Biological Molecules: Carbohydrates, Fats, Proteins, DNA, and Water

Comprehensive vocabulary flashcards covering the structure, properties, and qualitative tests for carbohydrates, lipids, proteins, DNA, and water.

Respiration

The metabolic process by which broken-down food substances release energy required for cellular activities and physiological work, such as muscle contraction for movement.

Plasma

The liquid component of blood that consists mainly of water, serving as a vital solvent that transports dissolved nutrients, gases, and waste substances throughout the body.

Dehydration

A medical condition occurring when fluid loss exceeds fluid intake, causing symptoms ranging from dry mouth, headache, and dark yellow urine to rapid heartbeat, confusion, sunken eyes, and low blood pressure.

Carbohydrate

An organic biological molecule composed of carbon, hydrogen, and oxygen, where the ratio of hydrogen atoms to oxygen atoms is always $2:1$.

Monosaccharide

A single sugar molecule, such as glucose or fructose ($C_6H_{12}O_6$), that is sweet, soluble in water, and small enough to pass through cell membranes without further digestion.

Disaccharide

A double sugar molecule with the chemical formula $C_{12}H_{22}O_{11}$ formed by chemically bonding two monosaccharide units together, such as maltose and sucrose.

Maltose

A disaccharide composed of two glucose molecules joined together, which can be hydrolysed back into individual glucose units by water and the biological catalyst maltase.

Sucrose

A non-reducing disaccharide found in plants, consisting of one glucose molecule bonded to one fructose molecule.

Polysaccharide

A complex carbohydrate polymer composed of many monosaccharide units joined together in long chains, including starch, glycogen, and cellulose.

Starch

A plant storage polysaccharide consisting of several thousand linked glucose units, existing in both branched and unbranched forms.

Glycogen

A highly branched storage polysaccharide made of linked glucose molecules, stored primarily in the liver and muscle cells of animals.

Cellulose

A structural polysaccharide made of glucose chains that forms plant cell walls to prevent bursting and acts as indigestible dietary fibre in humans to prevent constipation.

Benedict's Test

A chemical test for reducing sugars where blue Benedict's solution is added to a sample and heated in a water bath, yielding a green, yellow, orange, or brick-red precipitate.

Iodine Test

A diagnostic food test for starch where dark orange iodine solution is applied directly to a sample, turning blue-black if starch is present.

Triglyceride

A lipid molecule consisting of one glycerol molecule joined to three fatty acid chains through condensation reactions that release water.

Saturated Fat

A fat possessing fatty acid chains with no carbon-carbon double bonds, allowing chains to pack closely together to remain solid at room temperature while increasing bad cholesterol.

Unsaturated Fat

A healthier dietary lipid containing one or more double bonds in its fatty acid chains, preventing close packing and keeping it liquid at room temperature.

Trans Fat

An unhealthy fat synthesized by artificially adding hydrogen to liquid vegetable oils via hydrogenation, which raises bad cholesterol and lowers good cholesterol.

Ethanol Emulsion Test

A food test for lipids involving shaking a sample with $2\,\text{cm}^3$ of ethanol followed by $2\,\text{cm}^3$ of water, producing a cloudy-white emulsion if fats are present.

Protein

A complex organic macromolecule made of carbon, hydrogen, oxygen, and nitrogen (and sometimes sulfur), constructed from amino acids folded into specific three-dimensional structures.

Amino Acid

The monomer of proteins, featuring a central carbon atom bonded to an amino group, a carboxyl group, a hydrogen atom, and a variable $R$ group, with $20$ different types occurring in nature.

Polypeptide

A linear, thread-like chain of amino acid monomers linked together before folding into a functional three-dimensional protein.

Kwashiorkor

A severe protein deficiency condition seen in children, characterized by fluid retention resulting in a swollen abdomen along with cracked, scaly skin.

Biuret Test

A food test for proteins using a blue solution of sodium hydroxide and copper sulfate (biuret reagent), which turns violet or purple in the presence of protein.

DNA (Deoxyribonucleic Acid)

A helical polymer made of coiled nucleotide strands carrying genetic instructions that dictate cellular composition and metabolic activities.

Nucleotide

The fundamental monomer of a DNA strand, consisting of a deoxyribose pentose sugar, a phosphate group, and an organic nitrogenous base.

Complementary Base Pairing

The selective hydrogen bonding in double-stranded DNA where adenine ($A$) exclusively pairs with thymine ($T$), and guanine ($G$) exclusively pairs with cytosine ($C$).

Sugar-Phosphate Backbone

The structural chain of a DNA strand composed of alternating deoxyribose sugars and phosphate groups linked by strong covalent bonds.