Translation-in-Eukaryotes (2).ppt zoology

INITIATION ELONGATION AND TERMINATION OF TRANSLATION IN EUKARYOTES

1. Translation in Eukaryotes Translation is the process by which genetic information encoded in mRNA is used to synthesize proteins. In eukaryotic cells, this process occurs in the cytoplasm, where ribosomes bind to mRNA and translate the codons into a sequence of amino acids.

2. The Eukaryotic Ribosome Structure The eukaryotic ribosome is composed of two subunits: a small subunit (40S) and a large subunit (60S). These subunits are made up of ribosomal RNA (rRNA) and proteins. Function Ribosomes function as the site of protein synthesis, decoding the information in mRNA and assembling amino acids into polypeptide chains. Location Eukaryotic ribosomes are located in the cytoplasm, often associated with the endoplasmic reticulum (ER), where they synthesize proteins for secretion or integration into membranes.

3. Initiation of Translation 1 Small Subunit Binding The small ribosomal subunit binds to the 5' cap of mRNA, followed by the initiator tRNA carrying methionine (Met) to the start codon AUG. 2 Large Subunit Joining The large ribosomal subunit joins the complex, forming the complete ribosome with three tRNA binding sites: A, P, and E sites. 3 Initiation Factors Various initiation factors (eIFs) play crucial roles in guiding the assembly of the initiation complex and ensuring accurate initiation of protein synthesis.

4. Elongation of the Polypeptide Chain Codon Recognition A charged tRNA carrying the appropriate amino acid enters the A site, guided by base pairing with the mRNA codon. Peptide Bond Formation The amino acid on the tRNA in the A site is added to the growing polypeptide chain in the P site, catalyzed by peptidyl transferase. Translocation The ribosome moves one codon along the mRNA, shifting the tRNA in the A site to the P site, the tRNA in the P site to the E site, and ejecting the tRNA from the E site.

5. Termination of Translation 1 Stop Codon Recognition When a stop codon (UAA, UAG, or UGA) enters the A site, no tRNA can bind, signaling the end of translation. 2 Release Factor Binding Release factors (eRFs) bind to the A site, recognizing the stop codon and triggering the hydrolysis of the polypeptide chain from the tRNA in the P site. 3 Ribosome Dissociation The ribosomal subunits, mRNA, and tRNA dissociate, completing the translation process.

6. Post-Translational Modifications Modification Description Phosphorylation Addition of a phosphate group Glycosylation Addition of a carbohydrate Ubiquitination Addition of ubiquitin proteins Proteolytic Cleavage Removal of amino acids

7. Regulation of Translation in Eukaryotes mRNA Stability The stability of mRNA molecules can be regulated by factors like 5' caps, 3' poly(A) tails, and microRNAs, influencing the lifespan of mRNA and the number of proteins produced. Initiation Factors Initiation factors (eIFs) can be regulated by signaling pathways, affecting the efficiency of ribosome assembly and the initiation of translation. MicroRNAs MicroRNAs (miRNAs) can bind to target mRNAs, leading to their degradation or translational repression, controlling the expression of specific proteins. Stress Response Under stress conditions, cells activate signaling pathways that can inhibit translation, prioritizing the production of essential proteins and conserving energy.