Carbohydrates and Their Functions
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Questions and Answers

What role does sialic acid play in cancer cells?

  • It helps cancer cells store energy.
  • It enhances the growth of cancer cells.
  • It serves as a structural component in cancer cells.
  • It signals that a cell is 'self' to the immune system. (correct)

Which carbohydrate serves a structural role in plants?

  • Cellulose (correct)
  • Starch
  • Glucose
  • Fructose

What percentage of the human diet should ideally consist of carbohydrates by mass?

  • 50%
  • 75%
  • 40%
  • 66% (correct)

How much energy does one gram of carbohydrate release when oxidized by cells?

<p>4 kilocalories (C)</p> Signup and view all the answers

In which form do plants primarily store carbohydrates as energy reserves?

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

What is the most abundant class of bioorganic molecules on Earth?

<p>Carbohydrates (A)</p> Signup and view all the answers

What serves as the primary carbohydrate source for humans and animals?

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

What is the primary purpose of carbohydrate oxidation in humans?

<p>Releasing energy (A)</p> Signup and view all the answers

What happens to sucrose when it is cooked with acid-containing foods?

<p>It forms invert sugar. (C)</p> Signup and view all the answers

Which of the following oligosaccharides cannot be digested by humans?

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

What is the role of solanine in potatoes?

<p>To act as a defense mechanism (A)</p> Signup and view all the answers

Which blood type is considered a universal donor?

<p>Type O (A)</p> Signup and view all the answers

What is the defining characteristic of a storage polysaccharide?

<p>It stores monosaccharides for energy. (C)</p> Signup and view all the answers

What distinguishes a homopolysaccharide from a heteropolysaccharide?

<p>The types of monosaccharide monomers present (D)</p> Signup and view all the answers

How many monosaccharide units do oligosaccharides contain?

<p>3 to 10 (B)</p> Signup and view all the answers

What are the cyclic forms of monosaccharides primarily formed by?

<p>The reaction of carbonyl groups with hydroxyl groups (B)</p> Signup and view all the answers

What type of compounds are formed in the cyclic form of monosaccharides?

<p>Cyclic hemiacetals (A)</p> Signup and view all the answers

What is the link between the two monosaccharides in disaccharides called?

<p>Glycosidic bond (A)</p> Signup and view all the answers

Which disaccharide is known as malt sugar and is produced from starch breakdown?

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

What specific linkage occurs in maltose?

<p>α(1→4) linkage (A)</p> Signup and view all the answers

What is needed for the hydrolysis of D-maltose to occur?

<p>An acidic environment or enzyme maltase (A)</p> Signup and view all the answers

Which enzyme is responsible for breaking the glucose-glucose linkage in maltose?

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

What are disaccharides primarily characterized by?

<p>Being formed through an oxygen bridge between two monosaccharides (D)</p> Signup and view all the answers

Which of the following is NOT a common disaccharide seen in biological systems?

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

What is the main reason specific disaccharides are produced in cells?

<p>Enzymes catalyze their formation (A)</p> Signup and view all the answers

Which description correctly identifies an aldose with three carbons?

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

What is the correct term for a ketose with six carbon atoms?

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

Which of the following monosaccharides is considered chiral?

<p>D-Glyceraldehyde (B)</p> Signup and view all the answers

Which sugar is recognized as the blood sugar and is also referred to as dextrose?

<p>D-Glucose (A)</p> Signup and view all the answers

D-Fructose is biochemically significant for which of the following reasons?

<p>It is the sweetest-tasting sugar. (B)</p> Signup and view all the answers

What compound does D-Ribose primarily contribute to?

<p>Adenosine triphosphate (ATP) (C)</p> Signup and view all the answers

Which sugar is often referred to as brain sugar due to its presence in glycoproteins found in brain and nerve tissue?

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

Which monosaccharide is not typically found in its free form and is synthesized from glucose?

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

Dihydroxyacetone is characterized by what notable property?

<p>It is the simplest ketose. (A)</p> Signup and view all the answers

Which of the following chemical formulas corresponds to a ketopentose?

<p>C5H10O5 (D)</p> Signup and view all the answers

Which of the following statements about carbohydrates is true?

<p>Carbohydrates linked to proteins play a role in cell recognition. (D)</p> Signup and view all the answers

What is the general empirical formula for most simple carbohydrates?

<p>C_nH_2nO_n (A)</p> Signup and view all the answers

Which carbohydrate type cannot be hydrolyzed into simpler units?

<p>Monosaccharide (A)</p> Signup and view all the answers

What is produced when a disaccharide undergoes hydrolysis?

<p>Two monosaccharide units (B)</p> Signup and view all the answers

What distinguishes oligosaccharides from monosaccharides and disaccharides?

<p>Oligosaccharides consist of 3-10 monosaccharide units. (C)</p> Signup and view all the answers

Which statement is accurate about polysaccharides?

