Chapter 1 - Stereoisomers and Carbohhdrates

Question 1

Isomers

1. What is a isomer?
2. What is a structural isomer?
3. What are stereoisomers?

Answer 1

1. Isomers: Different chemical compounds with identical molecular formulas.
2. Structural Isomers: Identical molecular formula but different either in the position of a certain substitute than or in how the same atoms are combined into different functional groups.
3. Stereoisomers: Both the order in which atoms are joined and the functional groups are identical; all that differs is the three-dimensional spatial arrangement of the atoms.

Question 2

Structural Isomers

1. What are Positional Isomers?
2. What are Functional-group Isomers?

Answer 2

1. Positional Isomers: Presence of an atom or chemical group at different positions on the carbohydrate.
2. Functional-group Isomers: Same molecular formula but different functional groups.

Question 3

Polarized light and optical activity

1. What is Polarized light?
2. What do Optically active substances do?
3. What is optical activity measured by?
4. What are the two substances involved in optical activity?

Answer 3

1. Polarized light: Waves that vibrate in a single plane
2. Optically active substances: Rotate the plane of vibration of polarized light.
3. Optical activity is measured by specific rotation
4. Dextrorotatory (+) and Levorotatory (-)

Question 4

Polarized light and optical activity

1. What is a chiral center?
2. What is a chiral molecule?
3. What are Enantiomers?
4. What does a racemic mixture contain?
5. How many enantiomers does one chiral center have?
6. According to the Van’t Hoff’a rule, what is the formula for the maximum number of enantiomers?

Answer 4

1. Chiral Center: Atom in a molecule that has 4 different groups attached.
2. Chiral molecule: Molecule not identical with its mirror image (not superimposable on).
3. Enantioners: Molecules that are non-superimposable mirror images of each other; identical properties, but rotate plane-polarized light the same number of degrees in opposite directions.
4. A racemic mixture contains (+) and (-) in equal amounts
5. One chiral center = 2 enantiomers
6. Maximum number of enantiomers is 2n

Question 5

Geometric Isomerism (cis-trans)

1. What are Geometric Isomers?
2. What are Diastereoisomers?

Answer 5

1. Geometric Isomers: Different configurations because of the presence of a rigid structure in the molecule (ex: double bond)
2. Diastereoisomers: Stereoisomers that are not enantiomers.

Question 6

Types of Carbohydrates

1. What are carbohydrates synthesized by?
2. What is Glucose?
3. How much kcal of energy does a gram of digested carbohydrate give?
4. What are type of carbohydrates are best for diet?
5. What does the USDA recommend for percent range of daily calories?

Answer 6

1. Carbohydrates are synthesized by photosynthesis in plants. (Grains, cereals, bread, sugar cane)
2. Glucose is a major energy source.
3. A gram of digested carbohydrate gives about 4 kcal of energy.
4. Complex carbohydrates are best for diet
5. The USDA recommends about 45-65% daily calories from carbohydrates.

Question 7

Basic Carbohydrates

1. What is a Monosaccharide? What are two example of Monosaccharides?
2. What is a Disaccharide? What are two examples of Disaccharides? What is a linkage called?
3. What are oligosaccharides?
4. What are polysaccharides? What are 3 examples of polysaccharides?

Answer 7

1. A Monosaccharide is one sugar (saccharide) molecule. Ex: Glucose, fructose.
2. Disaccharides are two monosaccharides linked together. The linkage is called a glycosidic bond (sucrose, lactose)
3. Oligosaccharides are three to ten monosaccharides linked by glycosidic bonds
4. Polysaccharides are chains of linked monosaccharide units. Ex: Starch, glycogen, and cellulose

Question 8

Monosaccharides

1. What 3 things are monosaccharides composed of? What is the basic formula?
2. What two groups are considered chemical modifications to monosaccharides?
3. How are the functional groups of monosaccharides named?
4. How do you name molecules based on number of carbons in the main skeleton (3-6)?

