BIOC 3021 - Lecture 10 Review
How is the formula 2^N used to calculate the number of steroisomers of a family of sugars with the same chemical formula?
A molecule will have 2^N isomers where N refers to the number of centers of asymmetry, or chiral centers
What is a nucleotide sugar, and how are such activated sugars used in the biosynthesis of carbohydrate polymers, glycoproteins, and glycolipids?
A nucleotide sugar is something that helps synthesize carbohydrate polymers from monomers. The synthesis of carbohydrate polymers ins catalyzed by enzymes called glycotransferases. The cleavage of the phosphate ester linkages helps to drive the process in the direction of polysaccharide synthesis
What are the major human blood types, and what kinds of sugar derivatives determine a specific blood type?
A,B, and O carbohydrate structures are present on cell surfaces and attach to proteins and lipids Type 0 - 2 Galactose, 1 Fucose, 1 N-acetylglucosamine Type A - 2 Galactose, 1 Fucose, 1 N-acetylglucosamine, and 1 N-acetylgalactosamine Type B - 3 Galactose, 1 Fucose, 1 N-Acetylglucosamine
What is the role of O-glycosidic bonds in the formation of disaccharides, oligosaccharides, and polysaccharides? What is the difference bebtween an alpha and beta glycosidic bond, and what do the numbers designate with respect to O-glycosidic bond structures?
An O-glycosidic bond is the bond formed between the hemiacetal or hemiketal on the first carbohydrate and the hydroxyl group on the second molecule, usually another sugar. An alpha glycosidic bond occurs when the linkage from the anomeric carbobn radiates in a downward direction. A beta-glycosidic linkage occurs when the linkage from the anomeric carbon radiates in an upward direction The numbers correlate to the carbon that the bond is attached to on each molecule
Which of the following words refers to conformational differenctes? A) enantiomers B) chair and boat forms C) anomers D) epimers E) D- and L-forms
B) chair and boat forms
The O-glycosidic bond linking two monosaccharide units is the equivalent to the bond found in a/an: A) aldehyde B) ketone C) acetal D) hemiacetal E) ester
C) acetal
What do the terms configuration and conformation mean, and how do these terms apply to the three dimensional structure of carbohydrates?
Configuration is the 3-dimensional arrangement of substituent groups around a chiral center. Refers to the D/L orientation Conformations are different 3-dimensional arrangements of a molecule which result from free rotation about C-C single bonds. Conformation refers to chair and boat conformations
Alpha-1,4-linkages are present in: A) lactose and cellulose B) galactose and lactose C) lactose and maltose D) maltose and glycogen E) sucrose and lactose
D) maltose and glycogen
What are the distinguishing features of deoxy-sugars, of sugar phosphates, of sugar acids, sugar alcohols, of amino sugars, and of N-acetyl-sugars?
Deoxy-sugars lack a hydroxyl group at one of their carbons. 2-deoxyribose is the prime example of a deoxy-sugar because it lacks a hydroxyl group at carbon 2 Sugar Phosphates have at least 1 covalently bound phosphate residue. In general, phosphorylated sugars occur inside of cells where they function as intermediates in biochemical pathways Sugar acids have at least one carboxyl group. Galacturonic Acid is a common sugar acid. The sugar acids tend to be components of complex carbohydrate polymers that serve as structural materials in connective tissues and other extracellular polysaccharides Sugar alcohols have a hydroxyl group in place of the aldehyde or ketone group Amino sugars have an amino group substituted for one hydroxyl group N-acetyl-sugars also have an amino group substituted for one hydroxyl group. The N-acetyl derivatives of glucose and galactose are very common components of proteoglycans and lycoproteins
What does the term epimer mean, and why are most carbohydrate epimers not also enantiomers? Why do most epimers have different chemical names?
Epimers are steroisomers which differ in stetrochemistry at only one chiral carbon. They are generally not mirror images of each other, except for the trioses, and are not chemically equivalent to each other, so they have different names and chemical/physical properties
What are the characteristics of glycogen, and what is its function in humans? What is the monosaccharide component of glycogen? What two types of O-glycosidic linkages occur in the molecule and what is the percentage of each linkage type. What is the significance of reducing and on-reducing ends of glycogen?
Glycogen is the human storage polysaccharide. It conttains glucose units that form a spiral structure. It contains about 90% alpha-1,4-linkages and 10% alpha-1,6-linkages. The alpha-1,6-linkages are responsible for the branch points of glycogen
What are hemiacetals and acetals and by what chemical reactions ar ethey formed from alochols and aldehydes? What does it mean that monosacchardie anomers have a hemiacetal structure, and why do disaccharides have an acetal structure?
Hemiacetals are formed when an aldehyde and alcohol react. They are unstable unless the aldehyde and the alcohol are part of the same molecule so that a cyclic hemiacetal is formed. Hemiacetals are formed through cyclization of an aldose. An acetal is formed if a second alcohol molecule is reacted with the hemiacetal Disaccharides have an acetal structure because the reaction of two cyclized carbohydrates leads to the formation of an acetal. Monosaccharides are hemiacetals because they consist of only one molecule
What are the characteristics of the chair and boat conformational forms of glucose? What is the difference between an axial and an equatorial hydroxyl group? Why are certain conformational forms of sugars preferred? How is the distribution of conformational forms related to steric hindrance?
