Overview
This lecture explains how DNA leads to the production of proteins, focusing on the processes of transcription and translation in protein synthesis.
From DNA to Traits
- DNA contains genes that code for proteins, which are responsible for traits like eye color.
- Proteins perform essential roles in transport, structure, enzymes, and protection within the body.
Protein Synthesis Overview
- Protein synthesis is the process by which cells make proteins from genetic information in DNA.
- The two main steps are transcription (making mRNA from DNA) and translation (building a protein from mRNA).
Transcription
- Transcription occurs in the nucleus, where RNA polymerase creates a complementary mRNA strand from DNA.
- mRNA stands for messenger RNA, which carries the genetic message from DNA out of the nucleus.
- mRNA undergoes editing before being used for protein synthesis.
Translation
- Translation happens in the cytoplasm at the ribosome, which is made of rRNA (ribosomal RNA).
- tRNA (transfer RNA) carries amino acids and matches them to the mRNA using complementary base pairing.
- tRNA reads the mRNA in triplets called codons, each coding for a specific amino acid.
- The process begins with a start codon (usually AUG for methionine) and ends with a stop codon.
- Amino acids are linked by peptide bonds to form a protein.
The Genetic Code and Codons
- A codon chart is used to match mRNA codons to their corresponding amino acids.
- Multiple codons may code for the same amino acid, e.g., several codons for leucine.
- Start codons signal the beginning and stop codons signal the end of protein synthesis.
Key Terms & Definitions
- Protein Synthesis — the process of making proteins from DNA instructions via transcription and translation.
- Transcription — creating mRNA from DNA in the nucleus.
- Translation — building a protein from mRNA at the ribosome in the cytoplasm.
- mRNA (messenger RNA) — carries genetic code from DNA to the ribosome.
- tRNA (transfer RNA) — brings amino acids to the ribosome and matches them to codons on the mRNA.
- rRNA (ribosomal RNA) — forms the structure of the ribosome.
- Codon — a sequence of three RNA bases on mRNA that codes for an amino acid.
- Anticodon — a sequence of three bases on tRNA, complementary to an mRNA codon.
- Start Codon — usually AUG, signals the start of a protein.
- Stop Codon — signals the end of a protein-coding sequence.
Action Items / Next Steps
- Read further about mRNA editing and post-translational modifications.
- Practice using a codon chart to decode mRNA into amino acid sequences.