Thursday, 22 October 2020

Ground Cherry (Physalis angulata) Benefits

General Introduction:

Ground Cherry is wild grass if seen in general, people uproot this plant as it is a weed, but Physalis angulata have medicinal benefits. Ground cherry or physalis angulata is not found in every season, it appears in July-August. This plant cures many diseases, so do not throw it, if you can see it anywhere. Ground cherry plant is not usually available immediately if needed.


This plant is found in the plains. Apart from this, this plant is also found in Chhattisgarh in India and in countries like Sri Lanka, Australia, Africa. Cultivated in the Western Andes. It is mainly known in the US and Peruvian. It is in natural form in subtropical and tropical regions.

Kingdom: Plantae
Phylum: Spermatophyta
Subphylum: Angiospermae
Class: Dicotyledonae
Order: Solanales
Family: Solanaceae
Genus: Physalis
Species: angulata, ixocarpa, peruviana, alkekengi, minima, pubescens
Botanical Name: Physalis angulata, Physalis ixocarpa, Physalis peruviana, Physalis alkekengi, Physalis minima, Physalis pubescens

Common Name:

Chirpoti, Patpotani, Makoy, rasbhari, Cap Gooseberry, angular winter cherry, balloon cherry, cut leaf ground cherry, wild tomato, popti, periya-takkali, hogweed, Bush tomato, Indian gooseberry weed, etc.

Plant Description:

The botanical name of the Chirpoti plant or Cape Gooseberry - Physalis peruviana is a small plant. It is also called 'Makoy'. In Chhattisgarh, in western Uttar Pradesh, Patpotni and it is also called 'Chirpoti'. Along with it being a weed, many diseases are removed. This Ground Cherry (Physalis angulata) It is a small annual plant of the Solanasi family. This plant grows by seeds. Its leaves are dark green and thickly oval, its flowers light yellow; Its fruits are yellowish-orange inside a balloon-like calyx. Its outer covering is transparent. Eating its fruit feels bitter.

Ground Cherry or chirpoti home uses & Health Benefits:

Ground Cherry (Physalis peruviana) - This is an annual herb medicine plant. It is also a weed. But apart from being a weed, it is a medicinal plant, so it has the properties to remove many diseases. This plant is used for home remedies and benefits in many diseases.

Its many home remedies and benefits:

  • It is very important to take care of health in our life. But there are also many types of diseases. Doctors' medicines also do not work many times to prevent the disease, sometimes the domestic recipe works in this condition. There are many types of medicine plant which cures the disease. Among them, it is a Chirpoti plant.
  • Liver and stomach: By making a decoction of the leaves of the Chirpoti plant, drinking it increases digestive power and also increases appetite. And reduces inflammation in the liver.
  • Piles: In this disease, drinking decoction of leaves is beneficial. In addition, hiccups, cough, and who have trouble breathing. They should use the powder of its fruit.
  • Heart: This plant is also very beneficial for heart disease. It also reduces blood pressure. Using this fruit removes the problem of heart disease.
  • Low cholesterol: There are many types of diseases in our life. Eating too much oily food can cause serious illness such as cholesterol, but vitamin C and vitamin A being ground cherries can keep the body cholesterol low.
  • Treatment of Diabetes and cancer: This plant is found to have many disease-alleviating properties, which contain vitamin C in it, which helps a lot in the treatment of diabetes because it controls glucose and insulin. Cut leaf ground cherries are vitamin-C rich foods that can be cured with the use of this plant, including lung cancer and oral cancer.
  • Chemical Composition:

    Ground Cherry, which is a medicinal plant. But it is uprooted by many because it is a common weed. But many properties and chemical elements are found in this plant. Its leaves contain iron, phosphorus, vitamin C calcium, vitamin A. Apart from this, an element called carotene is also found which acts as an anti-oxidant.


    Many people may be allergic to this plant, they should stay away from it. Because it is found to be very low, limit its intake as excessive intake can also cause harm.

