RNA

RNA Structure and function:

The tertiary structure of RNA is similar to DNA, but there are several important differences:

• RNA usually forms intramolecular base pairs
• the information carried by RNA is not redundant because of these intramolecular base pairs.
• the major and minor grooves are less pronounced
• the structural, informational adaptor and information transfer roles of RNA are all involved in decoding the information carried by DNA

The 4 types of RNA

• tRNA (transfer RNA)
• mRNA
• rRNA
• snRNA

tRNA

tRNA is the information adapter molecule. It is the direct interface between amino-acid sequence of a protein and the information in DNA. Therefore it decodes the information in DNA. There are > 20 different tRNA molecules. All have between 75-95 nt.

All tRNA's from all organisms have a similar structure, indeed a human tRNA can function in yeast cells.

There are 4 arms and 3 loops. The acceptor, D, T pseudouridine C and anticodon arms, and D, T pseudouridine C and anticodon loops. Sometimes tRNA molecules have an extra or variable loop (this is shown in yellow in the adjacent figure).

tRNA is synthesized in two parts. The body of the tRNA is transcribed from a tRNA gene. The acceptor stem is the same for all tRNA molecules and is added after the body is synthesized. It is replaced often during lifetime of a tRNA molecule.

The adjacent image is a 3-D model of a yeast tRNA molecule which can code for ser. The model and the schematic above share the same color coding. You can rotate the molecule in the y axis to get better views of the structure.

Observe how the molecule is folded with the D and T pseudo-U C loops in contact, and with the acceptor stem and the anticodon loop at opposite ends.

The acceptor stem is the site at which a specific amino acid is attached by an amino-acyl-tRNA synthase. The anticodon reads the information in a mRNA sequence by base pairing.

Notice how the overall gross structure of the helix resembles that of DNA. Observe that the phosphoryl groups (shown in orange) are not on the outside of the helix like they are in DNA but are located in the groove. bases are paired similarly to DNA. In this image the acceptor stem is on the left and the anticodon loop is at the bottom. The D loop is in front of the T pseeudoU C loop at the top right.

mRNA

Messenger or mRNA is a copy of the information carried by a gene on the DNA. The role of mRNA is to move the information contained in DNA to the translation machinery.

mRNA is heterogeneous in size and sequence. It always has a 5 ' cap composed of a 5' to 5' triphosphate linkage between two modified nucleotides: a 7-methylguanosine and a 2 ' O-methyl purine. This cap serves to identify this RNA molecule as an mRNA to the translational machinery. In addition, most mRNA molecules contain a poly-Adenosine tail at the 3' end. Both the 5' cap and the 3' tail are added after the RNA is transcribed and contribute to the stability of the mRNA in the cell.

mRNA is not made directly in a eukaryotic cell. It is transcribed as heterogeneous nuclear RNA (hnRNA) in the nucleus. hnRNA contains introns and exons. The introns are removed by RNA splicing leaving the exons, which contain the information, joined together. In some cases, individual nucleotides can be added in the middle of the mRNA sequence by a process called RNA editing. In the figure the exons are represented as the region of variable sequence.

hnRNA and mRNA are never found free in the cell. Like DNA, they are bound by cations and proteins. These complexes are termed ribonucleoproteins or RNPs. The variability in sequence and structure means that no structure has been determined for a mRNA.

rRNA and ribosome synthesis

Ribosomal RNA (rRNA) is a component of the ribosomes, the protein synthetic factories in the cell. Eukaryotic ribosomes contain four different rRNA molecules: 18 s, 5.8 s, 28 s, and 5 s rRNA. Three of the rRNA molecules are synthesized in the nucleolus, and one is synthesized elsewhere. rRNA molecules are extremely abundant. They make up at least 80% of the RNA molecules found in a typical eukaryotic cell.

Synthesis of the three nucleolar rRNA molecules is unusual because they are made on one primary transcript that is chopped up into three mature rRNA molecules. These rRNA molecules and the 5 s rRNA combine with the ribosomal proteins in the nucleolus to form pre 40 s and pre 60 s ribosomal subunits. These pre-subunits are exported to the nucleus where they mature and assume their role in protein synthesis.

The rRNA molecules have several roles in protein synthesis. First, the 28 s rRNA has a catalytic role, it forms part of the peptidyl transferrase activity of the 60 s subunit. Second, 18s rRNA has a recognition role, involved in correct positioning of the mRNA and the peptidyl tRNA. Finally, the rRNA molecules have a structural role. They fold into three-dimensional shapes that form the scaffold on which the ribosomal proteins assemble. The model on the left shows a the three dimensional structure that the 5 s rRNA from the African frog, Xenopus laevis is thought to adopt.

snRNA

Small nuclear RNA (snRNA) is the name used to refer to a number of small RNA molecules found in the nucleus. These RNA molecules are important in a number of processes including RNA splicing (removal of the introns from hnRNA) and maintenance of the telomeres, or chromosome ends. They are always found associated with specific proteins and the complexes are referred to as small nuclear ribonucleoproteins (SNRNP) or sometimes as snurps.

