KINGDOM MONERA

                            

The kingdom monera is comprised only of bacteria. Not only are bacteria extremely small but they are structurally the simplest and most ancient of all organisms. All the bacteria are unicellular,consisiing of just single prokayotic cell.Prokaryotes lack many of the cellular structural  characteristics of more complex eukaryotic cells , including membrane-bound organelles and nuclei.

                            The bacteria are the most numerous of all the organisms.Bacteria have evolved an amazing diversity of means of acquiring the resources they need to live and reproduce.This remarkable diversity has enabled the bacteria to inhabit virtually every known environment on earth from the hot sulphur springs of Yellowstone to the glacial ice of the Arctic to the depths of the ocean floor.There are two major group of Monerans - ARCHAEBACTERIA(ancient bacteria) and EUBACTERIA(true bacteria).Eubacteria are further of  two types- BACTERIA & CYANOBACTERIA. Some other groups of Monerans include MYCOPLASMA , RICKETTSIAE  &  ACTINOMYCETES.

NUTRITION IN BACTERIA

The biologist recognise two main types of nutrition :

(a) AUTOTROPIHIC : organisms livces entirely on inorganic compounds.
(b) HETEROTROPHIC : organism thrives on organic substances.

Depending upon the energy source , the orgnisms are again classified into two categories :

(c) PHOTOTROPHS or PHOTOSYNTHETIC : these utilise light as the energy source.
(d) CHEMOTROPHS or CHEMOSYNTHETIC : these utilise chemical energy.

On the basis of source of electron,two nutritional types are:

(e) ORGANOTROPHS : source of electron is an organic compound.
(f) LITHOTROPHS : source of electron is an inorganic compound.

In view of all the above, four nutritional categories emerge out which are :

• PHOTOSYNTHETIC AUTOTROPHS or PHOTOLITHOTROPHS :these photosynthetic bacteria use inorganic electron donor such as H2S,H2,sulphur compound etc.these contain bacteriocholorophyll.Eg: CHLOROBIUM,CHROMATIUM.
• PHOTOSYNTHETIC HETEROTROPHS or PHOTO-ORGANOTROPHS : these use organic compunds as electron donors,such as organic acids,alcohols , etc. Eg : RHODOSPIRILLUM,RHODOPSEUDOMONAS.
• CHEMOSYNTHETIC AUTOTROPHS or CHEMOLITHOTROPHS : some autotrophic aerobic bacteria assimilate CO2 witnout using radiant energy. these obtain energy by the oxidation of some inorganic compunds e.g.: nitrifying bacteria(NITROSOMONAS,NITROBACTER) , sulphur bacteria(BEGGIOTA),iron bacteria(FERROBACILLUS),hydrogen bacteria(HYDROGENOMONAS)
• CHEMOSYNTHETIC HETEROTROPHS or CHEMO-ORGANOTROPHS :  these heterotrophic bacteria use organic compounds as substrates e.g.:ESCHERICHIA COLI.

AMINO ACIDS ARE SUBUNITS OF PROTEINS

Amino acids are small organic molecules,generally colourless crystalline solids which are soluble in water but insoluble in organic solvents.Amino acids are formed of C,H,O & N.Some amino acids may contain sulphur(S).There are over 2000 amino acids out of which only 20 amino acids and their derivatives occur in proteins.Amino acids found in proteins are called proteins amino acids whereas others are called non-protein amino acids.


Each amino acid exhibits one definig property viz. they all posess a carboxylic acid group and an amino group both linked to their alpha-carbon atom.Each amino acid also has a side chain atched to its alpha-carbon.The identity of this side chain is what distinguishes one amino acid from the other.

Amino group occurs in alpha-posotion or carbon next to terminal carboxylic group.Therefore,protein amino acids are also called alpha-amino acids.

In the cell where pH is close to 7, free amino acids exist in their ionised form but when they are incorporated into a polypeptide chain , the charges on amino and carboxylic groups disappear.This ionised structure is termed as zwitter ion.

Cells use amino acids to build proteins—polymers made of amino acids, which are joined head-to-tail in a long chain that folds up into a three dimensional structure that is unique to each type of protein.The covalent bond between two adjacent amino acids in a protein chain is called a peptide bond; the chain of amino acids is also known as a polypeptide. Peptide bonds are formed by condensation reactions that link one amino acid to the next. Regardless of the specific amino acids from which it is made, the polypeptide always has an amino (NH2) group at one end—its N-terminus—and a carboxyl (COOH) group at its other end—its C-terminus). 

 Amino acids in a protein are held together by peptide bonds. the four amino acids shown are linked together by three peptide bonds, one of which is highlighted in yellow. One of the amino acids, glutamic acid, is shaded in gray. the amino acid side chains are shown in pink. The two ends of a polypeptide chain are chemically distinct. One end, the N-terminus, is capped by an amino

group, and the other, the c-terminus, ends in a carboxyl group. The sequence of amino acids in a protein is abbreviated using either a three-letter or a one-letter code, and the sequence is always read from the N-terminus .

