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1.3.2Unit 1 — Cell Biology

Protein Synthesis

5 min read 4 parts Lesson 14 of 28

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Section 1 of 4The Players

1.3.2 Protein Synthesis

Making a protein involves copying the instructions and then reading them somewhere else in the cell.

DNA
  • DNA stays in the nucleus because it is too large to leave, and it holds the code for each protein.
mRNA
  • Messenger RNA is a single-stranded copy of one gene that can leave the nucleus and carry the code to the ribosome.
Ribosome
  • A tiny structure in the cytoplasm where amino acids are joined together to make the protein.
tRNA
  • Transfer RNA molecules bring specific amino acids to the ribosome in the order the code requires.

Section 2 of 4The Process

1
The section of DNA for one gene is copied into a molecule of mRNA in the nucleus.
2
The mRNA leaves the nucleus through a pore and travels to a ribosome in the cytoplasm.
3
At the ribosome, the mRNA code is read in groups of three bases.
4
tRNA molecules bring the matching amino acids, which the ribosome joins in the correct order to form a chain.
5
The chain of amino acids folds into a specific three-dimensional shape, which is the finished protein.

Section 3 of 4Why It Matters

Why It Matters
Specific proteins
  • Different genes produce different amino acid sequences, giving enzymes, hormones and structural proteins their different shapes.
Protect the DNA
  • Using an mRNA copy means the original DNA stays safe in the nucleus and is not damaged by repeated use.
Many copies
  • Many mRNA copies can be made from one gene, so a cell can produce large amounts of a protein quickly.
RNA difference
  • RNA is single-stranded and contains the base uracil instead of thymine.

Section 4 of 4Exam Checklist & Tips

1.3.2 – Key Points for the Exam

  • mRNA A single-stranded copy of a gene that carries the code from the nucleus to a ribosome.
  • Ribosome The site in the cytoplasm where proteins are assembled.
  • tRNA A molecule that carries a specific amino acid to the ribosome.
  • Amino acid The building block of proteins.
  • Protein synthesis The process of making proteins from amino acids using the code in a gene.

Common Mistakes

  • Saying DNA leaves the nucleus; it is the mRNA copy that leaves.
  • Mixing up the roles of mRNA and tRNA; mRNA carries the code and tRNA carries amino acids.
  • Writing that proteins are made in the nucleus; they are made at ribosomes in the cytoplasm.
  • Stating that RNA is double-stranded; it is single-stranded.
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