Carbohydrates Flashcards
(22 cards)
What are monomers?
- smaller units which can create larger molecules
What are polymers?
- molecules made from lots of monomers bonded together in a chain
What are some e.g.s of monomers + the polymers they form?
- glucose: starch, cellulose, glycogen
- AA: protein
- nucleotide: DNA + RNA
What are the 3 types of carbohydrates w e.g.s for each of them?
- monosaccharides (glucose, fructose, galactose)
- disaccharides (maltose, sucrose, lactose)
- polysaccharides (starch, cellulose, glycogen)
What are the 2 isomers of glucose?
- alpha (α) glucose
- beta (β) glucose
Draw the structure of an α-glucose + β-glucose.
- α-glucose: hydroxyl groups both at bottom
- β-glucose: hydroxyl groups on bottom left + top right
Describe how a disaccharide is formed.
- 2 monosaccharides join together by a glycosidic bond formed via a condensation reaction which involves the removal of a water molecule
Describe how a disaccharide is broken down into 2 monosaccharides.
- the glycosidic bond is broken via a hydrolysis reaction which involves the addition of a water molecule
What monosaccharides form the disaccharides maltose, sucrose + lactose via a condensation reaction?
- glucose + glucose —-> maltose + water
- glucose + fructose —-> sucrose + water
- glucose + galactose —-> lactose + water
What are polysaccharides?
- many monosaccharides (e.g. glucose monomers) joined by glycosidic bonds via condensation reactions to form chains
What are the functions of starch, glycogen + cellulose?
- starch: storage of glucose in plants (e.g. starch grains)
- glycogen: storage of glucose in animals + fungi (e.g. muscle + liver cells)
- cellulose: provides structural strength to cell walls of plants = preventing cell walls from bursting + allowing them to withstand pressure
Describe the structure of starch.
- formed from 2 α-glucose polymers: amylose + amylopectin
- amylose: unbranched, helix-shaped chains w 1-4 glycosidic bonds formed via condensation reactions
- amylopectin: also has 1-4 glycosidic bonds between α-glucose molecules but is branched bc of 1-6 glycosidic bonds formed via condensation reactions
Describe how the structure of starch relates to its function.
- helix/coiled chains: compact so large quantities of glucose can be stored in a small space
- branched: inc SA of terminal glucose molecules so can be easily hydrolysed to release glucose for respiration
- insoluble: doesn’t affect water potential so water doesn’t move into or out of cells
Describe the structure of glycogen.
- a chain of α-glucose molecules joined together via many condensation reactions
- has 1-4 glycosidic bonds between α-glucose molecules but is highly branched bc of many 1-6 glycosidic bonds
Describe how the structure of glycogen relates to its function.
- branches: compact so large quantities of glucose can be stored in a small space
- highly branched: inc SA of terminal glucose molecules so can be rapidly hydrolysed to release glucose for respiration
- insoluble: doesn’t affect water potential so water doesn’t move into or out of cells
Describe the structure of cellulose.
- long, straight chains of alternatively rotated (180°) β-glucose molecules joined together by 1-4 glycosidic bonds via condensation reactions
- chains lie parallel + are held together by many hydrogen bonds to form fibrils
Describe how the structure of cellulose relates to its function.
- parallel chains held together by many hydrogen bonds: provides collective strength allowing cells to withstand turgor pressure + support plant
- insoluble: doesn’t affect water potential so water doesn’t move into or out of cells
Describe the test for reducing sugars.
- add Benedict’s reagent + heat in a water bath
- if reducing sugar is present, solution turns from blue to green/yellow (low conc) or orange/brick red (high conc)
- bc copper (II) sulfate in Benedict’s reagent is reduced to copper (I) oxide
Describe the test for non-reducing sugars.
- if reagent remains blue after a Benedict’s test, add dilute HCl (to hydrolyse any glycosidic bonds in non-reducing sugar + expose reducing group) + heat to a boil
- add sodium hydrogencarbonate to neutralise solution
- then add Benedict’s reagent + heat
- if reducing sugar is present, solution turns from blue to green/yellow (low conc) or orange/brick red (high conc)
- bc copper (II) sulfate in Benedict’s reagent is reduced to copper (I) oxide
What are some e.g.s of reducing + non-reducing sugars?
- reducing: glucose, fructose, galactose, maltose + lactose
- non-reducing: sucrose
Describe the test for starch.
- add iodine
- if starch is present, solution turns from orange to blue/black
Why should an excess of Benedict’s reagent be used when carrying out a test for reducing sugars?
- so there’s enough copper (II) sulfate to react w any sugar present
