AQA A Level Biology Carbohydrates Flashcards

what are the monomers of carbohydrates called?

monosaccharides

what are polymers of carbohydrates called?

polysaccharides

what is a common property of all monosaccharides?

soluble in water

name the 3 core monosaccharides

• alpha glucose

• beta glucose

• galactose

• fructose

• these are all isomers

what is the structure of alpha glucose?

note carbon 1

what is the structure of beta glucose?

what is the structure of galactose?

what is the structure of fructose?

what is two monosaccharides joined together called?

disaccharide

what type of reaction forms a disaccharide?

condensation (water is produced also)

in a disaccharide, what type of bond occurs between the two monosaccharides?

glycosidic

which are the core disaccharides?

• maltose (C12H22O11)

• sucrose

• lactose

which monosaccharides form maltose?

• alpha glucose

• alpha glucose

which monosaccharides form sucrose?

• alpha glucose

• fructose

which monosaccharides form lactose?

• alpha glucose

• galactose

which reaction forms two monosaccharides from a disaccharide?

• hydrolysis

• requires water molecule

which carbon atoms does a glycosidic bond form between in maltose?

1,4

write an equation for the condensation of alpha glucose

alpha glucose + alpha glucose → maltose + water

which atoms are removed from the alpha glucose molecules in a condensation reaction?

• one OH molecule, and one H molecule from an OH

draw an equation for the condensation of alpha glucose

what are reducing sugars?

sugars that readily lose electrons to another substances

what are non reducing sugars?

sugars that do not readily lose electrons to another substance

which substances are reducing sugars?

• all monosaccharides

• most disaccharides, except for sucrose

which substances are non reducing sugars?

sucrose

describe how you would test for the presence of reducing sugars

• add benedicts reagant to food sample to boiling tube (it contains Cu2+ ions that are reduced)

• heat in a water bath at 80C for 5 minutes

• if a green/yellow/orange/brick red precipitate (increasing conc.) forms, the test is positive

• if the solution remains blue the test is negative

• qualitative test

describe how you would test for non reducing sugars

• can only test after have been negatively tested for reducing sugars

• add food sample to HCl in a boiling tube

• heat in a boiling water bath for 5 mins, to hydrolyse the disaccharide to form monosaccharides

• add an excess of sodium hydrogen carbonate (until litmus tests blue) to neutralise the acid, as benedicts requires an alkaline environment

• carry out the benedict’s test

• the same results apply

describe how you would make the benedict’s test quantitative

• use a colorimeter, calibrated it with a standard sample of Benedict’s solution, compare percentage light absorbency (higher %, less reducing sugars)

• filter out and dry the precipitate, then record its mass

describe how lactose intolerance arises and how it presents

• all humans produce lactase in their small intestine when they are babies, to digest lactose in formula/breast milk

• most humans stop producing lactase as the age - the exceptions produce it due to evolution by natural selection (mostly europeans)

• lactase hydrolyses lactose to alpha glucose and galactose, which is absorbed into bloodstream

• no lactase = no digestion, so lactose passes into the colon where bacteria ferment it, producing fatty acids and gases like CO2, CH4 and hydrogen - these cause symptoms like pain/bloating

what are the 3 core polysaccharides?

• glycogen (a glucose)

• starch (a glucose)

• cellulose (B glucose)

what are the core properties of polysaccharides?

• formed by condensation reaction

• can be broken down into constituent monomers by hydrolysis reactions

• insoluble in water

which monosaccharide makes up starch?

alpha glucose

which two polysaccharides is starch a mixture of?

• amylose

• amylopectin

describe amylose

• long unbranched chain of alpha glucose

• angles of glycosidic (all 1-4) give it a coiled structure

• the coil makes it compact so its good for storage

describe amylopectin

• long branched chain of alpha glucose

• it is branched due to having both 1-4 and 1-6 glycosidic bonds

• it has lots of side branches meaning it has more ends/terminal glucose molecules

• this means the enzymes that break it down can get to the glycosidic bonds easily, so glucose can be released quickly

• also coiled

describe the properties and functions of starch

• energy store in plants

• large molecules → insoluble → doesn’t affect water potential of cells → doesn’t make water enter cells by osmosis → cells do not burst → good for storage

• hydrolysis forms alpha glucose which is easy to transport and used for respiration

describe the structure of glycogen

• very similar to amylopectin (coiled with branches) but with a lot more branches

• as it has more 1-6 linkages

• these branches are shorter

describe the properties and functions of glycogen

• energy store in animals

• shorter chains, more branches mean more terminal glucose molecules

• this means that it is more readily hydrolysed than starch so stored glucose can be released faster, which is important for energy release in animals as they have higher respiratory needs

• very compact molecule so is good for storage

describe the structure of cellulose

• made of long, unbranched chains of B glucose (1-4 linkage)

• each molecule is inverted 180 from the previous one, allowing this

• the cellulose chains lie parallel to each other, and are linked together by collectively strong hydrogen bonds

• this forms strong fibres called microfibriles

• many microfibrils come together to form macrofibrils

describe the properties and function of cellulose

• structural molecule found in plants (cell walls)

• fibres make it very strong, preventing cell walls from bursting when too much water enters (help to maintain turgidity)

• difficult to digest as few organisms have cellulase

what is the iodine test for starch?

• add iodine to food

• blue black = positive

• orange = negative