Antibodies against snurps are found in a number of autoimmune diseases.

http://www.biochem.uwo.ca/meds/medna/RNA.html

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Paramecium

The paramecium is larger than the amoeba. It can be found in ponds with scum on them. It has more of a shape than an amoeba, looking like the bottom of a shoe. It is covered with tiny hairs that help it move. These hairs are called cilia. The paramecium is able to move in all directions with its cilia.

The paramecium eats tiny algae, plants, etc. The cilia propel the food into a tiny mouth opening of the paramecium. The food is then shoved down a little tube called a gullet that leads to the protoplasm or stuffing of the cell. The food is held in little cells called vacuoles. It has two other vacuoles at either end of its body to get rid of excess water and wastes. As with the amoeba, oxygen and carbon dioxide pass through the cell membrane of the paramecium.

The paramecium has two nuclei, a big and small one. The big one operates as the director of the cell's activities, rather like a little brain. The smaller one is used for reproduction. The paramecium splits in half (fission) just as the ameba does. First the smaller nucleus splits in half and each half goes to either end of the paramecium. Then the bigger nucleus splits and the whole paramecium splits. Occasionally two paramecium exchange material and form a new paramecium. This is called conjugation.

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Posted in: Microbiology

Tobacco mosaic virus (TMV)

TMV was the first virus to be discovered by the Dimitri Ivanowski in 1892 and crystallized by the W.M Stanley. It causes mosaic disease in tobacco plant. It belongs to tobamo virus group.

It is rod shaped, containing no envelope measuring about 300nm in length and 15-17 nm in diameter.

It has a protein capsid constituting of 95% of virus and a core of nucleic acid. The capsid is in the form of a tube with a cavity measuring about 2nm in diameter. It is composed of 2130 identical capsomers which are closely packed and arranged in the form of a regular spiral or helix.

There are about 49 capsomers for every 3 turns that is about 16 per turn of the helix. There are 130 turns in a complete virus capsid.

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Microsystis

Kingdom: Monera

Division: Cynophysia

Class: Cynophyceae

Order: Chrococcales

Family: Chrococcaceae

Genus: Microsystis

Microsystis is a free floating or planktonic blue green algae commonly found in fresh water bodies such as ponds pools lakes, etc. which maybe contaminated by sewage water. It generally forms dense water grooms. It is colonial form and the colonies are irregular. Each colony consists of a large number of densely packed small cells that are evenly distributed through out a common thin watery, gelatinous matrix. On mucilaginous matrix which is colourless and homogenous. The colony has many air space also called pseudo vacuoles or gas vacuoles which gives bouncy and allows the algae to float on the surface of water. The gas vacuole also helps in exchange of gases.

The cells are usually spherical. Each cell is typically cyanophychian with a central colourless incipient nucleus (centroplasm) and a peripheral highly pigmented chromoplasm. The chromoplasm contains phycocyanin (blue pigments), chlorophyll (green pigments) in large amounts and phycoerythrin (red pigments) in small amounts. The centroplasm consists of naked DNA without a nuclear membrane.

REPRODUCTION

It is by cell division of cells along the three planes. Sometimes a few cells may separate from the colony and develop into a new colony

ECONOMIC IMPORTANCE

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• Microsystis is known to cause to form water blooms and there for deprives the aquatic animals of the oxygen by preventing exchange of gas between the water and the atmosphere.

• It produces neurotoxin which causes nerve disorder in animals consuming water contaminated with microsystis. swimming in water with microsystis causes skin irritation and diseases
• Since microsystis grows abundantly in polluted water, it is used as a biological indicator for water pollution.

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Economic importance of genus Aspergillus.

Aspergillus has both harmful ans useful activities from the view of the human.

Harmful activities

Many species of Aspergillus such as A. glqaus A.flavus A. repns are responsible
of spoilage of exposed food stuff like jams, jellies, bread, tobacco and
many other product like leather & textiles. Many of the species are pathogenic to animals as well as human beigns. A. flavus,

A. fumigates and A.niger causes diseases of respiratory tracks commonly refered to as
aspergilloses. Aspergilloses is reported in birds, cattle, sheep, horses and human begins.

Symptoms of Aspergillosis resembles those of tuberculosis. Diesease of the human ear called otomycosis is caused by A.niger, A.flavus and A.fumigatus.

A.flavus produces a toxic substance called afflotoxin which has some carcinogenic effects and may cause cancer of liver in human begin and animals.

Conidia of Aspergillus are abundant in air. They usually spoil the laboratory culture. Many plant diseases-crown rot of ground nut and ball rot of cotton are caused by
species of Aspergillus.

Aspergillus nidulaus


A. niger

Useful effects

Several species are employed in cheese manufacturing.

