Biology of Disease

Lectures

Although targeted at Medics, Biology of Disease can be taken by Natscis as well, with a small chunk of 40-50 Bio Natscis taking the course every year. Very clinical in nature, BOD is nevertheless very useful for students wishing to eventually enter clinical research or understand the causative agents, progression, and treatment of various diseases. BOD focuses on immunology, as well as diseases caused by common pathogens such as bacteria, viruses, parasites, and fungi, followed by vascular pathologies and cancer.

Lectures start at 12pm on Mondays, Wednesdays, and Fridays. Each lecture block generally starts with an introduction to the pathogen or the disease, followed by a deep dive into how the pathogen infects its patient or a disease develops, immune evasion techniques employed by the pathogen, and the host immune response against the pathogen or disease which resolves or worsens the pathological condition. Techniques to prevent and treat the infection are also covered. Because the immune system is highly complex with many intersecting pathways, do not be surprised that many immune pathways are shared among different pathogens while having their own exceptions and quirks. There is also a series of Natsci Extension Lectures in Lent and Easter intended for Natscis that focus on the immune system in the context of various pathological conditions and serves as an addendum to the core curriculum. Do also consult the lecture and practical timetable because there are some days without lectures or practicals in Michaelmas and Lent (yay)!

The lecture synopses are given below:

Michaelmas:

• Immunology: The very first lecture topic is on immunology, which is a massive topic covered by 2 lecturers. The first lecturer covers a series of lectures including a general introduction to the innate immune system, inflammation, the complement system, followed by an introduction to the adaptive immune system such as B cells and antibodies. The second lecturer covers T cells, immune tolerance, autoimmunity and hypersensitivity, and transplantation. Although this block ends early in the academic year, it is possibly the most important block and is worth bearing in mind for the rest of the course as the effect of pathogens on the immune system and comparing and contrasting these effects are a big theme in the eventual exams.
• Viruses: Another big topic which starts off with a general introduction to viral pathogens. Viral transmission, persistence within the host, immune evasion, immune responses against viruses, and prevention and treatment of viral diseases are dealt with in the following lectures. Viruses commonly covered here include Influenza, Hepatitis A, B, and C, HIV, and various Herpesviruses, although knowledge of other viruses which are covered less extensively such as Covid-19 is greatly helpful in the eventual essay exams. Prions are also briefly discussed within this lecture block.
• Fungi: Fungal pathogens are discussed here, with Aspergillus and Candida being some classic examples. The block starts off with a general discussion on fungal characteristics, followed by fungal reproduction and diagnosis of fungal infections. Fungi are then grouped into systemic opportunists versus systemic pathogens, with each group having different pathogenesis and affecting different groups of patients. Lastly, treatment and prevention of fungal diseases are discussed.

Lent:

