- Both structures represent molecules having the formula C4H10.
- However, the arrangements of the atoms are different. These compounds are related as isomers (two compounds of the same formula, but different arrangement of atoms)
When a central carbon atom is bonded to 4 different groups, the mirror image is not identical to the original.
Biological Function of Carbohydrates
- • Immediate energy source for cell metabolism(glucose)
- • Nutritional sources of energy (glucose, fructose, maltose, lactose)
- • Short term storage of energy (starch, glycogen)
- • Structural component in plant cell walls (cellulose)
- • Markers on cell walls to identify cell type (e.g. blood type)
- • Carbohydrates are composed of C H and O.
- • The simple carbohydrates have the empirical formula CH2O – "hydrate" of carbon
- • All carbohydrates contain the "carbonyl group" ( C=O ) – either aldehyde or ketone
- • All carbohydrates contain several –OH groups (hydroxy groups).
General Types of Carbohydrates
- • Monosaccharides – the simple sugars – examples: glucose, fructose
- • Disaccharides – two monosaccharides bonded together – examples: sucrose, lactose
- • Polysaccharides- many glucose units linked together – examples: starch, cellulose
•Aldoses are monosacchrides with an aldehyde group and many hydroxyl (-OH) groups.
- Ketoses are monosacchrides with a ketone group and many hydroxyl (-OH) groups
D and L Notation
- •D,L tells which of the two chiral isomers we are referring to.
- •If the –OH group on the next to the bottom carbon atom points to the right , the isomer is a D-isomer; if it points left, the isomer is L.The D form is usually the isomer found in nature.
- • Monosaccharides are the simplest carbohydrates
- – cannot be broken down into simpler carbohydrates
- • They all contain several OH groups (hydroxy) and 1carbonyl group (C=O)
- • They are chiral molecules (they are not identical to their mirror images)
- • They differ in the arrangement of the groups around the chiral carbons.
- • A method is needed to unambiguously designate the spatial arrangement of atoms when drawing a structure.
- • A convention was developed by Emil Fischer (1852-1919) to show the exact arrangement of the atoms around a chiral carbon.
•Monosaccharides are classified:
- •According to # of carbons,
- •Glucose is a hexose
- •(a five carbon sugar is called a pentose)
- •According to the nature of the carbonyl
- •Glucose is an aldose •(sugars that have a ketone are called ketoses) •The complete classification of glucose is aldohexose
- •Glucose is a monosaccharide (can't be broken into simpler sugars)
- •Glucose is an aldose (contains an aldehyde group)
- •Glucose is a aldohexose (an aldehyde group with a total of 6 carbon atoms)
- •Glucose = "blood sugar"
- •Galactose is a monosaccharide (can't be broken into simpler sugars)
- •Galactose is a aldose (contains an aldehyde group)
- •Galactose is a aldohexose (contains an aldehyde and a total of 6 carbon atoms)
- •Galactose is a component of milk sugar ( lactose, a disaccharide)
- •Ribose is a monosaccharide (can't be broken down into simple sugars)
- •Ribose is an aldose (contains an aldehyde group)
- •Ribose is a aldopentose (contains an aldehyde and a total of 5 carbon atoms)
- •Fructose is a monosaccharide (can't be broken into simpler sugars)
- •Fructose is a ketose (contains a ketone group)
- •Fructose is a ketohexose (contains a ketone and a total of 6 carbon atoms)
- •Fructose is the sweetest of sugars
Reactions of Monosaccharides
Certain sugars have the ability to convert Cu+2 solutions (Benedict’s solution) to Cu2O, which is a red solid. Since the Cu+2 is reduced to Cu+1, these sugars are called reducing sugars
Cyclic Structures of Monosaccharides
- •Monosaccharides with 5-6 carbon atoms form cyclic structures
- •The hydroxyl group on C-5 reacts with the aldehyde group or ketone group
Haworth Structure for D-Isomers
The cyclic structure of a D-isomer has the final CH2OH group located above the ring.
Disaccharides can be broken down by acidic water (hydrolyzed) to give monosaccharides
- Maltose (malt sugar) glucose + glucose
- Lactose (milk sugar) glucose + galactose
- Sucrose (table sugar) glucose + fructose
Carbohydrates as Cell Markers
- • Modified carbohydrates are attached to cell membranes (cell walls)
- • They serve as ‘markers’ to identify the cell type
- • In this way, they tell the immune system that the cell belongs to the organism and is not a foreign organism (bacteria or parasite)
- • A common example of this is in the determination of blood types
- • Starch-storage form of glucose in plants – Amylose (20%): 200-4000 a glucose monomers attached a-1,4 in a continuous chain (polymer)
- • chains tend to coil so as to pack more tightly – Amylopectin (80%): Similar to amylose, but contains occasional branches on the main chain.
- • chains tend to coil like amylose
- • Glycogen("animal starch"- storage form of glucose in animals – mainly in liver and muscle – similar to amylopectin, but more highly branched
- • Cellulose: major structural material in plants – gives strength to cell walls
- – long chain of mainly unbranched glucose units
- – however, glucose units are linked via 1,4 b linkages.
- – chains tend to be aligned and held together by H bonds.
Summary-Functions of Carbohydrates
- • Carbohydrates are a used to provide energy for cellular functions (ex-glucose)
- • Carbohydrates are used to provide (relatively short term) storage of energy (starch)
- • Carbohydrates are an important component in cell walls of plants (cellulose)
- • Carbohydrate derivatives are used as cell markers (antigens for blood type)
Key Features of Organic Chemistry
- •Carbon forms 4 bonds when forming molecules (exception: carbon monoxide)
- •Compounds containing only carbon and hydrogen are called hydrocarbons.
- •Atoms bonded together by single bonds are can rotate about the bond.
- •Atoms bonded together by double bonds cannot rotate about the bond.
- •Compounds having the same molecular formula but different arrangement of atoms are called isomers
two mirror images