Question no. 82 of the joint CSIR-UGC/JRF-NET, December' 2014, Life Science- Booklet 'A'
Question no. 82 of the joint CSIR-UGC/JRF-NET, December' 2014, Life Science- Booklet 'A'
Which of the following statement best describe archaebacteria?
1. Mostly autotrophic, cell wall contains peptidoglycan, 60S ribosomes, live in extreme environment.
2. Divide by fission, not susceptible to lysozyme, live in extreme environments, mostly autotrophic.
3. Not susceptible to lysozyme, contain Golgi and linear chromosomes.
4. Chitinous cell wall, obligate aerobic, circular chromosome.
The archaebacteria have simply been categorized as prokaryotes able to withstand extreme environment successfully and so it is intuitively known fact only. These bacteria generally being chemoheterotrophs, they do not exploit carbon dioxide as the carbon source for biosynthesis and so need not be considered as autotrophs at the end. Next, the methanogens maybe anaerobes but the thermoacidophilic and halophilic bacteria are mostly aerobes among the archaebacteria so nothing conclusively c’d be said in this direction about archaebacteria as a whole. Finally, they need to have circular chromosome compulsorily with no usual peptidoglycane configuration with NAG and NAM in their wall yet pseudopeptidoglycan with nitrogenous compounds in association with NAG strictly lacking NAM can be seen present in their walls, in this way the last option remains a feasible choice here.
References:
Chitin: A Structural Biopolysaccharide with Multiple Applications
José P Martínez, University of Valencia, Valencia, Spain
María Pilar Falomir, University of Valencia, Valencia, Spain
Daniel Gozalbo, University of Valencia, Valencia, Spain
Published online: August 2014
DOI: 10.1002/9780470015902.a0000694.pub3
· Full Article on Wiley Online Library
· Abstract
· Images
Abstract
Chitin is a naturally occurring fibre‐forming polymer that plays a protective role in many lower eukaryotes similar to that of cellulose in plants. Chemically it is a long‐chain unbranched polysaccharide made of N‐acetylglucosamine residues linked through β‐1,4 covalent bonds; it is the second most abundant organic compound in nature, after cellulose. Taking into account the role played by chitin in different biological structures (i.e. fungal cell walls, insect peritrophic matrix, insect and crustacean cuticles, eggshells from nematodes, cyst wall of protozoa), its metabolism (biosynthesis and degradation) is essential for different morphogenetic events. Absent in vertebrates and plants, chitin participates in host–parasite interactions and represents a parasite‐specific target for chemotherapeutic attack and also plays a role in host immune responses. Because of its abundance in nature and its properties, biotechnological applications of chitin derivatives, such as chitosan and chito‐oligosaccharides, are currently an expanding area in biomedicine, pharmaceutical and food technology and agro‐biosciences.
Key Concepts:
· Chitin is a long‐chain unbranched polysaccharide made of β‐1,4‐linked anhydro‐2‐acetamido‐2‐deoxy‐d‐glucose (GlcNAc) which forms crystalline fibrillar structures following association of adjacent chains through hydrogen bonds between the N–H and the C?O groups.
· Nascent chitin is a growing chitin chain which is being synthesised by the chitin synthase and it represents a good substrate for chitinolytic enzymes.
· Microfibrillar chitin is a crystalline structure formed by chains of the polysaccharide which associate through hydrogen bonds between adjacent chains and it is responsible for the physico‐chemical properties of the polymer.
· The fungal cell wall is a supramolecular network outside the plasma membrane, formed by structural polysaccharides, including chitin, and proteins and glycoproteins, that protects the fungal cell and determines morphology, similarly to cuticle (exosqueleton) in insects.
· Insect cuticle (exosqueleton) is an extracellular matrix covering the epidermis and trachea, composed mainly by chitin (and proteins), which protects the animal and confers morphology.
· The peritrophic membrane (matrix) is an extracellular layer that covers the midgut in most arthropods and it is made of chitin, proteins and proteoglycans, and provides protection to the underlaying digestive cells.