Twenty types of amino acids are commonly found in proteins, each with a different side chain attached to the α-carbon atom .The same 20 amino acids are found in all proteins, whether they hail from bacteria, plants, or animals. How this precise set of 20 amino acids came to be chosen is one of the mysteries surrounding the evolution of life; there is no obvious chemical reason why other amino acids could not have served just as well. But once the selection had been locked into place, it could not be changed, as too much chemistry had evolved to exploit it. Switching the types of amino acids used by cells would require a living creature to retool its entire metabolism to cope with the new building blocks.

THE STRUCTURE OF DNA

Well before biologists understood the structure of DNA, they had recognized that inherited traits and the genes that determine them were associated with the chromosomes. Chromosomes were discovered in the nineteenth century as threadlike structures in the nucleus of eukaryotic cells that become visible as the cells begin to divide.As biochemical analysis became possible, researchers learned that chromosomes contain both DNA and protein.But which of these components encoded the organism’s genetic information was not clear.

DNA carries the hereditary information of the cell and the protein components of chromosomes function largely to package and control the enormously long DNA molecules. Biologists in the 1940s had difficulty accepting DNA as the genetic material because of the apparent simplicity of its chemistry .DNA, after all, is simply a long polymer composed of only four types of nucleotide subunits, which are chemically very similar to one another.

In 1950s, DNA was examined by X-ray diffraction analysis,a technique for determining the three-dimensional atomic structure of a molecule .The early results indicated that DNA is composed of two strands wound into a helix. The observation that DNA is double-stranded was of crucial significance. This structure immediately suggested how DNA could encode the instructions necessary for life, and how these instructions could be copied and passed along when cells divide.

 A DNA molecule Consists of Two Complementary Chains of Nucleotides

A molecule of deoxyribonucleic acid (DNA) consists of two long polynucleotide chains. Each chain, or strand, is composed of four types of nucleotide subunits, and the two strands are held together by hydrogen bonds between the base portions of the nucleotides.Each nucleotide is composed of a sugar– phosphate covalently linked to a nitrogenous base.

The nucleotides are covalently linked together into polynucleotide chains, with a sugar– phosphate backbone from which the  nitrogenous bases extend.

DNA molecule  is composed of two polynucleotide chains held together by hydrogen bonds between the paired bases. The arrows on the DNA strands indicate the polarities of the two strands, which run antiparallel to each other in the DNA molecule.

The two polynucleotide chains in the DNA double helix are held together by hydrogen-bonding between the bases on the different strands. All the bases are therefore on the inside of the double helix, with the sugar–phosphate backbones on the outside The bases do not pair at random, however: A always pair with T, and G always pairs with C  In each case, a bulkier two-ring base is paired with a single-ring base (a pyrimidine). Each purine–pyrimidine pair is called a base pair, and this complementary base-pairing enables the base pairs to be packed in the energetically most favorable  arrangement in the interior of the double helix. In this arrangement, each base pair has a similar width, thus holding the sugar–phosphate backbones an equal distance apart along the DNA molecule.The members of each base pair can fit together within the double helix because the two strands of the helix run antiparallel to each other—that is, they are oriented with opposite polarities.The antiparallel sugar–phosphate strands then twist around each other to form a double helix containing 10 base pairs per helical turn. This twisting also contributes to the energetically favorable conformation of the DNA double helix.

A consequence of the base-pairing requirements is that each strand of  a DNA double helix contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand—an A always matches a T on the opposite strand, and a C always matches a G. This complementarity is of crucial importance when it comes to both copying and repairing the DNA.

STRUCTURE OF GASTRO-INTESTINAL WALL

From the mid-esophagus to the anus, the wall of the gastrointestinal tract has the general structure illustrated in Figure  below.Most of the luminal (inside) surface is highly convoluted, a feature that greatly increases the surface area available for absorption. From the stomach on, this surface is covered by a single layer of epithelial cells linked together along the edges of their luminal surfaces by tight junctions. Included in this epithelial layer are exocrine cells that secrete mucus into the lumen of the tract and endocrine cells that release hormones into the blood. Invaginations of the epithelium into the underlying tissue form exocrine glands that secrete acid, enzymes,water,ions, and mucus into the lumen.

Just below the epithelium is the lamina propria , which is a layer of loose connective tissue through which pass small blood vessels, nerve fibers, and lymphatic vessels.The lamina propria is separated from underlying tissues by the muscularis mucosa which is a thin layer of smooth muscle that may be involved in the movement of villi,described subsequently.The combination of these three layers—the epithelium,lamina propria, and muscularis mucosa—is called the mucosa. Beneath the mucosa is the submucosa ,which is a second connective-tissue layer. This layer also contains a network of neurons, the submucosal plexus,and blood and lymphatic vessels whose branches penetrate into both the overlying mucosa and the underlying layers of smooth muscle called the muscularis externa.Contractions of these muscles provide the forces for moving and mixing the gastrointestinal contents.

