Water and Minerals: Structure, Properties, and Biological Functions
Structure and Properties of Water
Water exhibits strong cohesion between its molecules, resulting in high surface tension. It also has a high heat of vaporization, meaning a significant amount of energy is required to change it from a liquid to a gaseous state. Notably, water is denser in its liquid state than in its solid state. It serves as an excellent solvent for various substances and possesses a high specific heat, allowing it to act as a thermal buffer.
- Heat of Vaporization: The amount of energy necessary for one gram of liquid to become a gas.
- Specific Heat: The quantity of heat required to raise the temperature of one gram of any substance by one degree Celsius at a specific temperature.
Water’s capillarity allows it to ascend through very thin tubes.
Biological Functions of Water
- It is the universal solvent in organic and inorganic living matter.
- Water is the medium where most metabolic reactions occur, thanks to its ability to dissociate into ions.
- Many properties of proteins, lipids, and nucleic acids depend on their interactions with water.
- Water volume maintains cell turgidity in cells lacking a rigid membrane, such as in plants.
- Water behaves as a good absorber of temperature changes because it can gain and lose heat efficiently.
- Sweating expels water, which vaporizes and removes heat from the body.
- Ice floats on water, forming a thermally insulating layer that allows life to persist in seas and rivers.
Minerals
Minerals include water, atmospheric gases, and inorganic salts. They have different biological functions depending on whether they are precipitated or dissolved.
- Precipitated: They have a structural function, such as forming the internal skeleton of vertebrates (phosphates and carbonates), tooth enamel (calcium fluoride), cell walls of plant cells, and the otoliths of the inner ear in some animals (CaCO3).
- Dissolved: They maintain the internal environmental salinity (osmotic processes), balance the pH, and act as a buffer solution.
Examples of Minerals
- Cations:
- Na+, K+: Involved in the transmission of nerve impulses.
- Ca2+: Involved in muscle contraction, blood coagulation, and cardiac activity.
- Mg2+: Cofactor of enzymes in the synthesis of DNA and RNA.
- Anions: Cl-, SO4 2-, CO3 2-, phosphate (PO4-H2).
Glycerol: CH2OH-CHOH-CH2OH
Ketone: C=O in the middle of the molecule.
Aldehyde: C=O and H at the end of the molecule.
Carbohydrates
Carbohydrates are organic molecules composed of carbon, hydrogen, and oxygen. Their general formula is (CH2O)n. They are defined as polyalcohols with an aldehyde or ketone functional group. Carbohydrates are the most abundant biomolecules.
Classification of Carbohydrates
- Monosaccharides (Oses): Classified by the number of carbon atoms (3 to 7).
- Osides:
- Holosides:
- Oligosaccharides
- Polysaccharides: Homopolysaccharides, Heteropolysaccharides
- Heterosides
- Holosides:
Monosaccharides
Monosaccharides are the simplest carbohydrates and cannot be further decomposed.
Properties of Monosaccharides
- They are white and sweet.
- They dissolve in water.
- They do not dissolve in non-polar solvents.
- They have reducing power (they can donate electrons when bonding).
Examples of simple trioses include glucose and sucrose.
Buffer Solutions
For normal cellular processes to occur, the concentration of hydrogen ions (pH) must remain relatively constant (around 7). A buffer solution is an aqueous solution with a chemical composition that prevents significant changes in pH. It typically contains a weak acid and its corresponding anion, which acts as a proton donor or acceptor to compensate for an excess or deficit of H+ ions in the environment. An example of a buffer is bicarbonate (pH = 6.3).
Le Chatelier’s principle states that when factors influencing a system in equilibrium are altered, the system shifts to counteract the change. For example: H2CO3 ⇌ H+ + HCO3-.