Genetic Code and Translation Quiz

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?

The way a cell's mRNA-translating machinery groups the mRNA nucleotides into codons. Signup and view all the answers

What is a degenerate code?

Multiple codons encode a single amino acid. Signup and view all the answers

What is an unambiguous code?

Each codon specifies only one amino acid. Signup and view all the answers

What is a nonoverlapping code?

A single nucleotide is part of only one codon. Signup and view all the answers

What is a synonymous codon?

Different codons that specify the same amino acid. Signup and view all the answers

What is a universal code?

Genetic code that consists of 64 triplets of nucleotides called codons that are the same in all living organisms. Signup and view all the answers

What is an initiation codon?

A special codon (usually AUG) used to start synthesis of a polypeptide. Signup and view all the answers

What is a termination codon?

One of the three codons (UAA, UAG, UGA) that signal the termination of translation of a polypeptide. Signup and view all the answers

What are sense codons?

The 61 codons that specify amino acids. Signup and view all the answers

What are nonsense codons?

A codon that does not encode any amino acid. Signup and view all the answers

How is the reading frame of a nucleotide sequence set?

The initiation codon on the mRNA sets the reading frame. Signup and view all the answers

How are tRNAs linked to their corresponding amino acids?

Each of the 20 different amino acids has a corresponding aminoacyl-tRNA synthetase that links them to the correct tRNA molecule. Signup and view all the answers

What role do the initiation factors play in protein synthesis?

Initiation factors are proteins that are required for the initiation of translation. Signup and view all the answers

How does the process of translation initiation differ in bacterial and eukaryotic cells?

Bacterial initiation requires sequences in the 16S rRNA to bind to the Shine Dalgarno sequence; eukaryotic initiation involves recognition of the 5' cap and scanning for the AUG start codon. Signup and view all the answers

What are the elongation factors used in bacterial translation?

Three elongation factors are EF-TU, EF-TS, and EF-G. Signup and view all the answers

What events bring about the termination of translation?

Termination begins when a ribosome encounters a termination codon, allowing release factors to bind and cleave the polypeptide chain. Signup and view all the answers

Compare and contrast the process of protein synthesis in bacterial and eukaryotic cells.

Both share the universal genetic code, but differ in initiation, location of transcription and translation, mRNA stability, and ribosomal composition. 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?

Bacterial cells use transfer-messenger tmRNA to move the ribosome; eukaryotic cells use nonstop mRNA decay. 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.

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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.