Carbohydrate Chemistry Quiz

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Questions and Answers

What is the structural characteristic of reducing sugars that allows them to reduce silver ions?

Reducing sugars possess a hemiacetal structure, which includes a free aldehyde or ketone group.

Describe the significance of phosphate ester formation in monosaccharides.

Phosphate ester formation involves the hydroxyl groups of a monosaccharide, leading to stable derivatives that play vital roles in metabolic processes.

Identify the glycosidic bond type present in maltose and its component monosaccharides.

Maltose contains an a-1,4-glycosidic bond formed between two glucose units.

What are the main differences between sucrose and lactose in terms of their structure and source?

Sucrose is composed of glucose and fructose with an a-anomeric bond, while lactose consists of glucose and ẞ-galactose, primarily found in milk. Signup and view all the answers

Explain how invert sugar's optical activity differs from that of regular sucrose.

Invert sugar has a greater optical rotation than regular sucrose due to the hydrolysis of sucrose into glucose and fructose, producing new chiral centers. Signup and view all the answers

What is the general formula for monosaccharides and what does it signify?

The general formula for monosaccharides is $C_nH_{2n}O_n$, which signifies that monosaccharides consist of carbon, hydrogen, and oxygen in a specific ratio. Signup and view all the answers

Distinguish between aldohexoses and ketohexoses with examples.

Aldohexoses contain an aldehyde group, such as D-(+)-Glucose, while ketohexoses contain a ketone group, like D-(-)-Fructose. Signup and view all the answers

Explain the difference between a cyclic hemiacetal and a cyclic hemiketal.

A cyclic hemiacetal forms from the reaction of an aldehyde with an alcohol, while a cyclic hemiketal forms from the reaction of a ketone with an alcohol. Signup and view all the answers

Identify the major biochemical function of glucose in the human body.

Glucose serves as the primary energy source for cells in the human body. Signup and view all the answers

What are oligosaccharides, and how do they function in biological systems?

Oligosaccharides are short chains of monosaccharides linked together, functioning primarily in cell recognition and signaling processes. Signup and view all the answers

List two examples of pentoses and describe their significance.

D-Ribose and D-Xylulose are examples of pentoses, and they are significant as components of nucleotides and important in metabolic pathways. Signup and view all the answers

What is galactose, and how is it related to lactose?

Galactose is a monosaccharide that combines with glucose to form lactose, the sugar found in milk. Signup and view all the answers

How do disaccharides differ from monosaccharides in terms of structure?

Disaccharides are composed of two monosaccharide units joined together by a glycosidic bond, while monosaccharides are single sugar units. Signup and view all the answers

What is the primary structural difference between homopolysaccharides and heteropolysaccharides?

Homopolysaccharides consist of only one type of monosaccharide, while heteropolysaccharides are made up of different types of monosaccharides. Signup and view all the answers

Identify two examples of storage polysaccharides and briefly describe their roles.

Starch serves as a caloric distributor in the diet, while glycogen acts as the storage form of glucose in animals. Signup and view all the answers

In what way do oligosaccharides, like those found in onions, contribute to human health?

Oligosaccharides can promote the growth of beneficial intestinal bacteria, improving gut health and digestion. Signup and view all the answers

What carbohydrate complex is known for its role in cell recognition, and what are its two main types?

Glycolipids and glycoproteins are carbohydrate complexes important for cell recognition. Signup and view all the answers

Describe how cellulose is relevant to human nutrition despite being indigestible.

Cellulose serves as dietary fiber, which aids in digestive health by promoting regular bowel movements. Signup and view all the answers

What is the significance of amylopectin in the structure of starch?

Amylopectin is a branched chain polymer that constitutes 80-85% of starch, allowing for rapid energy release. Signup and view all the answers

Explain the role of heparin in the circulatory system.

Heparin acts as an anticoagulant, helping to prevent blood clots during procedures such as open heart surgery. Signup and view all the answers

What are the two main functions of chitin in nature?

Chitin provides structural support to organisms such as fungi and arthropods, and helps give rigidity to their exoskeletons. Signup and view all the answers

Study Notes

Carbohydrates - Structure and Function

Carbohydrates are the most abundant class of bioorganic molecules on Earth, produced by photosynthetic activity of green plants.
They are also called saccharides, due to the sweet taste of many carbohydrates.
Carbohydrates store chemical energy (glucose, starch, glycogen). A gram of digested carbohydrate yields approximately 4 kcal of energy.
Complex carbohydrates are good for the diet, and provide supportive structural components in plants and some animals (ex: cellulose, chitin).
Carbohydrate molecules also form part of the structural framework of DNA and RNA.
Carbohydrate "markers" on cell surfaces play a role in cell-cell recognition processes.