A.oryzae is used in the preparation of wine from rice and soya bean sauces. Some specises of aspergillus are the source of certain antibiotics like Flavicein,Aspergillin, Geodin, Funagalin, Patulin, Ustin etc.

A. niger is used in bio-assay of metals as it can detect copper even in traces.

A.gowssipii is used in the production of vitamin B. Some species are used in the production of fats. Several species are used in the industrial production of organic acids like citric acid and gluconic acid.

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Posted in: Microbiology

Saccharomyces

Class: Acromycetes

Order: Endomycetales

Family: Saccharomycetaeceae

Genus: Saccharomyces

Saccharomyces is saprophytic fungi (Yeast) found growing abundantly in sugary substance such as fruits, syrups, jams, nectar, honey, toddy etc. it is uni-cellular but sometimes the cell may remain attached giving the appearance of a pseudo mycelium. the cells are small oval or spherical in shape and grow as white or creamy colonies on the surface of solid nutrient media.

Each cell has a definite two layered cell wall made up of fungal cellulose with the chitin. The cell wall encloses the protoplasm which can be differentiated into outer ectoplasm and the inner endoplasm. The cell contains a large centroplasm consists of a single large nucleus, sub-cellular organelles like endoplasmic reticulum, ribosome, mitochondria, and reserved food material in the form of glycogen, volutin granules and oil globules.

REPRODUCTION

Saccharomyces reproduce by budding or fusion or by sexual reproduction.

BUDDING

It is the most common type of reproduction in which the parent cell gives rise to a small bud- like out growth. The nucleus of the parent cell divides in to two and one daughter nucleus along with cytoplasm enters the bud. The bud grows in size and may get a pinched-off from the mother cell or may remain attached to it intern forming bud, there by giving rise to pseudo mycelium.

SEXUAL REPRODUCTION
It is of isogamous type where two vegetative cells behave as gemates and put out small protuberances, which meats and forms conjugation tubes. The nuclei of the two gametes fuse along with cytoplasm and form a zygote which develops in to ascus. The diploid nucleus of the ascus under goes mitosis to form 4-8 ascospores which when release develop into new yeast cell.

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Posted in: Microbiology

Aspergillus

Class: Acromycetes

Order: Aspergillales

Family: Aspregillaceae

Genus: Aspergillus

Aspergillus is a wide spread fungus generally saprophytic and growing stale bread , fruits, vegetables, jams, jellies, foot wear etc. a few species of Aspergillus are parasitic causing lung disease (aspergillosis) and ear infection (outomycosis).

The mycelium consists of a hyaline branched, septate and multi nucleated hyphae. Most of the mycelium grows above the substratum. Some hyphae grow deep into the substratum and halt in the distribution of nutrient and encouraged.

REPRODUCTION

ASEXUAL REPRODUCTION

Asexual reproduction

From the vegetative mycelium many un-branched erect, fertile hyphae called conidiophores arise from thick-walled cells called foot cells. These conidiophores form a swollen dawn shaped vesicles at the tips. The vesicles produce bottle shaped structure called sterigmata, which produces chains of conidia at their tips in basipital sub sessions. The sterigmata are multi nucleated and maybe found in two layers in some spices. The asexual spore called conidia are small , unicellular ,spherical structure with a double layer wall. The outer layer is called epispore/ exime, which is spiny and inner layer called the endospores/ intine. The conidial wall is pigmented with shapes of black, blue, green, yellow etc. depending upon the species. The conidia germinate by the production of germ tube and develop into new hyphae. The conidia are light weighted and carried by a wind.

SEXUAL REPRODUCTION

Sexual reproduction

It is by means of gametengial contact between the male antheridium and female ascogonium, which maybe produced on the same or different hyphae. Fertilization results in the formation of fruiting body called ascocarps, cleistothecium , which encloses a number of asci, each containing 8 ascospores, which when liberated germinates to give rise to a new mycelium.

ECONOMIC IMPORTANCE

A.niger also called the black mold is used in the industrial production of citric acid and glycolic acid.

A.flavus is known to produce a mycotoxin called aflatoxin.

Many species are important in food spoilage and some are known to cause disease.

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Posted in: Microbiology

Penicillium

Class: Acromycetes

Order: Aspergillales

Family: Aspregillaceae

Genus: Penicillium

Penicillium is commonly called blue mold. It is a saprophytic found growing in decaying fruits and vegetables, especially citrus fruits-like orange and lemon. The mycelium consists of pale hyaline brightly hyphae which generally grow superficially on the substratum, the hyphae are septate branched and uni- nucleated.

