Biochemistry I: Carbohydrates

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Questions and Answers

What is a key function of D-Ribose in the body?

  • Structural component of RNA (correct)
  • Energy storage in adipose tissues
  • Source of calcium in bones
  • Precursor for glucose metabolism

Which monosaccharide is known as fruit sugar?

  • D-Galactose
  • D-Glucose
  • D-Fructose (correct)
  • D-Ribose

What is the normal blood glucose level range?

  • 120-140 mg/dl
  • 60-80 mg/dl
  • 70-100 mg/dl (correct)
  • 100-130 mg/dl

How can D-Galactose be primarily obtained?

<p>Hydrolysis of lactose (B)</p> Signup and view all the answers

Which statement correctly describes 2-Deoxy D-Ribose?

<p>It forms part of DNA structure. (A)</p> Signup and view all the answers

What is D-Fructose derived from commercially?

<p>Sugar cane and sugar beets (D)</p> Signup and view all the answers

Which of the following describes the origin of D-Glucose?

<p>Mainly produced during photosynthesis (C)</p> Signup and view all the answers

What is the role of D-Galactose in the human body?

<p>Part of glycolipids and glycoproteins (D)</p> Signup and view all the answers

What type of isomerism occurs between glucose and fructose?

<p>Structural Isomerism (B)</p> Signup and view all the answers

What characteristic defines stereoisomers?

<p>Same molecular and structural formulae but differ in configuration (B)</p> Signup and view all the answers

Which carbon atom is designated as the anomeric carbon in glucose?

<p>C-1 (B)</p> Signup and view all the answers

Which type of isomerism involves D- and L- enantiomers?

<p>Stereoisomerism (B)</p> Signup and view all the answers

What is formed when a cyclic structure has an aldehyde functional group?

<p>Aldose (B)</p> Signup and view all the answers

Which of the following represents a form of structural isomerism?

<p>Glucose and fructose (B)</p> Signup and view all the answers

Which of the following statements accurately describes monosaccharides?

<p>They consist of either one polyhydroxy aldehyde or ketone unit. (B)</p> Signup and view all the answers

What distinguishes anomerism from other types of stereoisomerism?

<p>Differences in the configuration around the anomeric carbon (A)</p> Signup and view all the answers

What type of carbon atom is required for a molecule to be classified as a stereoisomer?

<p>Chiral carbon atom (A)</p> Signup and view all the answers

Which of the following monosaccharides is classified as a hexose?

<p>Galactose (A), Fructose (B)</p> Signup and view all the answers

What type of saccharide is formed when two monosaccharides join together?

<p>Dissacharides (C)</p> Signup and view all the answers

Which of the following is a correct pair of aldose and ketose monosaccharides based on their number of carbon atoms?

<p>Tetrose: Erythrose and Erythrulose (D)</p> Signup and view all the answers

Identify the correct straight chain representation of glucose.

<p>An aldehyde with six carbon atoms. (B)</p> Signup and view all the answers

What maximum number of monosaccharides can form oligosaccharides?

<p>10 (C)</p> Signup and view all the answers

How are monosaccharides primarily categorized based on their functional groups?

<p>As aldoses and ketoses. (A)</p> Signup and view all the answers

Which of the following statements regarding carbon atom number in monosaccharides is true?

<p>Monosaccharides can have a range of three to seven carbon atoms. (D)</p> Signup and view all the answers

Which of the following best describes the definition of biochemistry?

<p>The study of the structure and function of biomolecules. (D)</p> Signup and view all the answers

Which biomolecules are classified as carbohydrates?

<p>Sugars like glucose and fructose. (A)</p> Signup and view all the answers

What is the general formula for carbohydrates?

<p>(CH2O)n (B)</p> Signup and view all the answers

Which type of carbohydrate consists of 1 unit?

<p>Monosaccharides (D)</p> Signup and view all the answers

What is true about the ratio of hydrogen to oxygen in carbohydrates?

<p>H:O is 2:1. (D)</p> Signup and view all the answers

Which of the following is an example of a heteropolysaccharide?

<p>Glycoproteins (C)</p> Signup and view all the answers

Which type of saccharide contains more than 10 units?

<p>Homo-Polysaccharides (B)</p> Signup and view all the answers

Which of these carbohydrates is classified as a polysaccharide?

<p>Chitin (B)</p> Signup and view all the answers

What are D- and L- isomers primarily defined by?

<p>Their relationship as mirror images (A)</p> Signup and view all the answers

Which of the following describes a racemic mixture?

<p>A mixture of equal amounts of D- and L-enantiomers (C)</p> Signup and view all the answers

What characteristic do epimers share?

<p>They differ at exactly one carbon atom, other than the anomeric carbon (B)</p> Signup and view all the answers

What is created when glucose cyclizes in solution?

<p>An additional asymmetric center (B)</p> Signup and view all the answers

Dextrorotatory substances are characterized by what property?