Answer 8

1. Carbon, Hydrogen, and Oxygen. Basic formula = (CH2O)n (n = Any integer 3 - 7)
2. Many monosaccharides contain chemical modifications such as amino groups and phosphate groups.
3. Functional group for a ketone carbonyl is named Ketose. Aldehyde carbonyl is named Aldose.
4. • 3 carbons: Triose
     - 4 carbons: Tetrose
     - 5 carbons: Pentose
     - 6 carbons: Hexose

Question 9

Stereoisomers and Stereochemistry

1. What 2 prefixes in a monosaccharide name helps identify each isomeric form? How do these Isomers differ?
2. What is stereochemistry?
3. What are stereoisomers D and L glyceraldehyde considered?

Answer 9

1. Prefixes D and L. These isomers differ in the spatial arrangement of atoms and are stereoisomers.
2. Stereochemistry is the study of different spatial arrangements of atoms.
3. D and L glyceraldehyde are nonsuperimposable mirror image molecules and are called Enantiomers (a subset of stereoisomers)

Question 10

Chirality

1. What is a Chiral carbon atom?
2. What can a molecule containing a chiral carbon exist as?
3. What is chirality in glyceraldehyde (the simplest carbohydrates) conveyed by?
4. How many chiral carbons do larger biological molecule often have?

Answer 10

1. A carbon atom that has four different groups bonded to it:
2. Any molecule containing a chiral carbon can exist as a pair of Enantiomers.
3. Chirality in glyceraldehyde is conveyed by a chiral carbon.
4. Larger biological molecules often have more than on chiral carbon.

Question 11

Chirality of Glyceraldehyde

1. How many Enantiomers does glyceraldehyde have?
2. On what part of the stereocenter is the OH located on the D and L Isomers?

Answer 11

1. Glyceraldehyde has a chiral carbon and thus has two Enantiomers.
2. The D isomer has the OH on the stereocenter to the right. Th L isomer has the OH on the stereo center to the left.

Question 12

Optical Activity

1. What are Enantiomers also known as?
2. What do Enantiomers interact with and why? What is it known as?
3. What does optical activity do?
4. With what device is optical activity measured by?

Answer 12

1. Enantiomers are also called optical Isomers.
2. Enantiomers interact with plane-polarized light to rotate the plane of the light in opposite directions. This is called optical activity.
3. Optical activity distinguishes the Isomers.
4. Optical activity is measured with a polarimeter

Question 13

Polarimeter measures rotation of Plane-polarized Light

1. How does normal light vibrate?
2. What happens when light passes through a polarizing filter (Polaroid sunglasses)
3. What does a polarimeter allow the determination of? What does it measure?

Answer 13

1. Normal light vibrates in an infinite number of directions perpendicular to the direction of travel.
2. Only light vibrating in one plane reaches the other side of the filter
3. A polarimeter allows the determination of the specific rotation of a compound. It measures its ability to rotate plane-polarized light.

Question 14

The Relationship between molecular structure and optical activity

1. Which Enantiomers always rotates light in a clockwise direction?
2. Which Enantiomers always rotates light in a counterclockwise direction?
3. Under identical conditions, how do Enantiomers always rotate light?

Answer 14

1. Dextrorotatory isomer rotates light in a (+) clockwise direction.
2. Levorotatory isomer rotates light in a (-) counterclockwise direction.
3. Under identical conditions, the Enantiomers always rotate light to exactly the same degree, but in opposite direction.

Question 15

Fischer Projection Formulas

1. How do Fischer projections represent bonds?

Answer 15

1. Fisher projections uses lines crossing through a chiral carbon to represent bonds. Projecting out of the page (horizontal lines) and into the page (vertical lines).

