Overview
This lecture explains how cells build proteins through translation, describes the roles of mRNA, tRNA, and ribosomes, and highlights real-world applications like mRNA vaccines.
Protein Synthesis and Translation
- Cells build billions of peptides (baby proteins) every day through translation.
- Proteins are essential for building cells, catalyzing reactions, and transporting oxygen.
- DNA, stored in the nucleus, contains genetic instructions.
- mRNA (messenger RNA) copies DNA instructions and leaves the nucleus to guide protein synthesis.
- mRNA is made of nucleotides: Adenine (A), Uracil (U), Cytosine (C), and Guanine (G).
- Proteins are made from amino acids, a different type of molecule than nucleotides.
- mRNA is read in three-nucleotide "words" called codons; each codon codes for an amino acid.
- There are 64 possible codons, including three stop codons that signal the end of translation.
The Translation Process
- Ribosomes are the cellular machines that translate mRNA into amino acid chains (peptides).
- Ribosomes are made of proteins and ribosomal RNA, and consist of two subunits.
- Translation has three steps: initiation (start), elongation (chain grows), and termination (end).
- Initiation begins when the small ribosome subunit binds mRNA at the start codon (AUG, methionine).
- tRNA (transfer RNA) delivers specific amino acids to the ribosome by matching its anticodon with mRNA codons.
- During elongation, ribosomes add amino acids one by one and move along mRNA.
- Termination occurs when a stop codon is reached, releasing the peptide.
From Peptides to Proteins
- Peptides (chains <50 amino acids) may join with polypeptides and fold into functional proteins.
- Proteins enable nearly all vital actions in organisms.
Evolutionary and Medical Implications
- The genetic code (codons) is nearly universal across all life, indicating a common ancestor.
- Natural ribosomes are much faster at protein synthesis than laboratory methods.
- mRNA technology, pioneered by scientists like Dr. Katalin Karikó, enabled rapid development of COVID-19 vaccines.
- mRNA vaccines teach cells to produce viral proteins, training the immune system for defense.
Key Terms & Definitions
- Protein — Large, functional molecule made of folded amino acid chains.
- Peptide — Short chain of amino acids (fewer than 50).
- Translation — The cellular process of converting mRNA sequence into an amino acid chain.
- mRNA (messenger RNA) — RNA copy of DNA instructions, used for protein synthesis.
- Codon — Three-nucleotide sequence in mRNA that codes for a specific amino acid.
- Ribosome — Cellular structure that assembles proteins using mRNA instructions.
- tRNA (transfer RNA) — Molecule that transports amino acids to the ribosome for protein assembly.
- Anticodon — Three-nucleotide sequence in tRNA complementary to a codon in mRNA.
- Start codon — AUG; signals the start of translation and codes for methionine.
- Stop codon — Codon that signals the end of translation.
Action Items / Next Steps
- Review the translation process (initiation, elongation, termination) and key molecules involved.
- Prepare for next lecture on gene expression.
- Optional: Visit BioInteractive.org/CrashCourse for additional resources.