• Parasites: This block delves into the world of parasites, organisms which make their living off a host. Following an introduction to parasitic lifestyles and life cycles, various parasites are discussed. Plasmodium (causative agent of malaria), Leishmania (causative agent of leishmaniasis) and various worms and helminths are among the totally lovely and not-at-all-nasty creatures you will cover. Similar to previous lecture blocks, emphasis is placed on immune evasion techniques and the host immune response to infection. Techniques to prevent and treat parasitic infections are also covered here.
• Bacteria: Yet another major lecture block in BOD, the bacteria block does a deep dive into the structure and function of various pathogenic bacteria. Much like previous lecture blocks, this one covers the initial stages of infection, colonisation, immune evasion, and host immune response to the pathogen. Various Gram-positive and Gram-negative bacteria are discussed, as are measures against bacterial infections such as antibiotics and vaccination. This block concludes with a review lecture of the various immune responses to the pathogens covered so far, such as viruses, parasites, fungi, and bacteria, which is extremely useful in consolidating the at times wildly confusing immune response pathways for eventual deployment on the at times wildly confusing battlefield that is the essay exam.
• Vascular Pathologies: This block covers conditions such as atherosclerosis, ischaemia, and various types of anaemia. It starts off with an introduction to both proper and dysregulated responses to vascular injury, setting the foundation for vascular pathologies that are covered in subsequent lectures. One lecture is then dedicated each to atherosclerosis, ischaemia and infarction, and anaemia. Throughout the block, risk factors for the various conditions and the role of different cells or components of the immune system in vascular injury and recovery are discussed.
• Cancer: The lecture block covering the Emperor of All Maladies. The first few lectures act as an introduction to cancer, with discussion on the various mutations of the genes involved in tumorigenesis and the focus of cancer as a multi-stage evolutionary process. Key hallmarks of cancer cells, such as genetic instability and a loss of growth control, are introduced as concepts and the biochemical basis behind these hallmarks discussed in subsequent lectures. Different classes of mutations ranging from point mutations to entire chromosome translocations and the various genes involved in cancer such as tumour suppressors and oncogenes are discussed in detail. Lastly, environmental causes of cancer such as cancer initiators (carcinogens) and cancer promoters as well as hereditary and non-hereditary risk factors of cancer are discussed. Because this block is very complex, it will be useful to classify things according to various categories, such as point mutation vs chromosomal translocations, tumour suppressor pathways vs oncogenic pathways, etc to simplify the consolidation of your knowledge. In addition, this block is very pathway heavy, and a good biochemistry background is very useful in incorporating extracurricular information in the exams. It will also be good to know and be able to sketch the basic sequence of events in a pathway for at least one tumour suppressor and one oncogene if you choose this topic in the essay exam.
• NST Extension Lectures 1 – 3: The first of the NST lectures, which all tend to focus more on the immune system in different contexts more than anything else. NST1 comes immediately following the parasitology block and focuses on the immune system’s role in parasitic infections. NST2 follows the bacteriology block and discusses the interplay between the immune system and bacteria in chronic bacterial infections. NST3 comes after the cancer lectures, focusing on chronic infection and wound repair in cancer formation.

Easter:

• NST Extension Lectures 4 – 8: The core curriculum ends in Lent, so in Easter, the only lectures you will attend are extension lectures. NST4 covers early life development of the immune system, followed by NST5, a lecture on immunosuppression and cancer. NST6 recaps viral evasion of the immune system, while NST7 covers cancers of the immune system. The final lecture of the year, NST8 discusses cancer immunotherapy. These lectures recap various topics covered during the core curriculum, as well as adding some new information which complements the core curriculum. Depending on how comfortable you have gotten with the core curriculum and whether you have managed to source extracurricular information on your own in Michaelmas and Lent, you can decide whether you want to attend some of the lectures, although going for them is still recommended because these are “big picture” lectures which helps in retaining overall information that are very important in the essays.

Supervisions

Practicals

Unlike most of the biology subjects you may have taken in part IA, BOD has, wait for it… TWO practicals every week! Each practical lasts 2 hours, and depending on your schedule, you may take it on different days of the week. Yours truly took practicals on Wednesdays and Fridays from 2pm to 4pm every week while on a subject combination of BOD, Biochemistry, and Cell and Development Biology. At the end of each practical session or block, you may have a wrap up talk summarising the session, which should be accessible online in case you fall ill.

In Michaelmas, practicals mainly consist of histology, which is the practice of staining and inspecting tissue structures under a microscope. Mostly, you will inspect images relating to the immune system following the content you cover during the lectures. You will have access to a worksheet which you can fill up with practical content during the lesson; this worksheet is ungraded and is purely for your own reference and it is up to you how to use it. Each practical mostly consists of online modules which you work through with a partner on computers in the lab, with histology pictures online for your reference where you are free to screenshot and fill in the abovementioned worksheet for your own revision. Do clarify with the demonstrators if you are unable to see a cellular structure or are unsure of anything. Oh, and if you are thinking of staying home to view the histology pictures, you are required to sign in at the lab unless you are told it is an online practical, but more importantly you lose access to the demonstrators, which are critical for your learning! Following the histology sessions in Michaelmas, you have a couple of lab sessions for virology, which involves hands-on work such as growing viruses and applying lab techniques which will come up in the written practical exam.

