monosaccharides and disaccharides Flashcards
what are monosaccharides?
are the monomers from which larger carbohydrates are made
what are examples of common monosaccharides?
glucose, galactose and fructose
how do monosaccharides join together?
by a condensation reaction
which two forms can monosaccharides occur as?
alpha-glucose and beta-glucose
what is the bond that the reaction would produce a disaccharide called maltose?
an alpha 1-4 glycosidic bond
how is maltose created?
when amylase breaks down starch
which two monosaccharides form maltose?
glucose + glucose
what is a disaccharide?
the sugar formed when two monosaccharides are joined by glycosidic linkage
what are examples of other disaccharides other than maltose?
sucrose and lactose
which two monosaccharides form sucrose?
glucose+fructose
which two monosaccharides form lactose?
glucose+galactose
how is sucrose formed?
by the condensation of a glucose molecule and a fructose molecule
how is lactose formed?
by the condensation of a glucose molecule and a galactose molecule
what is a polysaccharide?
a very large polymer comprising many monosaccharides, as with disaccharides they are joined by glycosidic bonds
how is a polysaccharide formed?
by the condensation of many glucose monosaccharides
what are the features and characteristics of polysaccharides?
-they are insoluble in water
-they are not sweet
-they do NOT form crystals
what do polysaccharides take the form of?
long chains; straight, spiral, branched and ringed
what is starch?
a large polysaccharide and is produced by the condensation of alpha-glucose units
what are the two distinct components of starch?
amylose and amylopectin
what structures does starch take?
spiral
how is starch used?
by plants as an energy store, it is usually stored in the chloroplasts of leaves
how is glucose stored?
as starch as it doesn’t affect water potential, it can also not diffuse out of the cell and can be stored in a small place
what is the iodine test for starch?
the test from which tests the presence of starch.
1) add a few drops of iodine solution (which is orange) to a sample
2) if starch is present, the solution interacts with the starch molecules and turns the sample blue-black
what is glycogen?
the animal kingdoms equivalent to starch, animals use glycogen as a store of energy.
how is glycogen formed?
by the condensation of alpha-glucose units
what are features of glycogen?
firstly, it is very similar structured to starch but is far more branched with a lot more 1-6 bonds.
-it is insoluble
-it is never found in plants
-used as a storage molecule for the same reason starch is used in plants
how can we breakdown glycogen?
it is necessary to breakdown glycogen by hydrolysis in the presence of an enzyme
what is cellulose?
it is an incredibly long polysaccharide with no branches, its bonds are beta-1-4 bonds
what are features of cellulose?
-very different from both starch and glycogen
-it is not a storage molecule
-used in plant cell walls to assist in maintaining the rigidity of the plant
-most animals cannot digest it as it is too hard to breakdown
-in our diet we refer to cellulose as fibre
how is cellulose formed?
by the condensation of beta-glucose monomers, not alpha-glucose like glycogen and starch
what is lactose?
the main sugar in milk, small children produce lots of lactose in order to digest this disaccharide
where does lactose travel through the body?
the small intestine and into the colon
what happens if undigested glucose reaches there colon?
bacteria, which live in the colon, will use it as food for themselves however when they digest this lactose they produce significant gas, causing nausea, diarrhoea, bloating, cramps and wind - this is LACTOSE INTOLERANCE
what are reducing sugars?
all monosaccharides are known as reducing sugars, meaning they can donate electrons in a chemical reaction
what disaccharides are reducing sugars?
lactose and maltose, sucrose is not
Benedict’s test for reducing sugars…
a chemical called ‘Benedict solution’ is used to test reducing sugars, the solution turns into a deep brick-red colour if the solution is in the presence of a reducing sugar
what are the precipitate colours depending on concentration?
very low - green
low - yellow
medium - orange
high - brick red
how can we test the presence of non-reducing sugars?
using the Benedict’s test also
