Protein Synthesis Flashcards
(12 cards)
What are the two main stages of protein synthesis
Transcription (DNA to mRNA, in nucleus) and Translation (mRNA to protein, at ribosomes).
What are the steps of transcription?
- Initiation – RNA polymerase binds DNA and unwinds it.
- Elongation – RNA polymerase builds complementary mRNA (5’ to 3’).
- Termination – RNA polymerase stops at terminator, releasing mRNA.
How is mRNA modified before leaving the nucleus?
- 5’ cap added (protects and helps ribosome binding),
- Poly-A tail (protects from digestion),
- Introns removed.
What is the triplet code?
A: 3 mRNA bases = 1 amino acid; AUG = start, UAA/UAG/UGA = stop codons.
What are the main molecules in translation?
• mRNA (message),
• Ribosome (site),
• tRNA (transfers amino acids via anticodon and terminal arm).
What are the steps of translation?
- Initiation – small ribosome binds 5’ cap, then large subunit joins at start codon.
- Elongation – tRNA adds amino acids; ribosome shifts (A→P→E sites).
- Termination – stop codon reached; release factor ends translation.
What are the two main mutation types?
• Substitution (silent, missense, nonsense),
• Frameshift (insertion or deletion shifts reading frame).
What causes mutations?
• Spontaneous (DNA replication errors),
• Induced (UV, X-rays, chemicals).
How does the lac operon work?
Inducible system; lactose inactivates repressor → transcription ON.
How does the trp operon work?
Repressible system; tryptophan activates repressor → transcription OFF.
What is epigenetics?
Study of how environment alters gene expression without changing DNA (e.g., methylation silences genes).
How is gene expression regulated in eukaryotes?
At four levels: transcriptional, posttranscriptional, translational, posttranslational.