REPRODUCTION

ASEXUAL REPRODUCTION

It is for the formation of conidia on special branch called conidiopores. The conidiophores is the long, slender septate grows right from the vegetative hyphae . They maybe branched or unbranched. The ultimate branches of the cornidiophore are called matulate. The metulate produce bottle shaped cells called sterigmata or phialides. The conidia are born in chains of basipital successions at the tip of each stigma. The terminal part of the cornidiophore has a brush or broom-like appearance knows as penicillus hence the name penicillium. The conidia are blue green, olive green or grey depending upon the species. They are globose in shape, uni-nucleate and has a smooth wall. They germinate and give rise to a new mycelium

SEXUAL REPRODUCTION

It is by means of gametangial contact between the male antheridium and female ascogonium which maybe produced on the same or different hyphae. Fertilization results in the formation of fruiting bodies called ascocarps, cleisthothecium which encloses the number of asci. Each containing 8 ascospores which when liberated germinates to give rise to a new mycelium.

ECONOMIC IMPORTANCE

The genus penicillium is of great ecomomic importance .concidering the dis advantage of fungus first. It causes great demage of furniture .fabrics etc. .The profuse growth growth of mycelium on the windows ,furniture etc, forms a blue coating .oe of the greatest demages iscaused to the fruits and vegetables for example. P.digitatum and P.expansum cause the decay of sitrus fruits . the latter spices are causing the decay of apples. Some of the spices are causing animat and human diease. For example. Pencillosis of lungs. However these can be controlled by careful hanling og material. Keeping them under restricted air supply , low temperature and dry condition

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Posted in: Microbiology

Rhizopus

Class: Zygomycetes

Order: Mucorales

Family: Mucoraceae

Genus: Rhizopus

Rhizopus is commonly called bread molds. It is a saprophytic fungus found growing on bread, jam, pickles, decaying vegetables and fruits etc. the plant body consists of white cottony mycelium growing over the substratum. The young mycelium consists of long aseptate coenocytic hyphae. The older mycelium has three types of hyphae

1. Stolons : they are staut cylindrical creeping hyphae . They are differentiated in to nodes and inter nodes.

2. Rhizoidal hyphae: it produces at the node of the stolon .they are highly branched and penetrated into substratum .they provide courage and absorb food.

3. Sporangiopore: they are Arial staut hyphae which arise from substratum from the time of asexual reproduction. They develop from the node in clusters. Initially the hyphae have the cell wall made up of fugal cellulose. It encloses the cytoplasm. Hyphae are asepetate coenocytic, small vacuoles, oil droplets and glycogens are distributed in the cytoplasm.

ASEXUAL REPRODUCTION

It is by the formation of spore. The sporangiopore are short staut and arise at the node of stolon in clusters. A single sporangium is developed at the apex of each sporangiopore. Each sporangium is spherical in shape with the columella in the centre. The space between the columella and the sporangial wall is filled with uni- nuclei, non-motile aplanospore. The spores are liberated by breaking of the sporangial wall they germinate to form new mycelium.

SEXUAL REPRODUCTION

It is isogamous bind gematangial copulation. The sex organs develop when two mating strands + and - comes close to each other. The two gametangia on the opposite strands are formed as protruebalance. The nuclei moves to the tip and separated from the remaining pro-gametangia by a septum. The remaining part forms the suspensor. The wall of the gametangia meets, dissole and the nuclei fuses to form coenozygospore , which develops a thick wall and form a zygospore . On germination it produces a pro-mycelium and a terminal sporangium.

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Posted in: Microbiology

Pythium

Class: Oomycetes

Order: Peronosporales

Family: Pythiaceae

Genus: Pythium

Pythium is a mold of cosmopolitan distribution and consisting of about 45 species which maybe aquatic or terrestrial inhabits. It is facultative parasite on fresh water algae and seedling of many plants like mustard, papaya, tobacco, beans, ginger, etc. it also occurs saprophytic ally in moist soil. Pythium infects the host plant by the wounds. It is also responsible for the “damping- off” disease of seedling. It is also causes “soft rot”,”root rot” etc. it is also involved in decay and decomposition of the plant remains in the soil.

The mycelium of Pythium appears as a white fluffy growth consisting of slender, branched, aseptatic coenocytic hyphae without rhizoids. In the host plant mycelium is both inter and intra cellular without hysteria formation. The cell wall is made up of fungal cellulose and the cytoplasm consists of , many nuclei and other membrane bound organelles like, the mitochondria, ribosome’s, endoplasmic reticulum etc. Reserved food materials are in the form of oil droplets and glycogen.

REPRODUCTION
Reproduction in Pythium is both asexual and sexual.

ASEXUAL REPRODUCTION
It is by the formation of biflagellate zoospore inside zoosporangia both at the tip of the sporangiopore. The sporangium is globule with an epical papilla. Some spices have filamentous or elongated sporangia, which are the same diameter of the hyphae and are they form indistinguishable from hyphae. The sporangiopore maybe simple or in branched. In some spices the sporangia germinates directly into new hyphae and hence they are called cornidium.

SEXUAL REPRODUCTION
It is oogamous and occurs in the formation of terminal oval or spherical oogonium and an elongated antheridium from adjacently on the same mycelium. Fertilization of the female gamete in the oogonium is by the male single functional nucleus in the antheridium which results in the formation of thick walled oospores.

