3.1.1 monomers and polymers + 3.1.2 carbohydrates Flashcards Preview

A Level Biology - Biological Molecules > 3.1.1 monomers and polymers + 3.1.2 carbohydrates > Flashcards

Flashcards in 3.1.1 monomers and polymers + 3.1.2 carbohydrates Deck (27)
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1

The variety of life , both past an present , is extensive , but the biochemical basis of life is similar for all living things

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2

Monomers are smaller units from which larger molecules are made.

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Polymers are molecules made from a large number of monomers joined together

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Monosaccharides , amino acids and nucleotides are examples of monomers

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A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a water molecule

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A hydrolysis reaction breaks a chemical bond between two molecules and involved the use of a water molecule

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Monosaccharides are the monomers from which larger carbohydrates are made .

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Some common monosaccharides include:

Glucose
Galactose
Fructose

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A condensation reaction between two monosaccharides forms a glycosidic bond .

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Disaccharides are formed by the condensation reaction of two monosaccharides

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Maltose is a disaccharide formed by the condensation of two glucose molecules

Glucose + Glucose = Maltose

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12

Sucrose is a disaccharide formed by a condensation reaction between glucose and fructose.

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Lactose is a disaccharide formed by a condensation reaction between a glucose molecule and a galactose molecule.

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Glucose has two isomers . Alpha glucose which has the H group on top and beta glucose which has the OH group on top

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Polysaccharides are formed by the condensation of many glucose units

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Glycogen is a polysaccharide composed of alpha glucose monomers

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Starch is a polysaccharide formed from alpha glucose monomers

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The polysaccharide Cellulose is formed by the condensation reaction of beta glucose molecules

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Glucose is a primary source of energy , it is important that glucose levels in the blood are controlled "blood sugar" as this prevents diabetes

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20

Benedict's test

To rest if a sugar is a reducing sugar which means it can donate electrons to a chemical, then benedicts test is conducted , the procedure is putting a food to be tested in soloution and adding benedicts Reagent the contents of the test tube is then boiled in a water bath to observe potential colour change . Benedicts test for reducing sugars is semi quantitative as you can estimate the amount of reducing sugar in a sample by the degree of colour change . A strong positive result would show a red colour change while a weak positive result would show a green colour change.

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All monosaccharides and most disaccharides like lactose and maltose are reducing sugars.

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Sucrose while being a disaccharide is not a reducing sugar

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Some sugars are non reducing to conduct a test for non reducing sugars the following steps are taken

The food being tested is of Ito soloution , hydrochloride acid is added to hydrolyse the bonds and the content of the test tube is boiled in a water bath for 5 minutes , after this sodium hydrogen carbonate is added to neutralise the acid, benedicts reagent is added and a colour change is obseved if the test indeed proves the sample
Is a non reducing sugar , this test is semi quantitative

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24

To confirm a food contained starch a sample of the food would be placed in solution , iodine would then be added to this solution and the contents of the test tube will then be mixed , the presence of starch is indicated be a blue black colouration.

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Starch is composed of monomers is alpha glucose . It is an energy store with a compact and coiled structure which is relatively branched , starch makes glycosidic bonds both (1,4) and (1,6) as the molecule is branched it can be easily hydrolysed. Stretch is a storage molecule in plants , amoylose makes up the straight part of the starch chain and amylopectin makes up the branches part . You test for starch using iodine . Starch is never found in animal cells only plant cells

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26

Glycogen is composed of the monomer alpha glucose , it has a similar structure to starch but is more branched meaning it has more (1,6) bonds, glycogen is easily hydrolysed to realise glucose because of the heavily branched structure , it makes (1,4) , (1,6) glycosidic bonds . Glycogen is stored in animal cells in the muscles and the liver . Glycogen is insoluble so doesn't effect the water potential of cells. Hlucogen can also be found in bacteria cells

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27

Cellulose is composed of beta glucose monomers in straight unbranched chains , it forms microfibrils as the straight chains bind together with hydrogen bonds . Cellulose is found in the cell walls of plant cells it helps the cells remain in tack and prevents them from bursting . Cellulose only makes (1,4) glycosidic bonds , alternate glucose monomers flip 180 degrees to alight the H and OH groups to make he glycosidic bonds

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