Proteins

Which option describes a conjugated protein?

A A globular protein with a prosthetic group

B A protein with an inorganic ion

C A protein with more than one polypeptide chain

D An enzyme with an inorganic ion

Your answer

21

Describe three ways fish gills are adapted for efficient gas exchange.

Explain why insects can function with open circulatory systems.

The largest fish is the whale shark. Whale sharks have an average mass of 20 tonnes.

The largest marine mammal is the blue whale. Blue whales have an average mass of 150 tonnes.

Use your knowledge of gas exchange and circulatory systems to suggest why marine mammals can grow to a much larger size than fish.

Explain how the structure of haemoglobin allows it to transport oxygen from the lungs to the tissues.

Type 1 diabetes mellitus is characterised by a lack of insulin production. Type 2 diabetes mellitus can involve reduced production of insulin and a decreased response to insulin.

* Scientists analysed the occurrence of diabetes in identical and non-identical twins.

Identical twins have the same DNA. Non-identical twins share approximately 50% of each other’s DNA.

The scientists selected 614 pairs of twins in which at least one of the individuals had diabetes: 109 pairs had type 1 diabetes; 505 pairs had type 2 diabetes.

The scientists calculated the percentage probability of an individual having diabetes when their twin has the disease.

The table shows the percentage probability of both individuals in a pair of twins developing either type 1 or type 2 diabetes.

Explain what conclusions can be drawn from the data in the table about the influence of the environment and genetics on the probability of developing diabetes.

Extra answer space if required.

Insulin is secreted from cells in the pancreas.

This is a photomicrograph of pancreatic tissue.

Identify the structures labelled A, B and C.

The graph shows the changes in the rate of insulin secretion in a person with type 2 diabetes after consuming glucose.

The table shows the changes in the rate of insulin secretion in a person with normal glucose tolerance after consuming glucose.

Plot the data from the table on the graph and draw a line of best fit.

The table lists statements about a molecule of insulin.

Complete the table by stating the level of protein structure (primary, secondary, tertiary or quaternary) to which the statement relates.

Bacteria can be genetically modified to produce insulin.

State how a plasmid containing the gene coding for insulin can be transferred into a bacterial cell.

Suggest how bacterial cells can be screened to check if they have taken up a recombinant plasmid.

In the future, type 1 diabetes could be treated by giving patients new pancreatic -cells that have been produced in a laboratory from stem cells.

State a feature of stem cells that allows them to be used to produce pancreatic -cells.

Future treatments for type 1 diabetes may be able to use stem cells from a patient’s body to produce new -cells.

Explain why patients receiving these new -cells would still need to be given immunosuppressant drugs.

Which statement about the structure of amino acids is not true?

A Amino acids contain amino and carboxyl groups.

B Amino acids contain the elements hydrogen, carbon and oxygen only.

C Each amino acid has a unique R group.

D The R groups in amino acids can be polar or non-polar.

Your answer

Which of the options is a feature of collagen?

A It allows alveoli to recoil

B It dissolves in water

C It is flexible

D It is the main protein found in hair

Your answer

Which statement about the secondary structure of a protein is correct?

A -pleated sheets contain -glucose.

B Disulfide bonds are not involved.

C Each single polypeptide is either an -helix or a -pleated sheet.

D Hydrogen bonds form between the R-groups of different amino acids.

Your answer

Haemoglobin is a globular protein.

Fig. 16.1 shows the structure of haemoglobin.

There are four levels of protein structure.

Name the bond present in the primary structure of a protein.

Name the structure labelled X.

State one feature, visible in Fig. 16.1, that shows that haemoglobin is a globular protein.

Sickle cell disease is a genetic disease that results from a substitution mutation in one of the genes that code for haemoglobin.

Fig. 16.2 below shows part of the mRNA sequence that codes for normal haemoglobin and the corresponding sequence of amino acids.

Fig. 16.2

Fig. 16.3 is a representation of the genetic code.

Use Fig. 16.3 to identify the missing amino acids 1 and 2 in Fig. 16.2.

Outline the role of RNA polymerase in the production of the mRNA sequence in Fig. 16.2.

In sickle cell disease, the haemoglobin contains the amino acid valine in one of the positions normally occupied by glutamic acid.

State the base sequence on the anticodon of a tRNA molecule that brings valine to the ribosome.

Microorganisms can be used to produce a variety of food products.

Microorganisms have simple nutrient requirements, which helps to reduce production costs.

List two other advantages of using microorganisms in food production.

Yoghurt is a food produced from milk using microorganisms.

Yoghurt production involves two bacteria: Lactobacillus delbrueckii and Streptococcus thermophilus.

The bacteria convert the lactose present in milk into lactic acid.

Lactic acid is an important contributor to the flavour of yoghurt. Lactic acid also helps to give yoghurt a longer shelf life than milk.

Suggest how lactic acid helps to extend the shelf life of yoghurt.

Both bacteria also break down some of the protein casein, which is present in milk.

Name the product of protein breakdown and describe the type of reaction that takes place.

The microorganism that is used to produce mycoprotein is a fungus.

