Carbohydrates Flashcards
(28 cards)
What are carbohydrates?
Most abundant biomolecules on earth, complex organic molecules formed from carbon dioxide and water which are used as a source of chemical energy by living organisms.
Carbohydrates have the empirical formula (CH2O)n.
What are the three main types of carbohydrates?
- Monosaccharides
- Oligosaccharides
- Polysaccharides
Define monosaccharides.
Simple sugars, colorless, crystalline solids, water soluble, most are sweet tasting.
Monosaccharides exist in open chain and ring structures.
What are trioses?
Simple sugars (monosaccharides) containing 3 carbon atoms, serve as intermediates in glycolysis, gluconeogenesis, and pentose phosphate pathway.
What is stereochemistry in relation to carbohydrates?
A molecule with n chiral centres can have 2^n stereoisomers.
What is an aldose?
A monosaccharide with an aldehyde group (carbonyl group at the end of the carbon chain).
What do the D and L designations refer to?
The stereochemistry of the sugar, determined by the orientation of the hydroxyl group on the chiral carbon furthest from the aldehyde group in a Fischer projection.
What is a Fischer projection?
A way of representing the structure of a molecule, specifically a carbohydrate, in a 2D plane.
Examples of D-aldoses include:
- D-glyceraldehyde
- D-ribose
- D-arabinose
- D-glucose
Define epimers.
Each of 2 isomers with different configurations of atoms about one of several asymmetric carbon atoms present.
What characterizes ketoses?
6 carbon sugar with a carbonyl group at C2 position, reducing sugars, asymmetric centres at C3, C4, and C5.
What occurs in monosaccharides during ring formation?
Covalent bond formation between carbonyl group and an oxygen atom of a hydroxyl group produces another asymmetric (chiral) centre.
What are anomers?
A specific type of stereoisomer that differ only in their configuration at the anomeric carbon, named alpha or beta.
What is the predominant conformation of b-D glucopyranose?
Chair form, as all axial positions are occupied by H atoms.
What is the envelope form?
The conformation of furanose rings, not planar.
How are O-glycosidic bonds formed?
When a hydroxyl group reacts with the anomeric carbon.
What are the biological functions of sugars?
- Energy source
- Structural roles
- Information (recognition)
What are storage polysaccharides?
Starch and glycogen, structurally very similar, homopolymers of a-D glucose.
What distinguishes amylose and amylopectin?
Amylose is unbranched, while amylopectin is branched with a1-6 linkages every 30 residues.
What is cellulose?
An unbranched polymer of glucose residues joined by b1-4 linkages, allowing formation of long straight chains.
What is chitin?
A linear homopolymer composed of N-acetylglucosamine linked by b1-4 glycosidic bonds, second most abundant polysaccharide on earth.
What are proteoglycans?
Glycans (95% carbohydrate) associated with a bit of protein (5%).
What role do glycoproteins and glycolipids play?
They are involved in recognition and communication.
Define blood groups in terms of carbohydrates.
Oligosaccharides synthesized by specific enzymes (glycosyltransferases) that define blood groupings.