ECONOMIC IMPORTANCE
Pythium dibaryanun causes the “damping-off” tobacco and chilies seedlings.
P. aphanidermatum causes soft rot of apple, papaya and beans.
P.myriotylum causes rhizome rot of ginger.
Pythium is also responsible for decomposition of organic matter in the soil

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Posted in: Microbiology

Gracilaria

Class: Rhodophyceae

Order: Graclariales

Family: Gracilariaceae

Genus: Gracilaria

Gracilaria is common marine red algae found growing attached to the sub-stratum such as rocks by a basal cushion disc, (lithophytes). It has large dichotomously branched thallus also called fronds. It is composed of closely compacted vertical thread like fronds which are which are dark red or pink branches reaching up to 50cm in height.

The matured thallus shows little anatomical difference and T.S of the thallus shows three zones. They are peripheral layer of cell, cortex and medulla. The peripheral layer of cell is small uni or multi nucleated, some of them producing unicellular hairs. Inner to the peripheral layer is the cortex made up of many small cells having ribbon shaped chromatophores. The inner core of the thallus is medulla which contains large iso- diametric cells. The fronds are monosithonous and have a gelatinous envelope on the surface.

Economic importance

Gracilaria is extensively used for extraction of polysaccahrides, Agar. Used as a solidifying agent in nutrient media in microbiology labs.

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Posted in: Microbiology

Cosmarium

Class: chlorophceae

Order: Zygnematales

Family: Desmidiaceae

Genus: Cosmarium

Cosmarium is a uni-cellular fresh water desmids occurring in ponds, rich in organic decaying matter, along with other free-floating algae. Usually it occurs in abundance in mucilaginous masses along the wall of reservoirs and water tanks especially in winter'

The cell posses a distinct median constriction called sinus. This divides them in to two distinct halves called semi- cells. Which remains join together by a connecting zone called isthmus. Each semi-cell maybe circular, elliptical or oval in shape. The cells posses a three layered transversely segmented walls with vertical poles arranged in a definite pattern. A single nucleus is found in the isthmus region. There is one or more chloroplast in each semi-cell with one or two pyrenoid.

Reproduction takes place by asexual reproduction (cell division) and isogamous sexual reproduction. Sexual reproduction results formation of zygospore.

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Posted in: Microbiology

Anabaena

Kingdom: Bacteria

Division: Cyanophyta

Class: Cyanophyceae

Order: Nostocales

Family: Nostocaceae

Genus: Anabaena

Anabaena is the filamentous form found occurring either in the single filament or as free-floating colonies or in a delicate means the stratum in permanent or semi- permanent form. Some spices of anabaena are endophytic and have within roots of circus and aquatic pteriodophyte azolla. The Trico are the same thickness through out, sometimes slightly alternated at the typical ends. They are straight cercinated or irregularly contorted concurringly with a hyaline watery sheet.

The cells are usually spherical or barrel shaped .they are typically cyanophyceae with a cell wall made up of peptidoglycogen enclosing the protoplasm. The protoplasm differentiated in outer and central colorless

The centroplasm has an incipient nuclei and the chromoplasm has phycocyrin , phcoerithrin, along with the chlorophyll on photosynthetic lamellae . The protoplasm of vegetative cells are usually filled with numerous psedovacuoles. The heterocyst’s in the filament are inter-colonial and are in a same shape as vegetative cells.

Thick walled resting cells called akinetes are found adjacent to the heterocysts.

Reproduction takes place by means of homogonium and akinetes.

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Posted in: Microbiology

Basic Structure of an Amino Acid

Basic Structure

All amino acids found in proteins have this basic structure, differing only in the structure of the R-group or the side chain.

The simplest, and smallest, amino acid found in proteins is glycine for which the R-group is hydrogen (H).

L-isomer
In proteins, only the L-isomer is found normally.

As you travel onward (from the carbonyl carbon to the amino group), the R group of L-amino acids will be on the left as shown in the molecular graphic on the right

Essential amino acids

Humans can produce 10 of the 20 amino acids. The others must be supplied in the food. Failure to obtain enough of even 1 of the 10 essential amino acids, those that we cannot make, results in degradation of the body's proteins—muscle and so forth—to obtain the one amino acid that is needed. Unlike fat and starch, the human body does not store excess amino acids for later use—the amino acids must be in the food every day.

The 10 amino acids that we can produce are alanine, asparagine, aspartic acid, cysteine, glutamic acid, glutamine, glycine, proline, serine and tyrosine. Tyrosine is produced from phenylalanine, so if the diet is deficient in phenylalanine, tyrosine will be required as well. The essential amino acids are argentine (required for the young, but not for adults), histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. These amino acids are required in the diet. Plants, of course, must be able to make all the amino acids. Humans, on the other hand, do not have all the enzymes required for the biosynthesis of all of the amino acids.

