B1.2 Proteins
Practice exam-style IB Biology questions for Proteins, aligned with the syllabus and grouped by topic.
Question 1
An amino acid has an alpha carbon bonded to an amine group, a carboxyl group, a hydrogen atom and one other group. What is the fourth group?
A.
Phosphate group
B.
R-group
C.
Glycerol group
D.
Glycosidic group
Question 2
What is released when two amino acids join by a condensation reaction?
A.
Water
B.
Carbon dioxide
C.
Hydrogen gas
D.
Ammonia
Question 3
What is an essential amino acid in humans?
A.
An amino acid made from other amino acids
B.
An amino acid used only in enzymes
C.
An amino acid that must be obtained from the diet
D.
An amino acid containing sulfur
Question 4
What happens to many proteins when high temperature causes denaturation?
A.
Their three-dimensional shape is disrupted
B.
Their amino acid sequence is translated
C.
Their R-groups are removed from the alpha carbon
D.
Their peptide bonds are always hydrolysed
Question 5
What directly determines the sequence of amino acids in a ribosome-built polypeptide?
A.
Random collision of amino acids
B.
Genetic information
C.
The final folded shape alone
D.
The number of peptide bonds only
Question 6
The diagram shows a generalized amino acid.
State the name of group X.
[1]
State two other groups attached to the alpha carbon.
[1]
Question 7
The genetic code specifies 20 amino acids for ribosome-built polypeptides. How many different tripeptide sequences are possible if any amino acid can occur at each position?
A.
60
B.
400
C.
160000
D.
8000
Question 8
The bond formed between the carboxyl group of one amino acid and the amine group of another is a:
A.
peptide bond
B.
ester bond
C.
phosphodiester bond
D.
glycosidic bond
Question 9
A buffered albumen solution becomes more cloudy after heating. What is the best explanation?
A.
Amino acids become nucleotides at high temperature
B.
Peptide bonds form between water molecules and albumen
C.
Protein hydrolysis converts albumen into glucose molecules
D.
Protein denaturation exposes hydrophobic regions and causes precipitation
Question 10
What stabilizes alpha helices and beta-pleated sheets in proteins?
A.
Hydrogen bonds between peptide backbone groups
B.
Ionic bonds between all R-groups
C.
Hydrophobic interactions between peptide bonds
D.
Disulfide bonds between phosphate groups
Question 11
What is meant by the primary structure of a protein?
A.
The coiling of the peptide backbone into helices
B.
The linear sequence of amino acid residues
C.
The compact shape of a whole polypeptide chain
D.
The arrangement of multiple polypeptide subunits
Question 12
In a water-soluble globular protein, where are many non-polar amino acid R-groups found after folding?
A.
Removed from the polypeptide backbone
B.
Clustered in the core away from water
C.
Exposed on the surface to form hydrogen bonds with water
D.
Attached to haem groups only
Question 13
Haemoglobin is classified as a conjugated protein because it contains:
A.
phospholipid tails embedded in a bilayer
B.
polypeptide subunits and non-polypeptide haem groups
C.
only one polypeptide chain folded into a globule
D.
only amino acids joined by peptide bonds
Question 14
What feature best distinguishes collagen from insulin?
A.
Collagen is a conjugated protein with haem groups
B.
Collagen is made from nucleotides rather than amino acids
C.
Collagen has no peptide bonds
D.
Collagen is fibrous and suited to tensile strength
Question 15
Write the word equation for formation of a dipeptide from two amino acids.
[1]
Outline how the peptide bond is formed.
[1]
Question 16
Distinguish between essential and non-essential amino acids in humans. [2]
Question 17
Explain why the possible variety of peptide chains is described as effectively enormous. [3]
Question 18
A peptide chain has four amino acid residue positions. Assume that any of the 20 amino acids can occur at each position.
Calculate the number of possible sequences.
[1]
State why this calculation does not mean ribosomes make random chains in cells.
[1]
Question 19
Outline how chemical diversity in R-groups contributes to protein diversity. [3]
Question 20
Distinguish between a non-conjugated protein and a conjugated protein, using one example of each. [3]
Question 21
Outline how the forms of insulin and collagen suit their functions. [3]
Question 22
A student heated equal volumes of albumen solution for the same time at different temperatures and measured absorbance with a colorimeter.
Describe the relationship between temperature and absorbance shown in the graph.
[1]
Explain why absorbance changes when albumen is heated.
[1]
Question 23
A diagram models formation of a dipeptide from two amino acids.
Identify the bond labelled Y.
[1]
State the small molecule released.
[1]
State why the two amino acids become residues in the dipeptide.
[1]
Question 24
Which interaction in tertiary structure is covalent and forms between two cysteine residues?
A.
Hydrophobic interaction
B.
Ionic bond
C.
Hydrogen bond
D.
Disulfide bond
Question 25
Why can proteins with similar backbones have very different forms and functions?
A.
Their peptide bonds contain different genetic codes
B.
Their carboxyl groups are converted into phospholipids
C.
Their R-groups differ in polarity, charge and hydrophobicity
D.
Their alpha carbons are absent in some amino acids
Question 26
What technology has allowed imaging of single protein molecules and their interactions at very small scales?
A.
Unaided visual observation
B.
A hand lens
C.
Paper chromatography
D.
Cryogenic electron microscopy
Question 27
A solution of egg albumen is heated and becomes opaque.
State the term used for the structural change in the protein.
[1]
Explain why heating can cause this change.
[1]
Question 28
A student investigates the effect of pH on albumen using buffer solutions and a colorimeter.
State the independent variable.
[1]
Suggest two variables that should be controlled.
[1]
Question 29
A vegan athlete eats mainly one cereal-based protein source.