The diagram is of a fermenter used for mycoprotein production.

Use the diagram to name the type of fermentation process used for mycoprotein production.

Justify your answer.

Suggest and explain why a cooling system is necessary.

The air inlet provides the fungus with oxygen for respiration, and ammonia.

Suggest and explain why the fungus is provided with ammonia.

Mycoprotein foods contain protein.

The presence of protein in a solution can be detected using biuret reagent.

In the presence of protein, biuret reagent turns from blue to violet.

A colorimeter can be used, along with biuret reagent, to determine the concentration of protein in a solution.

Outline how to use a colorimeter to determine the concentration of protein in a solution.

State one alternative method for determining the concentration of protein in a solution.

Collagen is found in tendons. Tendons attach muscles to bones.

Which of the following lists of properties, A to D, makes collagen suitable for this role?

A strong, inflexible, insoluble

B strong, flexible, soluble

C strong, inflexible, soluble

D strong, flexible, insoluble

Your answer

Rubredoxin is a protein found in bacteria. It contains around 50 amino acids. One iron ion is bound by the sulphur atoms of four cysteine amino acids.

The structure of rubredoxin is shown in Fig. 20.1.

Rubredoxin is known as a conjugated protein.

Use Fig. 20.1 to explain what is meant by the term conjugated protein.

Using the information provided about rubredoxin, state two similarities between the structures of rubredoxin and haemoglobin.

Rubredoxin and haemoglobin have different secondary and tertiary structures.

Using the information provided about rubredoxin, state two other differences between the structures of rubredoxin and haemoglobin.

Ferritin is a protein that is used to regulate iron levels within plant tissues.

It is a large spherical structure which can hold many iron (Fe³⁺) ions at its centre.

Iron can be toxic to plant tissues. Ferritin prevents the build-up of iron.

Fig. 20.2 shows the internal structure of ferritin.

Explain how hydrophilic and hydrophobic interactions contribute to the spherical shape of ferritin.

Fig. 1.1 shows the structure of the amino acid leucine.

On Fig. 1.1, draw a circle around the R group of leucine.

Students used thin layer chromatography to separate leucine from other amino acids. The chromatogram they produced is shown in Fig. 1.2.

What can you conclude about the chemical properties of leucine and amino acid X?

Amino acid Z was in the mixture analysed by the students. It is not shown on the chromatogram in Fig. 1.2. Amino acid Z has an R_f value that is 0.20 lower than that of amino acid Y.

Place a dot on the chromatogram in Fig. 1.2 to show the distance moved by amino acid Z.

Show your working.

Thin layer chromatography can also be used to separate photosynthetic pigments.

State a material that can be used as the stationary phase in thin layer chromatography.

State the precise location of photosynthetic pigments in a chloroplast.

When sequencing DNA, fragments of DNA are separated by electrophoresis.

Describe three differences between the process of thin layer chromatography and the form of electrophoresis used to sequence DNA.

Bread contains a mixture of polypeptides known as gluten.

Gluten consists of two types of polypeptide: gliadins and glutenins.

The table below contains statements about the structures of gluten polypeptides.

In the boxes next to each statement, write the level of protein structure (primary, secondary, tertiary, or quaternary) to which the statement refers.

Coeliac disease is caused by an immune reaction to gliadins in a person’s digestive system. The immune system produces antibodies that bind to part of the gliadin polypeptides, which causes inflammation.

Some people who stop eating foods that contain gluten still occasionally experience the symptoms of coeliac disease.

What can you conclude about:

• the structure of the antibody that causes coeliac disease; and

• what the antibody binds to when producing the symptoms of coeliac disease?

Gluten helps to trap carbon dioxide within bread dough. This enables bread to rise when it is baked.

The carbon dioxide is produced by baker’s yeast, Saccharomyces cerevisiae. This species of yeast is able to convert ethanol to acetyl CoA at low glucose concentrations.

Fig. 2 shows the oxygen consumption and carbon dioxide production of a population of S. cerevisiae grown in batch culture. The population was provided with glucose as their only initial source of carbon.

Fig. 2

Suggest and explain what conclusions can be drawn from Fig. 2 about the factors that affected the rate and type of respiration carried out by S. cerevisiae in this batch culture.

Describe two practical considerations to ensure the S. cerevisiae population grows successfully when the initial culture is established.

A group of students were designing an experiment to investigate the effect of temperature on the respiration rate of S. cerevisiae.

Their planned method included the following:

• S. cerevisiae yeast suspension will be divided into six equal volumes to form the experimental groups.

• Six temperatures will be tested: 15 °C, 20 °C, 25 °C, 30 °C, 35 °C and 40 °C.

• Beakers of S. cerevisiae will be placed in water baths to control the temperature.

• Respiration rate will be measured by using a pH probe to monitor changes in the pH of the suspensions.

• The experiment will be repeated four times.

Evaluate whether the students’ method is likely to produce valid results.

The students used a Student’s t-test to compare the results at 30 °C and 35 °C.

They calculated a t value of 2.200.

The critical value for p = 0.05 is 2.306.

Assuming their final method was valid, what can the students conclude from the result of the t-test?