Writing an Introduction

The introduction section is the beginning of the body of your lab report. It is meant to provide an outline and purpose for the experiment that prepares the reader with the context to understand the experiments that will follow. This section should give the reader a detailed background on the "what" and "why" of the experiment, and put the experiment into a broader context. This context should be beyond this lab course and should not refer to the course itself, your instructors, or other students. Before writing your own introduction, you should review the examples below and try to find the parts described in a recent research paper from the journal Biochemistry.

Content of an introduction

As with most parts of a scientific paper, the introduction is highly formulaic. Broadly it contains two parts: the background and description of the experiment. Although there is some variation, most Introductions include all the points listed below in the approximate order shown. The first three points are background and the final three points pertain to the experiment.

  • First describe the broader context and importance of the work to the scientific community.
  • Review the relevant current state of knowledge. Give the essential background that is not common knowledge to help the reader understand the paper.
  • Present an unanswered question in the field that will be the novel contribution of your paper. For elementary student lab exercises, you may not be asking a totally novel question, nonetheless you should still explain the broader relevance of such experiments to your reader and/or state that you are attempting to replicate past observations.
  • State the objective(s) in one of the last sentences/paragraphs of the Introduction.
  • Conclude by following the objective with a description of the experiments that will be carried out.
  • As needed, explain any specific background for the methods that is not common knowledge. Your assignment will specify when this is necessary in this course.

Style of an introduction

  • Cite references, such as the primary literature or a textbook, when stating any facts or information that you have not personally obtained in this work. See the Citations and References section of this document for more details.
  • Nearly all of the Introduction is written in the present tense because it refers to facts that are currently true. You may find it easiest to stick to this tense throughout.
  • Before presenting the current state of knowledge or your objective(s) you may find it relevant to describe specific data from recent relevant experiments. These data should be written in past tense because you are discussing something that was done at a specific time in the past.
  • The introduction is the only place in scientific writing where personal pronouns ("we" or "I") are expected. The two limited uses are described below. Avoid the personal pronoun in all other sections of your report.
    • When stating their objective(s), researchers nearly always use phrases like "In this work, we study..."; "Herein we report..."; "Here we present..."; "We report in this paper..."; etc. Please adopt this norm since the passive voice alterative is awkward and disappearing from modern published scientific literature.
    • When presenting the current state of knowledge, researchers use "we" to refer to relevant work that their team has performed. If you wish to build on your past work in this course by developing a narrative of ongoing inquiry, you may do so. Remember to cite your past report(s) in the References.
  • Everything we do in a lab setting has a broader context. Even though our experiments are designed to be teaching tools, it is unprofessional to write about them solely in that context. Avoid mentioning the "lab," "experiment," "instructor," or "students". From the reader's perspective, the organizational structure of research is team is not pertinent to the science.
    • Example. Avoid a sentence like this. "This experiment was conducted in order for students to learn the technique of PAGE electrophoresis."
  • We will assess your understanding of what you did in lab through your writing, not through tests. Therefore, when requested to explain theory, approach the task with the attitude that your report is your primary opportunity to demonstrate to your instructor what you understand.

Analysis of a sample Introduction from Biochemistry

This Introduction is much longer and more detailed than anything we will expect from you. However, it illustrates the above principles. It opens with the broader context (understanding HIV-1 PR is important for the development of therapies for HIV) in present tense with cited references as superscript numbers. In this example, limited past tense is used to give context to a specific subject. Throughout this example, I will omit extraneous text with an ellipsis (...).

The human immunodeficiency virus type 1 protease (HIV-1 PR) mediates the processing of the Gag and Gag-Pol polyproteins into mature structural and functional proteins essential for assembly and maturation into infective progeny virus.1-4 The HIV-1 genome encodes a single copy of the 99-amino acid protease. PR is translated in the pol open-reading frame and catalyzes its own release at its termini (autoprocessing) from the Gag-Pol polyprotein via transient dimerization (Figure 1A).1-3 ... The active site of the mature PR dimer has been the subject of intervention strategies for almost 25 years since its discovery, and clinical protease inhibitors form a crucial part of combination antiretroviral therapy.5-6

Next the authors present a brief review of the current state of knowledge. Note that the authors generally use present tense passive voice, but switch to past tense first person to describe their team's specific results.

However, the short replication cycle (1.2 days7) of HIV-1, together with the error-prone reverse transcriptase, contributes to the rapidly evolving selection of mutations in PR leading to drug resistance. Major and accessory mutations involving 37 of the 99 PR residues contribute resistance to clinical protease inhibitors in current use by several mechanisms.8,9 We recently characterized an extreme multidrug resistant clinical isolate of PR... We proposed that mutations at or near these sites, which significantly limit autoproteolysis, can prolong the lifetime of mature PR20, thereby compensating for its reduced catalytic activity during the viral replication cycle.26

The authors finish the current state of knowledge summary with an unanswered question followed by more background related to that question.

However, to the best of our knowledge, molecular mechanisms of drug resistance pertaining to autoprocessing, a pivotal step in PR regulation, have not been thoroughly explored. We recently characterized an extreme multidrug resistant clinical isolate...

In the last paragraph, the objective is stated. It is easy to identify by the use of "Here we" in the last paragraph.

Here we address the effects of clustered drug resistance mutations on a comprehensive set of properties, for the first time, such as the dimer dissociation constant (K dimer), kinetic parameters (k cat/K m and K i), thermal stability in the absence and presence of protease inhibitor, Gag processing, autoproteolysis, and autoprocessing governing PR function.

Finally, the experiment that will be described is explained.

Initially, we substituted all PR20 clusters (or cassettes) into PR and its precursor mimetic and, conversely, all PR clusters into PR20 and its corresponding precursor and examined the effect of these mutations on the mature protease. Kinetic parameters of PR-mediated hydrolysis of synthetic substrates were compared with the rate and order of Gag processing. Subsequently...

 

Analysis of a student sample Introduction

Read this complete sample Introduction written by a past student. Identify the (a) broader context, (b) current state of knowledge, (c) background of methods, (d) unanswered question, (e) objective of study, and (f) experiment. Mouse over each sentence to see if you are correct.

1 2+ and Zn 2+ at histidine residues positions 13 and 14. Such binding accelerates the rate of peptide aggregation and the formation of toxic fibrils and plaques.1

2+ binding site which includes 3 histidine residues. 2,3   Theoretical approaches have also been used to give information about the possible coordination intermediates between copper and Aβ peptide. 4

5 In ITC studies, ligand aliquots are injected into a sample of a macromolecule solution of known concentration to determine the heat released upon binding. This is measured indirectly by monitoring the power applied to the sample cell to keep the temperature difference between the sample cell and a reference cell constant. 6   Software has been developed that allows the determination of binding sites, ΔH values and equilibrium binding constants from the raw data generated from ITC experiments.

d) for the binding of Cu 2+ with Aβ is not known at physiological pH. d binding of Cu 2+ to the short Aβ peptide Aβ-(1-16) which contains the first 16 amino acid residues present in the complete peptide. 2+ binding but lacks the sequence critical for aggregation. Cu 2+ is only weakly soluble at physiological pH due to formation of a highly insoluble hydroxide species. 7 Thus, the binding affinity and thermodynamic parameters were measured at pH 5.5 and 6.0 in order to extrapolate thermodynamic parameters at a physiologically relevant pH.