Carbohydrates and Their Functions

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Questions and Answers

Which of the following is an example of a ketotriose?

Erythrose

Ribose

Dihydroxyacetone (correct)

Glyceraldehyde

Erythrose is categorized as a(n) _________.

Aldotetrose (correct)

Ketopentose

Ketotetrose

Aldotriose

Which of the following pentoses is a structural component of RNA?

Arabinose

Lyxose

Ribose (correct)

Xylose

What condition is associated with the appearance of arabinose in urine after the consumption of large quantities of certain fruits like cherries and grapes?

Alimentary pentosuria (A) Signup and view all the answers

Which hexose is also known as grape sugar or dextrose?

Glucose (C) Signup and view all the answers

Which of the following describes the relationship between erythrose and the hexose monophosphate shunt?

Erythrose is an intermediate within the shunt. (D) Signup and view all the answers

The suffix '-ulose' is added to the name of a monosaccharide to indicate the presence of which functional group?

Ketone group (A) Signup and view all the answers

What is the primary role of glucose in mammals?

Major metabolic fuel (C) Signup and view all the answers

What is the defining chemical characteristic of carbohydrates?

They are aldehyde or ketone derivatives of polyhydric alcohols. (A) Signup and view all the answers

Which of the following is NOT a primary biomedical function of carbohydrates?

Acting as the primary building block of enzymes. (B) Signup and view all the answers

Which of the following is an example of a carbohydrate derivative used as a drug?

Cardiac glycosides (D) Signup and view all the answers

Which of the following is a direct consequence of inherited enzyme deficiencies in carbohydrate metabolic pathways?

Diseases such as galactosemia and glycogen storage diseases. (A) Signup and view all the answers

How many sugar units are present in a disaccharide?

Two (A) Signup and view all the answers

Based on the general formula provided, what is the ratio between Carbon and H2O in a carbohydrate?

1:1 (D) Signup and view all the answers

What is an alternative name for monosaccharides?

Simple sugars or glycoses (D) Signup and view all the answers

A molecule is composed of more than 10 sugar units. According to the content provided, what type of carbohydrate is it?

Polysaccharide (D) Signup and view all the answers

A substance that rotates plane-polarized light to the left is best described as:

levorotatory and designated as (-) (D) Signup and view all the answers

Which of the following is NOT a characteristic of an anomeric carbon?

It is located at the carbon 2 of aldoses. (A) Signup and view all the answers

What structural difference defines the relationship between glucose and fructose as isomers?

The type of carbonyl functional group present. (B) Signup and view all the answers

Which statement accurately describes the relationship between glucose and galactose?

They are epimers, differing in configuration at carbon 4. (B) Signup and view all the answers

How does a deoxy sugar differ structurally from its parent sugar?

It has a hydrogen atom in place of a hydroxyl group. (C) Signup and view all the answers

Which of the following is NOT an example of optical isomerism?

Aldose-ketose isomers (C) Signup and view all the answers

How many asymmetric carbon atoms are present in a glucose molecule and a fructose molecule respectively?

4 and 3 (D) Signup and view all the answers

From the following options, which is a pair of epimers?

Glucose and Mannose (A) Signup and view all the answers

Which of the following is NOT an example of an amino sugar?

Fructose (A) Signup and view all the answers

Which amino sugar is a component of chondroitin sulfate?

Galactosamine (A) Signup and view all the answers

Which of the following is a characteristic of muramic acid?

It is a derivative of glucosamine and a component of peptidoglycans. (B) Signup and view all the answers

What type of linkage connects the carbohydrate residue to the noncarbohydrate residue in glycosides?

Acetal linkage (C) Signup and view all the answers

The noncarbohydrate portion of a glycoside is referred to as:

Aglycone (B) Signup and view all the answers

Which of the following is characteristic of invert sugar?

It contains equimolar amounts of glucose and fructose. (D) Signup and view all the answers

Why is sucrose useful in treating cerebral oedema?

It changes the blood osmotic condition, drawing water from tissues to blood (D) Signup and view all the answers

What is the relationship between neuraminic acid and sialic acids?

Sialic acids are acylated derivatives of neuraminic acid. (C) Signup and view all the answers

What is the primary consequence of unhydrolyzed disaccharides in the gut?

Likelihood of diarrhea (C) Signup and view all the answers

What distinguishes homopolysaccharides from heteropolysaccharides?

