structure and function of the cell envelope of gram negative bacteria.

its my own presentation

1. STRUCTURE AND FUNCTION OF THE CELL ENVELOPE OF GRAM NEGATIVE BACTERIA

2. PRESENTED BY QURAT UL AIN HAFIZA AISHA SIDDIQUE NAIHA ISHAQUE KASHAF GHOURI RITABA TAJ

3. INTRODUCTION By:QURAT-UL-AIN

4. CELL ENVELOPE The bacteria cell envelope is a complex multilayered structure that serves to protect these organisms from their unpredictable and often hostile environment. There are three principal layers in the cell envelope Cytoplasmic or inner membrane The peptidoglycan cell wall The outer membrane

5. CYTOPLASMIC MEMBRANE A cell is the basic unit of life, and all organisms are made up of one or many cells. One of the things that all cells have in common is a cell membrane. It is a barrier that separates a cell from its surrounding environment. This outer boundary of the cell is also called the plasma membrane. It is composed of four different types of molecules: Phospholipids Cholesterol Proteins Carbohydrates

6. Phospholipids Phospholipids make up the basic structure of a cell membrane. A single phospholipid molecule has two different ends: a head and a tail. The head end contains a phosphate group and is hydrophilic. This means that it likes or is attracted to water molecules . The tail end is made up of two strings of hydrogen and carbon atoms called fatty acid chains. These chains are hydrophobic, or do not like to mingle with water molecules.

7. Cholesterol, Proteins and Carbohydrates Cholestrol molecules are made up of four rings of hydrogen and carbon atoms. They are hydrophobic and are found among the hydrophobic tails in the lipid bilayer. Cholesterol molecules are important for maintaining the consistency of the cell membrane. They strengthen the membrane by preventing some small molecules from crossing it . Some plasma membrane proteins are located in the lipid bilayer and are called integral proteins. Other proteins, called peripheral proteins, are outside of the lipid bilayer. Carbohydrates, or sugars, are sometimes found attached to proteins or lipids on the outside of a cell membrane . Together, these carbohydrates form the glycocalyx . The glycocalyx of a cell has many functions. It provides cushioning and protection for the plasma membrane, and it is also important in cell recognition.

8. PEPTIDOGLYCANE & LIPOPROTEIN COMPLEX By:HAFIZA AISHA SIDDIQUE

9. The cell envelope of Gram-negative bacteria consists of two membranes, the outer membrane and the cytoplasmic membrane. The cytoplasmic membrane is composed of a phospholipid bilayer , whereas the outer membrane comprises an interior leaflet of phospholipids and an exterior leaflet of lipopolysaccharide (LPS); LPS is composed of lipid A, the core oligosaccharide and O antigen. In between the two membranes is the periplasmic space, which contains the peptidoglycan (PG) layer and periplasmic proteins. The PG layer comprises long polymers of the repeating disaccharide  N - acetylglucosamine – N - acetylmuramic acid (NAG–NAM) that are linked via peptide bridges.

10. PEPTIDOGLYCANE - LIPOPROTEIN COMPLEX The covalently linked peptidoglycan -lipoprotein complex of the gram-negative cell wall can be thought of as the inelastic foundation of the whole-cell envelope and is, therefore, somewhat analogous to the gram-positive cell wall, the plant cell wall, and the animal cell's glycocalyx . The peptidoglycan of gram negative bacteria has a relatively open molecular structure due to a deficiency of cross-linking .

11. PEPTIDOGLYCANE - LIPOPROTEIN COMPLEX Peptidoglycan is present in the gram-negative cell envelope in highly variable amounts. the peptidoglycan layer exerts morphological control over the cytoplasmic elements of the cell. Isolated peptidoglycan structures also maintain the shape of the cell. peptidoglycan layer is assembled from components produced in the cytoplasmic membrane The turgor pressure of the living cell would force the cytoplasmic membrane outward against the inelastic peptidoglycan layer .

12. We would expect the peptidoglycan layer to bind specific enzymes, in the same way that penicillinase is bound by the cell walls of Bacillus licheniformis and alkaline phosphatase ( APase ) is bound by certain gram-positive bacterial and plant cell walls, and to concentrate certain ions, much as grampositive walls concentrate Al3" and plant cell walls concentrate Ca2".

