Carbohydrates

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Questions and Answers

Which statement accurately describes the general chemical formula of carbohydrates?

(CHO₂)ₙ, indicating oxides of carbon and hydrogen
(C₂H₂O₂)ₙ, indicating dioxides of carbon and hydrogen
(C₂H₂O)ₙ, indicating dehydrates of carbon
(CH₂O)ₙ, indicating hydrates of carbon (correct)

Which of the following is NOT a primary function of carbohydrates in biological systems?

Acting as catalysts in enzymatic reactions (correct)
Long-term energy storage as starches
Playing roles in cellular recognition and adhesion
Structural components in cell walls of plants and bacteria

How does the classification of carbohydrates differ between monosaccharides, oligosaccharides, and polysaccharides?

Based on the presence of nitrogen, phosphorus, or sulfur
Based on whether they contain an aldehyde or ketone group
Based on the number of monosaccharide units they contain (correct)
Based on their ability to be hydrolyzed into smaller sugars

Oligosaccharides, by definition, always consist of more than ten monosaccharide units.

False (B) Signup and view all the answers

What structural feature distinguishes aldoses from ketoses?

the position of the carbonyl group Signup and view all the answers

A carbohydrate containing six carbon atoms is classified as a(n) __________.

hexose Signup and view all the answers

Match the carbohydrate class with its defining characteristic:

Monosaccharide = Single sugar unit that cannot be hydrolyzed further Disaccharide = Composed of two monosaccharide units linked together Polysaccharide = Large polymer consisting of many monosaccharide units Oligosaccharide = Carbohydrate composed of 3-10 monosaccharide units Signup and view all the answers

What is the significance of isomerism in monosaccharides regarding their biological functions?

Structural differences due to isomerism can significantly alter their properties and biological roles. (D) Signup and view all the answers

How are enantiomers of monosaccharides designated, and what structural feature determines this designation?

Designated as D- and L- based on the orientation of the hydroxyl group on the chiral carbon farthest from the carbonyl group. (D) Signup and view all the answers

In nature, L-sugars are more commonly found in biological systems than D-sugars.

False (B) Signup and view all the answers

Define epimers and provide a specific example.

Epimers are sugars that differ in configuration at only one chiral carbon. An example is D-glucose and D-galactose, differing only at carbon 4. Signup and view all the answers

__________ are special epimers that differ at the hemiacetal carbon, which is carbon 1 in aldoses.

Anomers Signup and view all the answers

Match the anomeric form with the position of the hydroxyl (OH) group relative to the CH₂OH group in a cyclic monosaccharide:

α-anomer = OH group is trans to the CH₂OH group β-anomer = OH group is cis to the CH₂OH group Signup and view all the answers

What chemical process leads to the formation of a hemiacetal in monosaccharides, and why is this significant?

A reaction where the carbonyl group reacts with a hydroxyl group within the same molecule, leading to ring formation. (B) Signup and view all the answers

Define mutarotation and explain its significance in the context of monosaccharides.

The spontaneous interconversion between α- and β-anomers of a sugar in solution, leading to a change in optical rotation. (B) Signup and view all the answers

The α-anomer is characterized by the OH group pointing 'up' in the Haworth projection of a cyclic sugar.

False (B) Signup and view all the answers

Describe the formation of a glycosidic bond.

A glycosidic bond is formed when a hydroxyl group from one monosaccharide reacts with a hydroxyl group on another, releasing a molecule of water in a condensation reaction. Signup and view all the answers

Sugars that can donate electrons to other molecules, as in Fehling’s reaction, are known as __________ sugars.

reducing Signup and view all the answers

Match each monosaccharide to its common biological role:

D-glucose = Primary energy source for cells D-fructose = Metabolic intermediate and sweetener D-galactose = Component of lactose (milk sugar) Signup and view all the answers

Why is sucrose considered a non-reducing sugar?

Because it lacks free aldehyde or ketone groups due to the involvement of both anomeric carbons in the glycosidic bond. (B) Signup and view all the answers

What change occurs in Fehling’s reaction when a reducing sugar is present, and how is this observed?

The sugar reduces copper(II) ions to copper(I) oxide, leading to a color change. (C) Signup and view all the answers

Hexose derivatives are formed exclusively through reactions with alcohols.

False (B) Signup and view all the answers

Define a glycoside and give an example of its role.

A glycoside is a compound formed when a hexose reacts with a compound such as an alcohol. Glycosides play roles in cell signaling and structure. Signup and view all the answers

A __________ is a protein to which carbohydrates are covalently attached.

glycoprotein Signup and view all the answers

Match the term with its correct definition related to carbohydrate structure:

Aldose = Monosaccharide with an aldehyde group Ketose = Monosaccharide with a ketone group Enantiomer = Non-superimposable mirror-image isomers Epimer = Isomers differing in configuration at one chiral carbon Signup and view all the answers

How do carbohydrates contribute to energy storage in living organisms?

