Biology Translation Process

Translation Overview

• Translation is the process of synthesizing proteins using the information encoded in nucleic acids
• It involves several stages, including:
  • Nucleotide acid structure
  • DNA replication
  • Transcription
  • Protein synthesis

The Genetic Code

• Proteins consist of 20 amino acids
• mRNA, which has only 4 nucleotides, codes for these amino acids
• A codon is a sequence of 3 nucleotides encoding an amino acid
• There are 64 possible codon combinations, some of which code for the same amino acid

Codons and Amino Acids

• A table (Figure 22-3) shows the amino acid corresponding to each codon
• The first position (5' end) determines the amino acid for the second position
• The third position (3' end) plays a role in determining the amino acid despite some redundancy

Reading Frames

• mRNA sequence is read in non-overlapping triplets
• The same sequence can be read with different meanings depending on the starting point (reading frame)

Mutations

• Point mutations lead to changes in the amino acid sequence
  • Nonsense mutations involve stopping the process prematurely
  • Silent mutations do not change the amino acid coded
  • Missense mutations change one amino acid to another
• Other mutations
  • Trinucleotide repeat expansion involves the duplication of sequences causing changes in the protein (e.g., Huntington's disease)
  • Frame-shift mutations cause a change in the reading frame due to additions or deletions of nucleotides. This changes the amino acid sequence after the mutation
• Cystic fibrosis arises from the deletion of 3 nucleotides, leading to a missing amino acid at position 508 in the CFTR protein

Protein Synthesis Requirements

• Amino acids
• tRNA molecules
• Aminoacyl-tRNA synthetases
• mRNA
• Ribosomes
• Protein factors
• ATP and GTP

tRNA Structure and Function

• tRNA molecules have an anticodon region that base-pairs with complementary codons on mRNA
• Anticodon sequence determines which amino acid binds to a specific tRNA
• Aminoacyl-tRNA synthetases attach amino acids to their corresponding tRNA molecules

Eukaryotic Ribosomes

• Ribosomes are sites for protein synthesis
• They consist of rRNA and ribosomal proteins
• They have binding sites for tRNA molecules carrying amino acids

Peptide Bond Formation

• Peptidyl transferase, located within the ribosome, catalyzes the formation of peptide bonds between amino acids

Steps in Protein Translation

• Initiation: assembly of translation components.
• Elongation: adding amino acids to the polypeptide chain.
• Termination: ending the process when a stop codon is reached.

Post-translational Modifications

• Various covalent modifications can occur after protein synthesis
  • Trimming
  • Covalent alterations (e.g., phosphorylation, glycosylation, hydroxylation, carboxylation)
  • Attachment of groups (e.g., farnesyl groups)
  • Acetylation

Energy Requirements

• 4 high-energy bonds are used for each amino acid added during protein synthesis.
  • Amino acid attachment to tRNA: 2 ATP bonds
  • Aminoacyl-tRNA binding to ribosome: 1 GTP bond
  • Ribosome translocation along mRNA: 1 GTP bond

Medical Relevance

• Antibiotics can bind to prokaryotic ribosomes, affecting translation
• Some toxins interfere with eukaryotic translation.