Overview
This lecture explains protein synthesis, focusing on the processes of transcription and translation, which convert genetic information from DNA into proteins.
Protein Synthesis Overview
- Protein synthesis has two main steps: transcription and translation.
- Cells use genes from DNA to create proteins through these processes.
DNA, Genes, and mRNA
- DNA is stored in the nucleus and contains thousands of genes coding for proteins.
- Genes are specific DNA sections with unique base sequences for specific amino acid sequences.
- DNA cannot leave the nucleus due to its size, but a small copy (mRNA) can.
- mRNA (messenger RNA) is a single-stranded copy of a gene, capable of leaving the nucleus.
Differences Between DNA and mRNA
- mRNA is single-stranded and shorter than DNA.
- mRNA uses uracil (U) instead of thymine (T).
Transcription Process
- Transcription copies a gene from DNA to mRNA using the enzyme RNA polymerase.
- RNA polymerase binds before the gene, separates DNA strands, and assembles complementary mRNA bases.
- In mRNA, A pairs with U, T pairs with A, C pairs with G, and G pairs with C.
- The DNA strand used for copying is called the template strand.
- After transcription, mRNA detaches and exits the nucleus.
Translation Process
- Translation occurs at the ribosome, where mRNA is read in codons (triplets of bases).
- Each codon codes for a specific amino acid; there are 20 amino acids.
- tRNA (transfer RNA) brings amino acids to the ribosome, matching mRNA codons with complementary anticodons.
- The ribosome links amino acids in order, forming a polypeptide chain.
- Once the chain is complete, it folds into a functional protein.
Key Terms & Definitions
- Transcription — Process of copying a gene from DNA into mRNA.
- Translation — Process of decoding mRNA to assemble amino acids into proteins.
- mRNA (messenger RNA) — Single-stranded RNA copy of a gene that leaves the nucleus.
- Codon — Sequence of three mRNA bases coding for an amino acid.
- tRNA (transfer RNA) — RNA that brings amino acids to the ribosome.
- Anticodon — Three-base sequence on tRNA complementary to an mRNA codon.
- Ribosome — Cell structure where translation and protein synthesis take place.
- RNA polymerase — Enzyme that synthesizes mRNA from a DNA template.
Action Items / Next Steps
- Review key differences between DNA and mRNA.
- Practice matching DNA, mRNA, and tRNA base pairs.
- Study the steps and components of transcription and translation.