In the chair form of D-glucose the hydroxyl groups are all in the equatorial position, except the hydroxyl group in the anomeric position can either be axial, making it alpha, or equatorial, making it beta The chair and boat conformations both have axial and equatorial positions. The preferred conformer has most bulky substituents in the equatorial positions, because if bulky groups are in adjacent axial positions there is steric hindrance. Certain conformation forms are preferred because they have lower energy levels
Can you identify the important characteristics of the following compounds? Can you distinguish between these different compounds and describe how they are related to each other? Monosaccharides: Glucose, Fructose, Galactose, Mannose, Ribose, Deoxyribose, N-acetyl-glucosamine, and N-acetyl-Galactosamine Disaccharides: Maltose, Isomaltose, Lactose, Cellobiose, and Sucrose Polysaccharides: Amylsoe, Amylopectin, Glycogen, Cellulose
Monosaccharides are made up of one sugar monomer. Glucose is a simple sugar. Fructose is a simple sugar, found in many plants, often bonded with glucose to form sucrose. Galactose is a simple sugar usually found combined with other sugars. Mannose is important in human metabolism. Ribose is a monosaccharide that is found in RNA. Deoxyribose is found in DNA N-acetyl-glucosamine is a monosaccharide derivative of glucose. Amide between glucosamine and acetic acid. Important in bacterial cell walls N-acetyl-galactosamine is an amino sugar derivative of galactose. In humans it is the terminal carb forming the antigen of blood type A Disaccharides are when two monomers are put together. Maltose is made up of two glucose units, often used in fermentation, linked with a 1-4 bond Isomaltose is an isomer of maltose linked with a 1-6 bond Lactose is made up of glucose and galactose, often found in dairy products Cellibiose is a disaccharide consisting of two glucose units in beta glycosidic linkage. It is obtained from parital hydrolysis of cellulose Sucrose is a nonreducing disaccharide made of glucose and fructose Polysaccharides consist of many monomers linked together, possibly up to thousands Amylose consists of D-glucose units bonded by 1-4 glycosidic bonds. it helps make up starch Amylopectin is a highly branched component of starch, connected by 1-4 glycosidic bonds. Glycogen is a storage carbohydrate for humans. It consists of alpha 1-4 and alpha 1-6 linkages. it forms spiral structures Cellulose is not digestible by humans, as it has beta 1-4 linkages. it forms a sheet like structure
What is the defining feature of a D- vs L-sugar? What is the definition of enantiomer and why do most biological compounds exist as only one enantiomer (stereoisomer)? How does the stereospecificity of biological reactions relate to the character of enzyme active sites?
Most, but not all, of the naturally occurring carbohydrates are of the D configuration. It is considered a D isomer if the bottom most chiral center hydroxyl group is on the right in a Fischer Projection, and an L isomer if it it on the Left Enantiomers are steroisomers which are mirror images of each other. Enantiomers rotate plane polarized light equally in opposite directions. A mixture of equal amounts of two enantiomers is a racemic mixture. A racemate does not rotate plane polarized light
What is the process of mutarotation, and how does this process result in alpha and beta anomers? why are two monosaccharide anomers actually different chemical compounds with differing chemical and physical properties?
Mutarotation is the equilibrium between alpha and beta anomers through the aldehyde (open chain) form. This results in alpha and beat anomers because when the compounds become cyclic their hydroxyl groups can either face up or down in its acetal form. If the hydroxyl group is facing down it is considered alpha, and if it is facing up it is beta. Their configurations give them different properties and thus make them different chemical compounds
What is an N-glycosidic bond and in what compounds are these bonds found?
N-glycosidic bonds are bonds where a nitrogen atom of an organic base (purine or pyrimidine) is covalently linked to the anomeric group of ribose or deoxyribose. An alpha linkage formes when the linkage from the anomeric carbon radiates downward, and a beta linkage occurs when the linkage from the anomeric carbon radiates upward. In disaccharides, oligosaccharides, and polysaccharides the monosaccharide units are linked to each other by glycosidic bonds
What is the defining characteristic of a reducing sugar? Why are monosaccharides reducing sugars but methylated derivatives (at the anomeric carbon) not reducing sugars? What are the reducing and the non-reducing ends of disaccharides and polysaccharides?
The defining characteristic of a reducing sugar is that it can undergo mutarotation in an aqueous medium. Monosaccharides are reducing compounds, but methylated derivatives are not because when the anomeric hydroxyl group is methylated it becomes locked in an acetal structure, and can no longer become reduced
What do the terms monosaccharide, disaccharide, oligosaccharide, and polysaccharide mean?
They refer to the number of monomer units that are linked together A monosaccharide has 1 unit Disaccharides have 2 units Oligosaccharides contain 2-10 units Polysaccharides contain many units (up to thousands)
What are the basic features of monosaccharides? What are the defining features of an aldose vs a ketose, and what are triose, tetrose, pentose, hexose, and heptose sugars?
[CH2O]n Monosaccharides are the basic building blocks from which all carbohydrate polymers are constructed. Aldoeses have an aldehyde functional group, and ketoses have a ketone fuctional group Trioses have 3 Carbon atoms Tetroses have 4 carbon atoms Pentoses have 5 carbon atoms Hexoses have 6 carbon atoms Heptoses have 7 carbon atoms
