Joyful excellence in homeschooling

Imago Education Logo

+27-(0)12-330-2030

Calendar for 2026

Not logged in

Lesson 6.4 DNA, RNA and protein synthesis

Details
Last Updated:

This lesson is only available to users who have subscribed to the Biology course. Please log in, or click here if you would like to gain access to the full course.

Introduction to the lesson

 Proteins are some of the most important molecules in the body. As we saw in chapter two, among many other things, proteins facilitate almost all the essential chemical reactions in the body, proteins transport oxygen to the body cells, and proteins provide some structural support (e.g. collagen). We know that the production of proteins is controlled by DNA. In this lesson, we will look in detail at how exactly DNA initiates and controls protein synthesis.

DNA, RNA and protein synthesis

Read the section “DNA, RNA, and protein synthesis” on p.118-122 of your text book.

Learning Activity 1

Answer the following questions in your exercise book.

  1. State how DNA controls the activities of a cell.
  2. Study Fig. 6.12 on p.119 and also look at Appendix 1 & 2.
    1. Answer Question 6.3 on p.119.
    2. What three triplet codes code for "stop"?State how DNA controls the activities of a cell.
  3. Based on the principle of complementary base pairing, write a complementary strand for each of the following strands of DNA (the first one is done for you):
    1. AAA AAT GTA TAC TTG ATT (original strand) : TTT TTA CAT CTG AAC TAA (complementary strand)
    2. AAT ATG ACG CTT CCC CTA ATT
    3. CAA TAA GGA GTA ACG GTT ATT
    4. ACG TTG CTA TAA AGG ATG ATT
    5. TAC GTA TGT CTT CGA CAA TAA ATT

An example of mutation

Learning Activity 2

Answer the following question in your exercise book.

  1. In your own words, describe what is meant by a mutation by substitution, with specific reference to sickle cell anaemia.

Protein synthesis

Learning Activity 3

Answer the following questions in your exercise book.


  1. Describe the first stage of protein synthesis – transcription.
  2. Describe the second stage of protein synthesis – translation.
  3. Explain the role of mRNA in the process of protein synthesis.
  4. Explain the role of rRNA in the process of protein synthesis.
  5. Explain the role of tRNA in the process of protein synthesis.
  6. Answer Questions 6.4 and 6.5 on p.122 of your text book.

Practical Investigation

In this practical investigation you will develop a model of the four stages in the process of protein synthesis. You will make a model of a DNA code for eight amino acids, the mRNA anticodon for these four amino acids, the tRNA codon and the four amino acids. The purpose of this is to help you visualize the process and to help you understand it better as you work with it in more detailed. Take note that this model is slightly simplified (especially step 3 with the tRNA and the amino acids). Consult your text book to see what tRNA molecules really look like as opposed to how they are depicted in this model.

  1. DNA code. The code which you are going to use is: CAA GTA AAT TGT GGA CTT CTT TTT ATT. For each triplet, make a strip of white paper (to represent the phosphate sugar backbone) pasted at right angles to three different coloured flags (each representing one nitrogenous base). For example, the first triplet is CAA. You could use blue to represent cytosine and green to represent adenine. You will then paste a blue flag and two green flags in that order to your white strip. Make all the strips using the same colour convention (e.g. blue=cytosine, green=adenine, orange=guanine, yellow=thymine). When you have made each triplet, stick them together with celotape.
  2. mRNA code. Work out the complementary mRNA codon for the DNA code provided. Make the mRNA code the same way you made the DNA code and make sure that they match up with the complementary base pairs.
  3. tRNA code and amino acids. Work out the complementary tRNA anticodons for the mRNA codons you worked out in step 2 (hint: it should be exactly the same as the DNA code of step 1 except with U instead of T). Now squares of white paper (to represent the amino acid) with three coloured flags (to represent the base pairs on the tRNA molecule). You are going to make the following amino acids: valine (CAA), histidine (GUA), leucine (AAU), threonine (UGU), proline (GGA), glutamine (CUU), glutamine (CUU) and lysine (UUU). Make sure that you design the strips of coloured paper so that it matches up with the mRNA strand. You do not have a tRNA for the last triplet because it is the stop-codon.
  4. Lay your model out and use it to explain the process to a friend or family member. Remember that you will first have the mRNA strand being copied from the DNA strand in the nucleolus (transcription). The mRNA strand will then leave the nucleolus and be joined to tRNA molecules in the ribosome (translation). Which enzymes are involved and where?
  5. Can you design a similar model to represent semi-conservative DNA replication?

The code you were given is the gene which codes for the amino acid sequences in the β polypeptide chains of the haemoglobin molecule. You read about this molecule in your reading today (p.119). What is different about this chain in people who have sickle-cell anemia?

Definitions and review

Definitions

  1.  Transcription
  2. Messenger RNA (mRNA)
  3. Translation
  4. Transfer RNA (tRNA)
  5. Anticodon
  6. Codon
  7. Polyribosomes

Mindmap

Add this section to your chapter six mindmap.