Homopolysaccharides contain only one type of monosaccharide, heteropolysaccharides may contain other groups (D) Signup and view all the answers

Which statement accurately describes the composition of starch?

It consists of amylose and amylopectin, differing in molecular structure and properties (C) Signup and view all the answers

What is the role of amylase in starch digestion?

It produces various forms of dextrins through partial hydrolysis (D) Signup and view all the answers

Glycogen is primarily stored in which two locations in higher animals?

Liver and muscles (D) Signup and view all the answers

Which process describes the formation of glycogen from glucose?

Glycogenesis (B) Signup and view all the answers

What is the significance of the postmortem drop of pH to 5.5 in regards to glycogen?

It halts postmortem glycogenolysis due to lactic acid formation (D) Signup and view all the answers

What are dextrins?

They are products of lower molecular weight when starch is partially hydrolyzed (B) Signup and view all the answers

Which characteristic is NOT associated with dextrins?

Composed of fructose units linked by β-1-2 bonds (D) Signup and view all the answers

What is the distinguishing feature in the classification of dextrins into amyIodextrin, erythrodextrin, and achrodextrin?

Their reaction with iodine resulting in color change (C) Signup and view all the answers

What is the purpose of limit dextrin?

It represents a fragment of starch that cannot be further broken down by β-Amylase (C) Signup and view all the answers

Why is cellulose not digestible by humans?

Due to the presence of β-1-4 glycosidic bonds (A) Signup and view all the answers

What is the primary function of agar in human applications?

As a laxative to aid in constipation (B) Signup and view all the answers

What type of glycosidic bond is present in inulin?

β-1-2 glycosidic bond (C) Signup and view all the answers

What is the main application of inulin in medical diagnostics?

As a marker to determine Glomerular Filtration Rate (GFR) (B) Signup and view all the answers

Which of the following is a common source of inulin?

Jerusalem artichoke roots (C) Signup and view all the answers

Study Notes

Carbohydrate Chemistry

Carbohydrates are defined chemically as aldehyde or ketone derivatives of higher polyhydric alcohols, or compounds that yield these derivatives during hydrolysis.
They are the chief source of energy.
They are constituents of compound lipids and conjugated proteins.
Degradation products act as catalysts.
Certain carbohydrate derivatives are used as drugs (e.g., cardiac glycosides/antibiotics).
Lactose is the principal sugar in milk produced by lactating mammary glands.
Degradation products are used in the synthesis of other substances (e.g., fatty acids, cholesterol, amino acids).
They are constituents of mucopolysaccharides that form the ground substance of mesenchymal tissues.
Inherited deficiencies in carbohydrate metabolic pathways can lead to diseases (e.g., galactosemia, glycogen storage diseases (GSDs), lactose intolerance).
Disruptions in glucose metabolism are associated with diabetes mellitus.

Classification of Carbohydrates

Carbohydrates are divided into four major groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
Monosaccharides contain one sugar unit (cannot be hydrolyzed).
Disaccharides contain two sugar units.
Oligosaccharides contain 3-10 sugar units.
Polysaccharides contain more than 10 sugar units.
Ratio of carbon to H₂O is 1:2.

Monosaccharides

Also known as simple sugars or glucoses
Cannot be hydrolyzed further
Can be subdivided further based on:
- Number of carbon atoms (trioses, tetroses, pentoses, hexoses)
- Presence of aldehyde or ketone groups (aldoses or ketoses)
Examples of trioses: Glyceraldehyde, Dihydroxyacetone.
Examples of tetroses: Erythrose.
Examples of pentoses: Ribose, arabinose, xylose, lyxose.
Examples of pentoses: Ribulose, xylulose.
Examples of hexoses: Glucose, mannose, galactose, fructose.

Importance of Monosaccharides

Ribose is a component of nucleic acids (RNA and DNA), ATP, GTP, and coenzymes NAD and FAD.
Arabinose is found in some fruits and can cause alimentary pentosuria when ingested in high amounts.
Fruit sugar (Fructose) is present in fruits and semen, and converted to glucose in the liver.
Seminal fluid is rich in fructose, used by sperm for energy.
Galactose is synthesized in the mammary gland, converted to glucose in the liver, and forms components for agar, glycosaminoglycan (GAG), and glycolipid.
Mannose is a component of many glycoproteins; doesn't occur freely in nature.
Glucose is a chief carbohydrate; the major metabolic fuel for mammals and a universal fuel for the fetus. Used by all tissues as energy. It is converted to glycogen and galactose in the liver and other tissues.
Fructose (fruit sugar), is also present in honey and semen; can be converted into glucose in the liver.
Seminal fluid is rich in fructose, used by sperm for energy.
Fructose is formed in seminiferous tubular epithelial cells from glucose.

