02.14 End of Chapter Questions

• D;

Study Notes:

Collagen:

• Type: Fibrous protein
• Function: Provides structural support in connective tissues like skin, bones, and tendons.
• Characteristics: Long, strong, and insoluble in water.

Hemoglobin:

• Type: Globular protein
• Function: Transports oxygen from the lungs to tissues and returns carbon dioxide from tissues to the lungs.
• Characteristics: Spherical shape, soluble in water, and contains heme groups for oxygen binding.

Option Analysis

A. Enzymes

• Definition: Proteins that act as biological catalysts to accelerate chemical reactions.
• Relevance to Collagen and Hemoglobin:
  • Collagen: Not an enzyme; it’s a structural protein.
  • Hemoglobin: Also not an enzyme; its primary role is oxygen transport.
• Conclusion: Incorrect. Neither collagen nor hemoglobin functions as enzymes.

B. Fibrous Proteins

• Definition: Proteins with elongated, fiber-like structures, primarily involved in structural roles.
• Relevance to Collagen and Hemoglobin:
  • Collagen: Yes, it is a fibrous protein.
  • Hemoglobin: No, it is a globular protein.
• Conclusion: Partially Correct. Only collagen fits this category, not hemoglobin.

C. Globular Proteins

• Definition: Proteins that are more spherical in shape and are typically soluble in water, often involved in metabolic functions.
• Relevance to Collagen and Hemoglobin:
  • Collagen: No, it is a fibrous protein.
  • Hemoglobin: Yes, it is a globular protein.
• Conclusion: Partially Correct. Only hemoglobin fits this category, not collagen.

D. Macromolecules

• Definition: Large complex molecules, which include proteins, nucleic acids, carbohydrates, and lipids.
• Relevance to Collagen and Hemoglobin:
  • Collagen: Yes, it is a macromolecule.
  • Hemoglobin: Yes, it is also a macromolecule.
• Conclusion: Correct. Both collagen and hemoglobin are macromolecules as they are large, complex proteins.

• C;

Understanding Disulfide Bonds

• Disulfide Bonds:
  • Definition: Covalent bonds formed between the sulfur atoms of two cysteine amino acids within or between protein molecules.
  • Function: Stabilize the three-dimensional structure of proteins, particularly important in extracellular proteins and those secreted outside the cell.
  • Formation: Involves the oxidation of thiol (-SH) groups to form a disulfide linkage (-S–S-).

Option Analysis

A. Condensation

• Definition: A chemical reaction where two molecules combine to form a larger molecule, typically with the loss of a small molecule like water.
• Relevance to Disulfide Bonds:
  • Condensation reactions are involved in forming peptide bonds between amino acids, not disulfide bonds.
  • Disulfide bond formation specifically involves the oxidation of thiol groups without the loss of water.
• Conclusion: Incorrect. Disulfide bond formation does not involve condensation reactions.

B. Hydrolysis

• Definition: A chemical reaction that involves the breaking of bonds in a molecule using water.
• Relevance to Disulfide Bonds:
  • Hydrolysis typically breaks bonds, whereas disulfide bond formation is about creating bonds.
  • Hydrolysis can break disulfide bonds but is not involved in their formation.
• Conclusion: Incorrect. Hydrolysis is associated with bond cleavage, not bond formation.

C. Oxidation

• Definition: A chemical reaction involving the loss of electrons, often associated with the addition of oxygen or the removal of hydrogen.
• Relevance to Disulfide Bonds:
  • Oxidation of the thiol (-SH) groups in cysteine residues leads to the formation of a disulfide bond (-S–S-).
  • This process involves the loss of electrons from the sulfur atoms, facilitating bond formation.
• Conclusion: Correct. The formation of disulfide bonds is an oxidation reaction.

D. Reduction

• Definition: A chemical reaction involving the gain of electrons, often associated with the removal of oxygen or the addition of hydrogen.
• Relevance to Disulfide Bonds:
  • Reduction can break disulfide bonds by adding electrons to the bond, converting it back to two thiol groups.
  • It is the opposite process of disulfide bond formation.
• Conclusion: Incorrect. Reduction is involved in breaking disulfide bonds, not forming them.
  

• B;

Study notes:

Water Molecule Polarity:

• Oxygen Atom (δ⁻): Possesses a partial negative charge.
• Hydrogen Atoms (δ⁺): Possess partial positive charges.

Hydration of Na⁺ (Cation):

• Orientation: Water molecules orient their oxygen ends (δ⁻) towards the Na⁺ ion.
• Reason: The negative oxygen attracts the positive sodium ion.

