Bacterial Cell Structure
Bacterial cell structure refers to the organization and components of a bacterial cell. It includes a cell wall, cell membrane, cytoplasm, ribosomes, and genetic material in the form of DNA. Bacterial cells lack a nucleus and other membrane-bound organelles found in eukaryotic cells. The structure of bacterial cells plays a crucial role in their function and interactions with the environment.
8 Key excerpts on "Bacterial Cell Structure"
eBook - ePub- Stephen H. Gillespie, Kathleen B. Bamford(Authors)
- 2012(Publication Date)
- Wiley-Blackwell(Publisher)
...1 Structure and classification of bacteria Bacterial classification is important, revealing the identity of an organism so that its behaviour and likely response to treatment can be predicted. Bacterial Structural Components Bacterial cell walls are rigid and protect the organism from differences in osmotic tension between the cell and the environment. Gram-positive cell walls have a thick peptidoglycan layer and a cell membrane, whereas Gram-negative cell walls have three layers: inner and outer membranes, and a thinner peptidoglycan layer. The mycobacterial cell wall has a high proportion of lipid, including immunoreactive antigens. Bacterial cell shape can also be used in classification. The following cell components are important for classification, pathogenicity and therapy. Capsule : a polysaccharide layer that protects the cell from phagocytosis and desiccation. Lipopolysaccharide : surface antigens that strongly stimulate inflammation and protect Gram-negative bacteria from complement-mediated lysis. Fimbriae or pili : specialized thin projections that aid adhesion to host cells. Escherichia coli that cause urinary tract infections bind to mannose receptors on ureteric epithelial cells by their P fimbriae. Fimbrial antigens are often immunogenic but vary between strains so that repeated infections may occur (e.g. Neisseria gonorrhoeae). Flagella : these allow organisms to find sources of nutrition and penetrate host mucus. The number and position of flagella may help identification. Slime : a polysaccharide material secreted by some bacteria that protects the organism against immune attack and eradication by antibiotics when it is growing in a biofilm in a patient with bronchiectasis or on an inserted medical device. Spores : metabolically inert bacterial forms adapted for long-term survival in the environment, which are able to regrow under suitable conditions. Bacteria have a single chromosome and lack a nucleus (prokaryotes)...
eBook - ePub- David Hames, Nigel Hooper(Authors)
- 2011(Publication Date)
- Taylor & Francis(Publisher)
...Like all cells, a prokaryotic cell is bounded by a plasma membrane that completely encloses the cytosol and separates the cell from the external environment (Figure 2). The plasma membrane, which is about 8 nm thick, consists of a lipid bilayer containing proteins (Sections E1 and E2). Prokaryotes lack the membranous subcellular organelles characteristic of eukaryotes (Section A2). The aqueous cytosol contains the macromolecules [enzymes, messenger ribonucleic acid (mRNA), transfer RNA (tRNA) and ribosomes], organic compounds and ions needed for cellular metabolism. Also within the cytosol is the prokaryotic ‘chromo-some’ consisting of a single circular molecule of DNA, which is condensed to form a body known as the nucleoid (Figure 2) (Section F2). Bacterial cell walls To protect the cell from mechanical injury and osmotic pressure, most prokaryotes are surrounded by a rigid 3–25 nm-thick cell wall (Figure 2). The cell wall is composed of peptidoglycan, a complex of oligosaccharides and proteins. The oligosaccharide component consists of linear chains of alternating N -acetylglucosamine (GlcNAc) and N -acetylmuramic acid (NAM) linked β1–4 (Section J1). Attached via an amide bond to the lactic acid group on NAM is a D -amino acid -containing tetrapeptide. Adjacent parallel peptidoglycan chains are covalently cross-linked through the tetrapeptide side-chains by other short peptides. The extensive cross-linking in the peptidoglycan cell wall gives it its strength and rigidity. The presence of D -amino acids in the peptidoglycan renders the cell wall resistant to the action of proteases, which act on the more commonly occurring L -amino acids (Section B1), but provides a unique target for the action of certain antibiotics such as penicillin. Penicillin acts by inhibiting the enzyme that forms the covalent cross-links in the peptidoglycan, thereby weakening the cell wall...
