3.2 Carbohydrates, Lipids and Proteins

Crash Course Biology: Biological Molecules – you are what you eat by Hank.


Condensation and Hydrolysis

Condensation is used to form peptide bonds, hydrolysis is used to break them.  Click to see animation.

Condensation & hydrolysis in peptides. Click to animate.



Condensation & hydrolysis in maltose. Click to animate.

Condensation & hydrolysis in maltose. Click to animate.




Condensation & hydrolysis of triglycerides. Click to animate.

Condensation & hydrolysis of triglycerides. Click to animate.


For AHL/ Option C content, jump here.



How-to: Make the animated gifs

  1. 3.2 Carbohydrates, Lipids and Proteins
    -Slide 22
    Summary of Condensation and Hydrolysis reactions
    Carbohydrates -> monosaccharides

    Is that a typo in one of the OH bonds?
    it says HO.

    • Hi Tenaxis,

      It is not a typo – the carbon bonds to the oxygen, which in turn bonds to the hydrogen. This way the carbon has four bonds, the oxygen two and the hydrogen one.

  2. Hi,
    i have a question… it’s difficult to find a standardized diagram of the structures of carbohydrates because different books/websites show HO bonds while others don’t, and there’s a great discrepancy as to where the hydroxyl bonds are placed (above or below the carbon bonds). is there a way i can find a truly accurate source for this?

    Thanks! 🙂

    • Hi Biostudent,

      That’s a good question. Bear in mind that the clearest way to present these models in a 2D diagram may not be precise with regards to ‘real life’ – but they do get the idea across. A ‘truly accurate’ version would be very difficult to draw. If you do a Google Images search for ‘3D structure of carbohydrates‘ you will see what I mean.

      I alternate the orientation of the -OH groups around the hexose ring as it makes more suggestion to the 3D structure and is in keeping with other sources. Some put the -OH on the outside and the -H on the inside to unclutter the diagram. What’s more important is that if you include the -OH you make sure that the C bonds to the O and not the H (remember H can only make one bond).

      Really, you need to choose and use the clearest version that is correct as far as IB Bio goes (not too advanced) and which you are comfortable with drawing.

      Good luck!


  3. Hello, Well i have a test next week and while reviewing my notes, i found a small inconscrepency, What does a 5 Carbon Fatty Acid look like? or what is the Generalized formula?

    • Hi Mariel,

      The generalised formula is CH3(CH2)nCOOH. n=repeated unit.

      The CH2 section in the middle can repeat many times, so a 5C fatty acid would have three of these, the CH3 at one end and the COOH at the other.


  4. On the Carbohydrates, Lipids, and Proteins slideshow, slide 17 has a typo. The fatty acid on the bottom left has a carbon which has 5 bonds.

  5. Hello,
    Do you have answers for the questions above? I want to check my work.
    Thank you.

    I really like this website, it helps a lot ^^

    • Hi Cornellya,

      I don’t think I do – sorry. Most can be found in the slides, links or subject guide, though.

      Thanks for the comment,


  6. Stephen you are amazing all your sources have helped me so much to guide my students in this IB experience through IB Biology. THANK YOU SO MUCH God bless you and your family- Zuhey Stout

  7. Hi Stephen,
    I normally prepare animations, power point presesntations, case study related to the topic, article basesd on the topic from newspaper for any topic. I was spellbound when I looked at the resource that you have got for each topic. I fell guilty to take it readymade, the hardowrk done by a person like you. I however use specific resource which I do not have in my collection.
    amazing presentations and I do understand how much of your hardwork has gone into it.
    Thanks a million for sharing. I have asked my students to use and I find the ones who use i-biology perform very well in the tests.

  8. Hi Stephen, I am actually planning to use your method of students doing self-study and making a website as a way of teaching IB biology with differentiation. I have two questions: 1) Do you have a MS for the Essential Biology worksheets? How do students assess themselves? 2.) What do you do for students who are weak in IT and have trouble making the website?

    • Hi Emerson – good to hear you’re having a go at some of these ideas.

      1. I don’t, sorry. I don’t really use them much anymore. When we did, students turned them in for checking or we did it together.

      2. I set up GoogleSites for the students and they maintained them – I’ve never had a problem with weak IT skills as we’re quite a techy school. I would recommend spending time with them in the early stages to walk them through some simple steps – or empower student tech leaders to help others.

      Good luck!


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