Carbohydrates Overview

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Questions and Answers

What is the empirical formula for many simpler carbohydrates?

(CH2O)n, n ≥ 3 (correct)

(CH2O)n, n ≥ 2

(CH2O)n, n ≥ 4

(C6H12O6)n, n ≥ 3

Which carbohydrate serves as a major metabolic fuel in mammals?

Galactose

Lactose

Glucose (correct)

Fructose

Which of the following is a function of carbohydrates in organisms?

Oxygen transport

DNA replication

Hormone production

Energy storage (correct)

What class of carbohydrates cannot be hydrolyzed into simpler carbohydrates?

Monosaccharides Signup and view all the answers

Which of the following diseases is associated with carbohydrate metabolism?

Diabetes mellitus Signup and view all the answers

What indicates the rotation direction of plane-polarized light when it passes through an optical isomer?

The chirality of the isomer Signup and view all the answers

Which type of ring structure is formed by aldoses?

Hemiacetal Signup and view all the answers

What is true about epimers in relation to glucose?

They are isomers that differ only at one specific carbon atom. Signup and view all the answers

Which of the following sugars is classified as a reducing sugar?

Galactose Signup and view all the answers

Which metabolic pathways involve derivatives of trioses and pentoses?

Glycolysis and pentose phosphate pathway Signup and view all the answers

What is the difference between aldoses and ketoses?

Aldoses have an aldehyde group, while ketoses have a ketone group. Signup and view all the answers

Which of the following is a characteristic of polysaccharides?

They consist of more than 10 monosaccharide units. Signup and view all the answers

What determines whether a sugar is classified as D- or L- isomer?

The orientation of the -OH group on the bottom-most chiral carbon in the Fischer projection. Signup and view all the answers

Which of the following statements about isomers is correct?

Optical isomers can rotate plane-polarized light in different directions. Signup and view all the answers

Which statement best describes the bonding in oligosaccharides?

They consist of 3 to 10 monosaccharides linked by glycosidic bonds. Signup and view all the answers

What type of glycoside is formed when the hemiacetal portion is glucose?

Glucoside Signup and view all the answers

Which of the following is an example of a deoxy sugar?

Deoxyribose Signup and view all the answers

What are cardiac glycosides primarily known for in medicinal use?

Strengthening heart contractility Signup and view all the answers

Which disaccharide is composed of glucose and fructose?

Sucrose Signup and view all the answers

Amino sugars such as D-glucosamine are primarily found in which of the following?

Glycoproteins Signup and view all the answers

Signup and view all the answers

Study Notes

Carbohydrates

Carbohydrates (saccharides) are the most abundant organic molecules in nature, widely distributed in plants and animals.
They have vital structural and metabolic roles, providing a significant portion of dietary calories for many organisms, acting as energy storage in the body, and as cell membrane components for intercellular communication.
The empirical formula for many simpler carbohydrates is (CH₂O)ₙ, where n ≥ 3.

Glucose

Glucose is the most crucial carbohydrate.
Dietary carbohydrates are absorbed into the bloodstream as glucose.
Other sugars are converted to glucose in the liver.
Glucose is the primary metabolic fuel for mammals.
It's a precursor for the synthesis of all other carbohydrates in the body, including glycogen for storage, ribose and deoxyribose in nucleic acids (DNA and RNA), galactose for lactose synthesis in milk, and components of glycoproteins and proteoglycans.

Carbohydrate Diseases

Diseases associated with carbohydrate metabolism include diabetes mellitus, galactosemia, glycogen storage diseases, and lactose intolerance.
The glycome represents the entire collection of sugars produced by an organism.

Classification of Carbohydrates

Monosaccharides: Classified by the number of carbon atoms (trioses, tetroses, pentoses, hexoses, heptoses) and whether they have an aldehyde or keto group.
Disaccharides: Formed from the condensation of two monosaccharides (e.g., lactose, maltose, sucrose, trehalose).
Oligosaccharides: Formed from the condensation of 3 to 10 monosaccharides.
Polysaccharides: Formed from the condensation of more than 10 monosaccharides. Examples are glycogen (branched glucose polymer), starches (which can be linear or branched polymers), dextrins, cellulose (plant cell walls), inulin (plant storage carbohydrate), chitin (structural component), and pectin (found in fruits).

Representing the Structure of D-Glucose

Fischer Projection: Straight-chain form.
Haworth Projection: α-D-glucose.
Chair Form: α-D-glucose.

