1.2 Carbohydrates Monosaccharides

LO: How are large molecules like carbohydrates constructed? What is the structure of a monosaccharide? How would you carry out the Benedict’s test for reducing sugars.

What are Carbohydrates made of? Like many organic molecules carbohydrates are made up of chains of individual molecules. Monomers – General formula CH20 Polymers – (CH20) n

The basic monomer unit is a sugar or saccharide. A single monomer is called a m______________. A pair of monosaccarides is called a d______________. A long chain of monosaccharides is called a ____________.

The basic monomer unit is a sugar or saccharide. A single monomer is called a monosaccharide. A pair of monosaccarides is called a disaccharide. A long chain of monosaccharides is called a polysaccharide.

Structure of glucose C6H12O6 Carbons form a ring, and they can make up to 4 bonds with other atoms Glucose comes in 2 forms (isomers)– alpha or beta small difference, but major consequences when it forms polysaccharides Each line represents a covalent bond Learn these!

Key properties of monosaccharides Other examples Reducing sugars Sweet tasting and soluble. General formula (CH20)n where n = 3 to 7. Best known is glucose a hexose (6 carbon sugar) with the formula C6H12O6. Carbon atoms form a ring. Draw diagram of Glucose Sweet tasting and soluble. General formula (CH20)n where n = 3 to 7. Best known is glucose a hexose (6 carbon sugar) with the formula C6H12O6. Carbon atoms form a ring. Draw diagram of Glucose

Reducing sugars All monosaccharides and some disaccharides (e.g maltose) are reducing sugars. Reducing sugars donate electrons to (or reduce) another chemical (e.g Benedict’s reagent).

The Benedict’s test. A test for reducing sugars. Benedict’s reagent is an alkaline solution of copper(II) sulphate (blue). When a reducing sugar is heated with Benedict’s reagent it forms an insoluble red precipitate of copper(I) oxide.

semi-quantitative The exact colour change will depend on the concentration of the reducing sugar. This difference means it can be used in a semi-quantitatively to estimate the amount of reducing sugar in the sample.

But what % concentration of glucose causes the different colours?

Practical Strong glucose solution enough to turn Benedict’s red Measuring cylinders Distilled water Boiling tubes Water baths Students to make up different known concentrations of glucose and attempt to find out what % causes the different colours

Splat Glucose ionic isotope monosaccharide soluble hydrolysis polysaccharide 24 Reducing sugar Lactose 12 covalent 3 Benedict’s reagent monosaccharide 6 disaccharide condensation

7. (i) glycosidic; NOT glucosidic 1 (ii) 1 carbon positions 1 and 2 on glucose and fructose; 2 formation of , water / H2O , from 2 OH groups (plus separation); 3 oxygen bridge / – O – , shown; 2 max [3]

8. similar ~ allow valid similarities such as same number , carbon / oxygen / hydrogen (atoms) / OH (groups); A hexose same formula; R similar / molecule ring / ring with O (atom) in it; correct ref CH2OH; contain C, H and O; 1 max different ~ assume candidate is writing about fructose unless told otherwise allow valid differences such as (fructose has) 5-membered ring / glucose has 6-membered ring; R pentose (4 C in ring v. 5C in ring / furanose v. pyranose in glucose) (in fructose) 2 CH2OH side chains / 1 CH2OH side chain in glucose; different angles between C atoms; ref alignment of H and OH groups (on carbon 3 / carbon 4); (in fructose) carbon 1 not in ring / carbon 1 in ring in glucose; 1 max [2]

Describe how the concentration of glucose in a solution may be estimated by using colour comparisons. © Pearson Education Ltd 2008 This document may have been altered from the original

Week 16 You could compare the reducing sugar content of orange juice and apple juice © Pearson Education Ltd 2008 This document may have been altered from the original

A range of glucose solutions was made up - graph Week 16 A range of glucose solutions was made up - graph Glucose conc./ % Glucose mass/mg Absorbance 0.1 0.5 2.5 1.0 5.0 1.5 7.5 2.0 10.0 © Pearson Education Ltd 2008 This document may have been altered from the original