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Questions and Answers
Which of the following is NOT a class of carbohydrates?
Which of the following is NOT a class of carbohydrates?
Sucrose is an example of a reducing sugar.
Sucrose is an example of a reducing sugar.
False
What is the general formula for carbohydrates?
What is the general formula for carbohydrates?
Cn(H2O)n
Fructose is classified as a __________ because it contains a ketone group.
Fructose is classified as a __________ because it contains a ketone group.
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Which of the following compounds is a reducing sugar?
Which of the following compounds is a reducing sugar?
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Match the type of monosaccharide to the number of carbon atoms:
Match the type of monosaccharide to the number of carbon atoms:
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Glucose is the primary source of energy for all living organisms.
Glucose is the primary source of energy for all living organisms.
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Carbohydrates are an essential class of biomolecules, primarily consisting of carbon, hydrogen, and __________.
Carbohydrates are an essential class of biomolecules, primarily consisting of carbon, hydrogen, and __________.
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What characterizes the primary structure of proteins?
What characterizes the primary structure of proteins?
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Denaturation of proteins can only be caused by heat.
Denaturation of proteins can only be caused by heat.
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What is a zwitterion?
What is a zwitterion?
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The secondary structure of a protein is characterized by __________ bonds between the backbone atoms of amino acids.
The secondary structure of a protein is characterized by __________ bonds between the backbone atoms of amino acids.
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Match each protein structure with its description:
Match each protein structure with its description:
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Which type of secondary structure is stabilized by hydrogen bonds and takes the form of a spiral?
Which type of secondary structure is stabilized by hydrogen bonds and takes the form of a spiral?
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Essential amino acids cannot be synthesized by the body.
Essential amino acids cannot be synthesized by the body.
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What is the effect of pH changes on proteins?
What is the effect of pH changes on proteins?
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The structure of __________ is a linear chain of beta-D-glucose molecules, making it a key component of plant cell walls.
The structure of __________ is a linear chain of beta-D-glucose molecules, making it a key component of plant cell walls.
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Which of the following is NOT a component of proteins?
Which of the following is NOT a component of proteins?
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What process is used to prepare glucose and fructose from sucrose?
What process is used to prepare glucose and fructose from sucrose?
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Starch is primarily found in animal tissues.
Starch is primarily found in animal tissues.
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What is the chemical formula of glucose?
What is the chemical formula of glucose?
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The two forms of glucose are known as _____ and _____ forms.
The two forms of glucose are known as _____ and _____ forms.
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Match the following forms of glucose with their description:
Match the following forms of glucose with their description:
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What is the result of heating glucose with hydrogen iodide (HI)?
What is the result of heating glucose with hydrogen iodide (HI)?
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D-glucose is less common than L-glucose in nature.
D-glucose is less common than L-glucose in nature.
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What is the role of the hydroxyl group on the fifth carbon in glucose?
What is the role of the hydroxyl group on the fifth carbon in glucose?
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The bond formed between two monosaccharides to create a disaccharide is called a _____ linkage.
The bond formed between two monosaccharides to create a disaccharide is called a _____ linkage.
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Which of the following best describes the cyclic structure of glucose?
Which of the following best describes the cyclic structure of glucose?
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The reaction of glucose with bromine water confirms the presence of a ketone group.
The reaction of glucose with bromine water confirms the presence of a ketone group.
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What kind of reaction does the cyclic structure of glucose prevent?
What kind of reaction does the cyclic structure of glucose prevent?
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Fructose contains _____ carbon atoms in its cyclic structure.
Fructose contains _____ carbon atoms in its cyclic structure.
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Match the following carbohydrates with their characteristics:
Match the following carbohydrates with their characteristics:
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What type of glycosidic linkage is found in sucrose?
What type of glycosidic linkage is found in sucrose?
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Malttose is a non-reducing sugar.
Malttose is a non-reducing sugar.
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What is the primary storage form of carbohydrates in animals?
What is the primary storage form of carbohydrates in animals?
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Lactose is composed of glucose and __________.
Lactose is composed of glucose and __________.
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Match the following disaccharides with their reducing properties:
Match the following disaccharides with their reducing properties:
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Which of the following statements is true regarding sucrose?
Which of the following statements is true regarding sucrose?
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Hydrolysis of disaccharides requires the addition of water.
Hydrolysis of disaccharides requires the addition of water.
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What process refers to the change in optical rotation due to changes in isomeric forms of a sugar?
What process refers to the change in optical rotation due to changes in isomeric forms of a sugar?
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A glycosidic linkage is a __________ bond that joins two monosaccharides.
A glycosidic linkage is a __________ bond that joins two monosaccharides.
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Which carbohydrate is primarily composed of branched glucose units?
Which carbohydrate is primarily composed of branched glucose units?
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All amino acids are zwitterions at physiological pH.
All amino acids are zwitterions at physiological pH.
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Identify the two main components of a peptide bond.
Identify the two main components of a peptide bond.
