Water, Minerals, Carbohydrates, and Buffers: Properties and Biological Functions
Properties of Water
- The water temperature in a liquid environment: freezing point (FP) is 0°C, boiling point (BP) is 100°C.
- Water has strong cohesion between its molecules (capillarity).
- High surface tension, causing surface tension.
- High heat of vaporization: much energy is needed to change liquid water to a gaseous state due to the large number of hydrogen bonds.
- It’s a good solvent for ionic and polar substances (due to its polarity).
- Has a high specific heat, so it can buffer heat.
Heat of Vaporization
The amount of energy required for a liquid to transform into a gas. This heat is high because of hydrogen bonds.
Specific Heat
The amount of heat that must be supplied to a gram of a substance to raise its temperature by one degree. The specific heat of water is high due to hydrogen bonds between water molecules.
Biological Functions of Water
- It is the most universal solvent for organic and inorganic molecules in living organisms. Water can dissolve ionic molecules like Na+ and Cl-.
- Water is the medium where most metabolic reactions occur, thanks to its ability to dissociate into H+ and OH- ions (H2O -> H+ + OH-).
- Many properties of proteins, lipids, and nucleic acids depend on their interactions with water.
- Acts as a vehicle for the transport of substances (nutrients and waste).
- Water volume in cells provides rigidity and turgidity in plants.
- Water behaves as a good “shock absorber,” regulating body temperature and resisting temperature changes.
- Ice floats in water and forms a thermal insulating layer, allowing life below.
Minerals
Biological mineral salts have different functions, depending on whether they are in a solid state (structural role, like in the skeleton) or dissolved.
- Form the internal skeleton of vertebrates.
- Form tooth enamel.
- Form the cell wall of plant cells.
- Form the otoliths in the inner ear of some animals.
Dissolved mineral salts maintain internal environmental salinity.
Carbohydrates
Organic molecules formed by C, H, and O, also known as carbohydrates. Their empirical formula is (CH2O)n. Defined as a molecule resulting from substituting a polyalcohol with an aldehyde or ketone group.
- Organic carbohydrates are the most abundant molecules in nature.
- Categorized as:
- Monosaccharides (or oses): aldoses or ketoses, based on the functional group, and trioses, tetroses, pentoses, hexoses, heptoses based on the number of carbon atoms.
- Osides: disaccharides & polysaccharides.
- Heterosides.
Monosaccharides (Oses)
Simple glucides that cannot be decomposed by hydrolysis. Monosaccharides are monomers from which other carbohydrates are constructed.
Properties
- Solid, white, and sweet.
- Dissolve in water but are insoluble in non-polar solvents.
- Have reducing power when they bind with other molecules or lose electrons.
Nomenclature
Use the root of the number of carbons with the suffix -ose (glucose, fructose…).
- Aldoses: Monosaccharides with an aldehyde functional group.
- Ketoses: Monosaccharides with a ketone functional group. The simplest are trioses.
Solutions and Buffers
Cellular processes require a roughly constant and neutral hydrogen ion concentration (pH ~7). Reactions inside living beings can release acidic and basic products, which can vary the pH.
A buffer solution is an aqueous solution with a suitable chemical composition to prevent significant changes in pH. A buffer always contains a weak acid and its conjugate base, which act as proton donors or acceptors, compensating for excess or deficiency of protons in the medium.
H2CO3 <—> HCO3- + H+. Carbonic acid/bicarbonate buffer has a pH of 6.3 and acts in the extracellular environment. If there is an increase in hydrogen ion concentration, the equilibrium shifts towards forming H2CO3, removing excess protons, according to Le Chatelier’s principle.
Le Chatelier’s principle states that when factors influencing equilibrium are modified, the equilibrium shifts to counteract the change.