Hydration of Cl⁻ (Anion):

• Orientation: Water molecules orient their hydrogen ends (δ⁺) towards the Cl⁻ ion.
• Reason: The positive hydrogen atoms are attracted to the negative chloride ion.

1. Monomer

• Globular Protein: ✗
  Explanation: Globular proteins are polymers composed of amino acid monomers, not monomers themselves.
• Fibrous Protein: ✗
  Explanation: Similar to globular proteins, fibrous proteins are polymers made from amino acid monomers.
• Monosaccharide: ✓
  Explanation: Monosaccharides are simple sugars and serve as the monomer units for carbohydrates.
• Disaccharide: ✗
  Explanation: Disaccharides are composed of two monosaccharide units linked together.
• Glycogen: ✗
  Explanation: Glycogen is a polysaccharide polymer made from glucose monomers.
• Starch: ✗
  Explanation: Starch is a polymer composed of glucose monomers.
• Cellulose: ✗
  Explanation: Cellulose is a polysaccharide made from glucose monomers.
• Lipid: ✗
  Explanation: Lipids are not polymers; they are composed of fatty acid and glycerol monomers.

2. Polymer

• Globular Protein: ✓
  Explanation: Globular proteins are large, complex molecules made by linking amino acid monomers.
• Fibrous Protein: ✓
  Explanation: Fibrous proteins are polymers composed of amino acids, forming long, fibrous structures.
• Monosaccharide: ✗
  Explanation: Monosaccharides are monomers, not polymers.
• Disaccharide: ✗
  Explanation: Disaccharides consist of two monosaccharide units, hence not polymers.
• Glycogen: ✓
  Explanation: Glycogen is a highly branched polymer of glucose units.
• Starch: ✓
  Explanation: Starch is a polymer made up of glucose units, including both linear and branched forms.
• Cellulose: ✓
  Explanation: Cellulose is a linear polymer of glucose units linked by β-glycosidic bonds.
• Lipid: ✗
  Explanation: Lipids are not polymers; they are made up of fatty acids and glycerol.

3. Macromolecule

• Globular Protein: ✓
  Explanation: Globular proteins are large molecules essential for various biological functions.
• Fibrous Protein: ✓
  Explanation: Fibrous proteins are large, structural macromolecules.
• Monosaccharide: ✗
  Explanation: Monosaccharides are small molecules, not macromolecules.
• Disaccharide: ✗
  Explanation: Disaccharides are also small molecules, not classified as macromolecules.
• Glycogen: ✓
  Explanation: Glycogen is a large, complex macromolecule used for energy storage.
• Starch: ✓
  Explanation: Starch is a macromolecule serving as energy storage in plants.
• Cellulose: ✓
  Explanation: Cellulose is a macromolecule providing structural support in plant cell walls.
• Lipid: ✓
  Explanation: Lipids are considered macromolecules due to their large size and complex structures.

4. Polysaccharide

• Globular Protein: ✗
  Explanation: Proteins are not carbohydrates and thus not polysaccharides.
• Fibrous Protein: ✗
  Explanation: Similar to globular proteins, fibrous proteins are not carbohydrates.
• Monosaccharide: ✗
  Explanation: Monosaccharides are single sugar units, not polysaccharides.
• Disaccharide: ✗
  Explanation: Disaccharides consist of two sugar units, not forming a polysaccharide.
• Glycogen: ✓
  Explanation: Glycogen is a highly branched polysaccharide used for energy storage in animals.
• Starch: ✓
  Explanation: Starch is a polysaccharide composed of amylose and amylopectin, serving as energy storage in plants.
• Cellulose: ✓
  Explanation: Cellulose is a linear polysaccharide providing structural support in plant cell walls.
• Lipid: ✗
  Explanation: Lipids are not carbohydrates and do not form polysaccharides.

5. Contains Subunits that Form Branched Chains

• Globular Protein: ✗
  Explanation: Proteins can have complex tertiary structures but do not form branched chains in the context of polymers.
• Fibrous Protein: ✗
  Explanation: Fibrous proteins are typically linear and do not form branched chains.
• Monosaccharide: ✗
  Explanation: Monosaccharides are single units and do not form branched structures on their own.
• Disaccharide: ✗
  Explanation: Disaccharides consist of two monosaccharides linked together without branching.
• Glycogen: ✓
  Explanation: Glycogen is highly branched, allowing rapid release of glucose when needed.
• Starch: ✓
  Explanation: Starch contains amylopectin, which is branched, alongside linear amylose.
• Cellulose: ✗
  Explanation: Cellulose is a linear polymer without branching, forming strong fibers.
• Lipid: ✗
  Explanation: Lipids do not form branched chains in their typical structures.

