1. The Cell Membrane Phospholipidbilayer: 2 surface layers of hydrophilic of polar head and inner layer of hydrophobic nonpolar tail. Peripheral proteins: Function as enzyme scaffold for support and mediator for cell movement Integral proteins: disrupting lipid bilayer. Other types known as transmembrane protein Glycoprotein: protein attached to the carbohydrate Glycolipid: Lipid attached to carbohydrate
Characteristics of Lipid bilayer Semi-permeable Consists of : 1) hydrophilic 2) hydrophobic Main function is to: Protect cell (as outercovering) Keep the things that are on the inside of a cell inside, and keep what things are outside the cell on the outside. It allows some things, under certain situations, to cross the phospholipidbilayer to enter or exit the cell.
Function of the Cell Membrane Protective outer covering for the cell. Cell membrane anchors the cytoskeleton (a cellular 'skeleton' made of protein and contained in the cytoplasm) and gives shape to the cell. Responsible for attaching the cell to the extracellular matrix (non living material that is found outside the cells), so that the cells group together to form tissues. Transportation of materials needed for the functioning of the cell organelles without using cellular energy. The protein molecules in the cell membrane receive signals from other cells or the outside environment and convert the signals to messages, that are passed to the organelles inside the cell. In some cells, the protein molecules in the cell membrane group together to form enzymes, which carry out metabolic reactions near the inner surface of the cell membrane. The proteins help very small molecules to get transported thru cell membrane, provided, the molecules are traveling from a region with lots of molecules to a region with less number of molecules.
The cell membrane Lipid bilayer of plasma membrane Lies between two dark line Prokaryote have less sterol as compared to the eukaryote, causing rigid structure Less-sterol wall in prokaryote is Mycoplasma Taken with TEM
2. The bacterial cell wall Has peptidoglycan Marks the difference between gram +ve and gram –ve bacteria
Peptidoglycan Polymer of disaccharide Also known as murein, is a polymer consisting of sugars and amino acids that forms a mesh-like layer outside the plasma membrane of bacteria (but not Archaea), forming the cell wall. The sugar component consists of alternating residues of N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids.
Gram positive and Gram negative bacterial cell walls A, Gram positive bacterium thick peptidoglycan layer contains teichoic and lipoteichoicacids. B, Gram negative bacterium thin peptidoglycan layer and an outer membrane that contains lipopolysaccharide, phospholipids, and proteins. The periplasmic space between the cytoplasmic and outer membranes contains transport, degradative, and cell wall synthetic proteins. The outer membrane is joined to the cytoplasmic membrane at adhesion points and is attached to the peptidoglycan by lipoprotein links.
Peptidoglycan in Gram positive bacteria Linked by polypeptides
Gram positive bacterial cell wall Teichoic acid - Lipoteichoic acid links to plasma membrane - Wall teichoic acid links to peptidoglycan May regulate movement of cations Polysaccharides provide antigenic variation
Gram negative bacteria outer membrane Lipopolysacharides, lipoproteins, phospholipids Forms the periplasm between the outer membrane and the plasma membrane Protection from phagocytes, complement and antibiotics O-polysaccharide antigen e.g. E. coli O157:H7 Lipid A is an endotoxin Porins (proteins) form channel through membrane
The Gram stain Mechanism Crystal violet-iodine crystals form in cell Gram positive - Alcohol dehydrates peptidoglycan - CV-I crystals do not leave Gram negative - Wall is lesser or - Wall is made up of pseudomurein (lack NAM and D-amino acids)
Acid-fast organisms are difficult to characterize using standard microbiological techniques (e.g. Gram stain - if you gram stained an AFB the result would be an abnormal gram positive organism, which would indicate further testing), though they can be stained using concentrated dyes, particularly when the staining process is combined with heat. Once stained, these organisms resist the dilute acid and/or ethanol-based de-colorization procedures common in many staining protocols—hence the name acid-fast.
