Chapter 11: Carbohydrates Flashcards
What is the molecular formula of carbohydrates?
(CH2O)n
carbon atoms hydrated
n is at least 3 (5 or 6 most common) sugars
What are other names of carbohydrates?
Sugars, glucose, or saccharides.
What are the classifications of carbohydrates?
monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
What is the chemical nature of carbohydrates?
Polyhydroxylated aldehydes or ketones
What are the classifications of monosaccharides?
- Monosaccharides made from aldehydes are called aldoses (ex. glyceraldehyde an aldotriose)
- Monosaccharides made from ketones are called ketoses (ex. dihydroxyacetone, a ketotriose)
What are the enantiomers of monosaccharides?
Most carbohydrates are chiral. creating A pair of enantiomers exhibiting mirror symmetry. Glyceraldehyde has two different structures that exhibit mirror symmetry. Such pairs of structures, known as enantiomers, cannot be superimposed by rotation.
What are the cyclization and formation of anomers of monosaccharides?
Cyclization generates α and β anomers. Anomers can interconvert unless the -OH group attached to anomeric C (C#1) is linked to another molecule.
The numerous hydroxyl groups that characterize carbohydrate structures also provide multiple points for chemical reactions to occur. One such reaction is an intra-molecular rearrangement in which the sugar’s carbonyl group reacts with one of its OH groups to form a cyclic structure.
What are the Haworth projections of monosaccharides?
In a linear Fischer projection, the horizontal bonds point out of the page and the vertical bonds point below the page. Glucose cyclizes to form a six-membered ring represented by a Haworth projection, in which the heaviest bonds point out from the plane of the page. The a and b anomers freely interconvert.
What are the chair conformations of monosaccharides?
The chair conformation: all the bulky groups (-OH & -CH2OH) occupy equatorial positions
What is a reducting sugar?
If anomeric C is NOT linked to another molecule:
* It can undergo oxidation
* By reducing Cu(II) to Cu(I)
* In Benedict’s reagent
* Test can be used to distinguish a
reducing sugar from a non-reducing one
The anomeric carbon of a monosaccharide is easy to recognize: It is the carbonyl carbon in the straight-chain form of the sugar, and it is the carbon bonded to both the ring oxygen and a hydroxyl group in the cyclic form of the sugar. The anomeric carbon can undergo oxidation, so it can reduce substances such as Cu(II) to Cu(I). This chemical reactivity, often assayed using a copper-containing solution known as Benedict’s reagent, can distinguish a free monosaccharide, called a reducing sugar, from a monosaccharide in which the anomeric carbon has already reacted with another molecule.
What are the different types of monosaccharides derivatives?
a) Glucosamine: an amino sugar
b) Glucuronate: NH3 replaces an OH group. Oxidation and reduction reactions yield sugars with carboxylate groups
c) Xylitol: additional hydroxyl groups (reduction)
What is the composition of common disaccharides?
A glycosidic bond links two monosaccharides to generate a disaccharide.
Lactose and sucrose are the most common disaccharides.
In nature, disaccharides occur as intermediates in the digestion of polysaccharides and as a source of metabolic fuel. For example, lactose, secreted into the milk of lactating mammals, consists of galactose and glucose:
What are the types of glycosidic bonds connecting the monosaccharides in common disaccharides?
- β(1->4) glycosidic bond (ex. lactose)
- α-1,β-2-glycosidic bond (ex. sucrose)
What is the composition of common polysaccharides?
Common polysaccharides are
- glycogen
- cellulose
- starch
What are the types of glycosidic bonds connecting the monosaccharides in common polysaccharides?
Monosaccharides are the building blocks of polysaccharides, in which glycosidic bonds link successive residues.
Each monosaccharide contains several free OOH groups that can participate in a condensation reaction, which permits different bonding arrangements and allows for branching.
Which amino acid is a glycoprotein attached to if the oligosaccharide is O-linked?
Glycoproteins can be O-linked if oligosaccharide is attached to a Ser of the protein
What are the composition and function of Proteoglycans?
Proteoglycans contain repeating units of a disaccharide and are found in the cartilage.
Small proteins bind to very large unbranched polysaccharides called glycosaminoglycans (GAG)
What are the composition and function of Peptidoglycans?
Peptidoglycans are polysaccharides containing repeating units (20-40) of a disaccharide cross-linked with short peptides (4-5 AA’s) found in bacterial walls
Draw the chemical composition of a Proteoglycan
What type of glycosidic bond does sucrose have?
α-1,β-2-glycosidic bond
Sucrose, or table sugar, is the most abundant disaccharide in nature
Which amino acid is a glycoprotein attached to if the oligosaccharide is N-linked?
Glycoproteins can be N-linked if oligosaccharide is attached to an Asn of the protein
What is the structure of cellulose?
It forms bundles with many intra- & inter- chain H-bonds playing a structural role in plants
What is the connectivity of cellulose?
Cellulose is an unbranched polysaccharide made of glucose connected with β(1->4) bonds
What is the connectivity of glycogen?
Found in animals, glycogen (branched) are composed of glucose units linked by α( 1->4) glycosidic bonds
What is the connectivity of starch?
Found in plants, starch which is a mixture of amylose (unbranched) and amylopectin (branched) is composed of glucose units linked by α( 1->4) glycosidic bonds
What is the connectivity of amylose found in plants in the form of starch?
The structure of amylose, the unbranched form of starch, with only α(1->4) glycosidic bonds, forms a large left handed helix
What is the connectivity of amylopectin found in plants in the form of starch?
Structure of amylopectin, the branched form of starch, has α(1->6) glycosidic bonds at the branches
