Monomers and polymers: Carbohydrates

Define monomers

the smaller soluble molecules from which larger molecules are made

Define polymers

molecules made from a large number of similar monomers joined together

what is an example of a monomer

monosaccharides, amino acids, nucleotides

what do monosaccharides join together to form

disaccharides and polysaccharides (carbohydrates)

what do amino acids join together to form

proteins/polypeptides

what do nucleotides join together to form

polynucleotides/nucleic acids (DNA and RNA)

why are NB lipids not polymers

they are not made up of similar repeating subunits - they have both fatty acids and a glycerol molecule

what is a condensation reaction

it joins two molecules together with the formation of a chemical bond and involves the release of a water molecule

what is a hydrolysis reaction

it breaks a chemical bond between two molecules and involves the use of a water molecule

what is an exam tip to do with a condensation reaction

if you are asked to show a condensation reaction, don’t forget to put the water molecule in as a product

what are some common monosaccharides

glucose, galactose and fructose

what is the formula shared by glucose, galactose and fructose

C6H12O6

what kind of bond is formed between two monosaccharides in a condensation reaction

glycosidic bond

what are the two isomers of glucose

a-glucose and B-glucose

how are disaccharides formed

by the condensation of two monosaccharides

what is the formula of all disaccharides

C12H22O11

what disaccharide is made from glucose+glucose

maltose

what disaccharide is made from galactose+glucose

lactose

what disaccharide is made from glucose+fructose

sucrose

what is the equation for two monosaccharides forming a disaccharide in a condensation reaction

C6H12O6 + C6H12O6 → C12H22O11 + H2O

what type of bond does a condensation reaction result in with glucose + glucose = maltose

a 1,4 glycosidic bond

in digestion, what are disaccharides hydrolysed into

monosaccharides

what happens after disaccharides are hydrolysed into monosaccharides

they can be absobed and assimilated by the body for processes such as respiration

what is the equation for a hydrolysis reaction

C12H22O11 + H2O → C6H12O6 + C6H12O6

what is broken during a hydrolysis reaction

the glycosidic bond

what is formed by the condensation of a-glucose

glycogen and starch

what is formed by the condensation of B-glucose

cellulose

how are polysaccharides formed

the condensation of many monosaccharide units

what are the two categories polysaccharides are split into

storage (glycogen - humans, starch - plants) and structural (cellulose - plants)

what is the storage carbohydrate of plants

starch - a carbohydrate polymer of alpha glucose

what is the purpose of starch being a polymer of glucose

it is easily hydrolysed into glucose to be used in respiration to produce ATP which can be hydrolysed to release energy

what is the purpose of starch being insoluble

it does not affect osmosis and is not easily lost from the cell

what is the purpose of starch being coiled into a helix

it’s compact so a lot can fit into a small space

what is the purpose of starch being branched

provides more ends for faster hydrolysis by enzymes to form a-glucose for use in respiration

how is glycogen similar to starch

it is also a polymer of alpha glucose

what is the function of glycogen

it is the storage carbohydrate in animals

how does glycogen differ from starch

• shorter chains

• more highly branced

• larger surface area

how are glycogen’s differences from starch useful

it allows glycogen to be more readily hydrolysed into glucose

what is the purpose of glycogen being a polymer of glucose

it is easily hydrolysed into glucose to be used in respiration to produce ATP which can be hydrolysed to release energy

what is the purpose of glycogen being insoluble

it does not affect osmosis and is not easily lost from the cell

what is the purpose of glycogen being coiled into a helix

it is compact so a lot can fit into a small space

what is the purpose of hydrogen being highly branched

it provides more ends for faster hydrolysis by enzymes to form a-glucose for use in respiration

cellulose is a polymer of what kind of glucose

beta

how does beta glucose differ from alpha glucose

the position of the H and OH groups on carbon 1 are inverted

what shape are the chains made by beta glucose molecules in condensation reactions

long, straight and unbranched

what does every other glucose molecule do to allow OH groups on carbon 1 and carbon 4 to be adjacent to each other and form a glycosidic bond

flip 180 degrees

chains of cellulose are joined together in what format

layers, held together by hydrogen bonds formed between OH groups

hundreds of chains of cellulose are held together by hydrogen bonds to form what?

microfibrils

microfibrils form hydrogen bonds between other microfibrils and together to form what?

a cellulose fibre

cellulose fibres are woven to form what?

a cellylose cell wall

what is the purpose of only 1,4 glycosidic bonds being present in cellulose

allows formation of long, straight, unbranched chains of B-glucose

what is the purpose of long, straight, unbranched chains of B-glucose in cellulose

it allows formation of many hydrogen bonds so microfibrils are created

what is the purpose of many microfibrils and cellulose fibres and many hyrdrogen bonds in cellulose

provides strength to the cell wall

what are the three different tests for carbohydrates

• benedict’s test for reducing sugars (glucose, galactose, lactose, maltose, fructose)

• benedict’s test for non-reducing sugars (sucrose)

• iodine in potassium iodine solution test for starch

what is the process for Benedict’s test for reducing sugar

1. add benedict’s solution to sample and heat to 95C

2. a colour change from blue to green/yellow/orange/red precipitate indicates the presence of reducing sugar

3. if there is no change in colour there to be a non-reducing sugar present

describe the process for Benedict’s test for non-reducing sugars (sucrose)

1. add benedict’s solution to sample and heat to 95C and if there is no change in the Benedict’s test for reducing sugar, boil a fresh sample with dilute hydrochloric acid for a few minutes to hydrolyse the glycosidic bonds

2. neutralise by adding solid sodium hydrogen carbonate

3. then add Benedict’s reagent, heat to 95C

4. as the sucrose has now been hydrolysed to glucose and fructose (reducing sugars) there will be a red precipitate formed and a colour change from blue to red

describe the test for starch - iodine solution test

1. add iodine in potassium iodide solution to your sample

2. a colour change from orange to blue-black indicates the presence of starch