6. Contains Amino Acids

• Globular Protein: ✓
  Explanation: Globular proteins are composed of amino acid monomers linked by peptide bonds.
• Fibrous Protein: ✓
  Explanation: Fibrous proteins are also made up of amino acids forming long, fibrous chains.
• Monosaccharide: ✗
  Explanation: Monosaccharides are carbohydrates, not composed of amino acids.
• Disaccharide: ✗
  Explanation: Disaccharides consist of two sugar units, not amino acids.
• Glycogen: ✗
  Explanation: Glycogen is a carbohydrate polymer, not containing amino acids.
• Starch: ✗
  Explanation: Starch is a carbohydrate polymer without amino acids.
• Cellulose: ✗
  Explanation: Cellulose is a carbohydrate polymer composed of glucose units, not amino acids.
• Lipid: ✗
  Explanation: Lipids are made from fatty acids and glycerol, not amino acids.

7. Made from Organic Acids and Glycerol

• Globular Protein: ✗
  Explanation: Proteins are made from amino acids, not organic acids and glycerol.
• Fibrous Protein: ✗
  Explanation: Similar to globular proteins, fibrous proteins are composed of amino acids.
• Monosaccharide: ✗
  Explanation: Monosaccharides are simple sugars, not formed from organic acids and glycerol.
• Disaccharide: ✗
  Explanation: Disaccharides are two monosaccharides linked together, not formed from organic acids and glycerol.
• Glycogen: ✗
  Explanation: Glycogen is a polymer of glucose units, not made from organic acids and glycerol.
• Starch: ✗
  Explanation: Starch is a polymer of glucose, not composed of organic acids and glycerol.
• Cellulose: ✗
  Explanation: Cellulose is a linear polymer of glucose units, not made from organic acids and glycerol.
• Lipid: ✓
  Explanation: Lipids, such as triglycerides, are formed from glycerol and fatty acids (organic acids).

8. Contains Glycosidic Bonds

• Globular Protein: ✗
  Explanation: Proteins contain peptide bonds, not glycosidic bonds.
• Fibrous Protein: ✗
  Explanation: Similar to globular proteins, fibrous proteins have peptide bonds.
• Monosaccharide: ✗
  Explanation: Monosaccharides are single sugar units and do not contain glycosidic bonds themselves.
• Disaccharide: ✓
  Explanation: Disaccharides are formed by glycosidic bonds between two monosaccharides.
• Glycogen: ✓
  Explanation: Glycogen is a polysaccharide with glycosidic bonds linking glucose units.
• Starch: ✓
  Explanation: Starch contains glycosidic bonds in both amylose and amylopectin components.
• Cellulose: ✓
  Explanation: Cellulose has β-glycosidic bonds linking glucose units.
• Lipid: ✗
  Explanation: Standard lipids do not contain glycosidic bonds.

9. Contains Peptide Bonds

• Globular Protein: ✓
  Explanation: Globular proteins are held together by peptide bonds between amino acids.
• Fibrous Protein: ✓
  Explanation: Fibrous proteins also contain peptide bonds linking amino acids.
• Monosaccharide: ✗
  Explanation: Monosaccharides are carbohydrates and do not contain peptide bonds.
• Disaccharide: ✗
  Explanation: Disaccharides consist of sugar units linked by glycosidic bonds, not peptide bonds.
• Glycogen: ✗
  Explanation: Glycogen is a carbohydrate polymer without peptide bonds.
• Starch: ✗
  Explanation: Starch is a carbohydrate polymer without peptide bonds.
• Cellulose: ✗
  Explanation: Cellulose is a carbohydrate polymer without peptide bonds.
• Lipid: ✗
  Explanation: Lipids do not contain peptide bonds.

10. One of Its Main Functions is to Act as an Energy Store

• Globular Protein: ✗
  Explanation: While some proteins can store energy, it is not their primary function.
• Fibrous Protein: ✗
  Explanation: Fibrous proteins primarily provide structural support, not energy storage.
• Monosaccharide: ✗
  Explanation: Monosaccharides are used for immediate energy but are not primary energy storage molecules.
• Disaccharide: ✗
  Explanation: Disaccharides serve as energy sources but are not the main storage forms.
• Glycogen: ✓
  Explanation: Glycogen is the primary energy storage polysaccharide in animals.
• Starch: ✓
  Explanation: Starch serves as the main energy storage polysaccharide in plants.
• Cellulose: ✗
  Explanation: Cellulose is a structural polysaccharide, not used for energy storage.
• Lipid: ✓
  Explanation: Lipids, such as triglycerides, are major energy storage molecules in organisms.

