Everything you need to know about bacteria. Some of the frequently asked questions are as follows:-
Q.1. Write technical terms for the following:
(i) Spherical bacteria
(ii) The cocci of bacteria that remain in pairs after dividing.
(iii) The bacterial cocci that remain in chains.
(iv) Bacterial cocci arranged in cubes of eight cocci.
(v) Bacterial cocci arranged in grape-like clusters.
(vi) Bacilli arranged in pairs.
(vii) bacilli arranged in chains.
(viii) Bacteria shaped like curved rods.
(ix) Bacteria that maintain a single shape.
(x) Bacterial cells with many shapes.
Ans: (i) Coccus (plural cocci)
(ix) Monomorphic and
Q.2. How do spirochetes move? Name two spirochetes.
Ans: Spirochetes move by axial filaments which are bundles of fibrils. Treponema pallidum, the causative agent of syphilis and Borrelia burgdorferi, the causative agent of lyme disease are two well known examples of spirochets.
Q.3. How does corkscrew motion or giggling motion help Treponema pallidum?
Ans: It helps to penetrate well inside the body tissue.
Q.4. What substance provides rigidity to bacterial cell walls? Give its structure.
Ans: The peptidoglycan which is a macromolecular network and consists of repeating disaccharide attached to polypeptides, provides rigidity to the bacteria] cell walls. The disaccharide comprises two monosaccharide’s N-acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM). The linkage between the two monosaccharide’s is known as, (3-1, 4 linkage. The tetra peptide side chains form the polypeptide links. The parallel tetra peptide side chains are linked by peptide cross bridge.
Q.5. What are Gram positive cell walls?
Ans: Cell walls which stain positive are Gram positive. They consist of peptidoglycan (murein) and are more thick than peptidoglycan in Gram negative bacteria.
The cell walls of Gram positive bacteria also possess teichoic acids which are of two types:
Ans: (1) lipoteichoic acid and
(2) wall teichoic acid.
The teichoic acid gives the cell wall antigenic specificity, the characteristic of which is also used to identify bacteria in serological tests.
Q.6. Why are some β-lactam antibiotics more effective than penicillin against Gram negative bacteria?
Ans: Because some β-lactam antibiotics are able to penetrate the outer membrane of Gram negative bacteria.
Q.7. Why is the antibiotic penicillin effective against Gram positive bacteria but not harmful to human red blood cells?
Ans: The penicillin interferes with the formation of peptidoglycan in Gram positive bacteria. Red blood corpuscles do not contain peptidoglycan and are not interfered with.
Q.8. The Mycoplasma is a wall less bacterium. How is its cell protected from osmotic lysis?
Ans: The plasma membrane of Mycoplasma possesses sterols, a class of lipids.
Q.9. What is a fluid mosaic model of plasma membrane (or cytoplasmic membrane)?
Ans: The plasma membrane comprises phospholipids bilayer and proteins which are not static but move freely within the membrane surface. This dynamic arrangement is known as fluid mosaic model.
Q.10. Recent studies reveal that mesosomes are artifacts and not true structures. How are they seen in electron-micrographs?
Ans: Infoldings of plasma membrane are formed during the dehydration process in electron microscopy. The mesosomes are not seen in electron micrographs requiring no dehydration in some modern techniques.
Q.11. How do the movements of materials across a membrane take place?
Ans: The movements of materials take place by means of active processes like active transport and group translocation or by passive processing as simple diffusion, facilitated diffusion and osmosis.
Q.12. What is the cytoplasm in a bacteria cell?
Ans: The bacterial cell is made of thick, aqueous, semitransparent and elastic internal matrix. The cytoplasm contains proteins (enzymes), carbohydrates, lipids, inorganic ions and several low molecular weight compounds.
Q.13. What is nucleoid?
Ans: The nuclear region in a bacterial cell is called nucleoid. The nucleoid comprises a single long circular molecule of double stranded DNA also referred to as bacterial chromosome There however, no nuclear membrane like in eukaryotic cells and it also lacks histones. In addition to a chromosome bacteria also contains small circular double stranded (extra-chromosomal) DNA molecules known as plasmids.