<p>They rotate polarized light to the right (D)</p> Signup and view all the answers

Which of the following pairs represents epimers of glucose?

<p>Galactose and Mannose (B)</p> Signup and view all the answers

What is the result of the cyclization of glucose regarding its structural forms?

<p>Formation of anomers such as α- and β- glucopyranose (D)</p> Signup and view all the answers

The measurement of specific rotation in a polarimeter is dependent on what?

<p>The concentration of the solution and the path length (D)</p> Signup and view all the answers

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Study Notes

Biochemistry I

  • Biochemistry is the study of the structure and function of biomolecules and their chemical reactions that occur in our body.
  • Biomolecules include carbohydrates, lipids, proteins, and nucleic acids.

Carbohydrates

  • Carbohydrates are molecules composed of C, H, and O with H & O existing in the ratio of 2:1.
  • The general formula is (CH2O)n, hence the name carbohydrates.
  • Carbohydrates consist of sugars, which are polyhydroxy aldehydes (e.g., glucose, galactose, mannose) or polyhydroxy ketones (e.g., fructose).

Classification of Carbohydrates

  • Monosaccharides are single sugar units.
  • Oligosaccharides contain 2-10 sugar units.
  • Polysaccharides contain more than 10 sugar units.
  • Homo-polysaccharides are composed of the same type of monosaccharide.
  • Hetero-polysaccharides are composed of different types of monosaccharides.
  • Examples include glucose, fructose, galactose, cellulose, chitin, starch, glycogen, glycoproteins, glycolipids, and various glycosaminoglycans (GAGs) such as hyaluronic acid, dermatan sulfate, heparin, chondroitin sulfate, and keratan sulfate.

α- and β- Anomers of Glucose

  • Glucose exists as a closed-chain structure in solution.
  • Due to cyclization, an additional asymmetric center is created at C-1, called the anomeric carbon.
  • This leads to the formation of two isomers: α-glucopyranose and β-glucopyranose.

Physiologically Important Monosaccharides

  • D-Ribose: An important structural component of ribonucleic acid (RNA) and other biomolecules like NAD and ATP.
  • 2-Deoxy-D-ribose: Participates in the structure of DNA.
  • D-Glucose: The most important and abundant monosaccharide.
  • Normal blood glucose level is 70-100 mg/dl.
  • The primary source of energy for living organisms.
  • Mainly made by plants and most algae during photosynthesis.
  • Present in fruit juices and obtained by hydrolysis of starch, sucrose, and maltose.
  • D-Fructose: Absorbed directly into the blood during digestion.
    • Found in honey, fruits, and berries.
    • Obtained by hydrolysis of sucrose and inulin.
    • Commercially derived from sugar cane and sugar beets.
    • Found in semen in the pyranose form.
  • D-Galactose: C-4 epimer of glucose.
    • Found in dairy products, avocados, and sugar beets.
    • Synthesized by the body, where it forms part of glycolipids and glycoproteins in various tissues.
    • A component of antigens present on blood cells.
    • Obtained by hydrolysis of lactose.

Monosaccharides

  • Simple sugars consisting of a single polyhydroxy aldehyde (Glucose, Galactose) or ketone unit (Fructose).
  • Cannot be hydrolyzed into simpler units.

Monosaccharides According to the Number of Carbon Atoms

  • Triose: Glyceraldehyde, Dihydroxyacetone
  • Tetrose: Erythrose, Erythrulose
  • Pentose: Ribose, Xylose, Ribulose, Xylulose
  • Hexose: Glucose, Galactose, Mannose, Fructose
  • Heptose: L-glycero-D-manno-heptose, Sedoheptulose

Monosaccharide Combinations

  • Disaccharides: Formed by two monosaccharides (e.g., sucrose, lactose, maltose).
  • Oligosaccharides: Formed by 3-10 monosaccharides.
  • Polysaccharides: Formed by 11 or more monosaccharides.

Structure of Monosaccharides

  • Glucose is a critical physiological and medicinal monosaccharide.
  • Represented in:
    • Straight-chain structure.
    • Ring/Cyclic structure (cyclic Fischer/Haworth projection).

Isomerism of Monosaccharides

  • Isomers are compounds with the same molecular formula but different structures or configurations.
  • There are two main types:
    • Structural Isomerism: Different structures with the same molecular formulae. (e.g., Aldose-Ketose isomerism)
    • Stereoisomerism: Same molecular and structural formulae, but different configurations. (e.g., Enantiomerism, Epimerism, Anomerism)

Types of Stereoisomerism

  • Enantiomerism (Optical isomerism): Mirror images of each other, denoted as D- and L-isomers.
  • Epimerism: Sugars differing from each other with respect to one carbon (excluding the anomeric carbon). (e.g., Galactose and mannose are epimers of glucose).
  • Anomerism: Two isomers (anomers) formed due to cyclization, which creates a new asymmetric center at C-1 (anomeric carbon). (e.g., α-glucopyranose and β-glucopyranose).

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