Genetic Code, Translation, and Protein Structure in Biology

What are codons in the genetic code?

Sequences of three nucleotides in mRNA that specify particular amino acids.

How many possible codons exist in the genetic code?

64 possible codons.

What is the significance of the start codon AUG?

It signals the beginning of translation.

What do stop codons (UAA, UAG, UGA) indicate?

They signal the termination of the polypeptide chain.

What determines the reading frame in mRNA?

The start codon dictates how the mRNA is read in groups of three nucleotides.

What is a frameshift mutation?

A shift in the reading frame that can lead to entirely different polypeptide sequences.

What is the directionality of polypeptide synthesis?

From the 5' N-terminus to the 3' C-terminus.

What marks the start of a polypeptide chain?

The first amino acid with an exposed amino group, known as the N-terminus.

What indicates the end of a polypeptide chain?

The last amino acid with an exposed carboxyl group, known as the C-terminus.

What occurs during each elongation cycle of polypeptide synthesis?

A peptide bond forms between the last amino acid in the chain and the incoming amino acid.

How many standard amino acids are there?

20 standard amino acids.

What determines the properties of an amino acid?

The unique side chain (R group) of each amino acid.

How are amino acids classified based on their side chains?

Into categories such as polar, non-polar, charged, and uncharged.

What is the primary structure of a protein?

The amino acid sequence that dictates the protein's final three-dimensional structure and function.

What role do chaperones play in protein synthesis?

They assist in the proper folding of polypeptides, preventing misfolding and aggregation.

What are the two main types of secondary structures in proteins?

α-helix and β-sheet.

What stabilizes secondary structures in proteins?

Hydrogen bonds between the backbone atoms of the polypeptide chain.

What is the tertiary structure of a protein?

The compact three-dimensional shape formed by the folding of secondary structures.

What interactions determine the stability of the tertiary structure?

Hydrophobic interactions, ionic bonds, hydrogen bonds, and Van der Waals forces.

What is quaternary structure in proteins?

The arrangement of two or more polypeptide chains (subunits) that form a functional protein.

What is the biological process of translation?

The decoding of mRNA codons to synthesize polypeptides, linking genetic code to functional proteins.

What cellular components are essential for translation?

Ribosomes, transfer RNA (tRNA), and amino acids.

What is the role of ribosomes in translation?

Ribosomes are the molecular machines that facilitate the translation of mRNA into proteins.

What do tRNA molecules do during translation?

tRNA molecules transport specific amino acids to the ribosome, matching their anticodons with the mRNA codons.

What are amino acids and why are they important?

Amino acids are the building blocks of proteins, and their sequence determines the protein's structure and function.

What are the three main stages of translation?

The three main stages of translation are initiation, elongation, and termination.

How is the genetic code read during translation?

The genetic code is read in triplets called codons, each corresponding to a specific amino acid.

What is the function of aminoacyl-tRNA synthetases?

Aminoacyl-tRNA synthetases catalyze the charging of tRNA with amino acids, ensuring fidelity in protein synthesis.

What is the significance of the anticodon in tRNA?

Each tRNA has an anticodon that is complementary and anti-parallel to the mRNA codon, ensuring accurate translation.

What structural feature of tRNA aids in its function?

tRNAs exhibit a cloverleaf secondary structure, which is essential for their function in translation.

What is the acceptor stem of tRNA?

The acceptor stem of tRNA is where the amino acid is attached, forming an ester bond at the 3' end.

What is the wobble hypothesis?

The wobble hypothesis explains how tRNAs can recognize multiple codons, particularly at the third position, allowing for degeneracy in the genetic code.

What are the two subunits of ribosomes composed of?

Ribosomes are composed of two subunits made of rRNA and proteins.

How do eukaryotic ribosomes differ from bacterial ribosomes?

Eukaryotic ribosomes are larger (80S) compared to bacterial ribosomes (70S), with distinct rRNA and protein compositions.

What are the three key sites of ribosomes during translation?

The three key sites are the A (aminoacyl), P (peptidyl), and E (exit) sites.

What initiates the formation of the initiation complex in translation?

The initiation complex forms when mRNA, initiator tRNA, and ribosomal subunits come together, requiring initiation factors.

What is the role of the Shine-Dalgarno sequence in bacterial translation?

The Shine-Dalgarno sequence helps position the ribosome correctly for translation initiation in bacterial mRNA.

What is the function of the peptidyl transferase center in ribosomes?

The peptidyl transferase center catalyzes the formation of peptide bonds between amino acids during translation.

What triggers termination in the translation process?

Termination occurs when a stop codon is reached, triggering the release of the completed polypeptide chain by release factors.

What is the role of elongation factors in translation?

Elongation factors facilitate the addition of amino acids to the growing polypeptide chain during elongation.

What is the significance of the 7-methylguanosine cap in eukaryotic mRNA?

The 7-methylguanosine cap is required for recognition of the mRNA during translation initiation in eukaryotes.

How does the error rate in tRNA charging compare to other processes?

The error rate in tRNA charging is remarkably low, approximately one mistake per 100,000 amino acids added.