Chirality and Isomerism in Carbohydrates

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Questions and Answers

What defines a chiral center in a molecule?

A carbon atom bonded to three identical groups

A carbon atom that is part of a ring structure

A carbon atom bonded to four different groups (correct)

A carbon atom involved in a double bond

Which statement correctly describes enantiomers?

They always have the same biological activity.

They are superimposable mirror images.

They are not superimposable mirror images. (correct)

They exist in different structural forms.

Which of the following statements about diastereomers is correct?

They cannot be classified as stereoisomers.

They are non-superimposable mirror images.

They differ at one or more chiral centers but not all. (correct)

They are identical in structure.

Why are amino acids always considered left-handed in terms of chirality?

They have one specific stereoisomer that is biologically active. Signup and view all the answers

Which factor will ensure that a carbon in a ring structure can be considered a chiral center?

Both halves of the ring emanating from it are different. Signup and view all the answers

What does the designation 'D' in a Fischer projection represent?

Dextro – right Signup and view all the answers

In a Fischer projection, how are vertical lines interpreted?

Bonds directed into the page Signup and view all the answers

How is handedness determined in monosaccharides represented in Fischer projections?

Using the highest numbered chiral center Signup and view all the answers

Which of the following is NOT a property of constitutional isomers?

Identical reactivity towards chiral environments Signup and view all the answers

Which statement is true regarding stereoisomers in relation to physical properties?

Their interaction with plane polarized light differs. Signup and view all the answers

What is the term used for enantiomers that rotate plane polarized light clockwise?

Dextrorotatory Signup and view all the answers

Which statement accurately describes the boiling and melting points of enantiomers?

They have the same boiling points and melting points. Signup and view all the answers

Which sugar formation involves the replacement of a hydroxyl group with an amino group?

Amino sugar formation Signup and view all the answers

Which cyclic form of monosaccharides resembles a 6-membered ring?

Pyranose Signup and view all the answers

In a Haworth projection, how is the D form characterized?

–CH2OH group is above the ring Signup and view all the answers

What type of acid is formed when a monosaccharide is oxidized with a weak oxidizing agent?

Aldonic acid Signup and view all the answers

Which of the following statements is true about interactions between chiral and achiral molecules?

Chiral compounds interact differently with achiral molecules. Signup and view all the answers

What is produced when the carbonyl group of a monosaccharide is reduced?

Sugar alcohols Signup and view all the answers

What is the general name for acetals formed from monosaccharides?

Glycosides Signup and view all the answers

Which type of reaction produces phosphate esters in monosaccharides?

Esterification Signup and view all the answers

What type of carbohydrate contains only a single sugar unit?

Monosaccharide Signup and view all the answers

Which carbohydrate primarily serves as an energy reserve in humans?

Glycogen Signup and view all the answers

How many monosaccharides are covalently bonded in a disaccharide?

Two Signup and view all the answers

Which term refers to carbohydrates that cannot be digested by human enzymes?

Polysaccharides Signup and view all the answers

What type of isomerism occurs when molecules have the same connectivity but different spatial arrangements?

Stereoisomerism Signup and view all the answers

What is the basic formula that represents carbohydrates?

C_n(H2O)_n Signup and view all the answers

Which of the following is a structural component of nucleic acids?

Ribose Signup and view all the answers

Which type of carbohydrate is commonly used for structural purposes in plants?

Cellulose Signup and view all the answers

In which of the following classifications is glucose categorized?

Hexose Signup and view all the answers

Which of the following sugars does NOT end in -ose?

Glyceraldehyde Signup and view all the answers

Which of the following statements is true about glucose?

It is primarily used as a source of energy. Signup and view all the answers

What is the composition of lactose?

1 glucose + 1 galactose linked by a β(1→4) linkage Signup and view all the answers

Which sugar is referred to as 'fruit sugar'?

Fructose Signup and view all the answers

Which enzyme breaks down maltose?

Maltase Signup and view all the answers

How is sucrose characterized in comparison to other disaccharides?

It is a nonreducing sugar. Signup and view all the answers

What distinguishes polysaccharides from monosaccharides?

Polysaccharides are made of many monosaccharide units. Signup and view all the answers

Which of the following is a characteristic of galactose?