Cyclic Structures of Monosaccharides

Cyclic form is due to the reaction between the carbonyl group and an alcoholic hydroxyl group.
- Furanose- 4 carbon ring
- Pyranose- 5 carbon ring
α- and β-sugars forms exist depending on the position of the hydroxyl group on the anomeric carbon.
Examples of sugars exist in both α and β forms: glucose and fructose.

Optical Activity and Isomers

Asymmetric carbon atoms are those with four different groups attached.
Optical activity refers to the ability of substances to rotate plane-polarized light.
Dextro- rotatory sugars rotate light to the right (+).
Levo- rotatory sugars rotate light to the left (-). Glucose is dextro- rotatory.
Optical isomerism refers to the ability of substances to exist in more than one form that are mirror images of each other (enantiomers).

Anomeric Carbons and Anomers

Anomeric carbon is obtained from the carbonyl group(C1 in aldoses and C2 in ketoses).
Anomers are isomers that differ only in the configuration of the hydroxyl group around the anomeric carbon.

Aldose-Keto Isomers

Aldose-keto isomers have the same molecular formula but different functional groups (e.g., glucose and fructose).

Oligosaccharides

A carbohydrate containing 3-10 monosaccharides.

Epimers

Epimers are diastereomers that differ in the configuration around one carbon atom

Disaccharides

Maltose. Is formed during the digestion of starch and glycogen.
Isomaltose. Is formed during the digestion of starch and glycogen.
Trehalose.
Lactose. Found in milk.
Sucrose. Common table sugar.

Sucrose Hydrolysis

Hydrolysis of sucrose using the sucrase (invertase) enzyme produces glucose and fructose. This process is known as inversion.
Honey primarily consists of invert sugars.

Polysaccharides

Starch, glycogen, cellulose, heteropolysaccharides e.g. mucopolysaccharides, agar, inulin.
These are polymers of monosaccharides.
Some are homopolysaccharides (one kind of monosaccharide).
Some are heteropolysaccharides (more than one kind of monosaccharide).

Starch

Starch is a polymer of glucose found in plants as storage.
Compositionally consists of amylose and amylopectin.
Amylose is unbranched and soluble in water, amylopectin is highly branched and insoluble in water.
Partial hydrolysis creates dextrins.

Glycogen

Glycogen is the animal starch.
A branched polymer of glucose.
Deposited in the liver and muscles for immediate energy.
Glycogenesis is the formation of glycogen.
Glycogenolysis is the breakdown of glycogen to glucose.
Highly branched, similar to amylopectin.

Dextrins

Created by partial hydrolysis of starch.
A group of lower molecular weight products.
Types are classified by their cleavage patterns. i.e.: amylo-, erythrod-, and achrodextrins.

Cellulose

Long chains of linked glucose molecules.
Cannot be digested by humans but increases the bulk of stool.

Agar

A homopolysaccharide obtained from seaweed.
Used as a laxative and in microbiology for culturing bacteria.

Inulin

Fructose linked together with β1-2 bonds.
Present in Jerusalem artichokes, onion and garlic.
Used to measure glomerular filtration rate (GFR).

Sugar Derivatives of Biomedical Importance

Deoxy Sugars
- Replacement of hydroxyl groups by hydrogen. Example: Deoxyribose.
Amino Sugars (hexosamines)
- Contain an amino group (-NH2). Example: Glucosamine, galactosamine, mannosamine, and others
Neuraminic acid
- Unstable. Found form of acylated derivatives known as sialic acids (N-acetyl neuraminate).
Muramic acid
- Component of peptidoglycan, forming cell walls of most bacteria.
Glycosides
- A carbohydrate molecule covalently attached to a non-carbohydrate molecule.
- The non-carbohydrate component is called an aglycone. Example: cardiac glycosides like digitalis.

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Description

Test your knowledge on carbohydrates with this quiz focusing on ketotrioses, pentoses, and hexoses. Explore their roles in metabolism, functional groups, and biomedical applications. Ideal for students of biochemistry and related fields.