eBook - ePub- Maddaly Ravi(Author)
- 2018(Publication Date)
- Bentham Science Publishers(Publisher)
...Microbial Structure and Function Maddaly Ravi The dense coat of bacteria, if present is called Cell wall Capsule Plasma membrane Envelop Loosely associated external bacterial coat is called Cell wall Capsule Slime layer Envelop Bacterial capsules and slime layers are composed of Proteins and polysaccharides Only proteins Only polysaccharides Neither proteins nor polysaccharides Bacterial strains that are referred to as “smooth” contain Capsules Cell walls Envelop Slime layer Bacterial strains that are referred to as “smooth” do not contain Capsules Cell walls Envelop Slime layer Capsules function for Staining bacteria Increasing the pathogenicity of bacteria Identifying bacteria Culturing bacteria Cell walls of bacteria are also known as Capsules Membrane Envelop Slime layer The most abundant bacterial cell wall component is Peptidoglycan Dextrose Starch Cellulose The number of peptidoglycan layers that Gram-positive bacteria have. is 10-50 5-10 1-5 4 The number of peptidoglycan layers that Gram-negative bacteria have is 1-4 2-10 1-2 5-10 The shape of Gram-positive bacteria is Rigid Flexible Can be rigid or flexible No definite shape The shape of Gram-negative bacteria is Rigid Flexible Can be rigid or flexible No definite shape The Gram-positive bacteria are usually Rods only Cocci only Rods and cocci Spirals The Gram-negative bacteria are usually Rods Rods and cocci Rods, cocci and spirals Rods, cocci, spirals and pleomorphic Spore formation occurs in Gram-positive bacteria Gram-negative bacteria Both Gram-positive and –negative bacteria The Gram-staining does not matter Spore formation does not commonly occur in Gram-positive bacteria Gram-negative bacteria Both Gram-positive and –negative bacteria The Gram-staining does not matter Penicillin has a greater inhibitory potential on Gram-positive bacteria Gram-negative bacteria Both Gram-positive and –negative bacteria The Gram-staining...
eBook - ePubHandbook of Microbiology
Condensed Edition
- Allen I Laskin(Author)
- 2019(Publication Date)
- CRC Press(Publisher)
...Bacterial Cell Wall Structure C. S. Cummins Introduction The bacterial cell wall is not composed of a single substance; it is a complex of polymers which can be separated in various ways in the laboratory, although it is likely that they are bound together covalently in the wall of the living cell. The study of bacterial wall structure essentially started in 1951 when Salton and Horne 1 reported chemical studies on cell wall fractions which could be seen to be pure by electron microscopy. Since that classical study, a great deal of work has been done, and the subject has been reviewed at fairly frequent intervals. 2 - 8 Reviews on specialized aspects of the subject (e.g., biosynthesis, structure of O-antigens, etc.) are referred to in the appropriate section below. Preparation Of Cell Wall Fractions For Analysis Detailed discussions of methods for cell disruption can be found in References 1 and 9 to 11 and elsewhere in this volume. The matter is considered here briefly because of the considerable influence which methods of preparation have on the final product. An outline of the essential features of the three commonly used procedures is given below. Ultrasonic Disruption Ultrasonic vibrations at 20 kHz or higher, produced in either a magnetostrictive or a piezoelectric oscillator, are applied to the bacterial suspension, usually by a probe connected to the oscillator. The bacteria are disrupted by the great pressure changes produced by the alternate development and collapse of gas cavities in the liquid. Considerable heating of the fluid takes place, and some form of cooling is necessary. Shaking with Small Glass Beads This method was introduced by Dawson in 1949. 12 It was used by Salton from the start of his classic investigations into cell wall composition 1 and has remained a standard procedure. For bacteria, glass beads (Ballotini) 0.1—0.12 mm in diameter are most satisfactory, although beads up to 0.2 mm have been used...
