Prokaryotic Bacteria Lecture Notes PDF

General feature of bacterial cell  Cells Cell is the smallest structural and functional unit of an organism Based on the level of organization cells can be categorized in to two 1. Eukaryotic cells 2. Prokaryotic cells 1. Eukaryotic cells EU means true and Karyote means nucleus...

General feature of bacterial cell  Cells Cell is the smallest structural and functional unit of an organism Based on the level of organization cells can be categorized in to two 1. Eukaryotic cells 2. Prokaryotic cells 1. Eukaryotic cells EU means true and Karyote means nucleus The eukaryotic cell has a true membrane bound nucleus, usually containing multiple chromosomes, a mitotic apparatus, a well defined endoplasmic reticulum and mitochondria. Example Algae,Protozoa and Fungi 2. Prokaryotic cell Pro means primitive Karyote means nucleus. The prokaryotic cell possesses naked DNA with out associated basic proteins, divides amitotically by binary fission and bounded by a semi rigid cell wall. Example Bacteria, Cyanobacteria and Archaebacteria Characteristics Prokaryotic Eukaryotic Nuclear Circular DNA molecule not Complex of DNA and structure covered with proteins basic proteins Localization of Dense tangle of DNA in In nucleus surrounded by nuclear structure cytoplasm; no nuclear membrane; nuclear membrane nucleoid DNA Nucleoid and plasmids In nucleus and in mitochondria Cytoplasm No mitochondria and no Mitochondria and endoplasmic reticulum, 70S endoplasmic ribosomes reticulum, 80S ribosomes Cell wall Usually rigid wall with murein Present only in fungi: layer; exception: mycoplasmas glucans, mannans, chitin, chitosan, cellulose Reproduction Asexual, by binary transverse In most cases sexual, fission possibly asexual  General feature of bacterial cell The smallest free living microorganisms that are visible only with the aid of microscope Bacteria represents the largest and diversified group of microorganisms that can exist as living cells They are able to carry out their own life processes: growth, energy generation and reproduction independent of other cells General feature of bacterial cell… In general bacteria Are typical prokaryotic cell Contain both DNA and RNA Most grow in artificial media Replicate by binary fission Contain rigid cell wall Are sensitive to antimicrobial agents  BACTERIAL CELL PARTS 1. Cell Wall Cell wall: is the outermost component part. Cell wall is used: To Protects bacteria against lysis Allows them to grow over a wide range of osmotic pressures. It gives Rigidity to bacterial cells, which determines their characteristic shape.  The main constituent of bacterial cell wall is a chemically complex polymer known as peptidoglycan.  Cell Wall Christian Gram recognized 2 different types of bacteria based on their staining reaction.  Gram-positive bacteria stain purple and have thick layers of peptidoglycan combined with teichoic acid.  Gram-negative bacteria stain pink and have much thinner layer of peptidoglycan covered with an outer lipid membrane.  2. Plasma Membrane The plasma membrane also called cytoplasmic or cell membrane The cytoplasmic membrane (5-10 nm thick) consists of proteins embedded in a bilayer of phospholipids Functions: Selective permeability, it controls which nutrients/ substances may transport into or out of the cell. Site for energy generation by oxidative phosphorylation Synthesis and assembly of cell wall components Section of enzymes and toxins Protects the cell against osmotic rupture Plasma Membrane Figure 4.14a. Flagella: are long whiplike appendages that move the bacteria toward nutrients and other attractants, a process called chemo-taxis. Made of chains of flagellin Anchored to the wall and membrane of a cell The system enables bacteria to detect changes in concentration of certain chemicals and to move either toward (positive chemotaxis) or away ( n e gat i ve c h e m o tax i s ) f ro m t h e s u b sta n c e depending on its nature. Figure 4.8 Flagella Arrangement Motile Cells Figure 4.9. Fimbriae or pili Pili are straight rigid rod like appendages. Shorter and thinner than flagella, composed of a single protein pilin. Function:  Facilitate adherence of bacteria to other bacterial, red blood cells, or lining of the intestine.  Provide a site for attachment of bacteriophages (bacterial viruses).  Enable bacteria that have a sex pilus to transfer genetic material across a pilus bridge by a process known as Conjugation.  Fimbriae /Pili  2. Bacterial Morphology Morphology describes the size and shape of bacteria They usually range from 0.1 to 10µm long Most spherical bacteria have diameters of 0.5 to 2µm, and rod shaped cells are generally 0.2 to 2µm wide and 1 to 10µm long. At the lower end of the scale some bacteria overlap with the largest viruses (the poxviruses)  2. Bacterial Morphology … At the upper end, some rod-shaped bacteria have a length equal to the diameter of some eukaryotic cells. Relative sizes of microorganisms  2. Bacterial Morphology … There are three basic shapes of bacteria with different arrangements 1. Cocci (singular coccus): round or oval shaped bacteria with different arrangement - Cocci in pair: Diplococci; Cocci in chain: Streptococci; Cluster: Staphylococci 2. Bacilli (singular bacillus): rod shaped bacteria with rounded, tapered (fusiform), square, or swollen ends  2. Bacterial Morphology … Very short rods that can sometimes almost be mistaken for cocci are called coccobacilli. Some rod-shaped bacteria have tapered ends and are therefore termed fusiform, whereas others are characteristically club- shaped and may be curved or bent 3. Spiral shaped: flexible, coiled, motile organisms that are called spirilla if the cells are rigid and spirochetes if they are more flexible and undulating.