Biological Molecules : Carbohydrates Flashcards
What are most carbohydrates ?
Polymers
name some carbohydrates that are polymers ?
proteins and nucleic acids .
what are polymers ?
Polymers are large, complex molecules composed of long chains of monomers (atoms /small molecules ) joined together.
give some examples of monomers ?
monosaccharides, amino acids and nucleotide.
what are monosaccharides?
the simplest carbohydrate .
what are carbohydrates made from ?
monosaccharides
What elements do all carbohydrates contain ?
C,H and O
what are the monomers from which carbohydrates are made from ?
monosaccharides
give examples of carbohydrates ?
glucose, fructose and galactose.
what is glucose ?
a hexose sugar
what is a hexose sugar ?
a monosaccharide with six carbon atoms in each molecule.
how many types of glucose are there ? name them
There are two types of glucose, alpha (a) and beta (|3)
what are they ?
isomers
what is an isomer
molecules with the same molecular formula as each other, but with the atoms connected in a different way
structure of them (written flashcards )
what reaction joins monosaccharides together ?
condensation
what is a condensation reaction ?
when two molecules join together with the formation of a new chemical bond, and a water molecule is released when the bond is formed.
what bond form as a water molecule is being released ?
glycosidic bond between the two monosaccharides
what is a disaccharide?
sugar
when does a disaccharide form ?
when two monosaccharides join together
what is sucrose?
sucrose is a disaccharide formed by condensation of a glucose molecule and a fructose molecule
what is maltose ?
maltose is a disaccharide formed by condensation of two glucose molecules
what is latose ?
lactose is a disaccharide formed by condensation of a glucose molecule and a galactose molecule.
what breaks polymers apart and into what?
hydrolysis reactions and into monomers
what is a hydrolysis ?
A hydrolysis reaction breaks the chemical bond between polymers using a water molecule. It’s basically the opposite of a condensation reaction.you add a water molecule and it becomes monomers
THe bendict test :
how is the benedicts test performed
Place two spatulas of the food sample into a test tube or 1 cm3 if the sample is liquid. Add about 1 cm3 depth of water to the tube and stir to mix.
Add an equal volume of Benedict’s solution and mix.
Place the tube in a water bath at about 95°C for a few minutes.
Record the colour of the solution.
what does the benedicts test test for ?
sugars
what are classified as reducing sugars?
Reducing sugars include all monosaccharides (e.g. glucose) and some disaccharides (e.g. maltose and lactose).
what happens if the benedicts test is positive for reducing sugars ?
it will form a coloured precipitate (solid particles suspended in the solution).
what does the colour mean ?
blue ->green->yellow->orange->brick red
The higher the concentration of reducing sugar, the further the colour change goes.
what can you use the diffrent colours to tell ?
you can use this to compare the amount of reducing sugar in different solutions. A more accurate way of doing this is to filter the solution and weigh the precipitate.
what does it mean if the test is negative ?
If the result of the reducing sugars test is negative, there could still be a non-reducing sugar present.
how do you test for non reducing sugars ?
To test for non-reducing sugars, like sucrose, first you have to break them down into monosaccharides.You do this by getting a new sample of the test solution, adding dilute hydrochloric acid and carefully heating it in a water bath that’s been brought to the boil. You then neutralise it with sodium hydrogen carbonate. Then just carry out the Benedict’s test as you would for a reducing sugar.
what do the results of the test show?
If the test is positive it will form a coloured precipitate (as for the reducing sugars test). If the test is negative the solution will stay blue, which means it doesn’t contain any sugar (either reducing or non-reducing).
what are Polysaccharides
Loads of Sugars Joined Together
when do polysaccharides form ?
formed when more than two monosaccharides are joined together by condensation reactions
what is the main energy storage material in plants ?
starch
what happens when plants need energy ?
Cells get energy from glucose. Plants store excess glucose as starch (when a plant needs more glucose for energy, it breaks down starch to release the glucose).
what is starch ?
Starch is a mixture of two polysaccharides of alpha-glucose — amylose and amylopectin
what is amylose ?
Amylose — a long, unbranched chain of a - glucose . The angles of the glycosidic bonds give it a coiled structure, almost like a cylinder. This makes it compact, so it’s really good for storage because you can fit more into a small space.
what is amylopectin
a long, branched chain of a - glucose . Its side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily. This means that the glucose can be released quickly.
why is starch good for storage ?
Starch is insoluble in water and doesn’t affect water potential ,so it doesn’t cause water to enter cells by osmosis, which would make them swell.
how do you test for starch?
If you do any experiment on the digestion of starch and want to find out if any is left, you’ll need the iodine test.
Add iodine dissolved in potassium iodide solution to the test sample. If there is starch present, the sample changes from browny-orange to a dark, blue-black colour.
what is the main energy storage in animals?
glycogen
how do animals store excess glucose ?
animals store excess glucose as glycogen — another polysaccharides of alpha-glucose
what is the structure of glucose like ?how is this advantageous ?
Its structure is very similar to amylopectin, except that it has loads more side branches coming off it. Loads of branches means that stored glucose can be released quickly, which is important for energy release in animals
It’s also a very compact molecule, so it’s good for storage .
what is the major component of cell walls in plants
cellulose
what is cellulose made of ?
Cellulose is made of long, unbranched chains of beta glucose.
what happens when beta glucose molecules form?
When beta-glucose molecules bond, they form straight cellulose chains.
why does cellulose provide structural support for plants ?
The cellulose chains are linked together by hydrogen bonds to form strong fibres called microfibrils. The strong fibres mean cellulose provides structural support for cells (e.g. in plant cell walls).
