Introduction to BacteriaDefinition , Structure and Function

Prepared by : Raghdah Abdulsalam MalibariID No. : ( 1200391 )

Supervision by : Dr. Magda AliFor year : 2012 - 2013

Saudi ArabiaMinistry of Higher EducationKing Abdulaziz UniversityFaculty of Science - Girls departmentBiology - Microbiology

Definition of Bacteria

Definition of Bacteria

Bacteria prokaryotic microorganisms a single-celled microscopic organisms that lack nuclei and other organized cell structures."Bacteria" is the plural form of "bacterium.“

While several bacterial species are pathogenic (capable of causing disease), most are non-infectious, and many have critical roles in decay, fermentation, nutrient recycling, and nitrogen fixation. Bacteria are usually classified as gram-positive or gram-negative based on a basic microbiological staining procedure called the gram stain. They come in a variety of shapes and sizes.

Shapes of Bacteria

Shapes of Bacteria

Size of Bacteria

Size of Bacteria

Cocci are true spheres with diameter ranging between 0.75 to 1.25 µm (and average of 1 µm).

Bacilli varyin length from 2-10 times their width.

Coccobacilli are very short bacilli.

Filaments are long threads of bacilli which have not separated into single cells.

Were are Bacteria found?!

Environment bacteria

Found everywhere under the earth to a distance of 400 meters - in the air at high altitudes, at

high temperatures around the craters - in the polar regions, objects within objects (animals in the digestive and respiratory

systems), their diet is the carbon dioxide and produce oxygen.

Structure of Bacteria and Function

FlagellaThe flagella (singular flagellum) are made up of a class of

linear proteins called flagellins. The basal body traverses the cell wall and cytoplasmic membrane to anchor the flagellum and enables it to whirl about its axis like a propeller.

Flagel lated bacteria are described as monotrichous, lophotrichous or peritrichous,depending on how the flagella are arranged .

Function: Flagella give bacteria the ability to move about activity.

Capsule

The capsule of most bacteria consists of a polysaccharide. The bacteria of a single species can be classified in different capsular serovars (or serotypes) based on the fine chemical structure of this polysaccharide.

Function: 1-Attachment to surfaces 2-protection against phagocytic engulfment,

occasionally killing or digestion 3- reserve of nutrients or protection against

desiccation

Plasma membranePlasma membranes in bacteria

are composed of Phospholipids contain a polar group attached to a 3 carbon glycerol back bone. There are also two fatty acid chains dangling from the other carbons of glycerol. The phosphate end of the molecule is hydrophilic and is attracted to water. The fatty acids are hydrophobic .

Membranes also contain proteins. Typically 20-30% of membrane ,Most of them are placed in the membranes so that the hydrophobic amino acids associate with the lipids in the membrane and the hydrophilic amino acids are outside the membrane interacting with either the cytoplasm.

Function: The plasma membrane is selectively permeable in that it helps control what moves into and out of its cell

Plasmid or Chromosome

The “cellular nucleus” in prokaryotes consists of a tangle of double-stranded DNA, not surrounded by a membrane and localized in the cytoplasm .- the formed, long DNA/protein fibers are called chromatin;- each fiber builds a so-called chromosome

-The plasmids of human pathogen bacteria often bear important genes determining the phenotype of their cells(resistance genes, virulence genes).

Function:Protein productionThe single most important purpose of the genetic material of any cell is that it holds all the information necessary for a cell to carry out its many functions. The sequence of bases in the DNA contain this information or genetic code. Generally, this is translated into messanger RNA and then into protein that then carry out the many necessary functions of the cell.

DNA is transcribed into RNA that is then translated into protein by the ribosome.

Examples of advantages plasmids bestow on the host-Antibiotic resistance - Some plasmids code for proteins that degrade antibiotics-a big advantage for pathogens.-Some encode for proteins which confer virulence factors on the host. For example- E. coli plasmid Ent P307 codes for an enterotoxin which makes E. coli pathogenic.-Conjugative plasmids - These allow exchange of DNA between bacterial cells.Additional function:As Antigen – producing enzyme

Cytoplasm and Ribosomes

- The cytoplasm contains a large number of solute low- and high-molecular weigh substances.

- RNA and approximately 20 000 Ribosomes\cell. Bacteria have 70S Ribosomes comprising 30S and 50S subunits.

Function: Ribosomes as the organelles for protein synthesis.

Figure 6.29 The 30S ribosomal subunit is a ribonucleoprotein particle

Figure 6.30 The 70S ribosome consists of the 50S subunit (blue) and the 30S subunit (purple) with three tRNAs

Cell Wall

Murein(syn.peptidoglycan)The most important structural element of the

wall is murein, a netlike polymer material surrounding the entire cell(sacculus). It is made up of polysaccharide chains cross linked by peptides.

The Structure of Murein

The Murein Building Block

The cell wall of Gram-positive bacteria: The murein sacculus may consist of as many as 40 layers (15–80 nm thick).

The membrane lipoteichoic acids are anchored in the cytoplasmic membrane, whereas the cell wall teichoic acids are covalently coupled to the murein. The physiological role of the teichoic acids is possibly they regulate the activity of the autolysins that steer growth and transverse fission processes in the cell. teichoic acids can activate the alternative complement pathway and stimulate macrophages to secrete cytokines.Cell wall-associated proteins frequently function as pathogenicity determinants (specific adherence; phagocyte protection).

The cellwall of Gram-negative bacteria:Here, the murein is only about 2 nm thick . The outer membrane is

the salient structural element. It contains numerous proteins (50% by mass) as well as the medically critical lipopolysaccharide.

— OmpA (outer membrane protein A) and the murein lipoprotein form a bond between outer membrane and murein.

— Outer membrane-associated proteins constitute specific structures that enable bacteria to attach to host cell receptors.

Lipopolysaccharide (LPS):This molecular complex,

also known as Endotoxin,is comprised of the lipoid A, the core polysaccharide .

Lipoid A:is responsible for the toxic

effect.

Function:1- the cell wall maintains the overall shape of a bacterial

cell.2- The cell wall is an essential structure that protects the

cell protoplast from mechanical damage and from osmotic rupture orlysis.