2.3.2 Globular and fibrous proteins: haemoglobin and collagen Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 2

The 20 questions

1. Which structural feature of haemoglobin allows it to carry oxygen?

   • A triple helix of three polypeptides held together by covalent cross-links
   • A single long fibrous chain that wraps around a central core of glycogen
   • A phosphate group bound to each amino acid, which binds oxygen molecules directly
   • A haem group containing an iron ion in each of its four polypeptide subunits

2. How many polypeptide subunits does a normal adult haemoglobin molecule contain?

   • 1
   • 4
   • 2
   • 3

3. Why is haemoglobin described as a globular protein?

   • Its polypeptide chains are folded into a compact, roughly spherical shape with hydrophilic groups on the outside
   • Its polypeptide chains are held together by cross-links in a repeating triple helix
   • Its polypeptide chains are long and unfolded, forming parallel strands that are insoluble in water
   • It is made of glucose units joined by glycosidic bonds into a spherical polysaccharide

4. Which feature of collagen gives it high tensile strength?

   • A single globular polypeptide with a central haem group that binds to iron ions
   • Three polypeptide chains wound together in a triple helix, cross-linked into fibrils
   • A short chain of amino acids joined by ester bonds that forms a flexible network
   • Hydrophobic interactions on the surface that repel water and keep the molecule rigid

5. Which amino acid is found at every third position in collagen's repeating sequence, allowing the three chains to pack closely?

   • Glycine
   • Haem
   • Cysteine
   • Glutamate

6. Why is collagen insoluble in water?

   • It is a globular protein with charged groups on its surface that repel water
   • It contains a haem group that is non-polar and so does not mix with water
   • It forms long fibres with many hydrophobic regions that pack together and do not dissolve
   • It is made of glucose units that are linked into an insoluble polysaccharide chain

7. Which tissues would be expected to contain large amounts of collagen?

   • Red blood cells, where oxygen transport is the main requirement
   • Liver cells, where glycogen is stored for energy release
   • Tendons and skin, where tensile strength is needed
   • Muscle cells, where contraction depends on haemoglobin

8. What is the main function of the haem group in haemoglobin?

   • It binds carbon dioxide only, so that haemoglobin can transport waste from the tissues to the lungs
   • It binds oxygen reversibly, allowing haemoglobin to load oxygen in the lungs and release it in tissues
   • It forms the cross-links between subunits that hold the haemoglobin molecule together
   • It catalyses the breakdown of glucose inside red blood cells to produce ATP for the cell

9. Why is haemoglobin's oxygen binding described as cooperative?

   • Binding of one oxygen molecule blocks the other subunits, so only one oxygen can ever be carried
   • Haemoglobin binds oxygen in one subunit at a time, which requires a separate enzyme for each subunit
   • Binding of one oxygen molecule makes it easier for the next oxygen to bind to the other subunits
   • Oxygen binds to haemoglobin only when carbon dioxide is absent, which prevents cooperation

10. What is the effect of a fall in pH on haemoglobin's affinity for oxygen, as in a respiring muscle?

    • Affinity rises to zero, so no oxygen can bind in the lungs at all
    • Affinity is unchanged, because pH has no effect on the shape of haemoglobin
    • Affinity falls, so more oxygen is released to the muscle tissue
    • Affinity rises, so more oxygen is held by haemoglobin in the muscle

11. Which change in the sequence of haemoglobin's beta chain causes sickle cell anaemia?

    • A single amino acid substitution, glutamate replaced by valine, at position 6
    • A change in the bases of the DNA that codes for a stop codon at the end of the chain
    • An extra haem group added to each beta subunit, which changes its colour
    • A deletion of the entire beta chain, so that the molecule has only two subunits

12. Why does a single amino acid change in haemoglobin cause sickle cell anaemia?

    • The substitution creates a new stop codon, so only half of each haemoglobin is made
    • The substitution creates a hydrophobic patch on the surface, causing haemoglobin to aggregate into fibres
    • The substitution removes the haem group, so the molecule can no longer bind oxygen at all
    • The substitution increases the solubility of the molecule, which makes the cell too large

