Biological Molecules: Water, Inorganic Ions, and Carbohydrates

Comprehensive vocabulary flashcards covering the chemical properties of water, buffer systems, biological inorganic ions, and carbohydrate chemistry including monosaccharides, disaccharides, and starch polymers.

Polar Molecule

A molecule with an uneven distribution of charge, such as water, in which the oxygen atom possesses a slight negative charge and the hydrogen atoms possess a slight positive charge.

Hydrogen Bond (Water)

A weak, relatively easily broken intermolecular bond formed between a slightly negative oxygen atom on one water molecule and a slightly positive hydrogen atom on an adjacent water molecule.

Hydrophilic

A descriptive term meaning 'water loving', referring to polar or charged molecules (such as glucose and amino acids) and ions that readily dissolve in water.

Hydrophobic

A descriptive term meaning 'water hating', referring to non-polar molecules (such as lipids) that do not dissolve in water.

Buffer

Chemicals or substances (such as hydrogencarbonate ions and the blood protein albumin) that resist changes in pH to maintain a constant pH environment.

Calcium Ion ($Ca^{2+}$)

An inorganic ion that forms calcium pectate in the middle lamella of plant cell walls, and is an essential component of bones and teeth, blood clotting, and muscle contraction in animals.

Iron Ion ($Fe^{2+}$)

An inorganic ion that forms part of the haem group in haemoglobin and is an important constituent of electron carriers in respiration.

Magnesium Ion ($Mg^{2+}$)

An inorganic ion that is essential for giving chlorophyll its light-absorbing properties.

Potassium Ion ($K^+$)

An inorganic ion that is important in maintaining electrical gradients across neurones.

Nitrate Ion ($NO_3^-$)

An inorganic ion that is an essential component of amino acids, nucleic acids, and chlorophyll.

Phosphate Ion ($PO_4^{3-}$)

An inorganic ion present in phospholipids of cell membranes, as well as a major component of adenosine triphosphate ($ATP$) and nucleic acids.

Monosaccharide

The basic carbohydrate monomer (single sugar), classified by the number of carbon atoms present, including trioses ($3$ carbons), pentoses ($5$ carbons), and hexoses ($6$ carbons).

$\beta$-glucose

An isomer of glucose and constituent monomer of cellulose, in which the hydrogen ($-H$) and hydroxyl ($-OH$) groups at carbon position $1$ are reversed compared to $\alpha$-glucose.

Isomers

Substances that share the same molecular formula but have different structural formulae, such as $\alpha$-glucose, $\beta$-glucose, and fructose.

Condensation Reaction

A chemical reaction in which two molecules join together through a covalent bond with the accompanying elimination and loss of one molecule of water ($H_2O$).

Hydrolysis Reaction

A reversible breakdown reaction in which a chemical bond is split by the addition of one molecule of water ($H_2O$), important in the digestion of food.

Glycosidic Bond

The covalent bond formed between two monosaccharides during a condensation reaction, such as an $\alpha\text{-1,4}$ bond formed between carbon $1$ and carbon $4$ of adjacent hexose units.

Maltose

A disaccharide formed when two $\alpha$-glucose molecules are linked together through a condensation reaction; formed during the digestion of starch.

Sucrose

A disaccharide formed when an $\alpha$-glucose molecule condenses with a fructose molecule; the form in which carbohydrate is transported through phloem in plants.

Amylose

An unbranched polysaccharide chain forming approximately $20\%$ of starch, consisting of $\alpha$-glucose monomers linked solely by $\alpha\text{-1,4}$ glycosidic bonds and coiled into spirals held by hydrogen bonds.

Amylopectin

A branched polysaccharide chain forming about $80\%$ of starch, composed of $\alpha$-glucose linked by $\alpha\text{-1,4}$ glycosidic bonds with $\alpha\text{-1,6}$ glycosidic branch points occurring up to once every $10$ monomers.

Starch

A compact, insoluble plant storage polysaccharide composed of a mixture of two $\alpha$-glucose polymers: amylose ($\approx 20\%$) and amylopectin ($\approx 80\%$).