eBook - ePub- Vincent A. Fischetti, Richard P. Novick, Joseph J. Ferretti, Daniel A. Portnoy, Mirian Braunstein, Julian I. Rood, Vincent A. Fischetti, Richard P. Novick, Joseph J. Ferretti, Daniel A. Portnoy, Mirian Braunstein, Julian I. Rood(Authors)
- 2019(Publication Date)
- ASM Press(Publisher)
...For example, the introduction of cryo-focused ion beam (cryo-FIB) combined with a scanning electron microscope (cryo-FIB-SEM) as a new close-to-nature approach was sold a few years after the first advent of FIB-SEMs for conventional resin-embedded biological samples. THE BACTERIAL CELL WALL Bacteria are mostly unicellular organisms which can be found in a wide variety of environments. Therefore, bacterial cell walls deserve special attention because they (i) provide the essential structure for bacterial viability by protecting against the often hostile environment, (ii) are composed of unique components found nowhere else in nature, (iii) are responsible for the shape of the bacteria, (iv) provide a halt for ligands and proteins for adherence to host cells, (v) expose receptor sites for drugs or viruses, (vi) represent the most important sites for attack of antibiotics, (vii) provide structures for immunological distinction and variation, and (viii) can cause symptoms of disease in animals and humans. Chemistry of the Bacterial Cell Wall Backbone The major backbone of the bacterial cell wall is the peptidoglycan, also called murein, which consists of repeating linear units of the disaccharide N -acetylglucosamine (NAG) linked to N -acetylmuramic acid (NAM). The disaccharides are cross-linked via often flexible pentapeptide amino acid chains forming a mesh-like framework (17). Chemically, the peptidoglycan consists of alternating β-1,4-linked N -acetylglucosamine (GlcNAc; NAG) and N -acetylmuramic acid (MurNAc, NAM, a variant of GlcNAc with a d -lactate attached to the C-3 by an ether bond). Termination of a peptidoglycan strand is achieved at the reducing end by a 1,6-anhydroMurNAc residue, in which the C-1 and C-6 of the sugar backbone are bound through an ether linkage. The appearance of the unusual 1,6-anhydroMurNac is used to determine the end of the strands...
eBook - ePub- Volodymyr Ivanov(Author)
- 2020(Publication Date)
- CRC Press(Publisher)
...The cell often has external filaments (cilia, flagella) for locomotion and attachment. 2. The cell is covered with a cell wall from cellulose (plants), chitin (fungi), silica (some algae), or other polymers to keep the cell volume stable under varying osmotic pressure; however, there may be no cell wall (animals) if osmotic pressure is stable. 3. The cytoplasm is isolated from the environment by a cytoplasmic (plasma) membrane, which is selectively permeable for nutrients and metabolites. The major difference between eukaryotic cells and prokaryotic cells is the presence of organelles. Organelles Three important organelles of eukaryotic cell are mitochondria, chloroplasts, and the nucleus. These organelles are bound by lipid membranes, which are more specifically permeable to molecules than the cytoplasmic membrane. The nucleus in eukaryotes contains the genetic material. The genome contains a number of separated DNA molecules called chromosomes. The nucleus is a place where DNA for new cells is synthesized and transcribed into mRNA. Mitochondria are organelles that generate biological forms of energy from the oxidation of low-molecular weight organic compounds. Chloroplasts are organelles assimilating light energy. The energy and reducing power generated by photosynthesis are used to convert carbon dioxide into organic carbon according to the equation: C O 2 + H 2 O + e n e r g y o f l i g h t → C H 2 O + O 2 + b i o l o g i c a l f o r m s o f e n e r g y where CH 2 O is the conventional empirical formula for carbohydrates, the primary products of photosynthesis. Quiz Bank The volume of 10 9 spherical cells with a diameter of 1000 nm would be A. 520 μm 3. B. 0.52 mm 3. C. 5.2 cm 3. D. 5.2 × 10 −6 m 3. The cellular function of the cytoplasmic membrane is A. protection of cell from disinfection. B. regulation of cell growth. C. control of the transport of ions. D. cell resistance to high temperature. The shape of filamentous bacteria demonstrates an adaptation to a A...
