AP Biology Questions: Ribosomes and Protein Translation

📚 Quick Study Guide

• 🧬 Ribosomes: These are molecular machines responsible for protein synthesis. They consist of two subunits: a large subunit and a small subunit.
• 🧩 Subunit Composition: Each subunit is made of ribosomal RNA (rRNA) and ribosomal proteins.
• 📍 Location: Ribosomes are found in the cytoplasm (free ribosomes) and on the endoplasmic reticulum (ER), forming the rough ER (bound ribosomes).
• 📝 Protein Translation Steps:
  1. Initiation: mRNA binds to the small ribosomal subunit, and the initiator tRNA (methionine) binds to the start codon (AUG). The large subunit then joins.
  2. Elongation: tRNA molecules bring amino acids to the ribosome, matching the mRNA codons. Peptide bonds form between the amino acids.
  3. Termination: A stop codon (UAA, UAG, or UGA) is reached. Release factors bind, causing the ribosome to disassemble and release the polypeptide.
• 🔑 Codons: Three-nucleotide sequences on mRNA that specify a particular amino acid.
• tRNA: Transfer RNA carries amino acids to the ribosome. Each tRNA has an anticodon complementary to an mRNA codon.
• 🧪 Energy Source: Protein synthesis requires energy in the form of GTP.
• 🎯 Post-Translational Modification: After translation, proteins may undergo folding, modification (e.g., glycosylation, phosphorylation), or be targeted to specific locations in the cell.

Practice Quiz

1. Which of the following is the primary function of ribosomes?
   1. A. DNA replication
   2. B. Protein synthesis
   3. C. Lipid synthesis
   4. D. Carbohydrate metabolism
2. The start codon AUG codes for which amino acid?
   1. A. Alanine
   2. B. Glycine
   3. C. Methionine
   4. D. Valine
3. What molecule carries amino acids to the ribosome during translation?
   1. A. mRNA
   2. B. tRNA
   3. C. rRNA
   4. D. DNA
4. Where does translation primarily occur in eukaryotic cells?
   1. A. Nucleus
   2. B. Golgi apparatus
   3. C. Endoplasmic reticulum
   4. D. Cytoplasm
5. What type of bond is formed between amino acids during elongation?
   1. A. Hydrogen bond
   2. B. Ionic bond
   3. C. Peptide bond
   4. D. Glycosidic bond
6. Which of the following is NOT a stop codon?
   1. A. UAA
   2. B. UAG
   3. C. UGA
   4. D. AUG
7. What is the role of release factors in translation?
   1. A. Initiating translation
   2. B. Elongating the polypeptide chain
   3. C. Terminating translation
   4. D. Folding the protein