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Posted in: Biotechnology

Scenedesmus

Scenedesmus is a widely distributed green algae found freely in stagnant water. It appears in pure culture in aquarium and in jar containing standing uncharged water in the laboratory.

It is colonial form with a number of cells in the coenobium (colony) being multiplies of two usually 4-8 cells. The cell are ellipsoidal or fusiform in shape and arranged in single or double series with long axis, parallel to one another so as to form a flat or curve plain. The two end cells of the coenobium may differ from the shape of the others and often teeth or spines or gelatinous bristles, which are projections of the mucilaginous cell envelope .each cell is un-nucleated and contain a single longitudinal laminate chloroplast with one pyrenoid.

Reproduction is by the formation of 2, 4,8,16 or 32 autospores by each cell in the colony. They remain laterally united to another to form a coenobium which is liberated by rupturing of the parent cell wall.

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Posted in: Microbiology

Spirulina

Spirulina is a planktonic blue green algae found growing in fresh water bodies, sewages etc. it consists of a unicellular trichrome’ which is helically or spirally twisted and hence the name Spirulina.

Each cell is typically cyanophyceae and is bounded by the cell wall enclosing the protoplasm and is differentiated in to outer pigmented chromoplasm consisting of the pigment phycocyanin and chlorophyll which give the green colour to the algae . The inner centroplasm consists of the incipient nucleus.

Reserved food materials such as cyanophytin starch, cyanophytin granules (protein) and oil globules are present in the cytoplasm

Reproduction occurs by cell division or fragmentation of the filaments.

ECONOMIC IMPORTANCE
Spirulina is excellent source of protein .vitamins and minerals, hence can be consumed as s food supplement (single cell protein) .it is also used as an animal feed due to its nutritional value.

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Posted in: Microbiology

Chlorella

Chlorella is a green algae generally found to occur as a plankton in fresh water bodies and damp walls, rocks etc. The thallus is unicellular some times growing small groups and colonies.

Each cell is small cylindrical or ellipsoidal in shape. The cell is surrounded by 3 layered cell wall. The wall shows the presence of sporopollinin. Each cell posses a single large cup shaped chloroplast which is parietal in position. The cells are unicellular. The nucleus lies in the chloroplast cup, other cell organelles like mitochondrion, ribosome etc are present.

Asexual reproduction takes place by the formation of non-motile autospores. Two to sixteen autospores are produced and they are liberated by the rupture of the parental cell wall.

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Posted in: Microbiology

Spirogyra

Spirogyra commonly called “pond silk” occurs in extensive muscles in living bright green free floating algae on the surface of stagnant ponds’ slowly running streams and fresh water streams. The thallus or plant body consists of long slender thread like un-branched filaments which are slimy to touch due to mucilage on there outer wall .

A cell enlarged

Each filament is composed of a single raw of similar cylindrical cells. Each cell consists of a cell wall made up of cellulose and protein in definite within the cell wall is a parietal layer of protoplasm enclosing a large central vacuoles. In the protoplasm is embedded 1-14 chloroplast.

Each chloroplast is in the form of a constitutes a green spiral band with toothed edges hence the name spirogyra. The chloroplast has large pyrenoids in them. There is a large single nucleus one or two nucleoli and it is suspended in the middle of the cell by cytoplasmic strands

Lateral conjugation

Reproduction occurs asexually by fragmentation of the filaments and during unfavorable conditions by the formation of walled resting spores. Sexual reproduction is by conjugation. Turning of two morphologically identical cells but physiologically dissimilar gametes.

scalariform conjugation

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Posted in: Microbiology

The Influenza (Flu) Virus

ext to the common cold, influenza or "the flu" is perhaps the most familiar respiratory infection in the world. In the United States alone, approximately 25 to 50 million people contract influenza each year. The symptoms of the flu are similar to those of the common cold, but tend to be more severe. Fever, headache, fatigue, muscle weakness and pain, sore throat, dry cough, and a runny or stuffy nose are common and may develop rapidly. Gastrointestinal symptoms associated with influenza are sometimes experienced by children, but for most adults, illnesses that manifest in diarrhea, nausea, and vomiting are not caused by the influenza virus though they are often inaccurately referred to as the "stomach flu." A number of complications, such as the onset of bronchitis and pneumonia, can also occur in association with influenza and are especially common among the elderly, young children, and anyone with a suppressed immune system.

Influenza is highly contagious and is more common during the colder months of the year. Contrary to traditional belief, however, the climate itself is not directly to blame for the increase in incidence, but rather is attributable to the greater amount of time spent indoors in close proximity to other individuals during inclement weather. The influenza virus is chiefly transmitted through airborne respiratory secretions released when an infected individual coughs or sneezes. Incubation typically is from one to two days from the time of infection, and most people begin to naturally recover from symptoms within a week. The vast majority of influenza-related deaths are caused by complications of the flu rather than the actual influenza virus.