Question 16

Compounds with Chiral Carbons

1. What is a racemic mixture?
2. What are diastereomers?
3. What is a Mesocompound?

Answer 16

1. A mixture of equal amounts of a pair of Enantiomers. Racemate; Optically inactive.
2. A pair of stereoisomers having two or more chiral centers and that are Enantiomers.
3. A compound with two or more chiral carbon atoms and an internal plane of symmetry that causes it to be Optically inactive.

Question 17

The D and L System

1. How are monosaccharides drawn?
2. Where is the most oxidized carbon located?
3. How are carbons are numbered?
4. If the chiral carbon with the highest number has the OH to the right, which isomer is the sugar?
5. If the chiral carbon with the highest number has the OH to the left, which isomer is the sugar?
6. What form are most common sugars in?

Answer 17

1. Monosaccharides are drawn in Fischer projections.
2. Most oxidized is located Closest to the top.
3. The carbons are numbered from the top.
4. If the chiral carbon with the highest number has the OH to the right, the sugar is a D
5. If the chiral carbon with the highest number has the OH to the right, the sugar is a L
6. Most common sugars are in the D form.

Question 18

Biological Monosaccharides

1. What is the most important sugar in the body? Where is it found? What are two common names? How is its concentration regulated?
2. How does glucose exist under physiological conditions? What two things are formed and how do they differ?
3. What is the molecular formula of an aldohexose?

Answer 18

1. Glucose. Glucose is found in many foods. Two common names are dextrose and blood sugar. It’s concentration in the blood is regulated by insulin and glucagon.
2. Under physiological conditions, glucose exists in a cyclic hemiacetal form where the C-5 hydroxyl reacts with the C-1 carbonyl group. Two isomers are formed which differ in the location of the OH on the acetal carbon, C-1
3. An aldohexose with molecular formula C6H12O6.

Question 19

Fructose

1. What are two alternative names for fructose?
2. What 3 things is fructose found in?
3. What is fructose known as in comparison to the other sugars?
4. What is the molecular name for fructose?

Answer 19

1. Levulose and fruit sugar.
2. Honey, corn syrup, and fruits
3. The sweetest sugar
4. Ketohexose (6 carbons)

Question 20

Galactose

1. What is galactose the principal sugar in?
2. What is Beta-D-galactosamine
3. How do glucose and galactose differ?

Answer 20

1. Galactose is the principal sugar in mammalian milk.
2. Beta-D-Galactosamine is a component of blood group antigens
3. Glucose and galactose differ only in the orientation of one hydroxyl group (only on the 4th carbon).
   - Beta-D-Galactose OH group is upwards, Beta-D-Glucose OH group is downwards.

Question 21

Ribose and Deoxyribose, Five-Carbon Sugars

1. What are both Ribose and Deoxyribose? What form do they exist in?
2. What is the official name of these compounds?
3. What is the only difference between Ribose and Deoxyribose?

Answer 21

1. Ribose and Deoxyribose are components of many biologically important molecules, that exist mainly in cyclic form.
2. Aldopentose.
3. The only difference between the two is the absence of the -OH group on Carbon 2 of Beta-D-2-deoxyribose.

Question 22

Benedict’s Reagent

1. What does Benedict’s reagent oxidize?
2. What type of solution is Benedict’s Reagent?
3. Why does the blue color of the reagent fade?
4. What can this test measure?

Answer 22

1. The aldehyde groups of aldoses are oxidized by Benedict’s reagent.
2. An alkaline Cu2+ (copper) solution.
3. The blue color of the reagent fades as the reaction occurs reducing Cu2+ to Cu+ with a red-orange precipitate forming as Cu2O results.
4. This test can measure glucose in urine.

Question 23

Reducing Sugars

1. What are the reducing sugars?
2. What can ketoses isomerize to and how?

Answer 23

1. All monosaccharides and the disaccharides EXCEPT sucrose are reducing sugars.
2. Ketoses can isomerize to aldoses via enediol reaction.

Question 24

Biologically Important Disaccharides
1. What is formed when an anoneric -OH reacts with another -OH on an alcohol or sugar? What is then lost and what is formed?

