3.1.2 carbohydrates Flashcards
what is a monosaccharide?
+ the monomers from which larger carbohydrates are made
+ simple sweet-tasting sugar
general formula ( CH2O)n
+ n can be anywhere from 3-7
+ glucose, galactose and fructose are common
what happens in a condensation reaction between 2 monosaccharides?
+ a glycosidic bond is formed
how are disassachrides formed?
+ by the condensation of two monosaccharides
what is maltose?
+ a disaccharide formed by condensation of two glucose molecules
what is sucrose?
+ a disaccharide formed by condensation of a glucose molecule and a fructose molecule
what is lactose?
+ a disaccharide formed by condensation of a glusoce molecule and a galactose molecule
what are the two isomers of glucose?
+ alpha-glucose
+ beta-glucose
how are polysaccharides formed?
+ by the condensation of many glucose units
how is glycogen and starch formed?
+ by the condensation of alpha-glucose
how is cellulose formed?
+ by the condensation of beta-glucose
What are carbohydrates?
+ contains only C,H,O atoms
+ carbon atoms form bonds with each other allowing for long chains to be formed
+ can be used as a backbone for other atoms to join in order to form other molecules
+ in all organisms the function is it act as an easily accessible source of energy
+ in plants, carbs also have a structural role
Formula of a triose sugar?
C3H6O3
Formula of tetrose sugar?
C4H8O4
Formula of pentose sugar?
C5H10O5
Formula of hexose sugar?
C6H12O6
Formula of heptose sugar?
C7H14O7
What is an isomer?
+ same molecular formula but different structure (their atoms are arranged to give them slightly different properties)
What is the test for starch?
+ add iodine solution
+ blue/black precipitate forms if
What is a reducing sugar?
+ a sugar that can donate electrons (or hydrogen) to other chemicals
What is Benedict’s Reagent?
+ an alkaline copper (II) sulphate solution
How do you test for reducing sugars?
- Test tube with food sample dissolved in water
- Add an equal volume of Benedict’s Reagent
- Heat the mixture in gently boiling water
How are disaccharides formed?
+ two alpha-glucose molecules C1 and C4 meet
+ hydroxyl group (OH) from C1 and C4 react
+ a condensation reaction occurs so water is removed- so there will be less oxygen and hydrogen
+ the bond formed is caused an alpha-1,4 glycosidic linkage
How to test for non-reducing sugars?
- add liquid food sample to a test tube
- add 1cm^3 of hydrochloric acid (hydrolyses the disaccharide)
- place in a beaker of water and boil for approx. one minute
- allow the test tube to cool
- add sodium hydrogencarbonate to neutralize the acid
- carry out Benedict’s test as for reducing sugars
- non-reducing sugar present = brick red precipitate
what are polysaccharides?
+ formed by combinations of many monosaccharides molecules
+ they are joined by glycosidic bonds that were formed by condensation reactions (many bonds present within polysaccharides)
+ they are insoluble as they are large, making them highly suited for storage
What is starch?
+ polysaccharide found in the form of small grains in plants
+ large amounts found in seeds and storage organs
+ major energy source
+ formed from many alpha-glucose monomer units linked via glycosidic bonds
What is the structure of starch?
+ large - can’t diffuse out of cells easily (good for storage)
+ can be hydrolysed easily - good for storage in small spaces
+ starch is insoluble - water is not drawn into cells by osmosis so doesn’t affect water potential
+ tightly coiled and compact - good for storage in small spaces
+ OH groups point inwards and form H-bonds with neighbouring molecules
What is glycogen?
+ found in animals and bacteria
+ formed from many monomers of alpha-glucose
+ has shorter chains and more branches
+ mainly stored in the muscles and the liver
+ however, isn’t the main long term storage in animals - constantly using it for source of glucose (energy)
What is the structure of glycogen?
+ same as starch except for…
+ more highly branched - more ends available for enzymes to breakdown - more rapidly broken down to glucose - more glucose available for respiration
What is cellulose?
+ formed from beta-glucose
+ the glucose molecules are orientated in a way that makes the OH groups stick outwards in opposite directions
+ these can form hydrogen bonds with neighbouring chains
+ forms straight and unbranched chains
+ chains run parallel to each other allowing for hydrogen bonds to form cross-linkages
+ overall high numbers of hydrogen bonds - provide considerable strength to cellulose
What is the structure of cellulose?
+ long straight, unbranched chains- provides rigidity which is required to provide support to a plant cell
+ cross-linked chains held together by hydrogen bonds - provides even further strength to the cell wall
+ arranged into fibrils which contain microfibrils- provides EVEN further strength to the cell wall
What is the function of cellulose?
+ stops the cell wall from bursting under osmotic pressure
+ this is because it exerts inward pressure that stops the influx of water
+ this means that the cells stay turgid and rigid, helping to maximise the SA of plants for photosynthesis
Cellulose in animals?
+ the beta-glycosidic bond cannot be broken by amylase, but requires a specific cellulose enzyme
