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Question 1
The diagram that shows the generalized structure of an amino acid is
A.
B.
C.
D.
Question 2
What is released when two amino acids join to form a dipeptide?
A.
Water
B.
Carbon dioxide
C.
Hydrogen gas
D.
Ammonia
Question 3
What is an essential amino acid?
A.
An amino acid that can be synthesized from other amino acids in the body
B.
An amino acid that is more important than other amino acids for protein synthesis
C.
An amino acid that must be obtained from food because it cannot be synthesized in sufficient quantity
D.
An amino acid that is found only in proteins from animal sources
Question 4
What usually remains intact when a protein is denatured by heating?
A.
The primary sequence of amino acid residues
B.
All ionic interactions between R-groups
C.
All hydrogen bonds stabilizing the folded protein
D.
The exact active site conformation
Question 5
An R-group that can donate a hydrogen ion and become negatively charged is best described as
A.
basic
B.
acidic
C.
non-polar
D.
peptidic
Question 6
The diagram that best represents a beta-pleated sheet is
A.
B.
C.
D.
Question 7
What type of interaction forms between the sulfur atoms of two cysteine residues in a protein?
A.
Hydrogen bond
B.
Disulfide covalent bond
C.
Hydrophobic interaction
D.
Ionic bond
Question 8
Draw a generalized amino acid and label the groups attached to the alpha carbon.
[4]
0
Question 9
A peptide chain contains four amino acid residue positions. If any of the 20 genetically coded amino acids can occur at each position, how many different sequences are possible?
A.
B.
C.
D.
Question 10
Albumen samples were incubated at different pH values for the same time and then tested with a colorimeter. Higher absorbance indicates greater turbidity.
What conclusion is supported by the results?
A.
Extreme pH values cause denaturation and precipitation of albumen proteins.
B.
Albumen proteins become more soluble at both very low and very high pH.
C.
Changing pH has no effect on the three-dimensional structure of albumen proteins.
D.
Neutral pH causes the greatest disruption of peptide bonds in albumen proteins.
Question 11
A mutation changes one amino acid residue in an enzyme. What is the most direct reason this could alter enzyme activity?
A.
The number of genetically coded amino acids increases above 20.
B.
The enzyme must become a nucleotide polymer rather than a polypeptide.
C.
The mutation must break every peptide bond in the enzyme molecule.
D.
The altered primary structure may change R-group interactions and therefore the enzyme conformation.
Question 12
What distinguishes haemoglobin from collagen as a conjugated protein?
A.
Haemoglobin is made of one polypeptide chain, whereas collagen is made only of amino acids not joined together.
B.
Haemoglobin includes non-polypeptide haem groups associated with its polypeptide subunits.
C.
Haemoglobin contains peptide bonds, whereas collagen contains no peptide bonds.
D.
Haemoglobin is fibrous, whereas collagen is a compact globular signalling molecule.
Question 13
Two amino acids join to form a dipeptide during protein synthesis.
State the word equation for formation of a dipeptide from two amino acids.
[1]
Outline how the peptide bond is formed.
[2]
State what is meant by an amino acid residue in a polypeptide.
[1]
0
Question 14
A student changes to a vegan diet and obtains most dietary protein from one cereal crop.
Define essential amino acid.
[1]
Distinguish between essential and non-essential amino acids.
[2]
Explain why relying on a single plant protein source may not meet amino acid requirements.
[1]
0
Question 15
An enzyme has the same amino acid sequence before and after exposure to an extreme pH, but it no longer catalyses its reaction.
State the term for loss of normal protein structure caused by extreme pH.
[1]
Explain how extreme pH can change protein structure.
[2]
Explain why the enzyme may lose function even though peptide bonds are not broken.
[1]
0
Question 16
Although all amino acids in a polypeptide have the same general backbone, proteins have very diverse forms and functions.
State the part of an amino acid that differs between amino acids.
[1]
Outline two chemical properties that R-groups may have.
