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S294/A

Module Examination 2015

CELL BIOLOGY

PART 1

Short answer questions Answer all SIX questions in this first part of the exam. Write your answers in the answer book provided, limiting your answer for each part of a question to a few sentences or more. You are advised to spend no more than 1 hour 15 minutes on this Part A of the paper, which carries 30 of the total marks for the examination. Each question is worth 5 marks.

Question 1

(a) The figure below is an electron micrograph showing part of a nerve cell (neuron) in the brain. The nucleus is labelled (N), as are examples of mitochondria (M).     

  

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(a) Name the structures labelled A–D

 

(b) What does the presence of many mitochondria and B indicate about one of the activities of the nerve cell?

 

(c) What are the functions of C?

 

(d) Explain what D is composed of, and why it has a dark appearance.

 

Question 2

Figure 2, below, shows three generations of a human family. Squares and circles represent males and females respectively and filled symbols indicate individuals affected by a rare but severe heritable condition. Symbols with a strike-through represent individuals who died before adulthood.

(a) From your inspection of the figure, what is the most likely pattern of inheritance? Explain your answer, using examples of individuals in the pedigree.

(b) Draw a Punnett square to illustrate the mating between individuals I-1 and I-2. You should clearly state the nomenclature you are using.

(c) Using your Punnett square, what can you say about which genotypes might correspond to the following individuals:

(i) I-2                 

(ii) II-1               

(iii) II-8

Question 3

(a) The following techniques can all be used to purify and/or analyse proteins.

• Gel filtration
• SDS-PAGE (Sodium dodecyl sulphate polyacrylamide gel electrophoresis)
• Immunoblotting

(a) Which of these techniques is most appropriate for purification of a significant amount of a protein from a mixture of proteins?

(b) Select two of the techniques and provide a brief account for each, including the following:

(i) how it is performed

(ii) the principle behind the technique

(iii) an explanation of how the procedure allows an investigator to purify or analyse proteins

(iv) at least one diagram to illustrate your answer

Question 4

(a) What is a redox reaction?

(b) What term describes the measure of the relative affinity of a reactant for electrons?

(c) Draw and clearly label a simple sketch of the mitochondrial electron transport chain (ETC) and illustrate how it generates a proton gradient. Your sketch should indicate the components of the chain (electron carriers), where they are located and the reactions that occur along the chain.

(d) State which of the electron carriers of the ETC has the greatest redox potential and which has the lowest redox potential. Explain how the redox potential of the ETC components relates to the direction of flow of electrons along the chain.

Question 5

(a) Draw and label a simple sketch showing a cross-section of an axoneme of a eukaryotic flagellum. You should include the following components in your sketch: cell membrane, dynein arms, microtubule doublet, microtubule singlet, nexin, radial spoke.

(b) Briefly describe the relationship between the structures you have drawn and labelled.

(c) Briefly describe how motor protein activity brings about movement of a eukaryotic flagellum.

Question 6

(a) Explain what is meant by the term apoptosis and name one of the apoptotic pathways.

(b) Briefly explain the main cellular events in apoptosis (as evident from microscopy studies).

(c) Describe how the process of apoptosis is an example of a cascade activity.

(d) Explain why the balance of Bcl-2 family proteins within a cell is crucial for controlling whether a cell lives or dies.

PART 2

Answer ALL parts of the question in this Part. Write all your answers to this Part in the answer book provided. You are advised to spend 45 minutes on this Part of the paper. Your answers should be written concisely, but in proper sentences. You should include diagrams and calculations in your answer where appropriate.

This Part carries 25% of the marks for the examination.

Question 7

You are supplied with a copy of an article titled ‘A division duet’ by Curt Wittenberg. Citation: Wittenberg, C. (2012), ‘A division duet’, Nature, vol. 481, pp. 273–4.

This article discusses the findings of a study by Bouchoux and Uhlmann, Bouchoux, C. and Uhlmann, F. (2011), Cell, vol. 147, pp. 803–14, which was concerned with the role of a phosphatase Cdc14 in controlling progression

through the cell cycle. Note: the article refers to ‘a kinase enzyme called CDK’ (first paragraph), but this is actually a family of cyclin-dependent protein kinases (Cdks), which you learned about in your studies of S294.

The following questions are based largely on this article but in some cases draw on relevant material from S294.

(a) From your studies of S294, answer the following questions on Cdks.

(i) Briefly outline the role of Cdks as regulators of cell cycle progression.

(ii) Cdks are constitutively expressed. What does this mean?

(iii) How are Cdks activated?

(b) As stated in the article, the phosphatase Cdc14 is involved in mitosis (M phase). What is its role?

(c) From your studies of S294, list the stages of mitosis in the order in which they occur.

(d) How, according to the article, is Cdc14 prevented from acting at earlier stages in the cell cycle?

(e) Briefly outline (in your own words) the two models that are described in the article to explain how stages in mitosis are triggered to occur in a defined order.

(f) (i) In what organism did Bouchoux and Uhlmann investigate Cdc14 activity?

(ii) The investigators performed both in vivo and in vitro experiments to investigate Cdc14 activity. From the information provided in the article, describe briefly (in your own words) the types of experiments they performed.

(g) What, according to the article, did Bouchoux and Uhlmann observe when they studied Cdc14 activity towards its target proteins in vitro?l

(h) Which of the two models for the sequential triggering of the stages in mitosis does their observation support? Explain your answer.

PART 3

Answer ONE of the questions in this Part. You are advised to spend about 1 hour on this question. You should follow any specific guidance in the question. Note that some questions specifically request inclusion of diagrams but in all cases you may include diagrams where appropriate. This Part carries 30% of the marks for the examination.

Question 8

Write an essay describing the different cell and tissue types of flowering plants, and how their structure relates to their function. You should include information about subcellular features and at least one diagram to illustrate your answer

Question 9

Write an essay titled ‘The function of enzymes is intimately related to their structure’. Your essay should include at least two relevant diagrams and a description or discussion of the following aspects:

• the relevant structural features of enzymes
• the key characteristics of enzyme function and how these are related to their structure
• three factors affecting enzyme activity

Question 10

Discuss the role of transcription factors in animal cell differentiation. Give the two regulatory methods of cell differentiation and the role of transcription factors in these two processes.

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Last updated: Sep 02, 2021 10:07 AM

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