How can two amino acids, ‘A’ and ‘B’, that are far apart along the polypeptide chain somehow end up next to each other in an active site?

How can two amino acids, ‘A’ and ‘B’, that are far apart along the polypeptide chain somehow end up next to each other in an active site? [4m]

Editor’s note: similar to questions asking is it necessary for amino acids at active site/ amino acids in tertiary structure to be close together in primary structure


The primary structure (unique number and linear sequence of amino acids) of the enzyme, which consists of the sequences and lengths of its amino acids, determine the secondary and tertiary structures.

The final shape of the protein is due to its primary structure, which refers to type, number and sequence of amino acids.


The polypeptide chain is folded into its secondary structure, either as an α-helix or β-pleated sheet, through hydrogen bonding between the CO and NH groups, along the polypeptide backbone.

The secondary structure is further folded and twisted into its tertiary structure by various interactions between the different R groups of the different amino acids; via hydrogen bonds, ionic bonds, hydrophobic interactions and disulphide linkages.


The folding and twisting of the polypeptide chain forms the 3D conformation of the enzyme, which results in a globular structure such that the amino acid residues far apart in the primary structure can be brought closer together in the active site.

What’s the difference between questions that ask you to” Describe” and questions that ask you to”Explain”?


State in words the main points of the topic –either phenomena or experiments

implies answer should include reference to (visual observations) associated with phenomena


Eg. Describe the differences between X and Y

Compare X and Y.

Note: Point-to-point comparison between X and Y is needed


May imply reasoning or some reference to theory, depending on context


EXPLAIN= Describe + give reasons.  Students have to quote values if a figure/ graph/table was given in the question.

What’s the difference between the old H2 Biology syllabus (Subject code: 9648) and the new revamped H2 Biology syllabus (Subject code: 9744)?

This question could be especially relevant for students who fall into one of the two categories mentioned below.

(1) Students who are retaking their A- level syllabus as a private candidate

These students took their A- levels during their JC days under the old 9648 syllabus, but for various reasons, did not register to re-take their A level examinations with the old 9648 subject code.  Bearing in mind that 2017 was the last year that the old 9648 syllabus is offered for re-takers, this pool of students will increase.

(2) Current students who are using their seniors’ material, or older materials

These students who are re-using old materials will find changes in the materials, with the addition of two new extension topics and the removal of most of the application syllabus.  However, much of the core syllabus in the old 9648 syllabus has been brought forth to the core ideas component of the new 9744 syllabus, as outlined below.


General outline of the 2 syllabi

The H2 syllabus has been revised for the A -level H2 Biology exam in 2017 (and subsequent years) with the updated framework as shown below.


(1) New Syllabus (9744)

New syllabus 9744 (2017) framework

Fig 1: H2 Biology curriculum framework, Syllabus 9744 ( GCE A-level syllabus examined in 2017 (and subsequent years))


The new 9744 syllabus is divided into two parts: Core Ideas and Extension Topics.

  1. Core Ideas

There are 4 Core Ideas:

  1. The Cell and Biomolecules of Life
  2. Genetics and Inheritance
  3. Energy and Equilibrium
  4. Biological Evolution


  1. Extension Topics

There are 2 Extension Topics:

  1. Infectious Diseases
  2. Impact of Climate Change on Animals and Plants


(2) Old syllabus (9648)

The old syllabus bears similarities to the new syllabus, but with the addition of two new topics, infectious diseases and climate change.

Straits Times Report


The H2 Biology framework for the previous syllabus is as shown below.

Old Syllabus 9644 (2016).jpg

Fig 2: H2 Biology curriculum framework, Syllabus 9648 ( GCE A-level syllabus examined in 2016)


The old 9648 syllabus is divided into two parts: the Core syllabus and the Applications syllabus.


  1. The Core syllabus.

There are 7 Core topics:

  1. Cellular Functions
  2. DNA and Genomics
  3. Genetics of Viruses and Bacteria
  4. Organisation and Control of Prokaryotic and Eukaryotic Genomes
  5. Genetic Basis for Variation
  6. Cellular Physiology and Biochemistry
  7. Diversity and Evolution


  1. The Applications syllabus.

There are 2 Applications topics:

  1. Isolating, Cloning and Sequencing DNA
  2. Applications of Molecular and Cell Biology

What’s different? What remains the same?

  1. Material content

Much of the core syllabus in the old syllabus has been brought forward to the core topics in the new syllabus.  There is extensive overlap and much material remains the same.


The 2 extension topics in the new syllabus are entirely new, with no precedent A level questions. A-level questions for these 2 topics will be released only from the 2017 papers onwards and beyond.


