B1.1 Carbohydrates and Lipids

Four major categories of biological molecules

Carbohydrates, lipids, proteins, nucleic acids

Monomers

Smaller units from which larger molecules are made

Polymers

Molecules made from a large number of repeating subunit monomers joined together in a chain

Polymerisation

The process by which monomers join to form polymers

Macromolecules

Large, complex molecules essential for life, built from many smaller repeating units. They have a high molecular mass

Monomer of carbohydrates (polysaccharides)

Monosaccharides

Monomer of lipids

Fatty acids, glycerol, phosphate groups

Monomer of proteins (polypeptides)

Amino acids

Monomer of nucleic acids

Nucleotides

Formation of macromolecules

Macromolecules are formed from condensation reactions, where molecules combine together to form covalent bonds and water is released

Examples of condensation reactions - Polysaccharides

Polysaccharides are formed when two hydroxyl groups on different monosaccharides form a glycosidic bond

Examples of condensation reactions - Polypeptides

Polypeptides are formed when two amino acid monomers interact to form a peptide bond

Examples of condensation reactions - Nucleic acids

Separate nucleotides are joined together to form a phosphodiester bond. This occurs between the 5C phosphate group of one nucleotide and the 3C pentose sugar of another

Digestion of polymers

Macromolecules are broken down into their monomers by a hydrolysis reaction. The covalent bonds are broken when water is added

Monosaccharides

They have a general formula of CnH2nOn. They are colourless crystalline molecules and are soluble in water

Two structures of glucose

When in aqeuous solutions glucose forms a ring structure: either alpha glucose or beta glucose (isomers). In alpha glucose, the hydroxyl group on 1C is below the ring. In beta glucose, it is above the ring

Polysaccharides of alpha glucose

Starch and glycogen

Polysaccharides of beta glucose

Cellulose

Properties of glucose

It has a stable structure due to strong covalent bonds. It is soluble in water due to its polar nature. It is easily transportable due to its solubility. It is a source of chemical energy when its bonds are broken

Starch

The storage polysaccharide of plants, stored as granules in chloroplasts. It is made of alpha glucose monomers and constructed from two different polysaccharides: amylose (10-30%) and amylopectin (70-90%).

Amylose

Unbranched helix-shaped chain with 1,4 glycosidic bonds between alpha glucose molecules. The helix shapes makes it more compact

Amylopectin

Contains 1,4 and 1,6 glycosidic bonds, creating a branched molecule. It can be easily hydrolysed for use during cell respiration

Glycogen

The storage polysaccharide of animals and fungi, contained in liver and muscles. It is made of alpha glucose joined by 1,4 and 1,6 glycosidic bonds. It is more branched than amylopectin which means it has more terminal glucose molecules that can be hydrolysed quickly.

Cellulose

A structural carbohydrate in the cell wall of plants. It is straight and unbranched with 1,4 glycosidic bonds. It is a polymer of beta glucose. In order to form a bond between beta glucose, every alternate molecule must invert itself

Glycoproteins

Made of carbohydrates and polypeptides. They act as receptor molecules for cell recognition/identification, ligands such as hormones and neurotransmitters, endocytosis, and cell adhesion

Glycoproteins and ABO blood types

Glycoproteins can act as antigens which can identify cells as either self or non self. A person’s blood type is determined by the glycoprotein antigens on the surface of red blood cells. Blood type A has type A glycoprotein antigens and antibodies against type B.

Examples of lipids

Fats, oils, waxes, steriods

Lipid

Molecules composed of a glycerol molecule and fatty acid hydrocarbon chains

Lipid solubility

Lipids contain hydrocarbon molecules which are non-polar, therefore they are insoluble in water. However, lipid solubility can be improved by combining them with glycolipids or lipoproteins

Amphipathic

Having both hydrophobic and hydrophilic regions. Example is phospholipid

Storage of lipids

Animals - adipose tissue

Plants - seeds