Cellular Biosynthesis: Cell Wall and Protein Pathways

Cell Wall Biosynthesis:
Precursor Formation:Synthesizes building blocks in the cytoplasm.
Transport:These are attached to a lipid carrier and moved across the cell membrane.
Polymerization and Cross-linking:The building blocks are linked and cross-linked to form a strong, rigid cell wall.
Protein Biosynthesis:
Transcription:DNA is copied into mRNA.
Translation:mRNA is translated by ribosomes into a protein by linking amino acids according to the mRNA sequence.

1. Biosynthesis of cell wall and protein S. Nahidha Begum, II M.Sc., Microbiology Department Of Microbiology, Sacred Heart College. .

2. The interplay between cell walls and proteins is fundamental for cell structure and function. Proteins such as enzymes and structural proteins are synthesized to modify and maintain the cell wall, ensuring its integrity and functionality. Interplay Between Cell Wall and Proteins

3. Biosynthesis of cell wall Bacterial cell walls contain a large, complex peptidoglycan molecule consisting of long polysaccharide chains made of alternating N-acetylmuramic acid (NAM) and Nacetylglucosamine (NAG) residues. Pentapeptide chains are attached to the NAM groups. The polysaccharide chains are connected through their pentapeptides or by interbridges

4. Such an intricate structure requires an equally intricate biosynthetic process, especially because the synthetic reactions occur both inside and outside the cell membrane. Peptidoglycan synthesis is a multistep process that has been best studied in the gram-positive bacterium Staphylococcus aureus. Two carriers participate: uridine diphosphate (UDP) bactoprenol. Bactoprenol is a 55-carbon alcohol that attaches to NAM by a pyrophosphate group and moves peptidoglycan components through the hydrophobic membrane . Biosynthesis of cell wall

5. Several enzymes are involved in the biosynthesis of cell wall components. They facilitate the synthesis of polysaccharides and proteins, which are crucial for maintaining the dynamic structure of the cell wall during growth and development. Enzymes in Cell Wall Biosynthesis

6. The synthesis of cell wall , occurs in eight stages : UDP derivatives of N-acetylmuramic acid and Nacetylglucosamine are synthesized in the cytoplasm. Amino acids are sequentially added to UDP-NAM to form the pentapeptide chain (the two terminal D-alanines are added as a dipeptide). *ATP energy is used to make the peptide bonds, but tRNA and ribosomes are not involved. The NAM-pentapeptide is transferred from UDP to a bactoprenol phosphate at the membrane surface. UDP-NAG adds NAG to the NAM-pentapeptide to form the peptidoglycan repeat unit. *If a pentaglycine interbridge is required, the glycines are added using special glycyl tRNA molecules, not ribosomes. The completed NAM-NAG peptidoglycan repeat unit is transported across the membrane to its outer surface by the bactoprenol pyrophosphate carrier. The peptidoglycan unit is attached to the growing end of a peptidoglycan chain to lengthen it by one repeat unit.

7. The synthesis of cell wall , occurs in eight stages : 7. The bactoprenol carrier returns to the inside of the membrane. * A phosphate is released during this process to give bactoprenol phosphate, which can now accept another NAM-pentapeptide. 8. Finally, peptide The same process occurs when an interbridge is involved; only the group reacting with the subterminal D-alanine differs. *In E. coli the free amino group of diaminopimelic acid attacks the subterminal Dalanine, releasing the terminal D-alanine residue. *ATP is used to form the terminal peptide bond inside the membrane. No more ATP energy is required when transpeptidation takes place on the outside. *The same process occurs when an interbridge is involved; only the group reacting with the subterminal D-alanine differs. *Peptidoglycan synthesis is particularly vulnerable to disruption by antimicrobial agents. Inhibition of any stage of synthesis weakens the cell wall and can lead to osmotic lysis. *Many antibiotics interfere with peptidoglycan synthesis. For example, penicillin inhibits the transpeptidation reaction, and bacitracin blocks the dephosphorylation of bactoprenol pyrophosphate. .

8. Biosynthesis of cell wall

9. Transpeptidation is a crucial step in bacterial cell wall biosynthesis, catalyzed by enzymes called transpeptidases. It involves the transfer of amino acid residues between peptides, forming cross-links in the peptidoglycan layer of the cell wall. The reaction occurs in two steps: Formation of a covalent enzyme intermediate between the transpeptidase and the donor peptide strand, releasing the terminal D-alanine residue. Transfer of the activated donor to an acceptor peptide, forming a new peptide bond and cross-linking the peptidoglycan chains. Transpeptidation is responsible for both the formation of cross-bridges in newly synthesized peptidoglycan and the attachment of newly made material to preexisting cell wall. It is an essential process for maintaining the structural integrity and shape of the bacterial cell. Transpeptidases are members of the penicillin-binding protein family and are targets of β-lactam antibiotics, which interfere with cell wall biosynthesis. . Transpeptidation.

10. Protein biosynthesis, or protein synthesis, is the cellular process of producing proteins, essential for various biological functions. Proteins act as enzymes, structural components, and hormones, playing critical roles in cellular processes. The process is divided into two main phases: transcription and translation. Bio synthesis of protein Biosynthesis of protein

11. Transcription Process : Initiation : RNA polymerase binds to the promoter region of a gene on the DNA. Elongation : RNA polymerase synthesizes a single strand of mRNA by adding complementary RNA nucleotides to the growing chain. Termination : The process continues until a termination signal is reached, releasing the newly formed mRNA. Post-Transcriptional Modifications   (Eukaryotes): Capping : Addition of a 5' cap for stability and recognition. Polyadenylation : Addition of a poly-A tail at the 3' end. Splicing : Removal of introns and joining of exons to produce mature mRNA.

12. Translation Process : Initiation : The ribosome assembles around the mRNA, and the first tRNA molecule binds to the start codon (AUG). Elongation : tRNA molecules bring amino acids to the ribosome, matching their anticodons with the mRNA codons. Peptide bonds form between amino acids, creating a polypeptide chain. Termination : The process ends when a stop codon (UAA, UAG, UGA) is reached, and the completed polypeptide is released. Components : mRNA : Carries the genetic code from DNA. Ribosomes : The site of protein synthesis, consisting of rRNA and proteins. tRNA : Transfers specific amino acids to the ribosome based on the mRNA sequence.

13. Biosynthesis of protein

14. Protein Folding

15. Protein Folding Folding Process : After translation, polypeptides fold into specific 3D structures essential for their function. Primary Structure : The linear sequence of amino acids. Secondary Structure : Local folding into alpha helices and beta sheets, stabilized by hydrogen bonds. Tertiary Structure : The overall 3D shape formed by the interaction of secondary structures. Quaternary Structure : Some proteins consist of multiple polypeptide chains (subunits) that assemble into a functional complex. Post-Translational Modifications Types of Modifications: Proteolysis : Cleavage of proteins into smaller peptides or amino acids. Phosphorylation : Addition of phosphate groups to specific amino acids, altering protein activity and interactions. Glycosylation : Addition of carbohydrate groups, affecting stability and function. Significance: These modifications can regulate protein activity, localization, and interactions, impacting cellular function .

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