IB Biology HL B1.2 Proteins Questions

Practise IB Biology HL B1.2 with questions that move from amino-acid and peptide-bond diagrams to protein folding, interactions, denaturation and structure–function reasoning.

Exam points

Identify an amino acid’s alpha carbon and its amine group, carboxyl group, hydrogen and variable R-group, and relate protein composition to C, H, O, N and usually S.
Classify R-groups as acidic, basic, polar hydrophilic or non-polar hydrophobic, and explain how their chemistry affects solubility, interactions, folding and function.
Explain amino-acid condensation: peptide-bond formation, water release, dipeptide or polypeptide products, N- and C-termini, and ribosomal chain assembly.
Distinguish essential amino acids that must come from dietary protein from non-essential amino acids made by the body, and explain deficiency, limiting amino acids and protein malnutrition.
Relate amino-acid type, number and order, genes, codons and translation to primary structure and the diversity of polypeptide sequences and protein functions.
Explain how high temperature, extreme pH, salts or heavy metals denature proteins by disrupting weak interactions, changing active sites and reducing biological activity.
Identify alpha helices and beta-pleated sheets as secondary structures stabilized by regular hydrogen bonds between peptide-group C=O and N-H atoms.
Define tertiary structure as the three-dimensional folding of one polypeptide and identify hydrogen-bond, ionic, disulfide-covalent and hydrophobic interactions between R-groups.
Define quaternary structure as two or more polypeptide chains forming one functional protein, using haemoglobin or insulin as examples.
Distinguish compact, often soluble globular proteins from long, often insoluble fibrous proteins and relate each form to catalysis, transport, signalling or structural strength.

Covered syllabus points

B1.2.1—Generalized amino acid structure B1.2.2—Condensation reactions B1.2.3—Dietary amino acids B1.2.4—Infinite variety of peptide chains B1.2.5—Effect of pH and temperature B1.2.6 (HL)—Chemical diversity in R-groups B1.2.7 (HL)—Primary structure impact B1.2.8 (HL)—Secondary structure B1.2.9 (HL)—Tertiary structure B1.2.10 (HL)—Effect of polar/non-polar amino acids B1.2.11 (HL)—Quaternary structure B1.2.12 (HL)—Globular vs. fibrous proteins

[Maximum number: 7]

(a)

Some of the twenty amino acids that are linked together to make polypeptides in human cells are essential in the diet and others are not. Distinguish between essential and non-essential amino acids.

[ 2 ]

(b)

The molecules of all amino acids include an amine group, a carboxyl group and an R-group. Draw a diagram to show the structure of an amino acid molecule.

[ 3 ]

Figure for Answer to Question (b) — IB Biology HL

and bonded to C ;

c.

Allow a specific amino acid R -
group in marking point c, such
as $\mathrm{CH}_{3}$ (in alanine).

(c)

The R-groups of amino acids are very diverse chemically. Interaction between R-groups in different parts of a polypeptide helps to determine the tertiary structure of a protein. List two types of interaction between R-groups.

[ 2 ]

[Maximum number: 2]

(a)

Label a peptide bond in the diagram of a polypeptide.

[ 1 ]

(b)

Outline the primary structure of proteins.

[ 1 ]

[Maximum number: 7]

Proteins are an extraordinarily diverse group of carbon compounds that have a wide range of roles in cells.

Describe the structure of proteins, including features that are common to all proteins and features that vary.

a. composed of one or more polypeptides / some are single polypeptides others made of 2 or more polypeptide chains / all proteins consist of, at least, one polypeptide chain;

b. a polypeptide/protein is a chain of amino acids;

c. (chains of) amino acids linked by peptide bonds;

d. twenty different amino acids/ amino acids have different R groups/ R groups can be hydrophilic/polar or hydrophobic/non-polar;

e. primary structure is the sequence/order (and number) of amino acids in the polypeptide;

f. any sequence/order of amino acids could be linked together hence many possible polypeptides/proteins;

g. secondary structure is the formation of alpha/ $\alpha$ helices and beta/ $\beta$ pleated sheets;

h. secondary structure stabilized by hydrogen bonding;

i. tertiary structure is the further folding of the polypeptide / tertiary structure is the threedimensional (3-D) conformation/structure/shape of a protein;

j. tertiary structure stabilized by interactions / ionic bonds/hydrogen bonds/disulfide bridges between R groups;

k. fibrous or globular are the two main classes of conformation/three-dimensional/ 3-D structure/shape;

l. conformation/three-dimensional (3-D) structure determined by amino acid sequence;

m. quaternary structure if two or more polypeptides are linked to form a (single) protein OR quaternary structure if a prosthetic group is linked (to form a conjugated protein);

Marking guidance:

Accept clearly annotated diagrams.

Mpc: accept a clearly annotated diagram of the bond between 2 drawn amino acids.

[Maximum number: 3]

The molecules of all amino acids include an amine group, a carboxyl group and an R-group. Draw a diagram to show the structure of an amino acid molecule.

Figure for Answer to Question 4 — IB Biology HL

and bonded to C ;

c.

Allow a specific amino acid R -
group in marking point c, such
as $\mathrm{CH}_{3}$ (in alanine).

[Maximum number: 1]

Label a peptide bond in the diagram of a polypeptide.

[Maximum number: 2]

Some of the twenty amino acids that are linked together to make polypeptides in human cells are essential in the diet and others are not. Distinguish between essential and non-essential amino acids.

[Maximum number: 4]

Proteins carry out many important functions in cells and in organisms.

Outline the process of protein denaturation.

[Maximum number: 2]

Describe how the diversity of amino acids gives proteins a broad range of forms.

[Maximum number: 1]

Outline the primary structure of proteins.

[Maximum number: 2]

Titin is the longest protein in the human body, consisting of a single strand of over 34000 amino acids.

Ribbon representation of part of titin, showing several broad arrow-shaped strands connected by looping sections of the protein chain.

Describe the secondary structures represented by the arrows in the diagram.

a. beta/ $\beta$ -pleated sheets;
b. (structure held in place by) hydrogen bonds between N-H and C=O on different amino acids
OR
hydrogen bonds between sections of polypeptide running parallel or antiparallel
OR
sections of polypeptide form a pleat (when they run in opposite directions) because of the tetrahedral bond angles;

[Maximum number: 2]

[Maximum number: 1]

Myoglobin is a globular protein in which nearly all the non-polar R-groups point towards the inside of the molecule. The outside surface contains all the polar R-groups. What can be deduced from this?

Disulfide bonds occur on the inside.

Hydrogen bonds form with water on the outside.

Ionic bonds form with water on the outside.

Covalent bonds occur on the inside.

[Maximum number: 1]

Hemoglobin is a conjugated protein consisting of four polypeptide chains with attached heme groups.

State the level of protein structure at which the polypeptide chains of hemoglobin are combined.

[Maximum number: 1]

Diagrams of three different proteins, X, Y and Z , are shown.

Which row describes the structure of each protein shown?

quaternary

globular

secondary

conjugated

fibrous

globular

tertiary

quaternary

primary

globular

secondary

fibrous

All question bank results loaded

Covered syllabus points

Question 1

Question (a)

Question (b)

Question (c)

Question 2

Question (a)

Question (b)

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14