<p>Polysaccharides can contain over 50,000 monosaccharide units. (C)</p> Signup and view all the answers

Carbohydrates consist of which type of molecules?

<p>Polyhydroxy aldehydes or ketones (D)</p> Signup and view all the answers

How do carbohydrates contribute to cellular functions?

<p>They are vital for genetic control and cellular interactions. (B)</p> Signup and view all the answers

Which structure is known to be formed when carbohydrates are linked to lipids?

<p>Membrane components (A)</p> Signup and view all the answers

What paves the way for the designation of carbohydrates as 'hydrates of carbon'?

<p>Their empirical formula C_n(H_2O)_n (C)</p> Signup and view all the answers

Flashcards

Cyclic Hemiacetal

A cyclic form of a monosaccharide formed by the reaction of the carbonyl group (C=O) with a hydroxyl group (-OH) on the same molecule.

Glycosidic Linkage

A bond formed between two monosaccharides when the hemiacetal carbon atom of one monosaccharide reacts with an -OH group of another monosaccharide.

Maltose

A disaccharide formed by the α(1→4) linkage of two D-glucose units, one of which must be α-D-glucose.

Maltase

The enzyme that breaks the α(1→4) linkage in maltose, releasing two D-glucose molecules.

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Hydrolysis

A process where a molecule is broken down by the addition of water.

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Oligosaccharides

A type of carbohydrate that contains three to ten monosaccharide units.

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Homopolysaccharide

A type of polysaccharide where only one type of monosaccharide monomer is present.

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Heteropolysaccharide

A type of polysaccharide where more than one type of monosaccharide monomer is present.

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Storage Polysaccharide

A polysaccharide that serves as a storage form for monosaccharides and is used as an energy source in cells.

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Starch

A storage polysaccharide found in plants, primarily in the form of amylose and amylopectin.

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Glycogen

A storage polysaccharide found in animals, mainly in the liver and muscles.

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Cellulose

A structural polysaccharide found in plants, which provides rigidity and support to cell walls.

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Carbohydrates: Abundance and Importance

Carbohydrates are the most abundant class of organic molecules found on Earth. They play a crucial role in the structure and energy storage of living organisms.

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Photosynthesis: Carbohydrate Production

Photosynthesis is the process by which plants convert light energy into chemical energy in the form of carbohydrates.

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Cellulose: Structural Support

Cellulose is a structural carbohydrate found in plants that provides support and rigidity.

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Starch: Energy Storage in Plants

Starch is a storage carbohydrate found in plants that serves as an energy reserve.

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Dietary Carbohydrates: Our Energy Source

Dietary carbohydrates are the primary source of energy for humans and animals. They are obtained from plant-based foods.

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Carbohydrate Oxidation: Energy Release

The breakdown of carbohydrates provides energy for cellular processes.

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Glycogen: Energy Reserve in Animals

Glycogen is a storage form of carbohydrates in animals that provides a short-term energy reserve.

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Sialic Acid: Immune System Recognition

Sialic acid is a complex sugar found on the surface of cells that acts as a “self” marker for the immune system.

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Aldotriose

A monosaccharide with 3 carbon atoms and an aldehyde functional group.

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Ketohexose

A monosaccharide with 6 carbon atoms and a ketone functional group.

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Aldopentose

A monosaccharide with 5 carbon atoms and an aldehyde functional group.

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Aldohexose

A monosaccharide with 6 carbon atoms and an aldehyde functional group.

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Ketopentose

A monosaccharide with 5 carbon atoms and a ketone functional group.

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D-Glyceraldehyde

The simplest monosaccharide with an aldehyde group; a chiral molecule.

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Dihydroxyacetone

The simplest monosaccharide with a ketone group; an achiral molecule.

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D-Glucose

The most common monosaccharide found in nature; a source of energy for many organisms.

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D-Galactose

A monosaccharide less common than D-glucose; synthesized from glucose for lactose formation.

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D-Fructose

The sweetest monosaccharide; found naturally in fruits and honey.

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Carbohydrates as Energy Source

Carbohydrates are the primary source of energy for living organisms. When broken down, they release energy that cells use to perform various functions.

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Carbohydrates as Building Blocks

Besides providing energy, carbohydrates serve as building blocks for other essential molecules like proteins, fats, and nucleic acids.

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Carbohydrates in Genetic Control

Carbohydrates play a vital role in the genetic control of growth and development within living cells.

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Carbohydrates in Cell Membranes

Carbohydrates are essential components of cell membranes, playing a role in structural support and regulating the passage of substances into and out of cells.

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Carbohydrates in Cell Recognition

Carbohydrates linked to proteins are involved in communication between cells and recognition of different molecules.

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Monosaccharide

A monosaccharide is the simplest type of carbohydrate, consisting of a single sugar unit.

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Disaccharide

A disaccharide is formed when two monosaccharides are joined together.

