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What is the primary purpose of carbohydrates in plants?
Which of the following groups do monosaccharides belong to?
How do carbohydrates contribute to the structure of RNA and DNA?
Which type of carbohydrate is characterized by being unable to be broken down into smaller groups?
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What role do carbohydrates play in cell-to-cell recognition?
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What are the two forms of carbohydrates that result from mutarotation called?
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In aqueous solution, which statement is true regarding glucose?
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Which of the following statements correctly describes a cyclic hemiacetal?
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How does the presence of the hydroxyl (-OH) functional group affect monosaccharides?
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What percentage of fructose in solution exists as furanose forms?
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Which characteristic makes sucrose a non-reducing sugar?
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What is the result of the hydrolysis of sucrose?
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What primary effect does overconsumption of sucrose have on dental health?
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Which property makes fructose sweeter than glucose?
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What type of bond links the two monosaccharides in a disaccharide?
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Why is invert sugar sweeter than sucrose?
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What is a common source of galactose?
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Which monosaccharide is known for being the end product of polysaccharide digestion?
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What is a function of oligosaccharides on blood cells?
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Which of the following statements about mucins is correct?
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What distinguishes homopolysaccharides from heteropolysaccharides?
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When starch is hydrolyzed, which enzyme is primarily responsible for breaking down amylose?
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Which component of starch is responsible for its branched structure?
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How does starch help in controlling body weight?
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What is the primary role of oligosaccharides attached to cell membranes?
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Which of the following statements highlights the biological importance of mucins?
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What is the storage form of carbohydrate in animals?
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What structural feature distinguishes glycogen from amylopectin?
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What is the primary role of cellulose in the human diet?
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Which type of polysaccharide is primarily used to nourish the embryo during pregnancy?
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What compound primarily aids in the digestion of cellulose in certain insects?
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What condition can arise from the loss of chondroitin sulfate in cartilage?
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In which animals is cellulose primarily digested due to special bacteria in the gut?
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What is a key function of heparin in the body?
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Study Notes
Carbohydrates
- Carbohydrates are composed of carbon (C), hydrogen (H), and oxygen (O).
- They occur as starch (energy source) and cellulose (structural support) in plants.
- Plants have a higher percentage of carbohydrates (30%) compared to animals (1%).
- They are a source of carbon for metabolic reactions.
- They are crucial for brain energy.
- Carbohydrates form part of the structural framework for RNA and DNA, allowing for flexibility of the rings and necessary for storage and expression of genetic molecules.
- They contribute to the structure of bacterial and plant cell walls.
- They are found linked to proteins (glycoproteins) and lipids (glycolipids), facilitating cell-to-cell recognition.
- They enhance bowel movements through dietary fiber.
- Carbohydrates are classified into four groups: monosaccharides, disaccharides, oligosaccharides, and polysaccharides.
Monosaccharides
- Simple sugars that cannot be broken down into smaller units.
- General formula (CH2O)n.
- Classified based on number of carbon atoms and position of the carbonyl group.
- Mutarotation causes a conversion between α and β forms.
- Different forms are called anomers.
- This rotation occurs in all reducing sugars (except some ketoses).
- The α and β anomers of carbohydrates are typically stable solids.
- In aqueous solution, they quickly equilibrate to an equilibrium mixture of the two forms.
- For example, in aqueous solution, glucose exists as a mixture of 36% α- and 64% β- (>99% of the pyranose forms exist in solution).
Hemiacetals
- When sugars form a ring through mutarotation, the product is called a cyclic hemiacetal.
- Hemiacetals readily open back to the aldehyde chain, so a small amount of the aldehyde chain is always present.
- The glucose chain is 0.01%.
Converting from Fischer to Haworth Projection
- Draw the Fischer projection of the molecule.
- Draw the basic ring structure.
- For D-sugars, -CH2OH is placed above the ring on C #5. For L-sugars, -CH2OH is placed below the ring on C #5.
- For α-sugars, -OH is placed below the ring on C #1. For β-sugars, -OH is placed above C #1.
Fructose Structures
- Fructose can undergo structural interconversion similar to glucose, with two pyranose forms and two furanose forms.
- In a solution of glucose or fructose, there will be four rings and one chain.
- Glucose is nearly all (99%) pyranose, while fructose has 30-40% furanose and 60-70% pyranose.
Properties of Monosaccharides
- The hydroxyl (-OH) functional group makes them soluble in polar solvents (solvents having -OH functional groups).
- They are reducing sugars because they have free aldehyde and ketone groups.
Common Monosaccharides
- Glucose: Found in sweet fruits, aldose sugar, sweet, crystalline, the end product of polysaccharide digestion.
- Fructose: Found in cane sugar, ketose sugar, 50% sweeter than glucose, crystalline. Does not convert to energy as efficiently as glucose and is usually converted to fat stores.
- Galactose: Found in milk, aldose sugar, sweet, crystalline.
Disaccharides
- Consist of two sugars linked by an o-glycosidic bond (ether link -O-).
