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The triplet code is a sequence of three DNA bases that codes for one specific amino acid. Free GCSE Edexcel Biology notes with key definitions and 11 FAQs.
From DNA Code to Protein Synthesis is part of Reproduction in GCSE Edexcel Higher Biology.
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The triplet code is a sequence of three DNA bases that codes for one specific amino acid. Free GCSE Edexcel Biology notes with key definitions and 11 FAQs.
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Use this lesson to stay inside Reproduction while connecting the detail back to the wider Topic 3: Genetics topic.
Read the core explanations from From DNA Code to Protein Synthesis before testing yourself from memory.
Your DNA contains the instructions for making every protein in your body. But how does a sequence of four letters (A, T, G, C) become a complex protein like haemoglobin or insulin?
Think of DNA as a recipe book written in a four-letter alphabet. Each 'word' in this recipe is exactly three letters long - we call this a triplet code. Just like changing one letter in a word changes its meaning, changing one base in the triplet changes which amino acid gets added to the protein.
Trap: Many students think one base codes for one amino acid. Actually, it takes three bases to code for each amino acid - that's why we call it the triplet code.
The order of bases in DNA directly controls the order of amino acids in the protein. Change the DNA sequence, and you change the protein. This is why genetic mutations can have such dramatic effects.
Picture a factory assembly line. The DNA sequence is like the instruction manual - it tells the workers (ribosomes) which parts (amino acids) to add and in what order. Get the instructions wrong, and the final product won't work properly.
Worked example: How DNA Sequence Determines Protein Structure
DNA sequence: ATG-CCG-GAA codes for which amino acid sequence?
Answer: Methionine-Proline-Glutamic acid
This direct relationship between DNA sequence and amino acid sequence explains why even small changes in DNA can have big effects. Change one base, and you might change one amino acid - which could change the entire protein's shape and function.
Ribosomes are the protein-making machines of the cell. They read the genetic template (like following a recipe) and assemble amino acids in the correct order to build proteins.
Think of ribosomes as highly skilled chefs. They read the recipe (genetic code), and carrier molecules act like waiters, bringing the right ingredients (amino acids) at exactly the right time. The chef adds each ingredient to the growing dish (protein chain) in the precise order specified.
Worked example: Protein Synthesis at the Ribosome
Describe how a ribosome makes a protein with 5 amino acids
Answer: Ribosome reads template → carriers bring amino acids → chain forms → protein released
Once the amino acid chain is complete, something remarkable happens - it folds up into a unique 3D shape. This folding isn't random; it's determined by the sequence of amino acids in the chain.
Imagine a long piece of string with different coloured beads (amino acids). Some beads are attracted to each other, some repel, and some are neutral. When you let go, the string automatically folds into a specific shape based on these attractions and repulsions.
This unique shape is crucial because it determines what job the protein can do. Enzymes need specific shapes to fit their substrates. Hormones need specific shapes to fit their receptors. Structural proteins like collagen need specific shapes to provide strength.
Trap: Students often think protein shape is random. Actually, the amino acid sequence completely determines the final 3D shape - change the sequence, change the shape, change the function.
Protein synthesis questions often test your understanding of the relationship between DNA, amino acids, and protein function. Here's how to tackle them like a pro.
Common exam mistakes include confusing the direction of information flow. Remember: DNA → amino acid sequence → protein shape → protein function. Information flows one way only.
Worked example: Answering a 6-Mark Protein Synthesis Question
Explain how the structure of DNA affects the proteins made in a cell. [6 marks]
Answer: A complete answer linking DNA structure → amino acid sequence → protein folding → specific function with examples
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Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Protein folding is the process by which a linear chain of amino acids spontaneously folds into a specific 3D shape. The folding is not random: it is determined by the sequence of amino acids, and the final shape determines the protein's function.
The triplet code is a sequence of three DNA bases that codes for one specific amino acid. There are 64 possible combinations coding for 20 amino acids, and the order of triplets in DNA controls the order of amino acids in the protein.
Three bases code for one amino acid, which is why it is called the triplet code. A common mistake is thinking one base codes for one amino acid.
Ribosomes are the protein-making machines of the cell. They read the genetic template and assemble amino acids in the correct order, while carrier molecules bring the specific amino acids to the ribosome, building a protein chain that is then released.
A protein's shape is crucial because it determines what job the protein can do. Enzymes need specific shapes to fit their substrates, hormones need specific shapes to fit their receptors, and structural proteins like collagen need specific shapes to provide strength.
Protein folding is not random: the amino acid sequence completely determines the final 3D shape. Change the sequence and the shape changes, which changes the function.
The order of bases in DNA determines the order of amino acids in the protein, with three bases coding for each amino acid. The amino acid chain folds into a unique 3D shape that determines its function, so changing one base can change the protein's shape and function.
The triplet code has 64 possible combinations of three bases. These 64 combinations code for 20 amino acids, with each triplet coding for one specific amino acid.
Peptide bonds join amino acids together. During protein synthesis, peptide bonds form between adjacent amino acids as the chain grows at the ribosome.
Information flows one way: DNA → amino acid sequence → protein shape → protein function. Confusing the direction of this information flow is a common mistake.
Enzymes need specific shapes to fit their substrates, and hormones need specific shapes to fit their receptors. Structural proteins like collagen also need specific shapes to provide strength, so a protein's shape determines its job.