Biology - Biological Molecules

Water, Carbohydrates, Proteins, Lipids, Collagen and Haemoglobin, Nucleic Acids and Nucleotides

Dipole

A molecule that has two poles, with a positive charge at one end and a negative charge at the other end

Solvent

A substance that dissolves a solute, resulting in a solution.

Alpha Glucose

A monosaccharide of glucose with a hydroxyl group on the first carbon atom arranged BELOW the plane of the ring structure. (ABBA)

Beta Glucose

A monosaccharide of glucose with a hydroxyl group on the first carbon atom but ABOVE the plane of the ring structure. (ABBA)

Fructose

An isomer of glucose with a 5 atom ring structure

Sucrose

Alpha glucose + Fructose

Lactose

Alpha glucose + Galactose

Maltose

Alpha glucose + Alpha glucose

Condensation Reaction

A chemical reaction that combines two molecules to form a larger molecule with the loss of a small molecule, such as water. (Used to form disaccharides)

Hydrolysis

A chemical reaction in which water is used to break down a compound into two or more smaller molecules. It is the opposite of a condensation reaction. (Used to break down disaccharides)

1,4-Glycosidic Bond

A covalent bond formed between the carbon-1 of one monosaccharide and the carbon-4 of another monosaccharide during a condensation reaction. This bond links carbohydrate molecules together.

1,6-Glycosidic Bond

A covalent bond formed between the carbon-1 of one monosaccharide and the carbon-6 of another monosaccharide during a condensation reaction. This bond typically occurs in branched polysaccharides like amylopectin or glycogen

Amylose

A straight-chain polysaccharide composed of many alpha glucose units joined by \text{1,4-glycosidic bonds} .

Amylopectin

A branched polysaccharide composed of alpha glucose units, linked by \text{1,4-glycosidic bonds} with branches primarily formed by \text{1,6-glycosidic bonds} . It is a component of starch.

Glycogen

A highly branched polysaccharide of alpha glucose units, serving as the primary energy storage in animals and fungi. It features \text{1,4-glycosidic bonds} and frequent \text{1,6-glycosidic bonds} for branching.

Cellulose

A straight-chain polysaccharide of beta glucose units, linked by \text{1,4-glycosidic bonds} . It is a major structural component of plant cell walls and is indigestible by humans.

Amino acid structure

An amino acid has a central carbon (α-carbon) bonded to an amine group (NH₂), a carboxyl group (COOH), a hydrogen, and an R group that varies between amino acids. This gives the general formula NH₂–CH(R)–COOH.

Peptide bond

A peptide bond is formed in a condensation reaction between the carboxyl group of one amino acid and the amine group of another, releasing water and linking them together.

Primary Structure of Protein

Primary structure is the specific sequence of amino acids in a polypeptide chain held together by peptide bonds

Secondary Structure of Protein

Secondary structure is the folding of the chain into α-helices or β-pleated sheets held by hydrogen bonds.

Tertiary Structure of Protein

Tertiary structure is the overall 3D shape formed by further folding due to interactions like hydrogen bonds, ionic bonds, and disulfide bridges.

Quaternary Structure of Protein

Quaternary structure is the arrangement of multiple polypeptide chains into a functional protein.

Disulfide Bridges

A disulfide bridge is a strong covalent bond formed between two cysteine amino acids, helping stabilise a protein’s tertiary structure.

Fibrous Protein

Fibrous proteins are long, insoluble molecules with many cross-linked polypeptide chains arranged in parallel. They have structural roles in organisms, such as providing strength and support in collagen, keratin, and silk.

Globular Protein

Globular proteins are compact, roughly spherical molecules with hydrophilic R groups on the outside, making them soluble in water. They have functional roles, such as enzymes, hormones, and antibodies.

Structure of Haemoglobin

Haemoglobin is a soluble globular protein made of four polypeptide chains (two α and two β), each with a haem group containing an Fe²⁺ ion that binds oxygen, allowing each molecule to carry up to four oxygen molecules.

Structure of Collagen

Collagen is a strong, insoluble fibrous protein made of three polypeptide chains wound into a triple helix, with glycine at every third position and hydrogen bonds stabilising the structure.

Unsaturated Lipid

An unsaturated lipid is a fat or oil in which the fatty acid chains contain one or more carbon–carbon double bonds (C=C), causing kinks that make the lipid liquid at room temperature.

Saturated Lipid

A saturated lipid is a fat in which the fatty acid chains have no carbon–carbon double bonds, so the chains are straight and solid at room temperature.

Glycerol

Glycerol is a three-carbon alcohol with a hydroxyl group (–OH) attached to each carbon, giving the formula C₃H₈O₃.

Triglyceride

A triglyceride is made of one glycerol molecule bonded to three fatty acid chains via ester bonds, formed in a condensation reaction.

Nucleic Acids

DNA and RNA

Nucleotide

A nucleotide is made of a nitrogenous base, a pentose sugar, and a phosphate group. It has an ester bond between the phosphate group and pentose sugar, and a glycosidic bond between the sugar and base.

Sugar in DNA and RNA

The difference is that ribose (in RNA) has a –OH group on the 2′ carbon, whereas deoxyribose (in DNA) has just a hydrogen (–H) at the 2′ carbon, meaning it lacks one oxygen atom.

Pyrimidines

Pyrimidines are single-ring nitrogenous bases in nucleotides, including cytosine, thymine (DNA), and uracil (RNA).

Purines

Purines are double-ring nitrogenous bases in nucleotides, including adenine and guanine.

ATP

ATP (adenosine triphosphate) is a nucleotide made of adenine, ribose, and three phosphate groups, which stores and releases energy for cellular processes when its phosphate bonds are hydrolysed.

Polynucleotides

Polynucleotides are formed when nucleotides join via phosphodiester bonds in a condensation reaction, linking the phosphate group of one nucleotide to the sugar of the next, creating a sugar-phosphate backbone with a direction from the 5′ phosphate end to the 3′ hydroxyl end.

Building DNA

DNA is built from two antiparallel polynucleotide strands held together by hydrogen bonds between complementary bases (A–T and G–C), forming the double helix, with a sugar-phosphate backbone running 5′ to 3′ on one strand and 3′ to 5′ on the other.