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Essential amino acids must be obtained from the __________.
Essential amino acids must be obtained from the __________.
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Which of the following is a characteristic of the carbohydrate cellulose?
Which of the following is a characteristic of the carbohydrate cellulose?
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Study Notes
Biomolecules
- Biomolecules are organic compounds essential for life.
- They are composed of carbon, hydrogen, oxygen, nitrogen, phosphorus, and sulfur.
- Biomolecules are classified into four major groups: carbohydrates, lipids, proteins, and nucleic acids.
Carbohydrates
- Carbohydrates are a large and diverse group of organic compounds.
- Carbohydrates are composed of carbon, hydrogen, and oxygen.
- The general formula for carbohydrates is Cn(H₂O)n.
Definition of a Carbohydrate
- Carbohydrates are defined as optically active polyhydroxy aldehydes or ketones.
- This means they can rotate plane-polarized light and contain multiple hydroxyl (-OH) groups.
- They are either aldehydes (containing the -CHO group) or ketones (containing the -C=O group).
Classification of Carbohydrates
- Carbohydrates are classified based on the number of sugar units they contain.
- Monosaccharides are simple sugars that cannot be broken down into smaller units.
- Oligosaccharides are composed of two to ten monosaccharide units linked together.
- Polysaccharides are complex carbohydrates made up of long chains of monosaccharides.
Reducing Sugars
- Reducing sugars are carbohydrates with a free aldehyde or ketone group.
- These sugars can be oxidized by mild oxidizing agents like Fehling's reagent or Tollens' reagent.
- Examples of reducing sugars include glucose and fructose.
Non-Reducing Sugars
- Non-reducing sugars lack a free aldehyde or ketone group.
- They cannot be oxidized by mild oxidizing agents.
- Examples include sucrose (table sugar) and starch.
Monosaccharides
- Monosaccharides are the simplest form of carbohydrates.
- They are classified by the number of carbon atoms they contain.
- Triose - 3 carbon atoms
- Tetrose - 4 carbon atoms
- Pentose - 5 carbon atoms
- Hexose - 6 carbon atoms
- An aldose contains an aldehyde group.
- A ketose contains a ketone group.
Glucose
- Glucose is a hexose sugar.
- It is an aldose, meaning it contains an aldehyde group.
- Glucose is the most common monosaccharide in nature.
- It is the primary source of energy for living organisms.
Fructose
- Fructose is a hexose sugar.
- It is a ketose, meaning it contains a ketone group.
- Fructose is naturally found in fruits and honey.
- It is sweeter than glucose.
Preparation of Glucose and Fructose
- Glucose and fructose can be prepared by the hydrolysis of sucrose (cane sugar).
- Sucrose is a disaccharide composed of glucose and fructose linked together.
- Acid hydrolysis breaks sucrose into glucose and fructose.
Starch
- Starch is a polysaccharide composed of glucose units.
- It's a major storage form of carbohydrates in plants.
- Starch is found in foods like rice, wheat, potatoes, and corn.
- Starch can be hydrolyzed to produce glucose.
Evidence for the Structure of Glucose
- Glucose's structure is confirmed by various experiments.
- Heating glucose with hydrogen iodide (HI) produces n-hexane, confirming the six-carbon straight chain.
Glucose Structure and Properties
- Glucose is a vital biological molecule with a complex structure. Important Properties: It contains a six-carbon straight chain (C₆H₁₂O₆).
- A carbonyl group (C=O) was confirmed by reaction with hydroxylamine, forming an oxime.
- An aldehyde group was confirmed by reaction with bromine water, forming a carboxylic acid.
- Five hydroxyl groups (OH) were confirmed by reaction with acetic anhydride, forming glucose pentaacetate.
- A primary alcoholic group (CH₂OH) was confirmed by oxidation with nitric acid, forming saccharic acid.
- Chiral carbons (with four different groups attached) define stereoisomers, with D-glucose the predominant natural form.
- The "D" or "L" designation signifies the hydroxyl group orientation on the chiral center.
The Cyclization of Glucose
- The initially proposed straight-chain structure couldn't completely explain observations.
- Certain aldehyde reactions (with NH₃, 2,4-dinitrophenylhydrazine (DNPH), or NaHSO₃) were not occurring as expected. This suggested a lack of a free aldehyde group.
- Glucose exists in two forms: α and β, which are explained by the cyclic structure.
- Alpha (m.p. 419 K) has a specific rotation of +111°.
- Beta (m.p. 423 K) has a specific rotation of +19.2°.
The Cyclic Structure of Glucose
- A hydroxyl group on carbon 5 reacts with the carbonyl group on carbon 1, forming a six-membered ring called a hemiacetal.
- This effectively locks the aldehyde group, explaining its lack of reaction with certain reagents.
- α and β forms are anomers, differing in the orientation of the hydroxyl group on carbon 1.
Key Takeaways
- Glucose's structure refinement exemplifies scientific advancement through experimentation.
