2.1 Carbohydrates

Sandringham college pete hamilton

Covalent Bonding involves the sharing of electrons

This may involve equal sharing or unequal sharing

Carbon atoms can form 4 covalent bonds

All chemical bonds possess energy which can be released when the bonds are broken

Carbohydrates• Compounds of :

– Carbon C able to form 4 covalent bonds

– Hydrogen H able to form 1 covalent bond

– Covalent bonds O able to form 2 covalent bonds

Fructose

Carbohydrates

• While often drawn as a linear skeleton, in solution carbohydrates often form hexagonal shaped ring molecules

This can be further abbreviated for your note taking as a simple hexagon

Macromolecules

• Macro = large• Molecules = 2 or more atoms covalently bonded• Usually referred to as polymers - chain like• Made from several repeating subunits

– The repeated subunits are called monomers– Like links in a chain

Monomers & Polymers

A monomer is a molecule that is able to bond in long chains.Polymer means many monomers. Polymers are also known as macromolecules or large-sized molecules.

Here is a monomer:

Here is a polymer:

This linking up of monomers is called polymerization.

Saccharides = sugars

Monosaccharides = single/simple sugars

Disaccharides = double sugar

Polysaccharide = many/complex sugars

Making or Breaking Polymers

• The chemical mechanisms that cells use to make and break polymers are similar for all classes of macromolecules.

dehydration synthesis

Making Polymers• Monomers are connected by

covalent bonds via a condensation reaction or dehydration reaction.– One monomer provides

a hydroxyl group and the other provides a hydrogen and together these form water.

– This process requires energy and is aided by enzymes.

Breaking Down Polymers

• The covalent bonds connecting monomers in a polymer are disassembled by hydrolysis.– In hydrolysis as the covalent

bond is broken a hydrogen atom and hydroxyl group from a split water molecule attaches where the covalent bond used to be.

– Hydrolysis reactions dominate the digestive process, guided by specific enzymes.

Monosaccharides

Monosaccharides: generally have molecular formulas containing C : H : O in a 1:2:1 ratio.

fructose C6H12O6.

glucose C6H12O6.

nb: most names for sugars end in -ose.

Monosaccharides

Monosaccharides are also classified by the number of carbons in the backbone.

• Monosaccharides, particularly glucose, are a major fuel for cellular work.• They are also building blocks for of other monomers, including those of

amino acids (protein) and fatty acids (lipids).

• While often drawn as a linear skeleton, in aqueous solutions monosaccharides form rings.

Monosaccharides

Disaccharides

Sucrose C12H22O11.

Examples of Disaccharides

Maltose

Formed from 2 glucose molecules, formed in germinating seeds from the breakdown of starch, providing energy

Sucrose

Formed from 1 glucose and 1 fructose molecule and is the form in which carbohydrates are transported in the phloem in plants

Lactose

Formed from 1 glucose and 1 galactose molecule, it is an energy source found in the milk of nearly all mammals

Polysaccharides of sugars have storage and structural roles

• Polysaccharides are polymers of hundreds to thousands of monosaccharides joined together

• One function of polysaccharides is energy storage – it is hydrolyzed as needed.

• Other polysaccharides serve as building materials for the cell or whole organism.

Starch:• is a storage polysaccharide composed entirely of glucose monomers -

Long chain of glucose molecules 200-500 units

• Used as an energy store in plants.

• Not soluble.

• Forms solid grains inside plant cells (often inside chloroplasts).

• The chains coil up into a basic spiral shape making the molecules compact.

• Hydrogen bonds hold the polysaccharide chain in the compact spiral shape.

Glycogen

• The storage polysaccharide in animals (equivalent to starch in plants).

• Found in liver and muscle cells where a store of energy is needed.

• Many fungi also store glycogen.

• Similar in structure to starch - but more branched.

• Forms tiny granules inside cells which are usually associated with smooth endoplasmic reticulum.

• Each glycogen molecule contains a upto 30,000 glucose units

Glycogen

Cellulose

• Most abundant organic molecule.

• 300-10,000 + glucose units

• It is very slow to decompose.

• 20-40% of the plant cell wall.

• Hydrogen bonding between monosaccharide molecules in the chain gives strength.

• Hydrogen bonding between cellulose molecules cause bundles called microfibrils to develop. These are held together in fibres.

• A cell wall will have several layers of fibres running in different directions - gives great strength almost equal to steel.

• Provides support in plants and stops plant cells bursting.

• Freely permeable to water and solutes.