MNS

Cell Membrane and its Organization Biological membranes: The boundaries of cells are formed by biological membranes The barriers that define the inside and the outside of a cell Transport systems confer on membranes the important property of selective permeability

Salient features of biological membranes: Membranes are sheet like structures Membranes consist mainly of lipids and proteins Membrane lipids are relatively small molecules that have both hydrophilic and hydrophobic moieties. Specific proteins mediate distinctive functions of membranes

Salient features of cell wall The cell wall of the bacterial cell is a complex, semirigid structure responsible for the shape of the cell. Major Functions: Supports the underlying, fragile plasma (cytoplasmic) membrane and protects it and the interior of the cell Prevent bacterial cells from rupturing Helps maintain the shape of a bacterium and serves as a point of anchorage for flagella Contributes to the ability of some species to cause disease and is the site of action of some antibiotics The chemical composition of the cell wall is used to differentiate major types of bacteria.

General composition: I. composed of disaccharides and polypeptides -repeating disaccharide chains formed by two monosaccharides linked end to end:  NAG (N-acetylglucosmine)  NAM (N-acetylmuramic acid

 NAG and NAM alternatively arranged  of these sugars alternatively linked to form carbohydrate backbone  Two rows are linked by polypeptide chain  Polypeptide link contain techoic acid side chains attach to NAM  Two common cell wall types in bacteria: 1. Gram positive cell wall 2. Gram negative cell wall

1. Gram Positive Cell Walls  thick, many layers of peptidoglycan,  strong, rigid  also contain teichoic acids composed of glycerol, ribitol and phosphate  Two types of techoic acid 1. Lipotechoic acid 2. Wall techoic acid

 Lipoteichoic acid  It spans the peptidoglycan layer and is linked to the plasma membrane  Wall teichoic acid  Linked to the peptidoglycan layer

2. Gram Negative Cell Wall  One or very few peptidoglycan layer and outer membrane  Peptidoglycan linked with outermembrane by lipoprotein  Space between peptidoglycan and outer membrane- periplasmic the peptidoglycan in periplasm  Outer membrane contains  lipoprotein,  phospho lipid and  lipopolysaccharide

The lipopolysaccharide (LPS) of the outer membrane is a large complex molecule that contains lipids and carbohydrates and consists of : (1) lipid A, (2)an O polysaccharide 1.Lipid A is the lipid portion of the LPS and is embedded in the top layer of the outer membrane. 2.The O polysaccharide extends outward from the Lipid A and is composed of sugar molecules. The O polysaccharide is useful for distinguishing species of gram negative bacteria.

Unusual wall structures 1. Mycobacterium species:  -Gram+ structure with mycolic acids a waxy material2. 2. Mycoplasma species:  -smallest bacteria  -no cell wall

 located inside the cell wall  functions to enclose the cytoplasm Composition: composed of a  Mostly phospholipid bilayer: 1. phosphate + glycerol = hydrophilic head-outer surface 2. fatty acid tails = hydrophobic tail-remain in inner surface

 membrane has two types of proteins I. peripheral proteins:  Loosely bound  easily removed by mild treatment  enzymes for metabolic reactions II. integral proteins / transmembrane proteins:  Embedded in plasma membrane  removed by disrupting the bilayer  channels for transport

 Act as selective barrier through which materials can transport  Selective permeability  Can produce certain enzymes to break nutrients and produce energy  Sometimes the pigments and enzymes of photosynthetic bacteria found in plasma membrane

 eukaryotes that lack a wall usually have glycocalyx instead: sticky carbohydrate layer exterior to the plasma membrane for strength, attachment, and cell recognition  No eukaryotes have peptidoglycan

 simple  phospholipid bilayer: basic structure  Composed of carbohydrate and sterols: resist osmotic lysis  integral and peripheral proteins: transport and metabolism (enzymes)

 Plasma membrane used for endocytosis: can uptake particle/large molecules or soluble particles with in the cell

Maintaining/determining cell shape Support and mechanical strength Ultimately responsible for the plant architectural design Has a metabolic role Physical barrier to a) pathogens and b) water in suberized cells Carbohydrate storage Signaling Plant Cell Walls- Structure and Function

Composition of Plant cell wall Many plant cells have both 1.a primary cell wall, which accommodates the cell as it grows, and 2.a secondary cell wall they develop inside the primary wall after the cell has stopped growing.

 Thinner  The main components of the primary plant cell wall include cellulose  In addition, the cell wall contains two groups of branched polysaccharides, the pectins and cross- linking glycans.  Give strength

 deposited inside the primary cell wall  More commonly, lignin are found in the secondary wall.  Lignin makes plant cell walls less vulnerable

A specialized region associated with the cell walls of plants, and sometimes considered an additional component of them, is the middle lamella Rich in pectins, the middle lamella is shared by neighboring cells and cements them firmly together. Positioned in such a manner, cells are able to communicate with one another and share their contents through special conduits.