[2]
Explain how R-group diversity contributes to diversity of protein function.
[1]
0
Question 17
Alpha helices and beta-pleated sheets are common secondary structures in proteins.
State what is meant by secondary structure.
[1]
Compare alpha helices and beta-pleated sheets.
[2]
State the orientation of R-groups in an alpha helix.
[1]
0
Question 18
A student used molecular models to compare the generalized structure of amino acids. The diagram shows one generalized amino acid with four labelled groups attached to the central carbon atom.
Identify the label for the alpha carbon atom.
[1]
State two labelled groups that must be present in all amino acids used to build proteins.
[1]
Explain why the R-group can give different amino acids different chemical properties.
[2]
0
Question 19
Two amino acids were modelled before and after joining to form a dipeptide. The diagram shows the atoms removed during the reaction and the bond formed between the two residues.
Identify the type of reaction shown.
[1]
State the name of the bond formed between the two amino acid residues.
[1]
polypeptide is produced from 51 amino acids by the same type of reaction. Calculate the number of water molecules released.
[1]
Explain why the two amino acids are described as residues after the dipeptide has formed.
[1]
0
Question 20
An integral membrane channel protein spans the phospholipid bilayer and permits ions to pass through its centre. What distribution of amino acid R-groups would best support this function?
A.
Only non-polar R-groups lining the channel and exposed to the aqueous cytoplasm
B.
Only acidic R-groups throughout the entire protein surface
C.
Hydrophilic R-groups facing the bilayer core and hydrophobic R-groups lining the channel
D.
Hydrophobic R-groups facing the bilayer core and hydrophilic R-groups lining the channel
Question 21
The number of possible amino acid sequences in a peptide of length can be represented by .
Calculate the number of possible sequences in a tripeptide.
[1]
State why the base of the expression is 20.
[1]
Explain why peptide chain variety is described as effectively infinite.
[2]
0
Question 22
Albumen samples were heated for the same time at different temperatures and then tested in a colorimeter. Higher absorbance indicates greater turbidity.
State the relationship shown between temperature and absorbance at high temperatures.
[1]
Explain why absorbance changes when albumen is heated strongly.
[2]
Suggest one variable, other than temperature, that should be controlled in this investigation.
[1]
0
Question 23
A mutation changes one amino acid in a soluble enzyme from a charged residue to a non-polar residue.
Define primary structure of a protein.
[1]
Explain how the amino acid substitution could alter conformation.
[2]
State why a change in conformation may affect enzyme activity.
[1]
0
Question 24
A folded single polypeptide contains R-groups that are distant in the amino acid sequence but close together in the final three-dimensional structure.
Define tertiary structure.
[1]
Outline two interactions that can stabilize tertiary structure.
[2]
Explain how a change in pH could disrupt tertiary structure.
[1]
0
Question 25
Insulin, collagen and haemoglobin all contain more than one component in their functional structures.
Define quaternary structure.
[1]
Distinguish between non-conjugated and conjugated proteins, using named examples.
[2]
State why the haem group is important in haemoglobin function.
[1]
0
Question 26
The table compares the intake of selected essential amino acids from three one-day plant-based meal plans with the estimated daily requirement for an adult.
| Meal plan | Total protein / g | Lysine / g | Methionine / g |
|---|---|---|---|
| Adult requirement | 50 | 2.0 | 1.0 |
| A | 68 | 1.5 | 1.2 |
| B | 57 | 2.4 | 0.8 |
| C | 61 | 2.1 | 1.1 |
Identify the meal plan that meets all the listed essential amino acid requirements.
[1]
Using the data, explain why total protein intake alone is not enough to judge protein quality.
[2]
Suggest why a varied vegan diet can meet amino acid requirements.