13.   PERIPLASMIC ZONE The  periplasm  is a concentrated gel-like matrix in the space  between the inner cytoplasmic membrane and the bacterial outer membrane called the  periplasmic space  in gram-negative bacteria. Using cryo -electron microscopy it has been found that a much smaller periplasmic space  is also present in gram-positive bacteria

14. OUTER LAYER By: NAIHA ISHAQUE

15. OUTER LAYER Outside the periplasm most important layer called outer membrane. T his lipid-protein bilayer is usually considered to be the outermost layer of the gram-negative wall. “ It is a membrane which possesses proteins, phospholipids, and lipopolysaccharides (LPSs) and which separates the external environment from the periplasm. ”

16. cont.. Outer membrane is similar to cell membrane bilayer structure . One of the unusual features of the outer membrane is its asymmetric distribution of lipids over its inner and outer faces. The outer face contains (virtually) all of the LPS, whereas the inner face has most of the phospholipid.

17. 3 DISTINCT PARTS OF LPS

18. cont.. Lipids attach with multiple sugar moities called LPS (endotoxin). Lipid A portion made of 2 Glucoseamine derivatives and each of which attached one phosphate group also called pyrophosphate, also 3 fatty acid chains are attached. This lipid A portion is endotoxic. Normally when the bacteria is living, Lipid A is embadded not coming out, only this Lipid A portion come outside when the bacteria is death, if bacteria is kill lipid A is exposed to body then body will react. Core polysaccharide Made of 10 sugars. Linked the region of lipid A and O polysaccharide.

19. cont... O polysaccharide (O-Antigen ) Structure is highly variable Also made of sugars. Immunogenic property Properties LPS prevents harmful substances and allowing useful substances. LPS also helps them to detect bacteriophage.

20. cont... PORIN PROTEINS: Porins are found in the outer membranes of Gram-negative bacteria, mitochondria, and chloroplasts. Low molecular weight . Transmembrane protein. Porin proteins form channels through which small molecules (600-700) dalton can pass. Porins protein helps in the entry of substances useful into the bacteria.

21. Synthesis Of Gram Negative Bacterial Cell Wall By: KASHAF GHOURI

22. THREE STAGES 1- Cytoplasmic Stage : Synthesis of precursors (NAG,NAM) 2- Membrane Stage : (Elongation and Transfer) Transfer of the precursors from cytosol to membrane and incorporation into the growing peptidoglycan 3- Extracellular Stage : ( Crosslinking ) Crosslinking of linear chains of peptidoglycan by membrane bound transpeptidases (beta- lactams )

23. Stage 1: Synthesis of precursors Glucose N- Acetylglucosamine (NAG) UDP (UDP-NAG) UDP (UDP-NAM) UDP-NAM- tripeptide UDP-NAM- pentapeptide L-Ala D- Glu L-Lys L-Ala D-Ala D-Ala-D-Ala UTP Phosphoenolpyruvayte Enol pyruvate Transferase

24. Stage 2: Elongatin And Transfer BACTOPRENOL : carrier molecule that plays major role in insertion of peptidoglycan precursors. Bonds to NAM/NAG/ pentapeptide precursors.

25. Stage 3 : Crosslinking Neighboring peptidoglycan chain are crosslinked through their peptide side chains This reaction is catalysed by transpeptidase Transpeptidase is a penicillin binding protein Beta- lactam inhibit tranpeptidase

26. Association of enzymes with specific cell wall components: By: RITABA TAJ

27. Cont.. Cell wall also contain variety of degradative enzymes and these have been localized within the periplasmic space and at cell surface. Wall associated degradative enzymes include : Deoxyribonuclease APase Ribonuclease Uridine 5’- diphosphatase

28. Cont.. 3’-nucleotidase 5’-nucleotidase ADP Both 3’ nucleotidase and 5’ nucleotidase localized in the outer cell wall layer of Ecoli and APase localized in the periplasmic space and also in the periplasmic space of Ecoli. It is clear that a wall associated enzymes may occur in more than one zone of gram negative cell wall.

29. Function Of Cell Wall Associated Enzymes : Cell wall associated enzymes of gram negative bacteria are very similar to the degradative enzymes. Digestive function, multilayered structure. Degradative enzymes which are located in the periplasmic area act on substrate which diffuse into the zone of the cell wall. Products are available to binding.