Study smarter with Fiveable
Get study guides, practice questions, and cheatsheets for all your subjects. Join 500,000+ students with a 96% pass rate.
Protein synthesis is the ultimate expression of genetic information—it's how your DNA actually does something in the cell. The AP Biology exam loves testing this process because it connects so many foundational concepts: the central dogma, gene expression, enzyme function, and the relationship between structure and function. You'll see questions asking how mutations at different steps affect the final protein, why eukaryotic and prokaryotic protein synthesis differ, and how cells regulate which proteins get made and when.
Here's the key insight: protein synthesis isn't just a sequence to memorize. Each step exists to solve a specific biological problem—protecting genetic information, ensuring accuracy, or allowing regulation. When you understand why each step happens, you can predict what goes wrong when it fails. Don't just memorize the order—know what molecular machinery is involved at each stage and what would happen if that machinery malfunctioned.
The first phase of protein synthesis involves copying genetic information from DNA into a portable, usable format. This separation protects the original genetic material while allowing the cell to regulate gene expression.
Before mRNA can be translated, eukaryotic cells must modify it for stability, transport, and accurate reading. These modifications act as quality control and regulatory checkpoints.
Compare: Prokaryotic vs. Eukaryotic mRNA—prokaryotes skip processing entirely because transcription and translation occur simultaneously in the cytoplasm. Eukaryotes require the 5' cap, poly-A tail, and splicing. If an FRQ asks why a eukaryotic mutation in splicing machinery causes problems but wouldn't affect bacteria, this is your answer.
Translation converts the mRNA nucleotide sequence into an amino acid sequence. The ribosome acts as the molecular machine that coordinates this process through three distinct phases.
Compare: A site vs. P site vs. E site—aminoacyl-tRNA enters at A (arrival), peptidyl-tRNA holds the chain at P (polypeptide), and empty tRNA exits at E (exit). The ribosome moves 5' to 3' along the mRNA, but the polypeptide grows from N-terminus to C-terminus.
Compare: Start codon vs. Stop codons—AUG is the only start codon and codes for methionine, while three different stop codons exist but code for no amino acid. A mutation changing a sense codon to a stop codon creates a nonsense mutation, producing a truncated protein.
The polypeptide chain emerging from the ribosome is not yet a functional protein. Post-translational modifications determine final structure, location, and activity.
Compare: Transcriptional regulation vs. Post-translational modification—both control protein activity, but transcription determines whether a protein is made, while post-translational modifications determine how an existing protein functions. FRQs often ask about multiple levels of gene regulation.
| Concept | Key Details |
|---|---|
| Transcription location | Nucleus (eukaryotes), cytoplasm (prokaryotes) |
| mRNA processing steps | 5' cap, poly-A tail, splicing |
| Start codon | AUG (codes for methionine) |
| Stop codons | UAA, UAG, UGA (no amino acid) |
| Ribosome sites | A (arrival), P (polypeptide), E (exit) |
| Key enzymes | RNA polymerase (transcription), ribosome/rRNA (translation) |
| tRNA function | Carries amino acids, anticodon matches mRNA codon |
| Post-translational examples | Phosphorylation, glycosylation, folding, cleavage |
Comparative thinking: What do the 5' cap and poly-A tail have in common in terms of their function, and how do their specific roles differ?
Concept identification: A mutation prevents the spliceosome from functioning. Would this affect a bacterial cell? Explain why or why not.
Process application: If a tRNA with the anticodon 3'-UAC-5' enters the ribosome, what codon is it reading, and what amino acid is it carrying?
Compare and contrast: How does the role of RNA polymerase in transcription compare to the role of the ribosome in translation? What does each enzyme "read" and "build"?
FRQ-style prompt: Describe how a single nucleotide substitution in DNA could result in a nonfunctional protein, tracing the effect through transcription, translation, and post-translational modification.