Three distinct types of influenza virus, dubbed A, B, and C, have been identified. Together these viruses, which are antigenically distinct from one another, comprise their own viral family, Orthomyxoviridae. Most cases of the flu, especially those that occur in epidemics or pandemics, are caused by the influenza A virus, which can affect a variety of animal species, but the B virus, which normally is only found in humans, is responsible for many localized outbreaks. The influenza C virus is morphologically and genetically different than the other two viruses and is generally nonsymptomatic, so is of little medical concern.

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Posted in: Microbiology

The Human Immunodeficiency Virus (HIV)

Perhaps no disease is more strongly identified with the late twentieth century than acquired immunodeficiency syndrome, commonly known as AIDS. Yet, according to a 2004 United Nations report on the state of the global AIDS epidemic, the disease has not yet begun to reduce its grip on the world population despite the fact that AIDS does not generally receive the same amount of public attention as it once did. On the contrary, infections are on the rise in many countries, including high income nations such as the United States. In 2003, nearly five million people contracted the human immunodeficiency virus (HIV) that causes AIDS, the greatest number of new infections in a single year since AIDS was first officially recognized as a disease in 1981.

The virus responsible for HIV was first isolated in 1983 by Robert Gallo of the United States and French scientist Luc Montagnier. Since that time, a tremendous amount of research focusing upon the causative agent of AIDS has been carried out and much has been learned about the structure of the virus and its typical course of action. HIV is one of a group of atypical viruses called retroviruses that maintain their genetic information in the form of ribonucleic acid (RNA). Through the use of an enzyme known as reverse transcriptase, HIV and other retroviruses are capable of producing deoxyribonucleic acid (DNA) from RNA, whereas most cells carry out the opposite process, transcribing the genetic material of DNA into RNA. The activity of the enzyme enables the genetic information of HIV to become integrated permanently into the genome (chromosomes) of a host cell.

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Posted in: Microbiology

Plant Cell Structure

Plants are unique among the eukaryotes, organisms whose cells have membrane-enclosed nuclei and organelles, because they can manufacture their own food. Chlorophyll, which gives plants their green color, enables them to use sunlight to convert water and carbon dioxide into sugars and carbohydrates, chemicals the cell uses for fuel.

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Posted in: Microbiology

Bacteria Cell Structure

They are as unrelated to human beings as living things can be, but bacteria are essential to human life and life on planet Earth. Although they are notorious for their role in causing human diseases, from tooth decay to the Black Plague, there are beneficial species that are essential to good health.

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Posted in: Microbiology

Animal Cell Structure

Animal cells are typical of the eukaryotic cell, enclosed by a plasma membrane and containing a membrane-bound nucleus and organelles. Unlike the eukaryotic cells of plants and fungi, animal cells do not have a cell wall. This feature was lost in the distant past by the single-celled organisms that gave rise to the kingdom Animalia. Most cells, both animal and plant, range in size between 1 and 100 micrometers and are thus visible only with the aid of a microscope.

The lack of a rigid cell wall allowed animals to develop a greater diversity of cell types, tissues, and organs. Specialized cells that formed nerves and muscles—tissues impossible for plants to evolve—gave these organisms mobility. The ability to move about by the use of specialized muscle tissues is a hallmark of the animal world, though a few animals, primarily sponges, do not possess differentiated tissues. Notably, protozoans locomote, but it is only via nonmuscular means, in effect, using cilia, flagella, and pseudopodia.

The animal kingdom is unique among eukaryotic organisms because most animal tissues are bound together in an extracellular matrix by a triple helix of protein known as collagen. Plant and fungal cells are bound together in tissues or aggregations by other molecules, such as pectin. The fact that no other organisms utilize collagen in this manner is one of the indications that all animals arose from a common unicellular ancestor. Bones, shells, spicules, and other hardened structures are formed when the collagen-containing extracellular matrix between animal cells becomes calcified.

Animals are a large and incredibly diverse group of organisms. Making up about three-quarters of the species on Earth, they run the gamut from corals and jellyfish to ants, whales, elephants, and, of course, humans. Being mobile has given animals, which are capable of sensing and responding to their environment, the flexibility to adopt many different modes of feeding, defense, and reproduction. Unlike plants, however, animals are unable to manufacture their own food, and therefore, are always directly or indirectly dependent on plant life.

Most animal cells are diploid, meaning that their chromosomes exist in homologous pairs. Different chromosomal ploidies are also, however, known to occasionally occur. The proliferation of animal cells occurs in a variety of ways. In instances of sexual reproduction, the cellular process of meiosis is first necessary so that haploid daughter cells, or gametes, can be produced. Two haploid cells then fuse to form a diploid zygote, which develops into a new organism as its cells divide and multiply.