Ans: The plasmids may contain 5 to 100 genes and the bacteria can survive with and without them. The genes carried by plasmids are known to be responsible for antibiotic resistance, tolerance to toxic metals, production of toxic substances, and synthesis of certain enzymes. The plasmid DNA is used for genetic manipulations in biotechnological targets.
Q.14. Why do bacterial cells possess ribosomes?
Ans: Bacterial cells like eukaryotic cells possess ribosomes which are the sites of protein synthesis. The ribosomes consist of two subunits and each subunit further consists of protein and a type of RNA popularly called ribosomal RNA or rRNA. The prokaryotic ribosomes are 70 S ribosomes while in eukaryotic cells there are 80 S ribosomes. Here S stands for Svedberg unit, named after its discoverer and is based on sedimentation under ultra-high speed centrifugation.
The 70 S ribosome comprises of small 30 S subunits containing one molecule of r RNA and large 50 S subunits containing two molecules of ribosomal RNA. The antibiotics streptomycin, neomycin and tetracycline are effective because of their characteristic to inhibit protein synthesis on the ribosomes.
Q.15. Name the important inclusions of bacteria.
Ans: Important bacterial inclusions are Metachromatic granules, polysaccharide granules, lipid inclusions, sulphur granules, carboxysomes and gas vacuoles.
Q.16. What are Metachromatic granules? Name the bacterium of which they form a characteristic feature.
Ans: The Metachromatic granules are collectively known as volutin that represents a reserve of inorganic phosphate (polyphosphate) that can be used in the synthesis of ATP. These large granules have been named so because they sometimes stain red with certain blue dyes like methylene blue. The Metachromatic – granules are a characteristic feature of Corynebacterium diphtheriae, the causative agent of diphtheria.
Q.17. Write technical terms for the following statements.
(i) Endospore like structures in Gram-negative bacteria that can withstand heat and chemicals and can be stained with endospore stain (giving positive results), are found in the bacterial species
(ii) The process of formation of endospores in bacteria
(iii) Return of a bacterial spore to its vegetative condition
(iv) Extra-chromosomal rings of DNA in bacteria
(v) Energy is expended to modify chemicals to carry them across the membrane
(vi) Materials travel from low to high concentration by permeases making the cell to expand energy
(vii) The movement of substances across the membrane where the substances move from higher to lower concentration without energy expansion by the cell, is called
(viii) After the cell wall of Gram positive bacteria are damaged by the enzyme lysozyme all that is left is called
Ans: (i) Coxiella burnetii
(v) Group translocation
(vi) Active transport
(vii) Passive movement (or passive process)
Q.18. What are Gram Negative Cell Walls?
Ans: The bacterial cells which give negative Gram’s stain test possess Gram negative cell walls. The peptidoglycan in them is joined with lipoproteins (lipids covalently linked to proteins) on the outer membrane. There is a space between the outer membrane and the plasma membrane which is referred to as periplasmic space.
The high concentration of degradative enzymes and transport proteins are housed in the periplasmic space. Gram negative cell walls are devoid of a substance called, teichoic acid, a polysaccharide found in Gram +ve cell walls.
The outer membrane of Gram -ve bacteria comprises lipoproteins, lipolysaccharides and Isphohpids. The outer membrane protects the cell from antibiotics like penicillin, digestive enzymes such as lysozyme, detergents heavy metals, bile salts and some dyes. Embedded in the outer membrane arc certain proteins called porins which permit passage of molecules, e,g., nucleotides, disaccharides, peptides, amino acids, vitamin B12 and iron.
The portion of lipopolysaccharide known as O-polysaccharide in lipopolysaccharide of outer membrane provides the bacterial cell with its antigenic characteristics useful for identification and differentiation of Gram negative bacteria. The lipid portion of lipopolysacchar.de known a Lipid A is an endotoxin and is toxic to the host’s blood stream or gastrointestinal tract. It is held responsible for fever and shock to the patient infected with pathogenic Gram negative bacteria.