Carbohydrates Overview and Classification

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Questions and Answers

What is glucosamine derived from?

Ribose with hydrogen replaced by OH group

Glucose with carboxylic group addition

Ribose with hydroxyl group replaced by hydrogen

Glucose with hydroxyl group replaced by amino group (correct)

What type of acid is produced by the oxidation of both the aldehyde and the last CH2OH group in a monosaccharide?

Glucuronic acid

Aldonic acid

Saccharic acid (correct)

Gluconic acid

Which of the following statements correctly describes sugar alcohols?

They are found only in disaccharides and polysaccharides

They typically exert a sweet taste but have no clinical applications

They can be synthesized from monosaccharides via reduction of aldehyde or ketone groups (correct)

They are formed by the oxidation of the aldehyde group

Which sugar acid is obtained by oxidizing the last carbon (C6) of glucose?

Glucuronic acid Signup and view all the answers

Which statement about mannitol's clinical application is true?

It serves as an osmotic diuretic in the treatment of brain edema Signup and view all the answers

What distinguishes the D-isomer from the L-isomer in terms of the hydroxyl (OH) group attachment?

The D-isomer has the OH group on the right. Signup and view all the answers

Which statement correctly describes anomers?

Anomers differ in the arrangement of groups around the same carbon atom. Signup and view all the answers

Which of the following statements about optical activity is correct?

The presence of an asymmetric carbon allows a compound to rotate plane polarized light. Signup and view all the answers

What is the primary characteristic of monosaccharides that gives them reducing properties?

Presence of a free aldehyde or free ketone group. Signup and view all the answers

In the context of the Haworth formula, what configuration characterizes the α-form of an anomer?

The OH group on the anomeric carbon is below the ring. Signup and view all the answers

Which of the following monosaccharides is classified as a ketotriose?

Dihydroxyacetone Signup and view all the answers

Which of the following is an example of an aldohexose?

Mannose Signup and view all the answers

What type of isomerism involves a change in the position of the hydroxyl group around an epimeric carbon?

Epimerism Signup and view all the answers

In terms of stereoisomers, which statement is true about D- and L- isomers?

They are mirror images of each other. Signup and view all the answers

Which carbon count corresponds with a pentose sugar?

5 Signup and view all the answers

Which statement accurately defines carbohydrates?

Carbohydrates are polyhydroxy-aldehydes or polyhydroxy ketones. Signup and view all the answers

Which carbohydrate type consists of a single monomer unit?

Monosaccharides Signup and view all the answers

Which monosaccharide has the aldehyde group configuration necessitating it to be classified as an aldo-sugar?

Ribose Signup and view all the answers

What is the defining feature of a ketose monosaccharide?

Presence of a ketone group Signup and view all the answers

What is a primary role of carbohydrates in the human body?

Serving as the main energy source. Signup and view all the answers

Which of the following pairs represent epimers?

Glucose and Galactose Signup and view all the answers

Which of the following is not classified as a monosaccharide?

Sucrose Signup and view all the answers

What distinguishes oligosaccharides from polysaccharides?

Oligosaccharides consist of 3 to 10 monosaccharide units. Signup and view all the answers

Which of the following derivatives of monosaccharides is involved in lubrication of joints?

Glycoproteins Signup and view all the answers

Which structure primarily categorizes aldehyde sugars?

Aldoses Signup and view all the answers

Which of the following is a characteristic of polysaccharides?

They are formed from more than 10 monosaccharide units. Signup and view all the answers

Study Notes

Carbohydrate Definition

Carbohydrates are polyhydroxy aldehydes, polyhydroxy ketones, or derivatives of these.
They can also be defined as aldehyde or ketone derivatives of polyhydroxy alcohol.
They are organic compounds composed only of carbon, hydrogen, and oxygen.
They are also called saccharides.
Examples are polyhydroxy aldehyde (PHA) and polyhydroxy ketones (PHK).