Atypical Cell Wall Mycoplasmas - Lack cell walls - Sterols in plasma membrane Archaea -Wall-less or Wallas of pseudomurein (lack Nam and D-amino acids)
Cell Wall-less Forms Few bacteria are able to live or exist without a cell wall. The mycoplasmas are a group of bacteria that lack cell wall. Mycoplasmas have sterol-like molecules incorporated into their membranes and they are usually inhabitants of osmotically-protected environments. Mycoplasmapneumoniae is the cause of primary atypical bacterial pneumonia, known in the vernacular as "walking pneumonia". For obvious reasons, penicillin is ineffective in treatment of this type of pneumonia. Sometimes, under the pressure of antibiotic therapy, pathogenic streptococci can revert to cell wall-less forms (called spheroplasts) and persist or survive in osmotically-protected tissues. When the antibiotic is withdrawn from therapy the organisms may regrow their cell walls and reinfect unprotected tissues.
Damage to the cell wall (Gram –ve): Lysozyme digests disaccharide in peptidoglycan (Gram +ve): Penicillin inhibits peptide bridges in peptidoglycan Protoplast is a wall-less cell Spheroplast is a wall-less gram positive cell - Protoplasts and spheroplasts are susceptible to osmotic lysis L forms are wall-less cells that swell into irregular shapes
External structures Many bacteria have structures that extend beyond or surround cell wall Flagella and pili extend from the cell membrane through the cell wall and beyond Capsules and slime layers surround the cell wall
4. Bacterial Cell Surface Structures Arrangements of Bacterial Flagella Monotrichous: Bacteria with a single flagellum located at one end (pole) Amphitrichous: Bacteria with 2 flagella one at each end Peritrichous: Bacteria with flagella all over the surface Atrichous: Bacteria without flagella Cocci shaped bacteria rarely have flagella
Structure of flagella in gram –ve and +ve bacteria
Chemotaxis Bacteria move away or towards subtances that are present in the environment through a nonrandom process Positive chemotaxis: movement towards attractants (nutrients) Negative chemotaxis: movement away from the repellent
Glycocalyx Capsule & Slime Layer Used to refer to all polysaccharide/polypeptide containing substances found external to cell wall Capsule Slime layers All bacteria at least have thin small layer
5. Glycocalyx Capsule More firmly attached to the cell wall. Have a gummy, sticky consistency and provide protection & adhesion to solid surfaces and to nutrients in the environment. Bacteria that possess capsules are considered encapsulated, and generally have greater pathogenicity because capsules protect bacteria, even from phagocytic white blood cells of the immune system. The adhesive power of capsules is also a major factor in the initiation of some bacterial diseases. Slime Layer A glycocalyx is considered a slime layer when the glycoprotein molecules are loosely associated with the cell wall. Bacteria that are covered with this loose shield are protected from dehydration and loss of nutrients.
Capsule Protective structure outside the cell wall of the organism that secretes it Only certain bacteria are capable of forming capsules Chemical composition of each capsule is unique to the strain of bacteria that secrete it Encapsulated bacteria are able to evade host defense mechanism (phagocytosis)
Slime Layer Less tightly bound to the cell wall and is usually thinner than the capsule Protects the cell against drying, traps nutrients and binds cells together (biofilms)
Biofilms A microbial community that usually forms slimy layer or hydrogel on a surface Bacteria attracted by chemicals via quorum sensing Composed of populations or communities of microorganisms adhering to environmental surfaces. The microorganisms are usually encased in extracellular polysaccharide that they synthesize. Can be found in sufficient moisture is present. Their development is most rapid in flowing systems where adequate nutrients are available
Biofilms Biofilm usually begins to form when free swimming bacterium attaches to a surface Share nutrients Shelter from harmful factors
Thoughts for the day.. What is the biofilm that forms on teeth called?
Case Study Delayed Bloodstream Infection Following Catheterization Patients with indwelling catheters received contaminated heparin with Pseudomonas fluorescens Bacterial numbers in contaminated heparin were too low to cause infection 84–421 days after exposure, patients developed infections