Except for the stomach, which has three layers, the muscularis externa has two layers: (1) a relatively thick inner layer of circular muscle , whose fibers are oriented in a circular pattern around the tube so that contraction produces a narrowing of the lumen;(2) and a thinner outer layer of longitudinal muscle whose contraction shortens the tube.Between these two muscle layers is a second network of neurons known as the myenteric plexus There are neurons projecting from the submucosal plexus to the single layer of cells on the luminal surface as well as to the myenteric plexus.The myenteric plexus is innervated by nerves from the autonomic nervous system and has neurons that project to the submucosal plexus.

Finally, surrounding the outer surface of the tube is a thin layer of connective tissue called the serosa .Thin sheets of connective tissue connect the serosa to the abdominal wall and support the gastrointestinal tract in the abdominal cavity.

 The macro- and microscopic structure of the wall of the small intestine is shown in Figure below.The circular folds (mucosa and submucosa) are covered with finger-like projections called villi.The surface of each villus is covered with a layer of epithelial cells whose surface membranes form small projections called microvilli  Interspersed between these absorptive epithelial cells with microvilli are goblet cells that secrete mucus that lubricates the wall of the small intestine. The combination of circular folds, villi, and microvilli increases the small intestine’s surface area about 600-fold over that of a flat-surfaced tube having the same length and diameter.The human small intestine’s total surface area is about 250 to 300 square meters, roughly the area of a tennis court.  The large surface area provided by the morphology of the small intestine allows for the highly efficient absorption of nutrients.  

Epithelial surfaces in the gastrointestinal tract are continuously being replacedbynewepithelialcells.Inthesmall intestine , new cells arise by cell division from cells at the base of the villi These cells differentiate as they migrate tothetopofthe villus, replacing older cells that die and are discharged into the intestinallumen. These dead cells release their intracellular enzymes into the lumen,whichthencontributetothe digestive process.About 17 billion epithelial cells are replaced each day, and the entire epithelium of the small intestine is replaced approximately every 5 days.

It is because of this rapid cell turnover that the lining of the intestinal tract is so susceptible to damage by treatments that inhibit cell  division, such as anticancer drugs and radiation therapy.Also at the base of the villi are enteroendocrine cells that secrete hormones that control a wide variety of gastrointestinal functions,including motility and exocrine pancreatic secretions.The center of each intestinal villus is occupied by both a single, blind-ended lymphatic vessel—a    lacteal   —and a capillary network. Most of the fat absorbed in the small intestine enters the lacteals.Material absorbed by the lacteals reaches the general circulation by eventually emptying from the lymphatic system into large veins through a structure called the thoracic duct.

METABOLIC PATTERNS AMONG LIVING ORGANISMS

 METABOLIC PATTERNS AMONG LIVING ORGANISMS

Organisms can also be classified according to their metabolic capabilities. While this method does not strictly follow evolutionary relationships, it is still very useful for understanding patterns of energy and metabolite flow, which is especially important in phototrophic organisms. A number of these patterns can be present simultaneously in a single organism,leading to names that are often intimidating.However, they are simply combinations of the individual metabolic patterns.A fundamental metabolic distinction is between autotrophs and heterotrophs.The“troph”part is derived from a Greek word meaning “to feed.”Autotrophs are “self-feeding” organisms that derive all their cellular carbon from CO2,whereas heterotrophs are organisms that derive cellular carbon from organic carbon compounds. A second pattern relates to the source of energy for cellular processes. Phototrophs derive their energy from sunlight, whereas chemotrophs derive energy from various types of chemical compounds. If these compounds are organic chemicals, the organisms are chemoorganotrophs. If they are inorganic chemicals,they are called chemolithotrophs.An organism that derives its energy from light and all its cellular carbon from CO2 is known as a photoautotroph. Most photosynthetic organisms can grow in this manner. If the organism grows by using light as an energy source, but assimilates organic carbon, it is known as a photoheterotroph.Many phototrophic organisms can also grow in this way, and in a large number of cases a single organism can grow either photoautotrophically or photoheterotrophically, depending on the availability of organic matter.Table below summarizes some of the metabolic relationships among living organisms.Oxygen is central to the metabolism of most cells. If an organism is capable of growing in the presence of oxygen, it is classed as an aerobe.If it cannot grow in the presence of oxygen, it is called an anaerobe.Some organisms can switch back and forth from aerobic and anaerobic metabolisms, and are call facultative aerobes. In most cases, aerobes utilize organic molecules as electron donors and O2 as an electron acceptor in a process called aerobic respiration. Other inorganic compounds can sometimes serve as electron acceptors, a process known as anaerobic respiration.Finally,organisms that use organic compounds as both electron donors and acceptors in the absence of oxygen live by carrying out fermentation.