The earliest fossil evidence of animals dates from the Vendian Period (650 to 544 million years ago), with coelenterate-type creatures that left traces of their soft bodies in shallow-water sediments. The first mass extinction ended that period, but during the Cambrian Period which followed, an explosion of new forms began the evolutionary radiation that produced most of the major groups, or phyla, known today. Vertebrates (animals with backbones) are not known to have occurred until the early Ordovician Period (505 to 438 million years ago).

Cells were discovered in 1665 by British scientist Robert Hooke who first observed them in his crude (by today's standards) seventeenth century optical microscope. In fact, Hooke coined the term "cell", in a biological context, when he described the microscopic structure of cork like a tiny, bare room or monk's cell. Illustrated in Figure 2 are a pair of fibroblast deer skin cells that have been labeled with fluorescent probes and photographed in the microscope to reveal their internal structure. The nuclei are stained with a red probe, while the Golgi apparatus and microfilament actin network are stained green and blue, respectively. The microscope has been a fundamental tool in the field of cell biology and is often used to observe living cells in culture. Use the links below to obtain more detailed information about the various components that are found in animal cells.

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Posted in: Microbiology

Introduction to Cell and Virus Structure

At first glance, the petal of a flower or the skin on the back of a human hand may seem smooth and seamless, as if they were composed of a single, indistinct substance. In reality, however, many tiny individual units called cells make up these objects and almost all other components of plants and animals. The average human body contains over 75 trillion cells, but many life forms exist as single cells that perform all the functions necessary for independent existence. Most cells are far too small to be seen with the naked eye and require the use of high-power optical and electron microscopes for careful examination.

The relative scale of biological organisms as well as the useful range of several different detection devices are illustrated in Figure 1. The most basic image sensor, the eye, was the only means humans had of visually observing the world around them for thousands of years. Though excellent for viewing a wide variety of objects, the power of the eye has its limits, anything smaller than the width of a single human hair being able to pass unnoticed by the organ. Therefore, when light microscopes of sufficient magnifying capability were developed in the late 1600s, a whole new world of tiny wonders was discovered. Electron microscopes, invented in the mid-twentieth century, made it possible to detect even tinier objects than light microscopes, including smaller molecules, viruses, and DNA. The detection power of most electron microscopes used today, however, stops just short of being able to visualize such incredibly small structures as the electron orbital systems of individual atoms. Atoms are considered the smallest units of an element that have the characteristics of that element, but cells are the smallest structural units of an organism capable of functioning independently.

Yet, until the mid-seventeenth century, scientists were unaware that cells even existed. It wasn't until 1665 that biologist Robert Hooke observed through his microscope that plant tissues were divided into tiny compartments, which he termed "cellulae" or cells. It took another 175 years, however, before scientists began to understand the true importance of cells. In their studies of plant and animal cells during the early nineteenth century, German botanist Matthias Jakob Schleiden and German zoologist Theodor Schwann recognized the fundamental similarities between the two cell types. In 1839, they proposed that all living things are made up of cells, the theory that gave rise to modern biology.

Since that time, biologists have learned a great deal about the cell and its parts; what it is made of, how it functions, how it grows, and how it reproduces. The lingering question that is still being actively investigated is how cells evolved, i.e., how living cells originated from nonliving chemicals.

Numerous scientific disciplines—physics, geology, chemistry, and evolutionary biology—are being used to explore the question of cellular evolution. One theory speculates that substances vented into the air by volcanic eruptions were bombarded by lightning and ultraviolet radiation, producing larger, more stable molecules such as amino acids and nucleic acids. Rain carried these molecules to the Earth's surface where they formed a primordial soup of cellular building blocks.

A second theory proposes that cellular building blocks were formed in deep-water hydrothermal vents rather than in puddles or lakes on the Earth's surface. A third theory speculates that these key chemicals fell to earth on meteorites from outer space.

Given the basic building blocks and the right conditions, it would seem to be just a matter of time before cells begin to form. In the laboratory, lipid (fat) molecules have been observed joining together to produce spheres that are similar to a cell's plasma membrane. Over millions of years, perhaps it is inevitable that random collisions of lipid spheres with simple nucleic acids, such as RNA, would result in the first primitive cells capable of self-replication.

For all that has been learned about cells in over 300 years, hardly the least of which is the discovery of genetic inheritance and DNA, cell biology is still an exciting field of investigation. One recent addition is the study of how physical forces within the cell interact to form a stable biomechanical architecture. This is called "tensegrity" (a contraction of "tensional integrity"), a concept and word originally coined by Buckminster Fuller. The word refers to structures that are mechanically stable because stresses are distributed and balanced throughout the entire structure, not because the individual components have great strength.

In the realm of living cells, tensegrity is helping to explain how cells withstand physical stresses, how they are affected by the movements of organelles, and how a change in the cytoskeleton initiates biochemical reactions or even influences the action of genes. Some day, tensegrity may even explain the mechanical rules that caused molecules to assemble themselves into the first cells.

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Posted in: Microbiology