Once the genetic message has been copied into mRNA, the cell must interpret that message and assemble amino acids in the correct order. Translation turns the mRNA code into a growing polypeptide.
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A student says, "mRNA already contains the right sequence, so it should be able to turn itself directly into a protein. Ribosomes and tRNA seem unnecessary."
Before reading on, explain why that reasoning is incomplete. If mRNA only carries the code, what else is needed to turn that code into a chain of amino acids?
mRNA carries the code, but the ribosome is the structure that reads that code and coordinates protein assembly.
During translation, the mRNA attaches to a ribosome. The ribosome moves along the mRNA sequence and reads it in codons, one three-base unit at a time. This provides the framework for matching the code to the correct amino acids.
The ribosome does not create the genetic message. It interprets the message that was already copied into mRNA during transcription.
Each tRNA molecule carries a particular amino acid. On the other end of the tRNA is an anticodon, a three-base sequence that can pair with a complementary codon on the mRNA.
This is why mRNA and tRNA have different roles. The mRNA carries the code. The tRNA brings the amino acid that matches that code. Without tRNA, the cell would have no effective way to connect a codon to the correct amino acid during translation.
At the ribosome, a tRNA anticodon pairs with a complementary mRNA codon. This matching ensures that the amino acid brought by that tRNA is placed in the correct position in the growing chain.
The order of codons on the mRNA therefore determines the order of amino acids in the polypeptide. If the mRNA sequence changes, the sequence of amino acids produced may also change.
Once the correct amino acids are positioned by codon-anticodon matching, the ribosome helps join adjacent amino acids with peptide bonds. As this process repeats, the amino acid chain lengthens. This is called polypeptide elongation.
The importance of this process is substantial. Enzymes, structural proteins, transport proteins and signalling proteins all depend on accurate amino acid sequences. Insulin is one real example of a protein product that depends on correct translation.
mRNA binds to a ribosome.
tRNA anticodons pair with complementary mRNA codons.
The ribosome joins amino acids with peptide bonds.
The polypeptide elongates as more codons are translated.
Translation uses the mRNA code to assemble amino acids into a polypeptide.
Ribosomes read mRNA codons, tRNA anticodons pair with them, and peptide bonds join amino acids during elongation.
Do not mix up codons with anticodons or say that mRNA carries amino acids.
Translation is important because it converts the coded information in mRNA into...
Look back at what you wrote in the Think First section. What has changed? What did you get right? What surprised you?
If the mRNA sequence contains the codons A U G G A A, write two complementary tRNA anticodons that could pair with them.
Then state which molecule carries the amino acids.
Explain why an incorrect amino acid sequence during translation could affect the function of insulin as a protein product.
1. What is the main role of the ribosome in translation?
2. Which statement correctly describes tRNA?
3. If an mRNA codon is A U G, which tRNA anticodon would pair with it?
4. What directly causes the amino acid sequence of a polypeptide to be ordered correctly?
5. Why is translation important to cell function?
6. Outline the roles of mRNA, tRNA and the ribosome in translation. 3 marks
7. Explain how codon-anticodon matching and peptide bond formation lead to polypeptide elongation. 4 marks
8. Evaluate the statement: "Correct translation is essential for producing a functional protein such as insulin." 5 marks
You should now be able to reject the idea that mRNA can "become" a protein on its own. Translation requires a ribosome to read the message and tRNA to deliver the matching amino acids so a polypeptide can be assembled.
mRNA codons: A U G G A A
Possible tRNA anticodons: U A C C U U
Molecule carrying amino acids: tRNA.
If translation produces the wrong amino acid sequence, the resulting insulin polypeptide may fold or function incorrectly. That can reduce or prevent its normal biological role as a protein hormone.
1. C - The ribosome reads mRNA codons and coordinates polypeptide assembly.
2. A - tRNA carries a specific amino acid and has an anticodon.
3. B - The complementary anticodon to A U G is U A C.
4. D - Codon-anticodon matching brings amino acids in the order specified by the mRNA.
5. B - Translation is essential because it produces proteins needed for many cellular functions.
Q6 (3 marks): mRNA carries the codon sequence that contains the genetic message [1]. tRNA carries specific amino acids and has anticodons that pair with mRNA codons [1]. The ribosome reads the mRNA and coordinates amino acid joining during translation [1].
Q7 (4 marks): During translation, a tRNA anticodon pairs with a complementary mRNA codon at the ribosome [1]. This brings the correct amino acid into position [1]. The ribosome then helps form a peptide bond between adjacent amino acids [1]. Repeated matching and bond formation lengthen the amino acid chain, causing polypeptide elongation [1].
Q8 (5 marks): The statement is correct because translation determines the amino acid sequence of a protein [1]. Ribosomes read the mRNA codons and tRNA brings the matching amino acids [1]. Peptide bonds then link those amino acids into a polypeptide [1]. If this sequence is incorrect, the resulting protein may not fold or function properly [1]. Therefore correct translation is essential for producing a functional protein such as insulin [1].
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