Lent practicals also contain histology sessions, mainly on the vascular pathologies and cancer, which come after you have covered the respective topics in the lectures. However, it starts off with a few practicals on parasitology, which again allows some lab techniques to be used. The meat of the Lent practicals is bacteriology, where you will be introduced to techniques on how to identify bacteria, as well as where each bacterium species can be found in humans, which is relevant for diagnosing bacterial infections. Much like Michaelmas, you will have access to an ungraded worksheet where you can fill in practical content during each practical, with the practical material being predominantly online. You just work through them while asking any questions to the demonstrators in the lab if you have any doubts.

In Easter, there are no official practicals in Easter save for optional revision classes for 2 topics: bacteriology and histology. Depending on how comfortable you are with the topics, you can choose to sign up for these revision classes to clarify any questions and understand the lab techniques better.

Revision and Exams

The BOD exam consists of 2 papers: a 3-hour essay paper where you write 4 essays and a 2-hour written practical where you are NOT required to perform any experiments yourself; instead, it is intended to test your knowledge on practical techniques. 65% of your grade rests on the essay, while 35% of your grade depends on the practical, and both exams are likely to be closed book online exams on the Inspera platform.

For the essay paper, there are 2 sections of 4 questions per section, and you choose 2 questions within each section for a total of 4 essays. Past year papers are plentiful, and you will find that questions often repeat from previous years, which simplifies revision somewhat. In addition, it may be advantageous to revise for a select few topics due to the sheer volume of content in the course: immunology is a great candidate as pretty much every topic in BOD links back to immunology, followed by viruses or bacteria as multiple essay questions often come out on these two topics in a single paper or even section. That said, expect curveballs and try to think of different question stems involving the same lecture content (for example, change “compare and contrast” to “evaluate” and plan your strategy for each question). Unfortunately, because this is a biology essay paper, you cannot run away from memorisation, and it pays well to regularly revisit past topics after their lecture blocks end to ensure they stick around in your head alongside other things such as your lecture/supervision timetable and the pervasive feeling of dread from being a Cambridge Natsci.

Writing the essay in the exam: unlike some other subjects (looking at you IA E&B and IB Biochem), time pressure is not as critical, as you have 45 minutes per essay question, and it is generally recommended to spend 5-10 minutes planning your essay before typing it. Your lecturers and supervisors in IA will probably already have beaten this horse to death, but I will say it again for good measure: answer the question and do not simply W+M1 what you know on the topic on the paper from memory. A well-addressed question with an adequate introduction and conclusion with relatively few examples in the middle will go much further than a brute force regurgitation of the lecture notes that fumbles around the question! For those aiming higher, incorporating pieces of extracurricular research will help greatly. A nice place to start will be reading clinical research papers on Google Scholar or PubMed (see useful resources).

As for the written practical, there are 5 sections: Bacteriology, Analysis of Tissue Sections, Analysis of Information Relating to a Clinical Case, Virology, and Immunology. Unfortunately, there are no past year papers (anecdotally, this is because releasing past year papers will make it too easy), although there is a sample practical paper in the form of a Moodle quiz and a document outlining the type of questions that will come out. Investing in filling in the Michaelmas and Lent practical worksheets during the practicals will pay dividends during practical revision. In addition, pay close attention to all the various virology, bacteriology (especially the techniques and plates that help you differentiate the species of bacteria), and immunological techniques, as any of these techniques are liable to be tested in sections 1, 4, and 5. As for histology, knowing how to identify different immune cells and structures such as but not limited to fibrin, scar tissue, necrotic tissue, and blood vessels on a tissue stain will go a long way in aiding you in sections 2 and 3.

One final note: it may be tempting to see the nearly 2x weightage of the essay compared to the practical and throw your practical to the Tripos wolves while focusing all your energy on the essay. DO NOT DO THIS. Your practical content is based on 5 well-defined topics that are at times straight lifts from your practical session slides. Spend some time on the practical to secure these relatively easy-to-get marks, or you will be regretting all your life choices you have made that led you to this point during the practical exam!

Useful resources

• The course Moodle site, which contains all the practical slides and the recorded wrap up talks
• Sources of papers that will help your essay stand out:
  • PubMed: https://pubmed.ncbi.nlm.nih.gov/
  • Google Scholar: https://scholar.google.com/