Phospholipids are composed of a phosphate head attached to two fatty acid tails. The phospholipid bilayer of a gram-negative bacterial cell is like most other phospholipid bilayers, including the ones present in our cells.The plasma membrane consists of a phospholipid bilayer.Encased within its boundaries are the ribosomes, cell nucleus, mitochondria, and more. The plasma membrane surrounds the bacterial cell.Overview of gram-negative bacteria structure We will go over each layer and its specific contents one by one, below. Beyond that is the peptidoglycan cell wall, and lastly we have the outer membrane. Outside of this is the periplasmic space. The contents of the cell are contained in the plasma membrane. We will examine these properties of gram-negative bacteria and, by doing so, see the differences that distinguish gram-negative bacteria from gram-positive bacteria. They have certain physical properties, that while invisible to the naked eye, allow them to pick up particular dyes in gram staining, which belie the characteristics of their cell wall and other structures. Cell wall molecules can also trigger adaptive immunity such as the production of antibody molecules against bacterial cell wall antigens.Gram-negative bacteria are classified as such due to their appearance after a gram stain test.An antigen is a molecular shape that reacts with antigen receptors on lymphocytes to initiate an adaptive immune response.PAMPs associated with the Gram-positive cell wall include peptidoglycan monomers, teichoic acids, lipoteichoic acids, and mannose-rich sugar chains.Inflammation is the means by which the body delivers defense cells and defense molecules to an infection site,however, excessive inflammation can be harmful and even deadly to the body.PAMPs bind to Pattern-recognition receptors (PRRs) on defense cells to trigger the production of inflammatory cytokines. The body activates innate immunity by recognizing molecules unique to microorganisms that are not associated with human cells called pathogen-associated molecular patterns or PAMPs.The Gram-positive cell wall activates both the body's innate immune defenses and its adaptive immune defenses.Surface proteins embedded in the cell wall can function as adhesins, secretion systems, and enzymes.Teichoic acids and lipoteichoic acids are interwoven through the peptidoglycan layers.Peptidoglycan prevents osmotic lysis in the hypotonic environment in which most bacteria live.The Gram-positive cell wall consists of many interconnected layers of peptidoglycan and lacks an outer membrane. ![]() Because of the nature of their cell wall, Gram-positive bacteria stain purple after Gram staining.There are two major branches of the adaptive immune responses: humoral immunity and cell-mediated immunity. The receptor on a T-lymphocyte is called a T-cell receptor (TCR). The epitope receptor on the surface of a B-lymphocyte is called a B-cell receptor and is actually an antibody molecule. The body recognizes an antigen as foreign when epitopes of that antigen bind to B-lymphocytes and T-lymphocytes by means of epitope-specific receptor molecules having a shape complementary to that of the epitope. A single microorganism has many hundreds of different shaped epitopes that our lymphocytes can recognize as foreign and mount an adaptive immune response against. An epitope is typically a group of 5-15 amino acids with a unique shape that makes up a portion of a protein antigen, or 3-4 sugar residues branching off of a polysaccharide antigen. The actual portions or fragments of an antigen that react with antibodies and with receptors on B-lymphocytes and T-lymphocytes are called epitopes. We recognize those molecular shapes as foreign or different from our body's molecular shapes because they fit specific antigen receptors on our B-lymphocytes and T-lymphocytes, the cells that carry out adaptive immunity. An antigen is defined as a molecular shape that reacts with antibody molecules and with antigen receptors on lymphocytes. Proteins and polysaccharides associated with the Gram-positive cell wall function as antigens and initiate adaptive immunity.
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