Overview
This lecture explains the process of translation in protein synthesis, detailing how mRNA is decoded in the ribosome to build polypeptide chains from amino acids.
Recap: Transcription
- Transcription occurs in the nucleus where a DNA segment is copied into messenger RNA (mRNA).
- Only the necessary region of DNA is unzipped and transcribed.
- mRNA is composed of codons—three-letter nucleotide sequences.
- Adenine pairs with uracil in RNA (no thymine), cytosine pairs with guanine.
Introduction to Translation
- Translation is the process of converting mRNA into a chain of amino acids (polypeptide).
- Translation occurs in the cytoplasm at the ribosome.
- mRNA exits the nucleus via the nuclear pore to reach the ribosome.
Components Needed for Translation
- mRNA: carries the genetic code from DNA.
- tRNA (transfer RNA): brings amino acids to the ribosome; contains anticodons complementary to mRNA codons.
- Ribosome: molecular machine (organelle) where protein synthesis takes place.
Process of Translation
- The ribosome reads mRNA in sets of three nucleotides (codons).
- tRNA molecules with complementary anticodons bind to mRNA codons.
- Each tRNA carries a specific amino acid corresponding to its anticodon.
- Amino acids are joined by peptide bonds, forming a growing polypeptide chain.
- Once a tRNA delivers its amino acid, it exits the ribosome to collect another.
Protein Formation
- There are 20 standard amino acids shared by all organisms.
- The sequence of amino acids determines the structure and function of the resulting protein.
- Multiple polypeptide chains may combine to form a functional protein.
Key Terms & Definitions
- Transcription — the process where DNA is copied into mRNA.
- Translation — the process where mRNA is decoded to assemble a polypeptide chain.
- mRNA (messenger RNA) — molecule that carries genetic instructions from DNA.
- tRNA (transfer RNA) — molecule that delivers amino acids to the ribosome during translation.
- Anticodon — three-nucleotide sequence on tRNA complementary to mRNA codon.
- Codon — three-nucleotide sequence on mRNA coding for a specific amino acid.
- Amino acid — building block (monomer) of proteins.
- Ribosome — cell organelle where proteins are synthesized.
- Polypeptide chain — long chain of amino acids linked by peptide bonds.
- Peptide bond — bond connecting amino acids in a polypeptide.
Action Items / Next Steps
- Review exam guidelines for proper terminology use in explanations of transcription and translation.
- Practice labeling diagrams and explaining processes step-by-step.
- Study definitions and relationships between key terms.