- The confirmed structure forms the basis for glucose's crucial biological role.
- Scientists’ meticulous lab work was crucial in determining the structure and unique behavior of glucose.
Cyclic Structures
- Glucose and fructose exist in cyclic forms (Haworth/pyranose structures).
- Cyclic forms result from intramolecular reactions between the carbonyl and a hydroxyl group.
- The ring has one less carbon than the linear form.
- Glucose has two cyclic forms (α and β), distinguished by the orientation of the hydroxyl group on carbon 1 in the Haworth projection structure.
- Fructose also exists in cyclic forms (α and β), differing by the orientation of the hydroxyl group on carbon 2 in the Haworth projection.
Disaccharides
- Disaccharides form from two monosaccharides.
- The bond between them is a glycosidic linkage, formed via a dehydration reaction.
- Different carbon atoms create different disaccharides.
Sucrose
- Sucrose is a disaccharide of glucose and fructose.
- The glycosidic linkage connects the C1 of glucose to the C2 of fructose.
- Sucrose is a non-reducing sugar because both anomeric carbons are involved in the glycosidic linkage.
- It rotates plane-polarized light to the right (dextrorotatory).
- Hydrolysis (with acid or enzyme sucrase) yields glucose and fructose, often called "invert sugar."
Maltose
- Maltose is a disaccharide with two glucose units.
- The glycosidic linkage connects C1 of one glucose to C4 of the other.
- Maltose is a reducing sugar because one anomeric carbon is free.
Lactose
- Lactose is a disaccharide of glucose and galactose.
- The glycosidic linkage connects C1 of galactose to C4 of glucose.
- Lactose is a reducing sugar (free anomeric carbon).
Important Points to Remember
- Reducing Sugars: Monosaccharides and disaccharides with a free anomeric carbon can undergo oxidation.
- Non-reducing Sugars: Disaccharides with both anomeric carbons in glycosidic linkage cannot undergo oxidation.
- Mutarotation: Change in optical rotation as equilibrium is established between α and β anomers.
- Hydrolysis: Breaking a disaccharide into its monosaccharides by adding water to a glycosidic bond.
- Glycosidic Linkage: Covalent bond joining monosaccharides in disaccharides and polysaccharides.
Polysaccharides: Starch, Cellulose, Glycogen
- Starch in plants, the primary storage form of carbohydrates, consists of:
- Amylopectin: Branched polymer of glucose.
- Amylose: Linear polymer of glucose.
- Cellulose is a structural component of plant cell walls, a linear polymer of β-D-glucose.
- Glycogen is the primary storage form of carbohydrates in animals, a highly branched polymer of glucose.
Amino Acids
- Amino acids are organic molecules with both an amino group (-NH₂) and a carboxyl group (-COOH).
- They are the building blocks of proteins. The α-carbon is bonded to:
- A hydrogen atom, an amino group, a carboxyl group, and a variable side chain (R group).
- α-amino acids are the most common.
- β-amino acids exist but are less prevalent.
- Classification: Based on side chain properties (acidic, basic, neutral). Also based on whether the body can synthesize them (essential vs. non-essential).
Peptide Bond
- A peptide bond is a covalent bond between two amino acids. It forms via a dehydration reaction (removing H₂O).
Zwitterions
- Amino acids exist as zwitterions in solution.
- A zwitterion has both a positive and a negative charge, but is neutral overall (e.g., NH₃⁺ and COO⁻).
Protein Structures
- Primary structure: Sequence of amino acids.
- Secondary structure: Local folding (α-helix, β-sheet), stabilized by hydrogen bonds.
- Tertiary structure: Overall 3D structure of a single polypeptide chain, formed by interactions between side chains (hydrophobic, ionic, disulfide bonds).
- Quaternary structure: Arrangement of multiple polypeptide chains in a protein complex, stabilized by interactions between chains (e.g. disulfide bonds).
Denaturation
- Denaturation disrupts protein's tertiary and/or secondary structure, caused by heat, pH changes, or chemicals.
- Reversible denaturation allows the protein to regain its original form.
- Irreversible denaturation permanently changes the structure.
Important Points to Remember
- Mutarotation is the change in optical rotation of a substance due to change in isomeric form of a sugar.
- Sucrose is a disaccharide formed from glucose and fructose.
- Starch is a polysaccharide, a significant storage form of carbohydrates in plants. Amylopectin is branched and insoluble in water, while amylose is linear and soluble in water. Cellulose is another structural polysaccharide.
- Amino acids are classified based on the functional groups present on their side chain.
- Proteins are formed by chains of amino acids connected by peptide bonds.
- Denaturation is a significant process in cooking, sterilization methods, and scientific study of proteins.
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Description
This quiz covers essential concepts related to biomolecules, focusing specifically on carbohydrates. It includes the definitions, classifications, and structural features of carbohydrates, which are vital organic compounds for life. Assess your understanding of these fundamental biological molecules.
