Cellular Respiration and Photosynthesis

ATP Synthesis

• ATP can be synthesized by the membrane-bound ATPase enzyme, which consumes protons during ATP synthesis from ADP and phosphate.
• The connection between electron transport, establishment of proton motive force (pmf), and ATP synthesis during respiration is known as oxidative phosphorylation, and during photosynthesis, it is called photophorylation.

Fimbriae and Pili

• Fimbriae and pili are interchangeable terms used to describe short, hair-like structures on the surface of procaryotic cells.
• They are composed of protein, shorter and stiffer than flagella, and slightly smaller in diameter.
• Fimbriae are generally involved in adherence of bacteria to surfaces, substrates, and other cells or tissues in nature, rather than bacterial movement.
• In E. coli, a specialized type of pilus, the F or sex pilus, stabilizes mating bacteria during conjugation, but the function of smaller, more numerous common pili is different.

Gram Staining

• Gram staining is a procedure used to stain bacteria, developed by Hans Christian Gram in 1884.
• Gram-positive cells stain purple, while Gram-negative cells stain red.

Peptidoglycan Layer

• The peptidoglycan layer is a crystal lattice structure formed from linear chains of two alternating amino sugars, N-acetylglucosamine (GlcNAc or NAGA) and N-acetylmuramic acid (MurNAc or NAMA).
• The alternating sugars are connected by a β-(1, 4)-glycosidic bond.
• Each MurNAc is attached to a short amino acid chain, containing L-alanine, D-glutamic acid, meso-diaminopimelic acid, and D-alanine in the case of Escherichia coli (a Gram-negative bacterium).
• Peptidoglycan is one of the most important sources of D-amino acids in nature.
• The peptidoglycan layer protects the cell from lysis caused by the turgor pressure of the cell, and it retains its shape throughout its life.

Enzymes Involved in Peptidoglycan Synthesis

• DD-transpeptidase is involved in cross-linking between amino acids in different linear amino sugar chains.
• murF, mraY, and murG are enzymes involved in peptidoglycan precursor biosynthesis.
• uppS is involved in cell wall biosynthesis, providing the precursor for the carrier lipid, undecaprenyl phosphate (C55-P).

Flippase

• Flippase is a transmembrane lipid transporter protein located in the membrane, which belongs to the ABC transporter or P4-type ATPase families.
• It is responsible for aiding the movement of phospholipid molecules between the two leaflets that compose a cell's membrane (transverse diffusion, also known as a "flip-flop" transition).

Teichoic Acids

• Teichoic acids are bacterial copolymers of glycerol phosphate or ribitol phosphate and carbohydrates linked via phosphodiester bonds.
• They are found within the cell wall of most Gram-positive bacteria, such as species in the genera Staphylococcus, Streptococcus, Bacillus, Clostridium, Corynebacterium, and Listeria.
• They can be covalently linked to N-acetylmuramic acid or a terminal D-alanine in the tetrapeptide crosslinkage between N-acetylmuramic acid units of the peptidoglycan layer.

Lipopolysaccharide (LPS)

• LPS is a component of the outer membrane of Gram-negative bacteria, serving as a permeability barrier, endotoxin, and serotyping agent.
• Mg++ bridges stabilize LPS and are essential for its permeability characteristics.

S-Layer

• S-layers are a part of the cell envelope found in almost all archaea, as well as in many types of bacteria.
• They consist of a monomolecular layer composed of only one (or, in a few cases, two) identical proteins or glycoproteins.
• S-layer proteins are poorly conserved or not conserved at all, and can differ markedly even between related species.