Explain why total protein mass alone may not show whether amino acid requirements are met.
[1]
Suggest how the diet could be adjusted to meet essential amino acid requirements.
[1]
Question 30
A mutation changes one amino acid in an enzyme but the peptide remains the same length.
Explain how this could alter enzyme function.
[1]
Question 31
Compare alpha helices and beta-pleated sheets as secondary structures. [4]
Question 32
Explain how a change in pH can affect the tertiary structure of a protein. [4]
Question 33
Explain why an integral membrane protein may have hydrophobic amino acids on the outside of its membrane-spanning region but hydrophilic amino acids lining a channel. [4]
Question 34
Explain why cryogenic electron microscopy is useful for studying protein form and function. [3]
Question 35
The table shows three peptide chain lengths and the number of possible sequences if any of the 20 coded amino acids can occur at each position.
| Chain length / residues | Possible sequences |
|---|---|
| 1 | 20 |
| 2 | 400 |
| 5 | ? |
Complete the missing value for a chain of five residues.
[1]
Describe the pattern shown in the table.
[1]
Explain why actual cellular polypeptides are not produced as random examples from all possible sequences.
[1]
Question 36
The table compares the essential amino acid content of three plant foods with a recommended intake pattern.
| Essential amino acid | Pattern / % | Wheat / % | Lentils / % | Peanuts / % |
|---|---|---|---|---|
| Leucine | 100 | 119 | 119 | 115 |
| Lysine | 100 | 58 | 144 | 78 |
| Met+Cys | 100 | 145 | 82 | 118 |
| Threonine | 100 | 126 | 152 | 113 |
| Tryptophan | 100 | 183 | 150 | 167 |
| Valine | 100 | 113 | 123 | 128 |
Identify the food with the lowest content of the limiting essential amino acid.
[1]
Describe one advantage of combining two of the foods.
[1]
Suggest why a varied vegan diet can meet protein requirements even if a single plant food is unbalanced.
[1]
Question 37
Albumen samples were placed in buffer solutions of different pH but kept at the same temperature. Absorbance was measured after 10 minutes.
State the dependent variable.
[1]
Describe the effect of pH on absorbance.
[1]
Explain how extreme pH could alter protein structure.
[1]
Question 38
A program estimated the percentage of residues in alpha helix and beta-pleated sheet for four proteins.
| Protein | Alpha helix / % | Beta-pleated sheet / % | Other structure / % |
|---|---|---|---|
| Myoglobin | 76 | 2 | 22 |
| Keratin | 63 | 8 | 29 |
| GFP | 7 | 52 | 41 |
| Porin | 12 | 58 | 30 |
Identify the protein with the greatest proportion of beta-pleated sheet.
[1]
Describe one trend in the secondary structure composition shown.
[1]
Explain what stabilizes these secondary structures.
[1]
Question 39
A bioinformatics program predicted the distribution of polar and non-polar residues in two proteins: a soluble enzyme and an integral membrane channel.
Identify which protein is most likely to be integral in the membrane.
[1]
Describe the evidence for your identification.
[1]
Explain how this residue distribution helps the membrane protein function.
[1]
Question 40
A protein variant differs from the normal protein by one amino acid substitution. The graph shows receptor binding by the normal protein and the variant.
Compare receptor binding by the two proteins.
[1]
Suggest how a single amino acid substitution could cause this difference.
[1]
State one reason why the substitution might have had little effect in another region of the protein.
[1]
Question 41
Cryogenic electron microscopy was used to study a protein complex before and after binding a small molecule. The table summarizes the number of subunits resolved and the measured resolution.
| Protein state | Subunits resolved | Non-polypeptide density | Domain angle / ° | Resolution / Å |
|---|---|---|---|---|
| Unbound | 4 | Not detected | 38 | 3.2 |
| Bound | 4 | Small molecule | 62 | 2.9 |
State whether the protein has quaternary structure, using the data.
[1]
Identify one feature of the data that supports a conclusion about conformational change.
[1]
Evaluate one limitation of using these data alone to infer protein function.
[1]
Question 42
Draw or describe the generalized structure of an amino acid.
[1]
Explain how amino acids form polypeptides and why sequence variety can be enormous.
[1]
Question 43
Distinguish between essential and non-essential amino acids.
[1]
Discuss dietary protein quality, with reference to vegan diets and amino acid requirements.
[1]
Question 44
Define denaturation and state one factor that can cause it.
[1]
Explain how temperature and pH can affect protein structure and how this can be investigated using a colorimeter.
[1]
Question 45
Calculate the number of possible sequences for a peptide of six residues if 20 amino acids can occur at each position.
[1]
Explain the relationship between genetic information, amino acid sequence and the proteome.
[1]
Question 46
A protein was exposed to increasing concentrations of a reducing agent that breaks disulfide bonds. Enzyme activity and the number of intact disulfide bonds were measured.
Describe the relationship between intact disulfide bonds and enzyme activity.
[1]
Explain why breaking disulfide bonds can reduce enzyme activity.
[1]
Suggest why some activity may remain after some disulfide bonds are broken.
[1]
Question 47
Define primary structure and conformation in proteins.
[1]
Explain how primary structure determines protein conformation and function.
[1]
Question 48
Outline the secondary structure of proteins.
[1]
Compare and contrast secondary, tertiary and quaternary structure in proteins.
[1]
Question 49
Distinguish between polar and non-polar amino acid R-groups.
[1]
Discuss how the distribution of polar and non-polar amino acids affects tertiary structure in soluble globular proteins and integral membrane proteins.
[1]
Question 50
Distinguish between globular and fibrous proteins.
[1]
Evaluate how protein form is related to function using insulin, collagen and haemoglobin.
[1]
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