  1. Scheme of assessment

Instead of a school-based Science Practical Assessment (SPA), the school-based biology practical component has been replaced by a practical paper in the format of an examinable paper taken nationwide.  This means that when previously school teachers would know which experiments would be tested under the SPA component, students would now have to take the practical component examination-style and all students would take the same practical paper.

The planning question from Paper 3 under the old syllabus has been removed and combined into the practical paper under the new syllabus.


The free-response questions (essay questions) have been reassigned to Paper 3 in the new syllabus, and language marks will be allocated for the quality of written communication.




How to study for A level H2 Biology

“How do I study for Biology?”

This is one of the most common questions I get from students.  Biology is difficult.  We all know that it’s nigh impossible to get all that information, word for word, into your head.  This is especially so, given the focus on MOLECULAR BIOLOGY for the biological sciences.

The good news is, “Hard work always beats talent, when talent fails to work hard.” – Kevin Durant

Here are some tips on how to study for Biology.  We will also canvass some of the commonly raised issues/questions by students here.

  1. Pay attention in school, during all your lectures and tutorials.

Notwithstanding that it’s an early morning lecture at an unearthly hour of 8 am, listen! There may be extra annotations given by the teachers, and tips by teachers could very well tell you which areas are the (more commonly tested) areas.

Some schools show animations of biological processes in action.  Being able to visualise how certain biological processes occur, will go a long way in aiding your understanding.  These biological processes include, inter alia, how the end-replication problem occurs at the ends of DNA, how the ribosome translocates one codon at a time (and the sequential involvement of E, P, A sites of the large ribosomal subunit).  When you are able to visualise these, you will be able to understand the sequential mechanics behind these biological processes, in contrast to blindly memorising.  And if you understand how these processes work, should an examination question be set on something other than the normal “template” questions, you will be better able to answer them.

1.1 Before the lecture / tutorial

If you are unable to multi-task, eg simultaneously understanding the lecture content, copying down annotations, and handling the occasional distractions by classmates- read the lecture notes BEFORE the lecture.  (Note: This was what I did when I was a student myself, eons ago.)

Reading the notes before the lecture will give you a rough gauge of what the teacher will be going through.  Having a rough idea of what’s going to happen, can save you time to “digest” what the lecturer is saying, and avoid being lost.

Be forewarned that biology is extremely content- heavy.  To finish the syllabus in time and allow for revision, you will find that lectures progress at an alarmingly fast pace.

And.. before the tutorial, you have to attempt the tutorial questions. (This goes without saying…. right? ) J

1.2 After the lecture / tutorial

Read the notes again after the lecture.  If there are still areas you are unclear, mark these out and clear your doubts.

If you have any doubts, please do not leave doubts till the eleventh hour before you start to clarify, when you may realise there are so many unanswered concepts you do not yet understand.  If you do not work well under stress, you will panic, when you realise you have to both understand and memorise!

  1. Practice many questions

Doing questions are a MUST.  What good is knowing all the content, but having no idea how to apply all these knowledge?

Completing your Ten-Year-Series is a given, these will be the easiest questions you will see.  The questions set by your school teachers will (usually) be more difficult.

  1. Be able to answer the Learning Outcomes

A quick way to test yourself, would be to answer the learning outcomes provided in your Syllabus structure.  You may even try assuming the learning outcomes as an essay question!

  1. Test yourself, under timed conditions

This means doing mock papers under timed conditions.  Then, using the answer key, you could mark the paper yourself to find out where you stand.

Students may under-estimate the amount of time they need during the examination.  It will be a pity if you do not attempt a question, not because you did not know how to do it but because you did not have enough time to!

  1. Organise and file your material topically

Organise your lectures and tutorials neatly according to topic.  Make sure each question set comes together with their answer key.  This will save you a lot of time trying to find the missing “partner” or missing “elements” which you may not realise you have misplaced!

  1. Understand, and then memorise.

Not the other way around.  Understanding before memorising, will allow you to be better able to apply your concepts to questions.  Of course, if you understand first before you memorise, it will be much easier for you to memorise. Isn’t blindly memorising without any understanding… painful?

  1. But… what if I don’t have enough time?

Time, can always be found.  The crux is, do you know how to find time?

Plan your time in half-hour blocks. Write your study session down and exactly what you have been doing.  Remember, a 4 hour- study session with friends is not productive if only 15 minutes of the session is  spent studying, while the rest of the session is spent gossiping/ chit-chatting/ catching up on the latest game (insert any other activity).

Find time to study in all the other pockets of time that you have, eg waiting for the bus, during train rides home, or even during lesson breaks!

Now… good luck! And you should start studying now.. ! 🙂

Up ↑