Importance

Main energy source
Serve a structural and protective role (Insoluble carbohydrate polymers “Mucopolysaccherides” )
Lubrication of joints and tendons (Glycoproteins & Proteoglycans).
Adhesion between cells and recognition.
Glycoconjugates (Glycoproteins or Glycolipids).
Participate in (Pentose Sugars):
- Nucleic Acids (DNA, RNA)
- Coenzymes (NAD, FAD)
- Regulatory molecules (cAMP, cGMP)
- High energy compounds (ATP, GTP).

Carbohydrate Classification

According to the number of sugar units:
- Monosaccharides: Cannot be hydrolyzed to simpler forms, consist of a single (PHA) or (PHK).
- Disaccharides: Formed from two monosaccharide units, linked together by a glycosidic bond.
- Oligosaccharides: Carbohydrates formed from 3 to 10 monosaccharide units.
- Polysaccharides: Polymers of monosaccharide units > 10. They may be linear (e.g., cellulose) or branched (e.g., glycogen).

Classification of Monosaccharides

Classified according to the presence of an aldehyde or ketone group, the number of carbon atoms, and both:
- Aldoses: Aldehyde group (-CHO)
- Ketoses: Ketone group (C=O)
- Trioses (3C)
- Tetroses (4C)
- Pentoses (5C)
- Hexoses (6C)
- Examples:
  - Dihydroxyacetone - ketotriose
  - Glyceraldhyde - aldotriose

Examples of Monosaccharides

Trioses (C3): Glyceraldehyde and Dihydroxyacetone
Tetroses (C4): Erythrose
Pentoses (C5): Ribose
Hexoses (C6): Glucose, galactose, mannose, and fructose

Characters of Monosaccharides

Physical characters:
- Stereoisomers: Compounds that have the same general formula (same number and type of atom), but with different arrangements of atoms in space.
- Examples of stereoisomers:
  - Aldo-keto isomers
  - Epimers: Change in the position of OH around the epimeric carbon.
  - Enantiomers (or mirror image isomer) (D & L Isomers): The best example is Glyceraldehydes which is present in 2 isomers: D- and L- forms. The L-isomer has an OH attached to the left of the asymmetric C atom, while the D-isomer has it on the right. N.B.: The D form is the physiologically predominant form.
  - Anomers (a & b): If the OH group of the anomeric carbon is on the right (down), the anomer is called the α-form. If the OH of the anomeric carbon is on the left (up), it is the β-form.

Asymmetric Carbon Atom

A carbon atom is considered asymmetric when it is attached to four different chemical groups.

Optical Activity

Optical activity is the ability of a compound to rotate plane-polarized light either to the right [dextrorotatory or d (+)] or to the left [levorotatory or l (-)].
All monosaccharides are optically active except dihydroxyacetone (as it does not contain an asymmetric carbon atom).

Chemical Properties of Monosaccharides

Reducing character:
- Due to the presence of a free aldehyde or free ketone group, all monosaccharides have reducing properties.
Monosaccharide derivatives:
- OH is replaced by an amino group:
  - Glucose → glucosamine
- OH is replaced by H:
  - Ribose → 2-deoxyribose
    - RNA → DNA
- Sugar acids: Sugars that contain a carboxylic group (COOH) by oxidation of a monosaccharide.
  - Aldonic acid: Oxidation of aldehyde C1
  - Uronic acid: Oxidation of the last C6 CH2OH
  - Saccharic acid: Oxidation of both the aldehyde and the last CH2OH
  - Examples:
    - Gluconic acid
    - Glucuronic acid
    - Glucaric acid
- Sugar Alcohol (Reduction):
  - The aldehyde or ketone group in monosaccharides can be reduced to the corresponding alcohol.
  - CHO or C=O → CH2OH.
  - Examples:
    - Ribose
    - Glucose
    - Mannose

Clinical Applications of Monosaccharide Derivatives

Sorbitol → Artificial sweeteners (to reduce weight)
Mannitol → Reduces acutely raised intracranial pressure by its osmotic effect (treatment of brain edema) and as an osmotic diuretic.

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Description

This quiz explores the fundamental definitions, importance, and classification of carbohydrates. Topics include their chemical structure, functions in biological systems, and their roles in cellular processes. Test your understanding of these essential organic compounds.