- Two types of glycosidic bonds: 1-4 glycosidic bonds and 1-6 glycosidic bonds.
- Formed by condensation of two monosaccharide molecules.
Abundant Disaccharides
- Sucrose: Common name - table sugar, obtained from sugar cane or beets, sweetest disaccharide. Made up of the monosaccharides glucose and fructose.
- During condensation, both carbonyl groups are involved, making sucrose a non-reducing agent.
- Lactose: Found in milk, made up of glucose and galactose.
- Maltose: A product of starch hydrolysis, made up of two glucose units.
Sucrose
- Hydrolyzed by acid or invertase (enzyme) to form glucose and fructose.
- This is referred to as the inversion of the sugar.
- Invert sugar is sweeter than sucrose due to the presence of fructose.
- Honey is sweeter than sucrose because of higher invert sugar content.
Biological Importance of Sucrose
- Sucrose provides a quick source of energy, leading to a rapid rise in blood glucose after ingestion.
- Overconsumption of sucrose can lead to tooth decay, as oral bacteria convert sugars (including sucrose) into acids that erode tooth enamel.
Oligosaccharides
- Found on cell membrane surfaces attached to proteins.
- May function as receptors.
- Determine blood groups A, B, O, and AB.
- Three different types of oligosaccharides may be found on the surface of red blood cells.
- All have a chain of sugars: N-acetyl galactosamine, N-acetylglucosamine, galactose, and L-fucose.
Glycoprotein
- Saliva contains a glycoprotein called mucin.
- The highly glycosylated properties of mucins make them resistant to breakdown and able to hold water, giving them gel-like properties.
- Mucins have various functions, mainly due to viscosity, for example, lubrication, tissue coating, and protection (including antimicrobial functions).
- Mucins play a role in non-immune protection in the oral cavity, such as forming protective coatings on teeth enamel and oral mucosa.
- Mucin overexpression is linked to lung diseases like asthma, bronchitis, COPD, and cystic fibrosis.
Polysaccharides
- Complex sugars with high molecular weights.
- Can be straight chain or branched.
- Two groups: homopolysaccharides and heteropolysaccharides.
Homopolysaccharides
- Produce only one type of monosaccharide on hydrolysis.
- Examples: starch, glycogen, and cellulose.
Starch
- A significant food storage in plants.
- Composed of two components:
- Amylose (straight chain)
- Amylopectin (branched).
Starch Hydrolysis
- Hydrolysis of amylose by α-amylase (found in the digestive tract of animals) produces maltose and glucose.
- β-amylase (found in plants) produces maltose.
- The combination of α-amylase and α-1-6 glucosidase hydrolyzes amylopectin to produce maltose and glucose.
Biological Importance of Starch
- Helps control body weight when combined with exercise, as it is inefficiently converted to body fat and is preferentially used as fuel.
- Vital for proper gut function.
- Serves as an important fuel source for the brain and active muscles.
Glycogen
- The storage form of carbohydrate in animals.
- Structurally similar to amylopectin but with more branching.
- Soluble in water.
- Hydrolyzed by α-1,6-glucanmaltohydrolase to produce maltose.
- Acid hydrolysis produces glucose.
- Non-reducing sugar.
Biological Importance of Glycogen
- The liver stores glycogen, easily and rapidly convertible to energy by the body.
- Muscles store glycogen for use during intense physical activity.
- The uterus stores glycogen during pregnancy to nourish the embryo.
- High glycogen levels improve endurance. Glycogen depletion is associated with fatigue.
Cellulose
- The most abundant extracellular polysaccharide.
- Structurally similar to amylose.
- Glucose linked together by β-1,4-glycosidic linkages.
- Insoluble in water.
- Absorbs water.
- Hydrolysis produces glucose molecules.
- Cellulase present in some insects allows for the digestion of cellulose.
Biological Importance of Cellulose
- In humans, cellulose is a major component of dietary fiber, essential for proper digestion.
- It cannot be broken down and passes through the system unchanged, acting as bulk or roughage to facilitate intestinal movements.
- Ruminants (cud-chewing animals) have specialized bacteria and microorganisms in their digestive tracts to process cellulose.
- Ruminants can absorb the broken-down cellulose and use its sugars as a food source.
Heteropolysaccharides
- Produce more than one type of monosaccharide upon hydrolysis.
- Examples: chondroitin and heparin.
Chondroitin
- Found in cartilage and as a component of the cell coat.
- Major component of the extracellular matrix, important for maintaining tissue structural integrity.
- Loss of chondroitin sulfate from cartilage is a major cause of osteoarthritis.
- Widely used as a dietary supplement for treating osteoarthritis, along with glucosamine.
Heparin
- An anticoagulant found in the liver and lung arterial wall.
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Description
Explore the essential role of carbohydrates in biology, including their composition, types, and functions in plants and animals. Understand how carbohydrates contribute to metabolic processes and genetic structures. This quiz also covers monosaccharides and their significance in nutrition.
