Overview
This lecture explains how genetic information in DNA leads to protein production through the processes of transcription and translation, highlighting the roles of different RNA types in protein synthesis.
DNA and Traits
- DNA contains genes which code for traits like eye color.
- Genes code for proteins that create pigments and other cell materials.
Importance of Proteins
- Proteins are essential for transport, structure, enzymes, defense, and other vital functions.
- Protein synthesis occurs constantly in living cells.
Introduction to Protein Synthesis
- Protein synthesis = making proteins from genetic instructions.
- Two main stages: transcription (DNA to mRNA) and translation (mRNA to protein).
Transcription
- Occurs in the nucleus.
- RNA polymerase enzyme builds a complementary RNA strand from DNA.
- Produces messenger RNA (mRNA) based on DNA sequence.
- mRNA undergoes editing before leaving the nucleus.
Translation
- mRNA exits nucleus to cytoplasm and attaches to a ribosome.
- Ribosome is made of ribosomal RNA (rRNA).
- Transfer RNA (tRNA) carries amino acids to the ribosome.
- tRNA matches its anticodon with mRNA codons (triplets of bases).
- Each codon specifies a particular amino acid, determined using a codon chart.
- AUG is the start codon, coding for methionine.
- Peptide bonds link amino acids, forming a protein chain.
- Translation ends at a stop codon (no amino acid added).
Genetic Code and Codons
- Codon = three-base sequence on mRNA; anticodon = complementary three-base sequence on tRNA.
- Multiple codons can code for the same amino acid (redundancy).
- Codon charts are tools to identify which codons code for which amino acids.
After Translation
- Protein chains fold and may be modified or transported as needed.
- Final protein structure determines its function.
Key Terms & Definitions
- Gene — segment of DNA coding for a specific protein.
- Protein Synthesis — creation of proteins from genetic information.
- Transcription — process of copying DNA into mRNA.
- Translation — process of assembling proteins from mRNA instructions.
- mRNA (Messenger RNA) — carries genetic code from DNA to ribosome.
- rRNA (Ribosomal RNA) — structural part of ribosomes.
- tRNA (Transfer RNA) — brings amino acids to the ribosome.
- Codon — three-base sequence on mRNA specifying an amino acid.
- Anticodon — three-base sequence on tRNA complementary to a codon.
- Peptide Bond — chemical bond connecting amino acids in a protein chain.
- Start Codon — (AUG) signals the start of translation.
- Stop Codon — signals the end of translation.
Action Items / Next Steps
- Explore mRNA editing and gene regulation for deeper understanding.
- Practice using a codon chart to decode mRNA sequences.
- Watch animations of translation for visualization.