They are converted into fats and stored as glycogen or starch. (C) Signup and view all the answers

What role does cellulose play in providing structural support in plants?

It is a major component of the cell wall, providing strength and rigidity. (C) Signup and view all the answers

Glycoproteins play a limited role in cell recognition and communication.

False (B) Signup and view all the answers

Describe how blood groups (A, B, AB, and O) are determined at the molecular level.

Blood groups are determined by differing carbohydrate structures on the surface of red blood cells. Signup and view all the answers

When carbohydrates are consumed in excess, the body converts them into __________ for long-term energy storage.

fat Signup and view all the answers

Match each disaccharide with its constituent monosaccharides:

Sucrose = Glucose + Fructose Lactose = Glucose + Galactose Maltose = Glucose + Glucose Signup and view all the answers

How do cells prevent excessive osmotic pressure when storing glucose, and what form does the glucose take?

By storing glucose as large, insoluble polymers like glycogen or starch. (B) Signup and view all the answers

What structural feature of glycogen enables rapid glucose release when needed?

Its extensive branching via α-1,6 glycosidic bonds, providing multiple points for enzymatic cleavage. (A) Signup and view all the answers

Amylose, a component of starch, is characterized by its branched structure with both α-1,4 and α-1,6 glycosidic bonds.

False (B) Signup and view all the answers

Describe the key structural difference between cellulose and chitin and their respective functional roles.

Cellulose is composed of glucose units linked by β-1,4 glycosidic bonds, providing rigidity to plant cell walls, whereas chitin is similar but has an acetylated amino group, forming strong, lightweight structures in fungal cell walls and arthropod exoskeletons. Signup and view all the answers

A bacterial cell wall contains a unique heteropolymer called __________ made of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM).

peptidoglycan Signup and view all the answers

Match each type of glycoconjugate with its primary function:

Glycoproteins = Involved in cell recognition, immune response, and signaling Proteoglycans = Provide structural support in cartilage and connective tissues Glycolipids = Involved in cell recognition and immune responses in cell membranes Signup and view all the answers

How do viruses exploit carbohydrates in the context of host cell infection?

Viruses use carbohydrates to bind to specific receptors on host cells, facilitating entry. (B) Signup and view all the answers

What role do altered carbohydrate patterns on cancer cells play in cancer research and potential treatments?

They are studied to identify unique markers that can be targeted for novel cancer treatments. (C) Signup and view all the answers

Lipopolysaccharides (LPS) are commonly found in Gram-positive bacteria and trigger weak immune responses.

False (B) Signup and view all the answers

Define peptidoglycans and explain their primary function in bacterial cells.

Peptidoglycans are heteropolymers found in bacterial cell walls, made of alternating NAG and NAM units linked by β-1,4 bonds. They provide strength and protection against external stressors and antibiotics. Signup and view all the answers

__________ are lipids with attached carbohydrates found in cell membranes that play roles in cell recognition and immune responses.

Glycolipids Signup and view all the answers

Match the polysaccharide with its biological role:

Cellulose = Provides structural support in plant cell walls Glycogen = Serves as the primary short-term energy storage in animal cells Starch = Functions as the principal energy reserve in plant tissues Chitin = Composes exoskeletons of insects and cell walls of fungi Signup and view all the answers

In the context of carbohydrate chemistry, which statement accurately distinguishes between epimers and anomers?

Epimers differ at a single chiral carbon, whereas anomers are a specific type of epimer differing at the hemiacetal or hemiketal carbon formed during cyclization. (B) Signup and view all the answers

Sucrose is classified as a reducing sugar because its glycosidic bond involves the anomeric carbons of both glucose and fructose, which allows it to freely donate electrons in Fehling’s reaction.

False (B) Signup and view all the answers

Explain how the structural differences between amylose and amylopectin contribute to their distinct roles in plant energy storage.

Amylose is a linear polymer that forms a helical structure, allowing for denser packing but slower glucose release. Amylopectin is highly branched, which provides more non-reducing ends for faster enzymatic breakdown and glucose release, making energy mobilization quicker but packing less efficient. Signup and view all the answers

In bacterial cell walls, peptidoglycans are composed of alternating units of N-acetylglucosamine (NAG) and ________, which are cross-linked to provide structural integrity and protection.

N-acetylmuramic acid (NAM) Signup and view all the answers

Match each polysaccharide with its primary function:

Glycogen = Short-term energy storage in animals Cellulose = Structural component of plant cell walls Chitin = Structural component of fungal cell walls and arthropod exoskeletons Starch = Energy storage in plants Signup and view all the answers

Flashcards

What are Carbohydrates?

Organic compounds with the formula (CH₂O)ₙ, essential for energy storage and structural components.

Monosaccharides

Simplest sugars that cannot be hydrolyzed into smaller sugars.