11. Usually Insoluble in Water

• Globular Protein: ✗
  Explanation: Globular proteins are typically water-soluble due to their polar surfaces.
• Fibrous Protein: ✓
  Explanation: Fibrous proteins are generally insoluble in water, providing structural roles.
• Monosaccharide: ✗
  Explanation: Monosaccharides are soluble in water.
• Disaccharide: ✗
  Explanation: Disaccharides are also water-soluble.
• Glycogen: ✗
  Explanation: Glycogen is soluble in water due to its highly branched structure.
• Starch: ✗
  Explanation: Starch is partially soluble; amylopectin is more soluble than amylose.
• Cellulose: ✓
  Explanation: Cellulose is insoluble in water, providing strong structural support in plants.
• Lipid: ✓
  Explanation: Lipids are hydrophobic and generally insoluble in water.

12. Usually Has a Structural Function

• Globular Protein: ✗
  Explanation: Globular proteins are primarily involved in enzymatic, transport, and regulatory functions.
• Fibrous Protein: ✓
  Explanation: Fibrous proteins provide structural support in tissues (e.g., collagen in skin).
• Monosaccharide: ✗
  Explanation: Monosaccharides serve as energy sources and building blocks, not structural components.
• Disaccharide: ✗
  Explanation: Disaccharides function mainly as energy sources.
• Glycogen: ✗
  Explanation: Glycogen is used for energy storage, not structural purposes.
• Starch: ✗
  Explanation: Starch serves as an energy reserve in plants.
• Cellulose: ✓
  Explanation: Cellulose provides structural integrity to plant cell walls.
• Lipid: ✗
  Explanation: Lipids are primarily involved in energy storage and membrane structure, not general structural support.

13. Can Form Helical or Partly Helical Structures

• Globular Protein: ✓
  Explanation: Globular proteins often contain alpha-helices and beta-sheets as part of their tertiary structure.
• Fibrous Protein: ✓
  Explanation: Fibrous proteins like collagen form helical structures to provide strength and flexibility.
• Monosaccharide: ✗
  Explanation: Monosaccharides are single units and do not form helical structures.
• Disaccharide: ✗
  Explanation: Disaccharides consist of two sugar units and do not form helical structures.
• Glycogen: ✗
  Explanation: Glycogen is a highly branched polymer without helical structures.
• Starch: ✓
  Explanation: Amylose, a component of starch, forms helical structures, while amylopectin is branched.
• Cellulose: ✗
  Explanation: Cellulose forms linear, rigid fibers without helical structures.
• Lipid: ✗
  Explanation: Lipids do not form helical structures.

14. Contains the Elements Carbon, Hydrogen, and Oxygen Only

Globular Protein: ✗
Explanation: Proteins contain nitrogen and sometimes sulfur, in addition to carbon, hydrogen, and oxygen.

Fibrous Protein: ✗
Explanation: Similar to globular proteins, fibrous proteins include nitrogen and sometimes sulfur.

Monosaccharide: ✓
Explanation: Monosaccharides consist solely of carbon, hydrogen, and oxygen.

Disaccharide: ✓
Explanation: Disaccharides are made up of two monosaccharides, containing only carbon, hydrogen, and oxygen.

Glycogen: ✓
Explanation: Glycogen is a polysaccharide composed of glucose units, containing only carbon, hydrogen, and oxygen.

Starch: ✓
Explanation: Starch is a polysaccharide made from glucose, containing only carbon, hydrogen, and oxygen.

Cellulose: ✓
Explanation: Cellulose is a polysaccharide consisting solely of carbon, hydrogen, and oxygen.

Lipid: ✗
Explanation: While most lipids contain carbon, hydrogen, and oxygen, some also include phosphorus (e.g., phospholipids) or nitrogen (e.g., sphingolipids).

Study notes:

1. Structural Proteins

• Examples: Collagen, Keratin, Elastin, Viral Coat Proteins
• Function: Provide support and shape to cells and tissues.
  • Collagen: Found in connective tissues like skin and bones, offering tensile strength.
  • Keratin: Present in hair, nails, and the outer layer of skin, providing protection.
  • Elastin: Found in elastic tissues such as arteries and lungs, allowing them to stretch and return to original shape.
  • Viral Coat Proteins: Form the protective outer layer of viruses.

