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?

4 kilocalories Signup and view all the answers

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

Starch Signup and view all the answers

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

Carbohydrates Signup and view all the answers

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

Plant materials Signup and view all the answers

What is the primary purpose of carbohydrate oxidation in humans?

Releasing energy Signup and view all the answers

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

It forms invert sugar. Signup and view all the answers

Which of the following oligosaccharides cannot be digested by humans?

Raffinose Signup and view all the answers

What is the role of solanine in potatoes?

To act as a defense mechanism Signup and view all the answers

Which blood type is considered a universal donor?

Type O Signup and view all the answers

What is the defining characteristic of a storage polysaccharide?

It stores monosaccharides for energy. Signup and view all the answers

What distinguishes a homopolysaccharide from a heteropolysaccharide?

The types of monosaccharide monomers present Signup and view all the answers

How many monosaccharide units do oligosaccharides contain?

3 to 10 Signup and view all the answers

What are the cyclic forms of monosaccharides primarily formed by?

The reaction of carbonyl groups with hydroxyl groups Signup and view all the answers

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

Cyclic hemiacetals Signup and view all the answers

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

Glycosidic bond Signup and view all the answers

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

Maltose Signup and view all the answers

What specific linkage occurs in maltose?

α(1→4) linkage Signup and view all the answers

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

An acidic environment or enzyme maltase Signup and view all the answers

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

Maltase Signup and view all the answers

What are disaccharides primarily characterized by?

Being formed through an oxygen bridge between two monosaccharides Signup and view all the answers

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

Glucose Signup and view all the answers

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

Enzymes catalyze their formation Signup and view all the answers

Which description correctly identifies an aldose with three carbons?

Aldotriose Signup and view all the answers

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

Ketohexose Signup and view all the answers

Which of the following monosaccharides is considered chiral?

D-Glyceraldehyde Signup and view all the answers

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

D-Glucose Signup and view all the answers

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

It is the sweetest-tasting sugar. Signup and view all the answers

What compound does D-Ribose primarily contribute to?

Adenosine triphosphate (ATP) 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?

D-Galactose Signup and view all the answers

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

D-Galactose Signup and view all the answers

Dihydroxyacetone is characterized by what notable property?

It is the simplest ketose. Signup and view all the answers

Which of the following chemical formulas corresponds to a ketopentose?

C5H10O5 Signup and view all the answers

Which of the following statements about carbohydrates is true?

Carbohydrates linked to proteins play a role in cell recognition. Signup and view all the answers

What is the general empirical formula for most simple carbohydrates?

C_nH_2nO_n Signup and view all the answers

Which carbohydrate type cannot be hydrolyzed into simpler units?

Monosaccharide Signup and view all the answers

What is produced when a disaccharide undergoes hydrolysis?

Two monosaccharide units Signup and view all the answers

What distinguishes oligosaccharides from monosaccharides and disaccharides?

Oligosaccharides consist of 3-10 monosaccharide units. Signup and view all the answers

Which statement is accurate about polysaccharides?

Polysaccharides can contain over 50,000 monosaccharide units. Signup and view all the answers

Carbohydrates consist of which type of molecules?

Polyhydroxy aldehydes or ketones Signup and view all the answers

How do carbohydrates contribute to cellular functions?

They are vital for genetic control and cellular interactions. Signup and view all the answers

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

Membrane components Signup and view all the answers

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

Their empirical formula C_n(H_2O)_n Signup and view all the answers

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.