Carbohydrates Flashcards
What are monosaccharides?
- monomers from which larger carbohydrates are made
What are some examples of monosaccharides?
- glucose
- galactose
- fructose
What forms a glycosidic bond?
- condensation reaction between two monosaccharides
What are disaccharides formed by?
- condensation of two monosaccharides joined by a glycosidic bond
What are the common disaccharides?
- maltose
- sucrose
- lactose
What is maltose formed by?
- condensation of two glucose molecules
What is sucrose formed by?
- condensation of a glucose molecule and a fructose molecule
What is lactose formed by?
- condensation of a glucose molecule and a galactose molecule
What are the two isomers of glucose?
- alpha and beta glucose
Describe the structure of alpha glucose
- in alpha glucose, in c1, the hydrogen is bonded above the hydroxide
Describe the structure of beta glucose
- in beta glucose, in c1, the hydroxide is bonded above the hydrogen
What are polysaccharides formed by?
- formed by the condensation reaction between many glucose monomers
What are some examples of polysaccharides?
- glycogen
- starch
- cellulose
Which polysaccharides are formed by the condensation of alpha glucose?
- glycogen and starch
Which polysaccharide is formed by the condensation of beta glucose?
- cellulose
What does starch occur as?
- amylose and amylopectin
What is the structure of amylose?
- unbranched chain of alpha glucose
- 1-4 glycosidic bonds
- coiled in a helix due to hydrogen bonding so is compact
What is the structure of amylopectin?
- branched chain of alpha glucose
- 1-4 glycosidic bonds
- 1-6 glycosidic bonds
Advantage of structure of amylose
- coiled due to hydrogen bonds so is compact making it good for storage as you can fit more glucose into a small space
Advantage of structure of amylopectin
- side branches increase surface area allowing enzymes that hydrolyse the molecule to get at the glycosidic bonds easily so that glucose can be released quickly
What is the structure of glycogen?
- heavily branched chains of alpha glucose
- 1-6 glycosidic bonds
- 1-4 glycosidic bonds
- more branched than amylopectin
Advantage of structure of glycogen
- heavily branched allows more hydrolysis to occur more easily so alpha glucose can be released quickly for respiration as animals are more metabolically active
- very compact molecule so good for storage
What is the structure of cellulose?
- unbranched chains of beta glucose
- 1-4 glycosidic bonds
- every other beta glucose molecules are flipped 180 degrees to form glycosidic bonds and forming cellulose chains
- cellulose chains linked together by hydrogen bonds to form strong fibres called microfibrils
Advantage of structure of cellulose
- strong fibres called microfibrils from hydrogen bonds between cellulose chains mean cellulose provides structural support for cells
What is the shape of amylose?
- unbranched and coiled as helix
What is the shape of amylopectin?
- branched
What is the shape of glycogen?
- heavily branched
What is the shape of cellulose?
- long unbranched straight parallel chains
Where is starch (amylose and amylopectin) found?
- plant cells
Where is glycogen found?
- animal cell granules in muscle and liver
Where is cellulose found?
- plant cell wall
What is the function of amylose?
- store product and energy
What is the function of amylopectin?
- store product and energy
What is the function of glycogen?
- store product in muscle and liver
What is the function of cellulose?
- provide structure in cell walls
Benedict’s test for reducing sugars
- heat sample with Benedict’s reagent
- if sample stays blue, no reducing sugar is present
- if sample forms green, yellow, orange or brick red precipitate, reducing sugar is present
What do reducing sugars include?
- all monosaccharides (glucose, galactose and fructose)
- some disaccharides (maltose and lactose)
What is a more accurate way of carrying out Benedict’s test?
- filter solution and weigh precipitate
- remove the precipitate and use colorimeter to measure the absorbency of the remaining Benedict’s reagent
What do non reducing sugars include?
- sucrose
Benedict’s test for non reducing sugar
- add dilute hydrochloric acid to test solution and heat
- neutralise sample by adding sodium hydrogen carbonate
- heat sample with Benedict’s reagent
- if sample forms green, yellow, orange or brick red precipitate, non reducing sugar is present
Why should you add dilute hydrochloric acid to Benedict’s test for non reducing sugar?
- to hydrolyse test solution into monosaccharides
Iodine test for starch
- add iodine in potassium iodide solution to test sample
- if test sample changes from browny orange to dark, blue black colour, starch is present
What are the properties of disaccharides?
- sweet tasting
- soluble in water
- osmotically active
What is the function of sucrose?
- energy transport and storage in plants
What is the function of lactose?
- energy transport and storage in mammal milk
What is the function of maltose?
- intermediate in starch digestion
What are oligosaccharides?
- chains of monosaccharides that are covalently linked to one another by glycosidic bonds containing 3-10 monosaccharides and may be linear or branched
What are the properties of polysaccharides?
- osmotically inactive (insoluble/colloidal)
- not sweet tasting
- energy storage or structural functions
- hydrolysed to monosaccharides by amylases or cellulases
What is the structure of chitin?
Advantage of structure of chitin
Draw the structure of alpha glucose
Draw the structure of beta glucose
Draw the formation of maltose by condensation
Draw the hydrolysis of maltose
During which processes are polymers hydrolysed in the body into monomers?
- digestion eg. Starch is hydrolysed into glucose
- glycogenolysis is where stores of glycogen is hydrolysed back into glucose when blood sugar levels drop
What catalyses hydrolysis in the body?
- enzymes
What is the advantage of starch being insoluble?
- won’t affect water potential
What is an advantage of cellulose being insoluble?
- won’t affect water potential
What is the advantage of glycogen being insoluble?
- won’t affect water potential
Why does the colour change occur at the top of the solution first (test for reducing sugars)?
- molecules have more kinetic energy at the top so more successful collisions and faster reaction at the top
Define reducing sugars
- these sugars can reduce the copper sulphate (blue) in Benedict’s reagent to copper oxide (brick red)
Define non reducing sugars
- reducing group is involved in glycosidic bond in sucrose and therefore, sucrose cannot reduce sopped sulphate to copper oxide
- when sucrose is hydrolysed through boiling with acid, the glycosidic bond is broken and therefore, the reducing group becomes exposed
