Overview
This lecture explains the process of translation in protein synthesis, distinguishing it from transcription and reviewing the key components and steps involved in forming a polypeptide chain from mRNA.
Recap: Transcription
- Transcription is the process of copying a DNA segment to produce messenger RNA (mRNA) in the nucleus.
- Only the required DNA section is unzipped and transcribed into mRNA, which carries the genetic code.
- The mRNA consists of codons (three-letter nucleotide sequences) that correspond to amino acids.
- Adenine (A) pairs with Uracil (U) in RNA; Cytosine (C) pairs with Guanine (G); Thymine (T) is not present in RNA.
Translation: Process and Location
- Translation converts the mRNA message into a sequence of amino acids, creating a polypeptide chain.
- Transcription occurs in the nucleus, but translation takes place in the cytoplasm at ribosomes.
- Ribosomes are the cellular structures (protein factories) where translation and protein synthesis occur.
Components Needed for Translation
- mRNA: Carries the genetic code from DNA.
- tRNA (transfer RNA): Picks up and delivers specific amino acids to the ribosome, based on the mRNA codon.
- Ribosome: Facilitates the matching of mRNA codons with tRNA anticodons and forms peptide bonds between amino acids.
Steps in Translation
- The ribosome reads the mRNA codons (three nucleotides at a time).
- tRNA molecules with complementary anticodons bind to the mRNA codons and deliver their amino acids.
- Each amino acid is joined to the growing polypeptide chain by a peptide bond.
- After delivering its amino acid, tRNA leaves the ribosome to collect another matching amino acid.
- This process repeats, forming a polypeptide chain of more than 50 amino acids, which can fold into a functional protein.
Summary of Key Processes
- Transcription copies the genetic message to mRNA in the nucleus.
- Translation reads the mRNA in the cytoplasm, assembling amino acids into a polypeptide chain at the ribosome.
- The sequence of amino acids determines the protein’s structure and function.
Key Terms & Definitions
- Transcription — Process of copying DNA into mRNA.
- Translation — Process of converting mRNA into a polypeptide chain.
- mRNA (messenger RNA) — Carries the genetic code from DNA to ribosome.
- tRNA (transfer RNA) — Transfers amino acids to the ribosome, matching codons and anticodons.
- Codon — Three-nucleotide sequence on mRNA specifying an amino acid.
- Anticodon — Three-nucleotide sequence on tRNA complementary to a codon.
- Ribosome — Organelle where protein synthesis occurs.
- Amino Acid — Building block (monomer) of proteins.
- Polypeptide — Long chain of amino acids (over 50) linked by peptide bonds.
- Peptide Bond — Bond linking two amino acids in a protein chain.
Action Items / Next Steps
- Review and use correct terminology for transcription and translation as outlined in exam guidelines.
- Study diagrams illustrating both processes and practice labeling key parts for tests.