[2]
0
Question 27
The graph shows how the number of possible amino acid sequences changes with peptide length, assuming that any of the 20 amino acids coded for by the genetic code can occupy each position.
| Peptide length / amino acids | Possible sequences |
|---|---|
| 1 | 20 |
| 2 | 400 |
| 3 | 8,000 |
| 4 | 160,000 |
| 5 | 3,200,000 |
Calculate the number of possible sequences for a tetrapeptide.
[1]
State how many times more possible sequences there are for a pentapeptide than for a tetrapeptide.
[1]
Explain why peptide chains can have an effectively infinite variety of possible sequences.
[2]
0
Question 28
The amino acid composition of the exposed surfaces of two proteins was analysed. Protein M is embedded in the middle region of a membrane. Protein S is soluble in cytoplasm.
Compare the abundance of hydrophobic R-groups on the exposed surfaces of proteins M and S.
[1]
Suggest why protein S has many polar and charged R-groups on its exposed surface.
[2]
Explain how chemical diversity of R-groups contributes to diversity of protein function.
[1]
0
Question 29
A protein was analysed before and after treatment with a compound that disrupts hydrogen bonding in the polypeptide backbone. The percentage of amino acid residues in different secondary structures was estimated.
| Secondary structure | Before treatment / % | After treatment / % |
|---|---|---|
| Alpha helix | 40 | 15 |
| Beta-pleated sheet | 35 | 20 |
| Unordered | 25 | 65 |
Describe the effect of the treatment on secondary structure.
[1]
State where the hydrogen bonds stabilizing alpha helices and beta-pleated sheets form.
[1]
Explain how alpha helices differ from beta-pleated sheets in shape.
[2]
0
Question 30
The diagram shows two proteins in different aqueous environments: a soluble globular protein in cytoplasm and an integral protein in a phospholipid bilayer.
State where hydrophobic amino acids are usually found in a water-soluble globular protein.
[1]
Explain why integral membrane proteins often have hydrophobic amino acids on the outside of the membrane-spanning region.
[2]
Suggest why the lining of an ion channel is often hydrophilic.
[1]
0
Question 31
Albumen protein solution was heated for the same length of time at different temperatures. After cooling, a colorimeter was used to measure absorbance. Higher absorbance indicates greater turbidity.
Describe the effect of temperature on absorbance.
[2]
Explain why denaturation of albumen increases absorbance.
[2]
Suggest one variable, other than temperature, that should be controlled in this investigation.
[1]
0
Question 32
A soluble enzyme was incubated for 10 minutes in buffer solutions of different pH. It was then returned to pH 7 and its activity was measured as a percentage of the activity of an untreated sample.
Identify the pH treatment after which enzyme activity was highest.
[1]
Explain why extreme pH can reduce enzyme activity even after the enzyme is returned to pH 7.
[2]
Evaluate the conclusion that pH changes always cause irreversible denaturation of proteins.
[2]
0
Question 33
Researchers made single amino acid substitutions in a small globular protein and measured the percentage of normal receptor binding. The substitutions occurred at different positions in the primary structure.
| Variant | Position / residue no. | Amino acid substitution | Receptor binding / % of normal |
|---|---|---|---|
| A | 21 | Ser â Pro | 79 |
| B | 44 | Asp â Trp | 11 |
| C | 72 | Gly â Arg | 54 |
| D | 95 | Leu â Ile | 97 |
Identify the variant with the greatest reduction in receptor binding.
[1]
Explain why a single substitution in the primary structure can change receptor binding.
[2]
Suggest why one substitution shown in the table had little effect on receptor binding.
[1]
Evaluate whether the data support the idea that protein conformations are precise and repeatable.
[1]
0
Question 34
A transmembrane channel protein was analysed. The hydropathy plot shows regions of the polypeptide with many non-polar amino acids. The diagram shows the predicted position of the protein in a phospholipid bilayer.
Identify the evidence from the hydropathy plot for membrane-spanning regions.
[1]
Explain why non-polar amino acids are common on the outside of the membrane-spanning regions.
[2]
Suggest why the lining of the channel contains polar or charged amino acids.
