2.2-Carbohydrates 1: Sugar Flashcards
What is the definition of carbohydrates?
A group of molecules containing, C,H and O
What is definition of glycosidic bond?
A bond formed between 2 monosaccharides by a hydrolysis reaction.
What are carbohydrates for?
Carbohydrates contain carbon, hydrogen and oxygen. Carbohydrates are the ‘ hydrated carbon’ , which means that for every carbon there are 2 hydrogen atoms and 1 oxygen atom. The function of carbohydrates are three fold. They act as a source of energy (e.g. glucose) as a store of energy (e.g. starch and glycogen) and as structural units (e.g. cellulose in plants and chitin in insects). Some carbohydrates are also part of other molecules such as nucleic acids and glycolipids. There are three main groups of carbohydrates: monosaccharides, disaccharides and polysaccharides. The common monosaccharides and disaccharides all, have names ending in -ose
What are monosaccharides?
Monosaccharides are the simplest carbohydrates. They are particularly important in living things as a source if energy. They are well suited to this role because if the large number of carbon- hydrogen bonds. They bare sugars which taste sweet are soluble in water and are insoluble in non-polar solvents.
Monosaccharides can exists as straight chains or in ring or cyclic forms. They have a backbone of single bonded carbon atoms with one double bonded to an oxygen atom to form a carbonyl group.
What do different sugars have?
-MONOSACCHRIDES
Different sugars can have different numbers of carbon atoms: hexose sugars have six carbon atoms, pentose sugars have five carbon atoms and triose sugar have three carbon atoms.
hexose sugars like glucose are the monomers of more complex carbohydrates and they bond together to form disaccharides or polysaccharides.
What do triose and tetrose sugars exist as in solution?
In solution triose and tetrose sugars exists as straight chains. However pentose and hexose are more likely to be found in a ring or cyclic form.
What can glucose exists as in both straight chain or cyclic form?
In both forms (straight chain or cyclic form) glucose can exists as a number of different isomers (molecules with the same formula but whose atoms are arranged differently in space). In the straight chain form, the -H and -OH can be reserved. In a ring shape, isomers can also form. The ring is formed when the oxygen is attached to the carbon 5bonds to carbon . Because the -OH and -H on carbon 1 can be above or below, the plane of the ring when the ring forms, there are 2 isomers alpha and beta glucose. This small differences appears insignificant, but becomes very important when glucose molecules polymerise into starch or cellulose.
What are disaccharides?
Like monosaccharides, disaccharides are sweet and soluble. The most common disaccharides are maltose (malt sugar), sucrose and lactose (milk sugar). Maltose and lactose are reducing sugars, whereas sucrose is a non reducing sugar.
When are disaccharides made?
Disaccharides are made when two monosaccharides join together.
There are lots of different combinations, which determine the disaccharide made:
- a-glucose+a-glucose——>maltose
- a-glucose+ fructose—->sucrose
- B-galactose+a-glucose—->Lactose
- B-glucose + B-glucose—->cellobiose
When they join a condensation reactions occurs to form a glycosidic bond. Two hydroxyl groups line up next to each other from which a water molecule is remove. This leaves an oxygen atom acting as a link between the two monosaccharide units.
What are disaccharides broken into?
Disaccharides ae broken into monosaccharides by a hydrolysis reactions, which requires the addition of water. The water provides a hydroxyl group (-OH) and a hydrogen (H),which helps the glycosidic bond to break. For example, cellobiose is obtained by the hydrolysis of the polysaccharide cellulose.
What is the molecular formula for a- Glucose?
C6H12O6
What is the role of a-Glucose?
Energy source.
Components of starch and glycogen, which act as energy stores.
What type of sugar does a-Glucose form?
Hexose
What is the molecular formula for B-Glucose
C6H12O6
What is the role of B-Glucose?
Energy source.
Components of cellulose, which provide structural support in plant cell walls.