13. Which description of a fibrous protein's structure is correct?

    • Branched polysaccharides that are hydrolysed to glucose in the liver
    • Spherical structures with a compact core containing haem groups
    • Repeating sequences of amino acids form regular, long, strand-like structures
    • Short peptides joined by ester bonds that form a flexible water-soluble network

14. Why is collagen well suited to resisting stretching in tendons?

    • Its glycogen content allows it to expand and contract without damage
    • Its globular structure allows it to deform easily and return to its original shape each time
    • Its triple helix is cross-linked into strong fibrils that resist being pulled apart
    • Its haem groups absorb mechanical energy when the tendon is stretched by muscle

15. Which of these describes the difference between globular and fibrous proteins in terms of solubility?

    • Both globular and fibrous proteins are insoluble because they are made of amino acids
    • Globular proteins are generally insoluble, whereas fibrous proteins are generally soluble
    • Globular proteins are generally soluble, whereas fibrous proteins are generally insoluble
    • Both globular and fibrous proteins are soluble because they contain glycosidic bonds

16. A student tests the oxygen binding of haemoglobin in a solution with a higher concentration of carbon dioxide. What is the most likely result?

    • Less oxygen is bound at each partial pressure, so the dissociation curve shifts to the right
    • More oxygen is bound at each partial pressure, so the dissociation curve shifts to the left
    • No change occurs, because carbon dioxide has no effect on the binding of oxygen to haemoglobin
    • Oxygen binds permanently, so the haemoglobin cannot release oxygen at any concentration

17. Which feature of haemoglobin is most important for its role in transport?

    • A quaternary structure that allows cooperative binding of oxygen through four subunits
    • A triple helix that gives it tensile strength against the pressure of blood flow
    • A fibrous structure that makes it insoluble in plasma and allows it to be stored in cells
    • A single polypeptide chain with no haem group, so it can move freely through the blood

18. Why is collagen rich in hydroxyproline and proline residues?

    • These residues help stabilise the triple helix structure of collagen
    • These residues are the sites where glycosidic bonds form to link collagen to starch
    • These residues are needed for the hydrolysis of collagen by enzymes in the blood
    • These residues are needed to bind the haem group that carries oxygen in collagen

19. Why is the oxygen dissociation curve of haemoglobin sigmoidal rather than a straight line?

    • Haemoglobin binds oxygen only after carbon dioxide has been released, which produces a delay in the curve
    • Oxygen binding is independent for each haem group, which gives a straight line across the full range
    • The haem groups bind oxygen only at one pH, creating a single flat plateau with no change in affinity
    • Cooperative binding means affinity increases as more oxygen binds, giving a steep middle section of the curve

20. Which of these is a fibrous protein found in hair and nails?

    • Keratin
    • Amylase
    • Haemoglobin
    • Insulin

Related quizzes

• Gas exchange surfaces and Fick's Law Quiz · 2.1.1 · 20 questions
• Cell membrane structure and the fluid mosaic model Quiz · 2.1.2 · 20 questions
• Osmosis, diffusion and membrane transport Quiz · 2.1.3 · 20 questions
• Nucleotides, DNA and RNA structure Quiz · 2.2.1 · 20 questions
• Transcription, translation, the genetic code and genes Quiz · 2.2.2 · 20 questions
• Amino acids, polypeptides and protein structure Quiz · 2.3.1 · 20 questions
• Enzyme mechanism, specificity and activation energy Quiz · 2.3.3 · 20 questions
• DNA replication and the Meselson and Stahl experiment Quiz · 2.4.1 · 20 questions
• Mutations and cystic fibrosis Quiz · 2.4.2 · 20 questions
• Monohybrid inheritance and pedigree diagrams Quiz · 2.5.1 · 20 questions