Isomerism of Sugars

D- and L-isomerism: Isomers with the same chemical formula but different structures.
Optical Isomerism: (d(+)/l(-)) Molecules that rotate plane-polarized light—either to the right (dextrorotatory—(+)) or left (levorotatory—(-)).
Pyranose and Furanose Ring Structures: Ring structures of monosaccharides similar to those of pyran (six-membered ring) or furan (five-membered ring).
Alpha- and Beta-Anomers: Variations in configuration of the -OH and -H groups on the anomeric carbon atoms.
Epimers: Isomers differing in the configuration around one carbon atom. Examples: glucose-mannose (epimerization at carbon 2), glucose-galactose (epimerization at carbon 4).
Aldose-Ketose Isomerism: Isomers that differ in the presence of an aldehyde or ketone group.

Reducing Sugars

Reducing sugars are chemicals that are also reducing substances that are involved in a chemical reaction.
This reaction enables the basis for a simple chemical test for glucose in poorly managed diabetes—by reduction of an alkaline copper solution. Examples: Glucose, galactose, and mannose.

Glycosides

Glycosides are comprised of hydroxyl groups, which include different compounds.
If the hemiacetal portion of this compound is glucose, the outcome is a glucoside; otherwise, it's a galactoside or another variant. An N-glycosidic bond is generated if the second group in the compound is an amine. An example of this type of bond is the bond between adenine and ribose in ATP (adenosine triphosphate) nucleotides.

Glycoconjugates

Glycoconjugates are important in medicine due to their effects on the heart.
Cardiac glycosides contain steroids (aglycones). Examples: Digoxin and Ouabain, which inhibit the Na⁺-K⁺-ATPase of cell membranes, and antibiotics like streptomycin.

Deoxy Sugars

Deoxy sugars are those wherein a hydroxyl group has been replaced by hydrogen. An example is deoxyribose found in DNA.

Amino Sugars

Amino sugars are components of glycoproteins, gangliosides, and glycosaminoglycans.
Examples include D-glucosamine, a component of hyaluronic acid, and D-galactosamine (chondrosamine), which is part of chondroitin.
Several antibiotics, including erythromycin, feature amino sugars.

Disaccharides

Disaccharides are composed of two monosaccharide units linked by a glycosidic bond. Key examples include maltose, sucrose, lactose, and lactulose.
Sucrose, maltose, and lactose are examples of significant disaccharides.

Polysaccharides

Polysaccharides serve various storage and structural functions.
Examples: starch (amylose and amylopectin), glycogen (animal storage carbohydrate), inulin (plant storage carbohydrate), cellulose (plant cell wall component), chitin (structural component in exoskeletons), and pectin (found in fruits).

Glycemic Index

Defined as the extent to which a starchy food raises blood glucose levels, compared to an equivalent amount of glucose or a reference food.

Proteoglycans, Glycoproteins and Glycolipids

Carbohydrate chains (glycans) are attached to proteins (proteoglycans and glycoproteins) or lipids (glycolipids) on the cell's surface playing key roles in functions such as cell recognition, adhesion, migration, immune response, and wound healing.

Glycosaminoglycans (GAGs)

Glycosaminoglycans are complex carbohydrates that contain amino sugars and uronic acids and are frequently linked to proteins, forming proteoglycans.
GAGs help hydrate tissues and create space to reduce pressure and support the structure and function of tissues.
Hyaluronic acid, chondroitin sulfate, keratan sulfate, heparin, and dermatan sulfate are some examples of GAGs.

Glycoproteins

Proteins (glycoproteins, also known as mucoproteins) have branched or unbranched oligosaccharides covalently bonded to them.
Glycosylation (sugars attaching to proteins) is a common post-translational modification crucial for protein function.
Glycoproteins are found in cell membranes, and many proteins are glycosylated—examples include immunoglobulins (antibodies), hormones such as follicle-stimulating hormone (FSH), luteinizing hormone (LH), and thyroid-stimulating hormone (TSH).

Sialic Acids

Sialic acids are derivatives of neuraminic acid, a nine-carbon sugar. They are involved in glycoproteins and gangliosides.

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Description

Explore the vital roles of carbohydrates in living organisms, focusing on their structural and metabolic functions. Understand the significance of glucose as a primary energy source and its role in various biochemical pathways. Additionally, learn about carbohydrate-related diseases that impact metabolism.