Protein Synthesis In Eukaryotic Cells

• What is the genetic code composed of?

  Sets of 3 nucleotides in mRNA

  
• How many amino acids are there in total?

  20 amino acids
• What determines the reading frame in mRNA translation?

  Where the reading frame starts (5'–3')

  
• What happens if there is an error in the reading frame?

  It may result in a nonfunctional protein
• What codon signals the start of translation?

  AUG codon

  
• What is the role of tRNA in translation?

  Matches amino acids to codons in mRNA

  
• How long is a typical tRNA molecule?

  About 80 nucleotides long
• What structure does tRNA form due to internal base-pairing?

  Cloverleaf structure

  
• What is the function of aminoacyl-tRNA synthetases?

  Catalyzes formation of covalent bonds between tRNA and amino acids

  
• How many aminoacyl-tRNA synthetases are there?

  20 synthetases in total
• What is the product of the reaction catalyzed by aminoacyl-tRNA synthetases?

  Charged tRNA

  
• What is the role of ribosomes in protein synthesis?

  They facilitate translation of mRNA into proteins

  
• Where are ribosomes located?

  In the cytoplasm, free or attached to ER
• What are the two subunits of a ribosome?

  Small subunit and large subunit

  
• What does the small ribosomal subunit do?

  Matches tRNA to codons

  
• What is the function of the large ribosomal subunit?

  Catalyzes formation of peptide bonds

  
• What are the three tRNA binding sites in ribosomes?

  A, P, and E sites

  
• What initiates protein synthesis?

  Assembly of factors on small ribosomal subunit

  
• What is the first amino acid in newly synthesized proteins?

  Methionine
• What happens when the small ribosomal subunit binds to mRNA?

  It scans mRNA until it finds AUG

  
• What leads to the dissociation of some translation initiation factors?

  Recognition of AUG codon

  
• What is the process of elongation in protein synthesis?

  A 4-step cycle repeated to synthesize proteins

  
• What occurs during the first step of elongation?

  A new charged tRNA binds to the A site

  
• What happens in the second step of elongation?

  Peptide bond forms between new aa and polypeptide chain

  
• What is translocation in the context of elongation?

  Movement of ribosomal subunits along mRNA

  
• What signals the termination of translation?

  Stop codons UAA, UAG, UGA

  
• What do release factors do during termination?

  Bind to stop codon at the A site

  
• What happens to the polypeptide chain during termination?

  It is freed from tRNA by addition of H2O

  
• What are polyribosomes?

  Assemblies of multiple ribosomes on mRNA
• What is required for proteins to become fully functional?

  Post-translational processing
• What are post-translational modifications (PTMs)?

  Covalent modifications that regulate protein activity
• What is proteolysis?

  Breakdown of proteins into amino acids
• What are proteases?

  Enzymes that hydrolyze peptide bonds
• What is the role of proteasomes?

  Degrade proteins tagged for destruction

  
• How are short-lived proteins tagged for destruction?

  By covalent attachment of ubiquitin
• What regulates protein expression?

  Regulation of mRNA expression and protein breakdown
• What are examples of control mechanisms in protein expression?

  Regulation at mRNA and protein levels