component of nucleotides like ATP and nucleic acids like RNA. Ribulose plays a role in CO2 fixation.
  • Hexoses: Glucose, also known as grape sugar, is the primary nutrient for living organisms. It is degraded for energy through cellular respiration and is a constituent of starch, cellulose, and glycogen. Galactose is a component of lactose. Fructose is found in fruits, either free or combined with glucose.

O-glycosidic Bonds

  • Maltose: Malt sugar is a product of starch or glycogen hydrolysis. It consists of two glucose molecules linked by an easily hydrolyzable bond. It is a reducing sugar.
  • Lactose: Milk sugar is formed by the union of galactose and glucose. It is a reducing sugar.
  • Sucrose: Table sugar is extracted from sugar cane and beet. It is not a reducing sugar.
  • Cellobiose: A product of cellulose hydrolysis. It is a reducing sugar.

Polysaccharides

Polysaccharides are insoluble granules that accumulate in the cytoplasm. They do not increase osmotic pressure as free glucose molecules would.

  • Cellulose: A linear polymer of glucose molecules. Hydrogen bonds between and within chains give cellulose its strength. It can be hydrolyzed to glucose by cellulases.
  • Starch: Composed of amylose (helical glucose chains) and amylopectin (branched glucose chains). Found in roots, tubers, and seeds. Hydrolyzed by amylases to glucose and maltose.
  • Glycogen: The reserve polysaccharide in animal cells, similar to amylopectin. Stored in the liver and skeletal muscle, where it is easily hydrolyzed to glucose.