Biological molecules and carbohydrates

C12H22O11 Formation of disaccharides from two monosaccharides is a condensation reaction Glycosidic bonds are usually formed between C1 and C4, hence the bond name would be ,4 glycosidic bond This reaction is reversible through the process of hydrolysis Properties of disaccharides Physical: Storage Polysaccharides in Plants Main storage polysaccharide in plant absent in animals Consist of two components - amylose Biological molecules and carbohydrates amylopectin, both of which are made up of many alpha-glucose units A suspension of amylose in water gives a blue-black colour with iodine-potassium iodide solution, whereas that of amylopectin gives a red-violet colour this forms the basis for the test of starch Amylose: It is an unbranched polymer of several hundreds to few thousands of alpha-glucose linked together by alpha 14 glycosidic bonds, which cause the amylose chain to coil helically into more compact shape For every complete turn of the helix, there are 6 alpha-glucoses units Helix is held together by hydrogen bonds formed between -OH groups Since most of the -OH groups of the alpha-glucose units project into the interior of the helix, cross-linking of amylose chains is not possible Amylose is not polar, unless the temp is high enough to overcome the hydrogen bonds holding the helix together Amylopectin: It is a branched polymer of alpha-glucose units whose number is more than twice of that in amylose The alpha-glucose units in the main chain are linked by alpha 14 glycosidic bonds, while the side chains are attached to the main chain by alpha 16 glycosidic bonds Branching decreases the ability of the chains to bind together with one another and increases the binding of water molecules to the chains, amylopectin is more soluble than thee unbranched amylose in water Both components of starch form a complex 3D structure where the amylose helices are entangled in the branches of the amylopectin molecules Structure of Amylopectin In plants, it is packed into spherical plastids called starch grains, which occur particularly in chloroplasts of plant cells or in specialized structures such as seeds or potato tubers 2 ways to hydrolyse starch back to glucose:

Biological molecules and carbohydrates

They are broken down in the small intestine during digestion to give the smaller monosaccharides that pass into the blood and through cell membranes into cells. However, a cell may not need all the energy immediately and it may need to store it.

Monosaccharides are converted into disaccharides in the cell by condensation reactions.

Biological molecules and carbohydrates

Further condensation reactions result in the formation of polysaccharides. These are giant molecules which, importantly, are too big to escape from the cell.

Carbohydrates - Biological Molecules - MCAT Review

These are broken down by hydrolysis into monosaccharides when energy is needed by the cell. Polysaccharides Monosaccharides can undergo a series of condensation reactions, adding one unit after another to the chain until very large molecules polysaccharides are formed.

This is called condensation polymerisation, and the building blocks are called monomers. The properties of a polysaccharide molecule depend on: It exists in two forms: The molecules coil into a helical structure. It forms a colloidal suspension in hot water.

It is completely insoluble in water. Section of the amylose molecule A section of the amylose molecule - click on image to open Section of the amylopectin molecule A section of the amylopectin molecule - click on image to open Glycogen Glycogen is amylopectin with very short distances between the branching side-chains.

Starch from plants is hydrolysed in the body to produce glucose. Glucose passes into the cell and is used in metabolism. Inside the cell, glucose can be polymerised to make glycogen which acts as a carbohydrate energy store.

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Cellulose is a third polymer made from glucose. Section of a cellulose molecule Cellulose - click on image to open Cellulose serves a very different purpose in nature to starch and glycogen.

It makes up the cell walls in plant cells. These are much tougher than cell membranes. This toughness is due to the arrangement of glucose units in the polymer chain and the hydrogen-bonding between neighbouring chains.Content.

Opportunities for skills development. Monosaccharides are the monomers from which larger carbohydrates are made.

Carbohydrates and proteins, two of the larger types of biological molecules, also called macromolecules, are actually chains of molecules called polymers.

The smaller molecules that build up these chains are called monomers. The simplest, smallest carbohydrates are glyceraldehyde and dihydroxyacetone. The 3 common monosaccharides are glucose, fructose, and galactose. Glucose is our blood sugar and the product of photosynthesis.

All living things contain organic macromolecules: Lipids, proteins, carbohydrates and nucleic acids. Characteristic for these organic molecules is that they are made up of only a small number of elements: carbon, hydrogen, oxygen, and to smaller amounts nitrogen, phosphorus and sulfur.

Biological molecules and carbohydrates

Carbohydrates are one of four major classes of biological molecules, along with nucleic acids, lipids, and are the most abundant biological molecules, and are an important nutritional component of many foods. The key biological molecules are carbohydrates, lipids, proteins and nucleic acids.

These molecules either become part of our bodies or are used to provide us with energy.

Carbohydrates - Biology - Revision World