· Chitin biosynthesis is a strongly regulated process, both spatially and temporally, as chitin deposition is essential for fungal growth and development (moulting) in arthropods. Chitin synthases are membrane bound enzymes that incorporate the substrate (UDP‐N‐acetylglucosamine) from the cytosol to the nascent chitin chain that is extruded outside the membrane.
· Chitinases are chitin‐hydrolysing enzymes that play important roles in the physiology of chitin‐containing eukaryotes, and chitinolytic bacteria are active in a scavenging role by degrading massive amounts of chitin in marine and soil biomass, avoiding its accumulation and favouring the utilisation of chitin as a renewable source.
· The absence of chitin in vertebrates and plants makes the chitin metabolism a potentially useful parasite‐specific target for chemotherapeutic attack. In mammals, chitin regulates immune responses playing a role in inflammation, and allergic diseases. In plants, chitin elicits defence responses, and in leguminous plants, chitin oligosaccharides produced by rhizobia promote plant nodulation.
· Owing to their abundance in nature and properties, chitin, chitosan and their derivatives have gained potential interest for a wide range of areas, including biopharmaceutical and biomedical applications.
Keywords: polysaccharide; chitosan; chitinase; chitin synthetase
Cell Walls of Archaea https://www.boundless.com/microbiology/
Archaeal cell walls differ from bacterial cell walls in their chemical composition and lack of peptidoglycans.
LEARNING OBJECTIVE
· State the similarities between the cell walls of archaea and bacteria
KEY POINTS
· Archaea are single-celled microorganisms that lack a cell nucleus and membrane-bound organelles.
· Like other living organisms, archaea have a semi-rigid cell wall that protects them from the environment.
· The cell wall of archaea is composed of S-layers and lack peptidoglycan molecules with the exception of methanobacteria who have pseudopeptidoglycan in their cell wall.
TERMS
The contents of a cell except for the nucleus. It includes cytosol, organelles, vesicles, and the cytoskeleton.
A complex carbohydrate that forms the main constituent of the cell wall in most plants and is important in the manufacture of numerous products, such as paper, textiles, pharmaceuticals, and explosives.
· chitin
A complex polysaccharide, a polymer of N-acetylglucosamine, found in the exoskeletons of arthropods and in the cell walls of fungi; thought to be responsible for some forms of asthma in humans.
FULL TEXT
As with other living organisms, archaeal cells have an outer cell membrane that serves as a protective barrier between the cell and its environment . Within the membrane is the cytoplasm, where the living functions of the archeon take place and where the DNA is located. Around the outside of nearly all archaeal cells is a cell wall, a semi-rigid layer that helps the cell maintain its shape and chemical equilibrium. All three of these regions may be distinguished in the cells of bacteria and most other living organisms.
Archaea
Cluster of halobacterium (archaea)
A closer look at each region reveals structural similarities but major differences in chemical composition between bacterial and archaeal cell wall. Archaea builds the same structures as other organisms, but they build them from different chemical components. For instance, the cell walls of all bacteria contain the chemical peptidoglycan. Archaeal cell walls do not contain this compound, though some species contain a similar one. It is assembled from surface-layer proteins called S-layers. Likewise, archaea do not produce walls of cellulose (as do plants) or chitin (as do fungi). The cell wall of archaeans is chemically distinct. Methanogens are the only exception and possess pseudopeptidoglycan chains in their cell wall that lacks amino acids and N-acetylmuramic acid in their chemical composition. The most striking chemical differences between Archaea and other living things lie in their cell membrane. There are four fundamental differences between the archaeal membrane and those of all other cells: (1) chirality of glycerol, (2) ether linkage, (3) isoprenoid chains, and (4) branching of side chains.
https://www.boundless.com/microbiology/textbooks/boundless-microbiology-textbook/cell-structure-of-bacteria-archaea-and-eukaryotes-4/cell-walls-of-prokaryotes-34/cell-walls-of-archaea-263-284/