It is synthesized in the mammary glands. Signup and view all the answers

Which monosaccharide is a vital component of RNA?

Ribose Signup and view all the answers

What role do polysaccharides often play in food preparation?

They function as thickening agents. Signup and view all the answers

What is the primary function of glucagon in glucose metabolism?

To increase glucose levels. Signup and view all the answers

Study Notes

Introduction to Carbohydrates

Most abundant class of bioorganic molecules on Earth.
Produced by green plants through photosynthesis, primarily as cellulose (structural) and starch (energy reserve).
Humans obtain carbohydrates mainly through dietary intake of plant materials.

Functions of Carbohydrates in Humans

Serve as a primary energy source through oxidation.
Store energy temporarily as glycogen.
Provide carbon for synthesizing other biological substances.
Form structural components of DNA (ribose, deoxyribose).
Contribute to cell membrane structure and cell recognition processes (glycolipids and glycoproteins).

Classification of Carbohydrates

Monosaccharides: Single sugar units (e.g., glucose, fructose).
Disaccharides: Two monosaccharides linked (e.g., sucrose).
Oligosaccharides: 3 to 10 monosaccharides linked.
Polysaccharides: Many monosaccharides linked (e.g., starch, cellulose).

Monosaccharides

Composed of polyhydroxyaldehydes or polyhydroxyketones.
Typically contain 3 to 7 carbon atoms.
Named with suffix –ose (exception: glyceraldehyde and dihydroxyacetone).
Classified by carbon count (triose, tetrose, pentose, hexose) and functional group (aldose vs. ketose).

Stereoisomerism

Isomers differ in spatial orientation.
Chiral centers give rise to enantiomers (nonsuperimposable mirror images).
Presence of chiral centers and structural rigidity lead to stereoisomerism.
Constitutional isomers differ in connectivity, while stereoisomers have the same connectivity.

Chirality

Defined by chiral centers where a carbon atom bonds to four distinct groups.
Chiral molecules are not superimposable on their mirror images.
Determining chiral centers requires examining molecule structure (e.g., ring systems).

Fischer Projection

A 2D representation of chiral molecule arrangements.
Chiral centers appear at the intersection of vertical and horizontal lines.
Vertical lines point into the page; horizontal lines point out.

Haworth Projection

A 2D structural notation illustrating the 3D cyclic forms of monosaccharides.
Distinguishes between D and L configurations based on the position of the –CH2OH on C5 and the anomeric carbon (C1).

Biochemically Important Monosaccharides

Glucose: Main energy source; also known as dextrose or blood sugar; regulated by insulin and glucagon.
Galactose: Component of lactose and glycoproteins; synthesized in mammary glands.
Fructose: Sweetest sugar; found in fruits and added to diets; requires less quantity for sweetness.
Ribose & Deoxyribose: Essential components of RNA and DNA, respectively.

Disaccharides

Formed from two monosaccharides via glycosidic linkages.
Maltose: Composed of two glucose; derived from starch; broken down by maltase.
Lactose: Milk sugar; composed of glucose and galactose; broken down by lactase.
Sucrose: Common table sugar composed of glucose and fructose; non-reducing sugar, broken down by sucrase.

Polysaccharides

Long chains of monosaccharides linked by glycosidic bonds, known as glycans.
Generally not sweet and do not undergo Tollen’s or Benedict’s tests.
Limited water solubility with thick colloidal properties; used as thickeners in food products.

Reactions of Monosaccharides

Oxidation: Produces different acidic sugars based on oxidizing agents; weak agents yield aldonic acid, strong yield aldaric acid.
Reduction: Converts carbonyl groups to hydroxyl groups, forming sugar alcohols (alditols).
Formation of Phosphate Esters: Hydroxyl groups react with oxyacids, crucial for carbohydrate metabolism.
Amino Sugar Formation: Replacement of hydroxyl group with an amino group, crucial for glycosaminoglycans.
Glycoside Formation: Hemiacetals react with alcohol to form glycosides, existing in α and β forms.

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Description

Explore the fascinating world of chirality and isomerism found in carbohydrates. This quiz covers concepts such as enantiomers, diastereomers, and the structural features contributing to chirality. Test your understanding of chiral centers and their implications in molecular chemistry.