Questions and Answers
What is the one gene, one enzyme hypothesis?
The one gene, one enzyme hypothesis states that each gene encodes a single, separate protein.
What are isoaccepting tRNAs?
Molecules that have different anticodon sequences but accept the same amino acids.
What is the significance of the fact that many synonymous codons differ only in the third nucleotide position?
Synonymous codons code for the same amino acid, and the third nucleotide pairing is weak, allowing for nonstandard pairings.
What is a reading frame?
Signup and view all the answers
What is a degenerate code?
Signup and view all the answers
What is an unambiguous code?
Signup and view all the answers
What is a nonoverlapping code?
Signup and view all the answers
What is a synonymous codon?
Signup and view all the answers
What is a universal code?
Signup and view all the answers
What is an initiation codon?
Signup and view all the answers
What is a termination codon?
Signup and view all the answers
What are sense codons?
Signup and view all the answers
What are nonsense codons?
Signup and view all the answers
How is the reading frame of a nucleotide sequence set?
Signup and view all the answers
How are tRNAs linked to their corresponding amino acids?
Signup and view all the answers
What role do the initiation factors play in protein synthesis?
Signup and view all the answers
How does the process of translation initiation differ in bacterial and eukaryotic cells?
Signup and view all the answers
What are the elongation factors used in bacterial translation?
Signup and view all the answers
What events bring about the termination of translation?
Signup and view all the answers
Compare and contrast the process of protein synthesis in bacterial and eukaryotic cells.
Signup and view all the answers
How do prokaryotic cells overcome the problem of a stalled ribosome on an mRNA that has no termination codon?
Signup and view all the answers
Study Notes
One Gene, One Enzyme Hypothesis
- Each gene encodes a single protein, modified to one gene, one polypeptide hypothesis due to multi-polypeptide enzymes.
- Established a crucial link between DNA sequences and protein synthesis.
Isoaccepting tRNAs
- Different anticodon sequences that correspond to the same amino acid.
Synonymous Codons
- Codons that have the same meaning and code for the same amino acid.
- Third nucleotide position pairing is often weak, allowing for "wobble" and nonstandard pairings, ensuring correct amino acid insertion.
Reading Frame
- The method by which mRNA nucleotides are grouped into codons during translation.
Codon Types
- Degenerate Code: Multiple codons can encode one amino acid.
- Unambiguous Code: Each codon specifies only one amino acid, e.g., UUU always codes for phenylalanine.
- Nonoverlapping Code: Each nucleotide belongs to a single codon, producing one type of polypeptide from a polynucleotide sequence.
Universal Code
- Consists of 64 codons, identical across all living organisms.
Initiation & Termination Codons
- Initiation Codon (AUG): Starts polypeptide synthesis.
- Termination Codons (UAA, UAG, UGA): Signal the end of translation.
Sense and Nonsense Codons
- Sense Codons: 61 codons that specify amino acids.
- Nonsense Codons: Codons that do not encode amino acids.
Setting the Reading Frame
- Initiation codon on mRNA determines the reading frame.
tRNA-Amino Acid Linking
- Each amino acid is linked to its tRNA by specific aminoacyl-tRNA synthetases.
Role of Initiation Factors
- Proteins essential for the start of translation.
- Bacterial initiation factors (IF-1, IF-2, IF-3) have distinct roles in ribosome assembly and tRNA delivery.
- Eukaryotic initiation factors assist in recognizing mRNA structures and resolving secondary structures.
Difference in Translation Initiation
- Bacterial cells use the Shine-Dalgarno sequence for ribosome binding.
- Eukaryotic cells use a 5' cap and Kozak sequence to find the start codon.
Bacterial Elongation Factors
- EF-TU: Delivers charged tRNA to the ribosome.
- EF-TS: Recharges EF-TU with GTP.
- EF-G: Aids in ribosomal translocation along the mRNA.
Termination of Translation
- Initiated when a termination codon is reached at the ribosome’s A site.
- Release factors (RF-1, RF-2, RF-3) bind to the ribosome, ultimately cleaving the polypeptide from tRNA.
Comparison of Protein Synthesis in Bacteria and Eukaryotes
- Both share a universal genetic code and similar elongation/termination processes.
- Eukaryotic transcription occurs in the nucleus; bacterial transcription and translation happen simultaneously.
- Bacterial mRNA is typically short-lived, while eukaryotic mRNA lasts longer.
- Ribosomal structures differ in composition and size between the two cell types.
Handling Stalled Ribosomes
- Prokaryotic cells use transfer-messenger RNA (tmRNA) to alleviate stalled ribosomes.
- Eukaryotic cells employ nonstop mRNA decay to degrade stalled mRNA starting from the 3' end.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Description
Explore key concepts of the genetic code and the translation process with this informative quiz. Delve into topics such as the one gene, one enzyme hypothesis and its evolution to the one gene, one polypeptide hypothesis. Enhance your understanding of genetics and protein synthesis.