eBook - ePubBiology
A Self-Teaching Guide
- Steven D. Garber(Author)
- 2020(Publication Date)
- Jossey-Bass(Publisher)
...The notable exceptions are bacteria and cyanobacteria (often referred to interchangeably as blue-green bacteria or blue-green algae). The largest, most well-defined subcellular structure, or organelle, is the nucleus, unless even larger vacuoles are present. Vacuoles are large, fluid-filled spaces found in many cells, particularly plant cells. The nucleus contains the long, thin structures composed of deoxyribonucleic acid (DNA) and protein – the chromosomes. These structures contain genes, which are the individual units of information that inform the cell what to do and how and when to do it. All the instructions concerning the life processes of the cell emanate from these chromosomes (see Figure 2.6). Nucleic acids are a major group of organic compounds that are composed of subunits called nucleotides, which contain carbon, hydrogen, oxygen, phosphorus, and nitrogen. It is the sequence of nucleotides that gives the specific nucleic acid its distinctive properties. DNA and ribonucleic acid (RNA) are two important nucleic acids found in cells. They are fundamental in the storage and transmission of genetic information that controls the cell's functions and interactions. A dark area within the nucleus of most cells, seen when the cells are not dividing, is known as the nucleolus (see Figure 2.6). This area contains a high concentration of RNA and protein. Sometimes a nucleus contains several nucleoli, which are formed by a specific region on one chromosome called the nucleolar organizer. All the nuclear structures are embedded in a viscous colloidal material, the nucleoplasm. The nucleus is bounded by a membrane, the nuclear membrane, which consists of two complete membranes similar in structure to the cell membrane. The nuclear membrane is very selective, restricting certain substances that readily pass through the cell membrane into the cytoplasm but are unable to pass through the nuclear membrane. Figure 2.6 An electron micrograph of a nucleus...
eBook - ePubCell Biology
A Short Course
- Stephen R. Bolsover, Andrea Townsend-Nicholson, Greg FitzHarris, Elizabeth A. Shephard, Jeremy S. Hyams, Sandip Patel(Authors)
- 2022(Publication Date)
- Wiley-Blackwell(Publisher)
...SECTION 1 THE STRUCTURE OF THE CELL The cell is the fundamental unit of life. A cell comprises a complex and ordered mass of protein, nucleic acid, and many biochemical species separated from the world outside by a limiting membrane. Cells expend energy to maintain a highly ordered state, and this expenditure of energy and the ability to repair themselves distinguishes living cells from lifeless packets of biological material such as viruses. In the first two chapters we will describe the basic structure of cells and how they can be observed with a microscope. We will describe how, in animals, cells containing the same DNA database assume very different shapes and functions and organize themselves into tissues. Chapter 1 : A Look at Cells and Tissues Chapter 2 : Membranes and Organelles 1 A LOOK AT CELLS AND TISSUES With very few exceptions, all living things are either a single cell or an assembly of cells. This chapter will begin to describe what a cell is, and further chapters will say much more. However, to begin with, we can briefly describe a cell as an aqueous (watery) droplet enclosed by a lipid (fatty) membrane. Cells are, with a few notable exceptions, small (Figure 1.1), with dimensions measured in micrometers (μm, 1 μm = 1/1000 mm). They are more or less self‐sufficient: a single cell taken from a human being can survive for many days in a dish of nutrient broth, and many human cells can grow and divide in such an environment. In 1838 the botanist Matthias Schleiden and the zoologist Theodor Schwann formally proposed that all living organisms are composed of cells. Their “cell theory,” which nowadays seems so obvious, was a milestone in the development of modern biology...
