Question

RECALL Identify the following by describing their functions: EF-G, EF-Tu, EF- Ts, EF-P, and peptidyl transferase.

Short answer

EF-G assists in ribosome translocation, EF-Tu delivers aminoacyl-tRNAs, EF-Ts regenerates EF-Tu with GTP, EF-P aids in the first peptide bond formation, and peptidyl transferase catalyzes peptide bond formation.

Step-by-step solution

Understanding EF-G

EF-G (Elongation Factor G) is a protein that plays a key role in the elongation phase of protein synthesis during translation. It facilitates the translocation of the ribosome along the mRNA by hydrolyzing GTP.

Understanding EF-Tu

EF-Tu (Elongation Factor Tu) is responsible for delivering aminoacyl-tRNAs to the ribosome during protein synthesis. It binds to GTP and aminoacyl-tRNA, forming a complex that then binds to the ribosome.

Understanding EF-Ts

EF-Ts (Elongation Factor Ts) acts as a nucleotide exchange factor for EF-Tu. It facilitates the exchange of GDP for GTP on EF-Tu, allowing EF-Tu to participate in another round of aminoacyl-tRNA delivery.

Understanding EF-P

EF-P (Elongation Factor P) assists in the formation of the first peptide bond during protein synthesis. It acts as a catalyst to help stabilize ribosome-tRNA interactions when the ribosome encounters specific sequences that are difficult to translate.

Understanding peptidyl transferase

Peptidyl transferase is an enzymatic function of the ribosome's large subunit. This enzyme catalyzes the formation of peptide bonds between adjacent amino acids during the translation process, thus elongating the nascent polypeptide chain.

Key concepts

EF-G function

EF-G (Elongation Factor G) is crucial in the elongation phase of protein synthesis. It ensures that the ribosome moves correctly along the messenger RNA (mRNA) during translation.
EF-G binds to the ribosome and hydrolyzes guanosine triphosphate (GTP) to guanosine diphosphate (GDP), providing the necessary energy for this movement.

• Translocation: The ribosome shifts the growing polypeptide chain from the A-site (aminoacyl-tRNA site) to the P-site (peptidyl-tRNA site).
  
• Energy Source: GTP hydrolysis is essential for this shift.

This step ensures the ribosome is ready to accept the next charged tRNA, continuing the assembly of the protein.

EF-Tu function

EF-Tu (Elongation Factor Tu) plays a critical role in delivering the correct aminoacyl-tRNA to the ribosome during translation.
It binds to GTP and aminoacyl-tRNA to form a stable complex. This complex then docks at the A-site of the ribosome.

• Aminoacyl-tRNA Delivery: EF-Tu ensures that the proper tRNA with the corresponding amino acid reaches the ribosome.
  
• GTP Hydrolysis: Upon successful docking and matching of codon-anticodon pairs, EF-Tu hydrolyzes its GTP to GDP.

After GTP hydrolysis, EF-Tu is released and ready to be recharged for another round of aminoacyl-tRNA delivery.

EF-Ts function

EF-Ts (Elongation Factor Ts) acts as a guanine nucleotide exchange factor for EF-Tu. It essentially 'recharges' EF-Tu by allowing it to exchange its GDP for a fresh GTP.
This process is crucial because EF-Tu can only bind to aminoacyl-tRNA when it is bound to GTP.

• Nucleotide Exchange: EF-Ts facilitates the removal of GDP from EF-Tu and the binding of GTP.
  
• Recycling EF-Tu: This allows EF-Tu to go back and fetch another aminoacyl-tRNA for the ribosome.

This continuous recycling helps maintain the efficient flow of protein synthesis.

EF-P role

EF-P (Elongation Factor P) assists during the formation of the first peptide bond. This role is extremely crucial in initiating protein synthesis for specific challenging sequences like polyproline stretches.
EF-P stabilizes ribosome-tRNA interactions to help overcome translation stalling.

• Peptide Bond Formation: EF-P aids in forming the bond between the first two amino acids.
  
• Translation Assistance: It helps when the ribosome encounters difficult sequences that could otherwise stall the process.

EF-P ensures smooth initiation and continuation of the protein synthesis process.

peptidyl transferase activity

Peptidyl transferase is an essential enzymatic activity of the ribosome’s large subunit. It catalyzes the formation of peptide bonds between amino acids.

• Catalytic Function: The ribosome's peptidyl transferase ensures the correct amino acids are joined together.
  
• Bond Formation: This activity happens at the P-site where the peptide chain increases in length with each new amino acid.

The peptidyl transferase reaction is vital because it elongates the nascent polypeptide chain, enabling the growth of a functional protein.

protein synthesis

Protein synthesis is the process by which cells build proteins according to the instructions in their DNA.
It involves two main stages: transcription and translation.

• Transcription: DNA is transcribed into messenger RNA (mRNA).
  
• Translation: The ribosome translates the mRNA into a sequence of amino acids, forming a protein.

The process relies on multiple factors, including ribosomal subunits and elongation factors like EF-G, EF-Tu, EF-Ts, and EF-P.
These factors work together to ensure the accurate and efficient construction of proteins, essential for various cellular functions.

ribosomal function

The ribosome is a complex molecular machine found within all living cells. It is the site where protein synthesis occurs. Ribosomes have two main subunits: the large subunit and the small subunit.

• mRNA Binding: The small subunit binds to the mRNA template.
  
• Amino Acid Assembly: The large subunit houses the peptidyl transferase activity, facilitating the formation of peptide bonds.
• Coordination: Ribosomes ensure the correct placement and sequence of amino acids.

Through these functions, ribosomes play a central role in translating genetic information into functional proteins required for cell survival and function.