Classification of Carbohydrates

Simpler formula CnH2nOn or Cn(H2O)n (hydrates of C).
Classified based on products of acid hydrolysis:
- Monosaccharides: simple sugars containing a single polyhydroxy aldehyde or polyhydroxy ketone unit. Pure forms are water-soluble, white, crystalline solids.
- Disaccharides: contain 2 monosaccharide units covalently bonded; crystalline and water-soluble substances. Upon hydrolysis, they produce monosaccharides.
Oligosaccharides: contain 2-10 monosaccharide units.
Polysaccharides: consist of tens of thousands of monosaccharide units covalently bonded.
- Homopolysaccharides: polymers of a single monosaccharide (e.g., glycogen, cellulose, starch).
- Heteropolysaccharides: contain more than one kind of monosaccharide (e.g., hyaluronic acid, heparin, chondroitin sulfate).
Derived carbohydrates: sugars that have undergone some reactions converting them into other products (e.g., sugar acids, sugar alcohols, deoxysugars, and sugar amines).

Classification of Monosaccharides

Classified based on the number of carbon atoms (triose, tetrose, pentose, hexose, heptose, octose).
May be either aldoses (contains aldehyde group) or ketoses (contains a ketone group).

Biochemically Important Monosaccharides

Glucose: most abundant and important, found in grapefruit, dextrose, blood sugar (70-100 mg/100 mL of blood).
Fructose: ketohexose, sweetest sugar, found in many fruits and honey.
Galactose: component of milk sugar; also called brain sugar.
Ribose: aldopentose; constituent of the heart muscle and an intermediate in metabolic pathways, important in RNA and DNA.

Cyclic Forms of Monosaccharides

Hemiacetals/Hemiketals: dominant form of monosaccharides.
- Formed by reaction of aldehyde/ketone and alcohol groups within the molecule.
- Hemiacetals form five and six membered rings.
- Example: a-D-glucose and β-D-glucose are two cyclic hemiacetal forms of D-glucose that are readily interconvertible in aqueous solution. This interconversion is known as mutarotation.
Anomers: cyclic monosaccharides that differ only in the position of substituents on the anomeric carbon.

Reactions of Monosaccharides

Oxidation: monosaccharides can be oxidized to acidic sugars using different oxidizing agents.
- Weak oxidizing agents oxidize only the aldehyde end forming aldonic acid.
- Strong oxidizing agents can oxidize both ends forming an aldaric acid.
Reduction: carbonyl group in a monosaccharide is reduced to a hydroxyl group using hydrogen as the reducing agent. The resultant product is called sugar alcohol.
Phosphate ester formation: hydroxyl groups react with inorganic oxyacids to form inorganic esters.
Amino sugar formation: one hydroxyl group of a monosaccharide is replaced by an amino group.
Glycoside formation: Cyclic forms react with alcohols to form acetals, called glycosides.

Storage Polysaccharides

Starch: chief caloric distributor in the diet; reserve carbohydrate for plants. Composed of amylose (water-soluble, linear) and amylopectin (water-insoluble, branched).
Glycogen: animal starch; stored in liver and muscle cells; similar to amylopectin but has a lower molecular weight and a more highly branched structure.

Structural Polysaccharides

Cellulose: fibrous carbohydrate found in all plants; structural component of the cell wall; a-1,4-glucosidic bonds are present making it difficult to hydrolyze.
Chitin: similar to cellulose, but its monomer is N-acetyl-glucosamine; forms the exoskeletons of crabs, lobsters, shrimp, insects, and other arthropods.
Carageenan: sulphated polysaccharide extracted from red algae; used in the food industry to enhance texture.

Acidic Polysaccharides

Hyaluronic acid: repeating unit consists of β-D-glucuronic acid and N-acetyl-D-glucosamine, acting as a lubricant for joints.
Heparin: consists of repeating units of D-glucuronic acid and D-glucosamine; anticoagulant.
Chondroitin sulfate: consisting of repeating units of D-glucuronic acid-D-glucosamine sulfate; structural role in cartilage, bone, and cornea of the eye.
Alginic acid: extracted from seaweed; consists of repeating units of β-1-4 bonded mannuronic and α-1-4 bonded L-guluronic acid.

Dietary Considerations and Carbohydrates

Glycemic Index: rating scale for foods based on how quickly the food is converted to glucose in the body. Lower GI values are more desirable.
Unavailable Carbohydrates: dietary fiber; not hydrolyzed by digestive enzymes, but aids in the formation of bulk in the intestines, allowing for easier removal of fecal matter.

Glycolipids and Glycoproteins

Glycolipids: lipid molecule with one or more carbohydrate covalently bonded to it.
Glycoproteins: protein molecule with one or more carbohydrate covalently bonded to it.
These are important in cellular functions such as cell-cell recognition, cell adhesion and cellular communication.

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Description

This quiz covers key concepts in carbohydrate chemistry, focusing on reducing sugars, glycosidic bonds, and the differences between sucrose and lactose. Additionally, it explores the significance of phosphate ester formation in monosaccharides and the unique optical activity of invert sugar. Test your knowledge on the structural characteristics and reactivity of these important biomolecules.