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Polysaccharide

A polysaccharide is a large complex carbohydrate composed of many monosaccharide units joined in long chains.

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Carbohydrate Formula

The general formula for many simple carbohydrates is CnH2nOn, which reflects their composition of carbon, hydrogen, and oxygen.

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Study Notes

Carbohydrates

  • Carbohydrates are the most abundant bioorganic molecules on Earth.
  • They constitute about 75% of dry plant material by mass.
  • In the human body, carbohydrates are present at a relatively low abundance.
  • Carbohydrates in humans comprise about two-thirds of the average diet by mass.

Cell Surface Carbohydrates and Cancer

  • Recent studies show unusually high concentrations of sialic acid on the surface of some cancer cells.
  • Sialic acid is a complex monosaccharide.
  • It's also found on all normal cells, serving as a signal for the immune system to identify "self."
  • Cancer cells with high levels of sialic acid go undetected by the immune system, allowing them to evade destruction.

Occurrence and Functions of Carbohydrates in Plants

  • Green plants produce carbohydrates via photosynthesis.
  • Photosynthesis involves CO₂, H₂O, and solar energy.
  • Plant enzymes convert these precursors into carbohydrates and release oxygen (O₂).
  • Carbohydrates serve as structural elements in plants in the form of cellulose.
  • Carbohydrates in the form of starch store energy reserves for plants.

Types of Carbohydrates

  • Monosaccharides: Simple sugars, such as glucose and fructose. They cannot be broken down into simpler sugars by hydrolysis.
  • Disaccharides: Two monosaccharides joined together. Examples include sucrose (table sugar) and lactose (milk sugar). Hydrolysis of a disaccharide yields two monosaccharides.
  • Oligosaccharides: Contain 3-10 monosaccharide units.
  • Polysaccharides: Complex carbohydrates composed of many monosaccharide units linked together. These include starch (plant energy storage) and glycogen (animal energy storage).

Classification of Monosaccharides

  • Based on carbonyl group:
    • Aldoses have an aldehyde functional group.
    • Ketoses have a ketone functional group.
  • Classified by the number of carbon atoms:
    • Triose (3 carbons)
    • Tetrose (4 carbons)
    • Pentose (5 carbons)
    • Hexose (6 carbons)
    • Heptose (7 carbons)

Example Monosaccharides

  • Give examples of various sugars (aldo- and keto- pentose and hexoses)
    • D-glucose
    • D-galactose
    • D-fructose
    • D-ribose

Cyclic Forms of Monosaccharides

  • Monosaccharides in solution usually exist in ring forms (cyclic hemiacetals) rather than open-chain forms.
  • The ring forms are in equilibrium with the open-chain forms.
  • Alpha (α) and beta (β) forms of cyclic sugars differ in the spatial arrangement of the hydroxyl group on the anomeric carbon.

Biochemically Important Monosaccharides

  • D-Glyceraldehyde: Simplest chiral monosaccharide, important intermediate in glycolysis.
  • Dihydroxyacetone: Simplest achiral monosaccharide. Important intermediate in glycolysis.
  • D-Glucose: Important energy source, prevalent in nature; in many fruits, blood sugar.
  • D-Fructose: Sweest tasting sugar, fruit sugars, commonly in plant foods.

Biochemically Important Disaccharides

  • Maltose: Two glucose units joined by an α(1→4) glycosidic linkage.
  • Cellobiose: Two glucose units joined by a β(1→4) glycosidic linkage.
  • Lactose: Composed of one glucose and one galactose unit, joined by a β(1→4) glycosidic linkage.
  • Sucrose: Composed of one glucose unit and one fructose unit, linked via a nonreducing α,β(1→2) glycosidic linkage.

Oligosaccharides

  • Raffinose and stachyose are oligosaccharides found in beans, cabbage, and other vegetables. Humans lack the digestive enzymes to break them down.

Polysaccharides

  • Important components of plant cell walls and animal tissues.
  • Examples include starch, glycogen, cellulose, and chitin.
  • Starch is a storage form of glucose for plants.
  • Glycogen is a highly branched storage form of glucose in animals.
  • Cellulose is a structural component of plant cell walls.
  • Chitin is a structural component in the exoskeletons of arthropods.

Blood Types and Oligosaccharides

  • Blood type is determined by specific oligosaccharides on the surface of red blood cells.
  • Different sugar arrangements determine A, B, AB, or O blood types.

Glycolipids and Glycoproteins

  • Glycolipids and glycoproteins are important for cell recognition and interactions.
  • Carbohydrate chains on these molecules facilitate cell-to-cell communication and interactions with other molecules like bacteria and viruses.

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Description

This quiz delves into the role of carbohydrates in living organisms, specifically focusing on their abundance in plants and their implications in human health, particularly in cancer. Explore how these vital molecules are produced and their significance in the diet.

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