CHEM1004 Study Guide - Final Guide: Amine, Asymmetric Carbon, Catabolism
TOPIC THREE: Carbohydrates
Terminology:
A carbohydrate is defined as a polyhydroxyalderhyde or a polyhydroxyketone, or
a substance that gives these compounds of hydrolysis. They have the general
formula of CnH2nOn where n varies from 3 to 8. The suffix –ose indicates that a
molecule is a carbohydrate, and triose, tetrose, etc. denote the number of
carbons that a carbohydrate contains.
Carbohydrates can be classified into 3 groups:
• Monosaccharide (simple sugar) – the monomers of carbohydrates, that
cannot be broken down to a simple carbohydrate.
• Oligosaccharide – usually 2-10 simple sugar residues
• Polysaccharide – polymers of the simple sugars.
And aldose is a monosaccharide that contains a ketone group, and a ketose is a
monosaccharide that contains a ketone group. Often aldo- and keto- are omitted
and these compounds are referred to by how many carbons they contain.
Function of Carbohydrates:
Carbohydrates are a diverse group of macromolecules. They can be used as an
energy source, like lactose in milk. Or they can have structural purposes, like
making up the cell walls of bacteria. Carbohydrates are very important materials
to both plants and animals.
Functional Groups in Carbohydrates:
Among neutral organic compounds, the following atoms are found:
• Carbon – 4 covalent bonds (stereocentre)
• Hydrogen – 1 covalent bond
• Nitrogen – 3 covalent bonds
• Oxygen – 2 covalent bonds
The following functional groups are found in carbohydrates:
• Ether
• Ester
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• Carbonyl (aldehyde or ketone)
• Carboxylate
• Hydroxyl (alcohol)
• Amino (protonated)
Carbohydrate Chirality:
The R and S system of naming chiral compounds are not used for carbohydrates.
Instead, assignments of dextrorotatory (D) and levorotatory (L) are used. For
dextrorotatory molecules, they rotate plane-polarized light in a clockwise
direction, with their hydroxyl group found on the right. They are the biological
form for carbohydrates. For levorotatory molecules, they rotate plane-polarized
light in an anticlockwise direction, with their hydroxyl group on the left.
Anomers are isomers of monosaccharides that differ only in their configuration
about the asymmetric carbon. They can have 2 forms – alpha and beta. For alpha
anomers, the –OH group on the anomeric carbon is on the side of the ring
opposite from the –CH2OH terminal. For beta anomers, the –OH group is on the
same side of the ring as
the terminal –
CH2OH
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Biologically Important Monosaccharide Derivatives:
A variety of chemical and enzymatic reactions produce derivatives of the simple
sugars. The most common are sugar alcohols, deoxy sugars, sugar phosphates
and amino sugars.
Sugar Alcohols
In sugar alcohols, no ketones or aldehydes are present. Instead, a hydroxyl group
is present. Sugar alcohols are used in artificial sweeteners and are digested
slowly by the body.
Deoxy Sugars
Deoxy sugars are monosaccharides with
one or more hydroxyl groups replaced
by hydrogens. The most common
example are RNA and DNA nucleotides.
Sugar Phosphates
Sugar phosphates, especially phosphate
esters of glucose, fructose and other
monosaccharides, are important metabolic intermediates. The ribose moiety of
nucleotides such as ATP is phosphorylated at the 5’ position.
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Document Summary
A carbohydrate is defined as a polyhydroxyalderhyde or a polyhydroxyketone, or a substance that gives these compounds of hydrolysis. They have the general molecule is a carbohydrate, and triose, tetrose, etc. denote the number of carbons that a carbohydrate contains. Carbohydrates can be classified into 3 groups: formula of cnh2non where n varies from 3 to 8. The suffix ose indicates that a: monosaccharide (simple sugar) the monomers of carbohydrates, that, oligosaccharide usually 2-10 simple sugar residues, polysaccharide polymers of the simple sugars. And aldose is a monosaccharide that contains a ketone group, and a ketose is a monosaccharide that contains a ketone group. Often aldo- and keto- are omitted and these compounds are referred to by how many carbons they contain. cannot be broken down to a simple carbohydrate. They can be used as an energy source, like lactose in milk. Or they can have structural purposes, like making up the cell walls of bacteria.
