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How does the information in a gene become a protein, and why is the genetic code nearly universal?

Explain the basic processes of transcription and translation and how they result in the expression of genes, including the universal nature of the genetic code (NGSSS SC.912.L.16.5 and SC.912.L.16.9; Reporting Category 1, Molecular and Cellular Biology).

A benchmark-level answer on gene expression for the Florida Biology 1 EOC: transcription of DNA to mRNA, the codon and the genetic code, translation at the ribosome, and why the code is universal.

Generated by Claude Opus 4.813 min answer

Reviewed by: AI editorial process; not yet individually human-reviewed

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  1. What this topic is asking
  2. The flow of genetic information
  3. Transcription: DNA to mRNA
  4. The genetic code and codons
  5. Translation: mRNA to protein
  6. Why the genetic code is universal
  7. Try this

What this topic is asking

The NGSSS benchmarks SC.912.L.16.5 and SC.912.L.16.9 ask you to explain transcription and translation (how a gene becomes a protein) and why the genetic code is universal. For the Florida Biology 1 EOC you need the two-step pathway from DNA to protein, the idea of a codon, how to read the genetic code, and the big conclusion that nearly all organisms use the same code. Items often ask you to transcribe a sequence or to explain why a gene works in a different organism.

The flow of genetic information

Transcription: DNA to mRNA

In transcription, the enzyme RNA polymerase reads a gene's DNA template and builds a complementary strand of mRNA. The base-pairing rules are like DNA's, with one change: RNA uses uracil (U) instead of thymine.

  • DNA A pairs with RNA U
  • DNA T pairs with RNA A
  • DNA G pairs with RNA C
  • DNA C pairs with RNA G

So a DNA template T-A-C-G is transcribed into mRNA A-U-G-C. The mRNA then leaves the nucleus through a nuclear pore and goes to a ribosome. The EOC tests this with a transcription problem, and the classic trap is writing thymine (a DNA base) into the RNA.

The genetic code and codons

Because there are three bases per codon and four possible bases, there are 64 codons coding for the 20 amino acids (so several codons can specify the same amino acid). To read a codon chart on the EOC, take the mRNA three bases at a time and look up each amino acid.

Translation: mRNA to protein

In translation, the mRNA is read at the ribosome:

  1. The ribosome attaches to the mRNA and reads it one codon at a time.
  2. A matching transfer RNA (tRNA), carrying the correct amino acid, pairs its anticodon with each codon.
  3. The amino acids are joined in order by peptide bonds, forming a growing chain.
  4. At a stop codon, the finished protein (polypeptide) is released and folds into its working shape.

The order of bases in the gene therefore sets the order of amino acids, which sets the protein's structure and function. A change in the DNA (a mutation) can change a codon and so change the protein.

Why the genetic code is universal

This universality is the basis of biotechnology: it is what lets scientists insert a human gene into bacteria to make insulin.

Try this

Q1. State what happens in transcription and where it occurs. [2]

  • Cue. A gene's DNA is copied into messenger RNA (mRNA) in the nucleus, using RNA base pairing (A with U, G with C).

Q2. Explain why a human gene can be inserted into bacteria to make a human protein. [2]

  • Cue. The genetic code is essentially universal, so the bacterium reads the same codons as the same amino acids and produces the same protein.

Exam-style practice questions

Practice questions written in the style of FLDOE exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.

FL Biology 1 EOC (2023 released style)1 marksDuring transcription, a DNA strand has the sequence T-A-C-G. What is the sequence of the messenger RNA (mRNA) made from it? (A) A-T-G-C. (B) A-U-G-C. (C) U-A-C-G. (D) T-A-C-G.
Show worked answer →

A 1-point multiple-choice item on transcription and base pairing with RNA.

The correct answer is B. In transcription, RNA bases pair with the DNA template using A-U and G-C (RNA uses uracil instead of thymine). The DNA T-A-C-G is read as A-U-G-C in mRNA. A uses thymine (DNA, not RNA), C and D do not follow the pairing rules.

For transcription, remember the DNA base A pairs with RNA's uracil (U), not thymine.

FL Biology 1 EOC (2024 released style)1 marksA gene from a jellyfish that codes for a glowing protein is inserted into a bacterium, and the bacterium then makes the same glowing protein. What does this best demonstrate? (A) Bacteria and jellyfish are the same species. (B) The genetic code is essentially universal, read the same way by nearly all organisms. (C) Proteins are made of nucleotides. (D) The gene changed into a bacterial gene.
Show worked answer →

A 1-point item on the universal genetic code (SC.912.L.16.9), a favorite EOC application.

The correct answer is B. Because almost all organisms read the same codons as the same amino acids, a gene moved from one organism to another is translated into the same protein. That is why a bacterium can make a jellyfish protein. This universality is also evidence of common ancestry. The other options misstate the biology.

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