[1]
Contrast the arrangement of hydrophobic amino acids in this channel protein with a water-soluble globular protein.
[1]
0
Question 35
Cryogenic electron microscopy and biochemical analysis were used to compare three proteins: insulin, collagen and haemoglobin. The stimulus summarizes their subunits, non-polypeptide components and overall shapes.
| Protein | Subunits | Non-polypeptide component | Overall shape | Main role |
|---|---|---|---|---|
| Insulin | 2 polypeptide chains (A and B) | None | Compact, globular | Hormone that regulates blood glucose |
| Collagen | 3 polypeptide chains | None | Long, fibrous triple helix | Structural support in connective tissues |
| Haemoglobin | 4 polypeptide subunits (2α and 2ÎČ) | 4 haem groups | Roughly globular | Transport of oxygen in red blood cells |
Identify the conjugated protein in the stimulus and give the evidence for your answer.
[2]
Explain how collagen form is related to its function.
[1]
Explain how insulin form is related to its function.
[1]
Evaluate the value of cryogenic electron microscopy for studying these proteins.
[1]
0
Question 36
A student used molecular models to represent the formation of a dipeptide from two generalized amino acids.
I.
Draw a generalized amino acid, showing all groups attached to the alpha carbon.
[2]
II.
Annotate the product of the reaction to show the peptide bond and the molecule released.
[2]
Explain how longer polypeptide chains are formed from amino acids.
[2]
Discuss why the same type of chemical reaction can produce a very large variety of proteins.
[2]
0
Question 37
The table compares the amino acid profiles of three plant foods used in a vegan diet. The values are expressed relative to the adult human requirement for each essential amino acid group.
| Food | Protein / g per serving | Histidine | Isoleucine | Leucine | Lysine | Met + Cys | Phe + Tyr | Threonine | Tryptophan | Valine |
|---|---|---|---|---|---|---|---|---|---|---|
| Seitan | 21 | 1.1 | 1.0 | 1.2 | 0.3 | 1.2 | 1.1 | 1.0 | 1.0 | 1.1 |
| Lentils | 18 | 1.1 | 1.2 | 1.3 | 1.6 | 0.5 | 1.2 | 1.1 | 1.0 | 1.1 |
| Maize | 7 | 0.9 | 0.9 | 1.0 | 0.7 | 1.1 | 1.0 | 0.8 | 0.4 | 0.9 |
I.
Define an essential amino acid.
[1]
II.
Explain why a food with a high total protein content may still be a poor sole protein source.
[2]
Using the table, suggest why combining two or more of the foods would be preferable to relying on one food.
[2]
Evaluate the claim that vegan diets cannot meet human amino acid requirements.
[2]
0
Question 38
A ribosome can build peptide chains using 20 amino acids coded for in the genetic code. The number of possible sequences for a chain of amino acid residues is .
I.
Calculate the number of possible tripeptide sequences.
[1]
II.
Explain why a tripeptide containing amino acids A, B and C can have more than one sequence.
[2]
Explain why the variety of possible peptide chains is described as effectively infinite for protein-length chains.
[2]
Discuss the relationship between the genome and the proteome in determining which of the possible proteins are actually produced in a cell.
[2]
0
Question 39
A nutrition label states that a snack contains protein. During digestion, its proteins are hydrolysed and the products are absorbed for use in cells.
I.
State the monomers produced by digestion of proteins.
[1]
II.
Distinguish between condensation and hydrolysis in relation to peptide bonds.
[2]
Explain why absorbed amino acids can be used to build proteins that are different from the proteins in the snack.
[2]
Discuss why the R-group must be included when drawing a generalized amino acid, even though it is not the same in all amino acids.
[2]
0
Question 40
A protein contains two regions of secondary structure, one forming a coiled structure and the other forming a pleated sheet.
I.
Identify the two types of secondary structure shown.
[1]
II.
State where the hydrogen bonds that stabilize secondary structure form.