Answer 24

1. A glycosidic bond. Water is lost to form an acetal.

Question 25

Maltose 1. How is maltose formed? 2. What type of sugar is maltose? 3. Maltose is formed as an intermediate in what process? 4. Why is maltose a reducing sugar?

Answer 25

1. Maltose is formed by linking two D-glucose molecules to give a 1,4 glycosidic linkage. 2. Maltose is malt sugar. 3. Maltose is formed as an intermediate in starch hydrolysis. 4. Reducing sugar due to the hemiacetal hydroxyl.

Question 26

Lactose and Galactosemia 1. How is Lactose formed? 2. What type of sugar is lactose? 3. What must happen in order to use lactose as an energy source? 4. How is lactose intolerance formed? 5. How does a person form the genetic disease Galactosemia? 6. What happens to people who lack the enzyme lactase?

Answer 26

1. Lactose is formed by joining Beta-D-galactose to D-glucose to give a B-1,4-glycoside. 2. Lactose is milk sugar. 3. For use as an energy source, lactose must be hydrolyzed to galactose must be converted to a phosphorylated glucose molecule. 4. Lactose intolerance results from lack of lactase to hydrolyze the glycosidic link of lactose. 5. When enzymes necessary for the galactose to glucose conversion are absent, the genetic disease Galactosemia results. 6. People who lack the enzyme lactase (~20%) are unable to digest lactose and have the condition lactose intolerance.

Question 27

Sucrose 1. How is sucrose formed? 2. How is nonreducing determined? What is the glycosidic "O" part of? 3. what is the solubility of sucrose? What type of carbohydrate is it? 4. Can sucrose be synthesized by animals? 5. What are 3 names for sucrose? 6. What health defects is sucrose linked to?

Answer 27

1. Sucrose is formed by linking â-D-glucose with Beta-D-fructose to give a 1,2 glycosidic linkage 2. Nonreducing is determined by a negative reaction in Benedict test. The glycosidic O is part of an acetal. 3. Sucrose is water soluble. It is an important plant carbohydrate - easily transported in plant circulatory system. 4. Cannot be synthesized by animals. 5. Table sugar, cane sugar, beet sugar. 6. Sucrose is linked to dental cavities

Question 28

Polysaccharides - Starch 1. What are starches? 2. What are starches polymers of? 3. What is the end product if the links are only 1,4 links? What is the configuration of the end product? What percentage of the end product consists in starch? 4. What is the end product if the links are both 1,4 AND 1,6? What is the configuration of this end product?

Answer 28

1. Stashes are storage forms of glucose found in plants. 2. They are polymers of â linked glucose 3. Only 1,4 links means the polymer is linear = amylose. Amylose usually assumes a helical configuration with six glucose units per turn. Comprises about 80% of plant starch. 4. Both 1,4 and 1,6 links means the polymer structure is branched = amylopectin. Highly branched with branches of approximately 20-25 glucose units.

Question 29

Glycogen 1. What is glycogen? 2. What is the configuration of glycogen? 3. Where is glycogen stored?

Answer 29

1. The major glucose storage carbohydrate in animals. 2. A highly branched chain polymer like amylopectin. Has more frequent branching - 10 monomers. Glycogen (AND Amylopectin)is an â(1,4) chain with â(1-6) branches. 3. Glycogen is stored in the liver and muscle cells.

Question 30

Cellulose 1. What is cellulose? 2. What is the configuration of cellulose? 3. What is the name of the repeating disaccharide of cellulose? 4. Why can't animals hydrolyze cellulose? 5. How is cellulose digested?

Answer 30

1. Cellulose is the major structural polymer in plants 2. It is a linear homopolymer composed of Beta-D-glucose units linked Beta-1,4 3. Beta-cellobiose 4. Animals lack the enzymes necessary to hydrolyze cellulose. 5. The bacteria in ruminants (i.e cows) can digest cellulose so that they can eat grass, etc.