2. Enzymes

• Examples: Amylase, Lactase, DNA Polymerase
• Function: Act as biological catalysts to speed up chemical reactions.
  • Amylase: Breaks down starch into sugars in saliva and the pancreas.
  • Lactase: Digests lactose into glucose and galactose in the small intestine.

3. Hormonal Proteins

• Examples: Insulin, Vasopressin (AVP)
• Function: Serve as chemical messengers regulating physiological processes.
  • Insulin: Regulates blood glucose levels by facilitating glucose uptake into cells.
  • Vasopressin (AVP): Controls water balance in the body by increasing water reabsorption in kidneys.

4. Respiratory Pigments

• Examples: Haemoglobin, Myoglobin
• Function: Transport and store oxygen.
  • Haemoglobin: Transports oxygen in red blood cells from the lungs to tissues.
  • Myoglobin: Stores oxygen in muscle tissues for use during intense activity.

5. Defensive Proteins

• Examples: Antibodies, Fibrinogen
• Function: Protect the body against pathogens and assist in immune responses.
  • Antibodies: Recognize and neutralize foreign antigens like bacteria and viruses.
  • Fibrinogen: Involved in blood clotting by forming fibrin threads that trap blood cells.

6. Contractile Proteins

• Examples: Actin, Myosin
• Function: Facilitate muscle contraction and movement within cells.
  • Actin: Interacts with myosin to enable muscle contraction.
  • Myosin: Generates force and movement by sliding along actin filaments during muscle contraction.

7. Storage Proteins

• Examples: Casein, Ovalbumin
• Function: Store essential nutrients and amino acids for future use.
  • Casein: Found in milk, providing amino acids for growth and development.
  • Ovalbumin: Present in egg whites, serving as a nutrient source for the developing embryo.

• dissolve easily in water;
• sweet;
• general formula (CH2O)n / contain the elements carbon, hydrogen and oxygen / hydrogen and oxygen are present in ratio of 2 : 1;

• lactose could be a source of energy;
• it could be digested to, monosaccharides / glucose and galactose, which could then be
• used as building blocks for larger molecules;

• condensation;

• glycosidic bond;

• glucose correctly drawn;
• galactose correctly drawn; [2]

Carbon atoms need not be numbered. Note that galactose will probably be drawn ‘upside down’ as in the disaccharide – the conventional way of drawing it is also shown in the diagram above. The form used to make the disaccharide is the beta form of galactose,
but students will not need to know this, other than for interest.

• alpha glucose / α-glucose;
• the –OH group on carbon atom 1 is below the ring;

• carry out a Benedict’s test on both solutions;
• lactose would give a brick-red / brown precipitate, sucrose would not;
• accept positive result for lactose, negative result for sucrose

• C of COOH joined to N of NH2 for both peptide bonds;
• peptide bonds shown as C=O joined to –NH (i.e. water has been eliminated);
• all three amino acids joined and in correct sequence; accept even if errors in bonding

• primary structure;

• water;

• ring drawn around –OH or whole R group (–CH₂OH) of serine;

• rings drawn around two peptide bonds and bonds labelled appropriately;

• ring drawn around –NH group one side of a peptide bond and group labelled A;

• held in place by hydrogen bonding;
• secondary structures;
• all the –NH and –C=O groups of, peptide bonds / polypeptide backbone, are involved;

• molecule made from repeating subunits;
• subunits similar or identical to each other;
• giant molecule / macromolecule;

• XXX, XXY, XYY, XYX, YYY, YYX, YXX, YXY;

• 2³

• A identified as lipid,
• B identified as phospholipid;

• junction between head and tail for all three tails is indicated on diagram;;
• Allow 1 mark if only one or two junctions indicated

• fatty acids;
• glycerol;

• head of phospholipid is labelled phosphate;

• phospholipid / B;

• phosphate is, charged / polar / hydrophilic;

• Lipid:
  • energy store / insulator / buoyancy / source of metabolic water / any other suitable example;
• phospholipid:
  • any reference to the importance of phospholipids in structure of membranes;

1 mark for each correct row. No half marks.

• 1 mark for structural feature, 1 mark
• for linking this feature to its function,
• e.g. haemoglobin contains iron.
• iron combines with oxygen;

• molecule has more than one polypeptide chain;
• R molecule has four polypeptide chains

• carbon, hydrogen, oxygen, nitrogen, iron;;
• 2 marks for all five correct, 1 mark for four correct, 0 marks for 3 or fewer correct