[2]
Compare and contrast an alpha helix with a beta-pleated sheet.
[3]
Explain why secondary structure alone does not fully describe the final shape of a protein.
[1]
0
Question 41
An enzyme contains charged R-groups and pairs of cysteine residues. Its activity was measured after incubation at different pH values and after treatment with a reducing agent that breaks disulfide bonds.
Describe the relationship between pH and enzyme activity shown in the graph.
[1]
Explain how a change in pH can alter tertiary structure through effects on ionic bonds.
[2]
Using the table, suggest why disulfide bonds are important in this enzyme.
[2]
0
Question 42
Albumen protein solutions were heated for the same time at different temperatures. After cooling, absorbance was measured with a colorimeter as an indication of turbidity.
I.
State what an increase in absorbance indicates about the albumen solution.
[1]
II.
Explain why heating can increase the turbidity of an albumen solution.
[2]
Analyse the graph to infer the temperature range over which denaturation is greatest.
[2]
Evaluate the reliability of this method for investigating the effect of temperature on protein structure.
[3]
0
Question 43
Two enzymes from different organisms were tested at a range of pH values. Enzyme activity was expressed as percentage of maximum activity for each enzyme.
I.
Identify which enzyme has the lower optimum pH.
[1]
II.
Compare the activity of the two enzymes at extreme pH values.
[2]
Explain how a change in pH can reduce the function of a protein such as an enzyme.
[3]
Suggest why it is not valid to state one universal optimum pH for all proteins.
[2]
0
Question 44
A section of a newly discovered soluble protein contains regions rich in hydrophobic, polar uncharged, acidic and basic R-groups.
I.
Distinguish between hydrophobic and hydrophilic R-groups.
[2]
II.
State how acidic and basic R-groups can become charged.
[1]
Explain how chemical diversity in R-groups contributes to the folding of this soluble protein.
[3]
Discuss why R-group diversity is needed for proteins to have diverse functions.
[2]
0
Question 45
A single base substitution in a gene changes one amino acid in a globular enzyme. The altered enzyme is stable but has much lower activity than the original enzyme.
I.
Define primary structure of a protein.
[1]
II.
Explain why changing one amino acid can alter protein conformation.
[2]
Discuss why the altered enzyme may have much lower activity even though it is not completely denatured.
[2]
Evaluate the statement: the amino acid composition of a protein is more important than the amino acid sequence.
[2]
0
Question 46
The diagram represents a transmembrane channel protein in a phospholipid bilayer. The channel allows hydrated ions to pass through the membrane.
I.
Distinguish between polar and non-polar amino acids.
[2]
II.
State where hydrophobic amino acids are usually found in a water-soluble globular protein.
[1]
Explain how the distribution of polar and non-polar amino acids enables a transmembrane channel protein to remain embedded in the membrane and transport ions.
[3]
Compare the expected amino acid distribution in a soluble globular protein with that in the membrane-spanning region of this channel protein.
[2]
0
Question 47
Cryogenic electron microscopy was used to image three proteins: insulin, collagen and haemoglobin. The images allowed researchers to infer how the parts of each protein are arranged.
I.
Define quaternary structure.
[1]
II.
Distinguish between conjugated and non-conjugated proteins using the proteins shown.
[2]
Explain how the form of insulin and collagen is related to their functions.
[3]
Evaluate the importance of cryogenic electron microscopy for understanding protein structure and function.
[2]
0
Question 48
A soluble enzyme loses activity when transferred from pH 7 to pH 3. Returning the enzyme to pH 7 restores only part of the original activity.
I.
Identify four types of interaction that can stabilize tertiary structure.
[2]
II.
Explain how acidic pH can disrupt ionic bonding in a protein.
[2]
Explain why the enzyme may regain only part of its activity after being returned to pH 7.
[2]
Evaluate the statement that disulfide bonds are the only important bonds in tertiary structure because they are covalent.
[2]
0
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