2.3.1 Amino acids, polypeptides and protein structure Quiz: Pearson Edexcel Biology A (Salters-Nuffield), Unit 2

The 20 questions

1. What are the three components common to all amino acids?

   • A glycerol backbone, a carboxyl group and a long hydrocarbon tail bonded to nitrogen
   • An amine group, a carboxyl group and a variable R group, all bonded to a central carbon atom
   • A hydroxyl group, a glucose unit and an ester bond bonded to a central carbon atom
   • A phosphate group, a pentose sugar and a nitrogenous base bonded to a central carbon

2. How many different standard amino acids are used to build proteins in living organisms?

   • 20
   • 64
   • 61
   • 4

3. What type of bond joins two amino acids in a polypeptide chain?

   • Glycosidic bond
   • Peptide bond
   • Phosphodiester bond
   • Ester bond

4. Which reaction forms a peptide bond between two amino acids?

   • Oxidation, in which hydrogen is removed from each amino acid
   • Condensation, in which one molecule of water is removed
   • Hydrolysis, in which one molecule of water is added
   • Photolysis, in which light energy breaks the amine groups apart

5. A polypeptide is made from 12 amino acids. How many peptide bonds does it contain?

   • 10
   • 12
   • 24
   • 11

6. Which level of protein structure is determined by the sequence of amino acids in the chain?

   • Tertiary structure
   • Quaternary structure
   • Primary structure
   • Secondary structure

7. Which bonds are involved in holding the secondary structure of a protein, such as an alpha helix, in place?

   • Glycosidic bonds between sugar units attached to the backbone
   • Hydrogen bonds between the carbonyl and amine groups of the peptide backbone
   • Peptide bonds between the R groups of neighbouring amino acids
   • Ionic bonds between the carboxyl groups in the middle of the chain

8. Which bond type is a covalent link that can stabilise tertiary structure through two cysteine residues?

   • Glycosidic bond
   • Hydrogen bond
   • Ionic bond
   • Disulfide bridge

9. Which interaction between R groups is most likely to be found in the interior of a globular protein?

   • Peptide bonds between R groups on the surface
   • Hydrophobic interactions between non-polar R groups
   • Ionic bonds between charged R groups at the surface
   • Hydrogen bonds between the surface R groups and water

10. What is the quaternary structure of a protein?

    • The coiling of a polypeptide into an alpha helix stabilised by hydrogen bonds
    • The bonding of a polypeptide to a sugar unit to form a glycoprotein
    • The arrangement of two or more polypeptide chains into a single functional protein
    • The linear sequence of amino acids in a single polypeptide chain

11. Why does changing a single amino acid in a protein's primary structure sometimes change its function?

    • It changes the genetic code so that a different gene is expressed in the cell
    • It can alter the bonds and folding of the chain, changing the three-dimensional shape and active site
    • It changes only the colour of the protein, which has no effect on its function
    • It always increases the length of the chain by one amino acid, which then blocks the active site

12. Which feature of a globular protein is most closely linked with its solubility in water?

    • Long fibrous chains of collagen that pack together in bundles
    • A lack of any charged groups at the surface of the molecule
    • Hydrophobic R groups on the outside of the molecule that repel water
    • Hydrophilic R groups on the outside of the molecule that interact with water

13. What is the best description of a fibrous protein?

    • Short chains of amino acids joined by ester bonds that act as energy stores
    • Spherical molecules that are soluble in water and function as enzymes or transporters
    • Chains of glucose units joined by glycosidic bonds that are used for structural support
    • Long strands of polypeptide that form structural sheets or fibres and are generally insoluble in water

14. Which of these is a globular protein?

    • Keratin
    • Collagen
    • Elastin
    • Haemoglobin

15. What is the approximate number of amino acids in a polypeptide that has a mass of 11 000 daltons, if the average amino acid has a mass of 110 daltons?

    • 10
    • 1100
    • 100
    • 1000

16. Why is a protein's three-dimensional structure important for its function?

    • Its shape determines the genetic code used by the protein to specify amino acids
    • Its shape determines only the colour of the protein and does not affect its activity
    • Its shape determines the active site or binding site that interacts with specific molecules
    • Its shape determines how many amino acids the protein contains, which sets its length

17. Which of these describes the R group of an amino acid?

    • The amine group that is used in condensation reactions to release water
    • The variable side chain that differs between amino acids and determines their properties
    • The carboxyl group that forms the peptide bond with the next amino acid
    • The central carbon atom to which all of the other groups are attached

18. A protein has two identical polypeptide chains held together by hydrogen bonds and ionic bonds. Which level of structure does this describe?

    • Primary structure
    • Secondary structure
    • Quaternary structure
    • Tertiary structure

19. Which of these interactions is responsible for the coiling of the polypeptide chain into an alpha helix?

    • Peptide bonds between the R groups of distant amino acids
    • Glycosidic bonds between the amine groups of adjacent amino acids
    • Hydrogen bonds between groups on the backbone spaced four residues apart
    • Phosphodiester bonds between the carboxyl groups of distant amino acids

20. A student compares a collagen fibre with a haemoglobin molecule. Which statement correctly contrasts their structures?

    • Collagen is made of glucose units, whereas haemoglobin is made of fatty acids linked to glycerol
    • Collagen is a globular protein that is soluble, whereas haemoglobin is a fibrous protein that is insoluble
    • Collagen is a fibrous protein with a repetitive triple helix, whereas haemoglobin is a globular protein with a compact shape
    • Collagen and haemoglobin are both fibrous proteins with identical structures and functions

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