    Saturday, 20 June 2020

    Dudhiya Medicinal Plant

    Dudhiya (Euphorbia hirta): The special thing is that breaking the stem of this grass produces white milk, so it is called (Dudhiya) milky grass. Doodhiya grass This is a common grass but this medicine is grass. It is easily found anywhere. This grass is known by different names in many places. Such as - commonly Dudhi, Dudhiya grass, Dugdh grass, Doodhiya, Milky grass, Nagarjuni sapling, Shirak, Milk grass, Milk, Dudheli, milk squirt, milky latex, etc. are known by many names. This is an Ayurvedic medicine. This grass is usually found in the plains of all places. It is found more in India. It is mostly found in the village area. This grass is used as a domestic and herbal medicine.

    There are many plains of India where this milky grass is found. It is also found in other states like Chhattisgarh. Doodhiya plant It is mostly seen during the rainy season. This Doodhiya plant and other plants which are adjacent to the ground. They also appear only during the rainy season. This is because this Doodhi grass and its other species do not live during the heat and cold because all the grass which is adjacent to the ground.

    All the grass adjacent to the ground is eaten by ox and goat or other animals that eat grass. All the variables are taken, due to which these grasses are not visible during summer and winter. It is mainly of two types. Which looks the same but is red and green in color. This plant is found in fields, canals, drains, ponds, riverbanks, and around houses. Apart from Euphorbia hirta, it also belongs to other species, which are herbaceous grasses.
    Doodhiya Medicinal Plant

    Species of Dudhiya plant

    Euphorbia pilulifera
    Euphorbia thymifolia
    Euphorbia convolvuloides
    Euphorbia thymifolia linn

    Scientific classification

    Kingdom: Plante
    Clade: Angiosperm
    Order: Malpighiales
    Family: Euphorbiaceae
    Genus: Euphorbia
    Local name: Dudhiya Grass
    Botanical name: Euphorbia hirta Linn.


    The outer covering of this grass is as follows: its leaf is thick green and red. Its leaves are in opposite pairs on the stem. Its flower is white in color. The flowers are single, the fruits are three Volvo and its seeds are small, surrounded on all sides. It has a white or brown taproot.

    Home medicine use

  • It is used in home medicine. It cures many diseases such as Asthma, dysentery, prickling prickles, itching, and snake bite, this milky grass is used.
  • Many diseases are cured with the use of the milky plants, the use of this plant removes all the stomach problems such as stomach intestines, diarrhea, stomach pain, and stomach worms are cleaned.
  • Breaking the stalk of the milky plant which produces white milk, using this milk can remove facial spots.
  • This milky plant is used for relief from severe headaches, toothache, Asthama, and arthritis.
  • Applying one to two drops of milk of this milk grass once a day removes weakness of the eyes and benefits the eyes, especially which is not visible at night.
  • This milky grass eradicates thousands of diseases including impotence, infertility, and premature ejaculation.

  • Snakebite: Grind 10-15 leaves of milky grass and 6-7 black pepper together and use. Place it in the place where it is cut and give it to the person to eat.

    Itching: Milky grass is also used for itching, grinding it in 10-20 grams of fresh milky grass and mixing it with cow's butter, it is cleaned well after 3-4 hours.

    On pricking the thorns: On pricking the thorns, we apply a paste of milky grass.

    Chemical composition

    Some chemicals are found in milky grass such as Limonene, Carbucrol, Cymol, and Salicylic acid. Glycosides are found in the leaf and stem.


  • The excessive use of milky grass causes heart damage.
  • Pregnant women should not use this plant. The use of this milk plant will harm pregnant women.
  • Sunday, 14 June 2020

    Bacterial disaese in poplar plants

    It is a bacterial poplar tree disease in which large spots appear due to stem and branch. Its pathogen Pseudomonas syringae P.V. The syringe is Van Hall.

    Bacterial leaf spot and Canker in poplar

    Pathogen: Pseudomonas syringae PV. syringe van Hall


    • Leaf Spot: Leaf Spot Disease at Poplar Plant. This disease is found in this stem, branch, and branch. This symptom is seen in dead plants one to two years old where less canker is formed.
    • The leaves of the poplar plant sometimes appear yellow, sometimes forming large spots.
    • Terminal and side shoots turn black with blackback buds, black lesions appear on stem. These grains produce bacteria, which when dried appear as white deposits on the stem.


    Populus spp.: All species present in New Zealand are susceptible but leaf spotting is most prevalent on Populus ciliata, P. deltoides, P. szechuanica, P. trichocarpa, P. yunnanensis, and their hybrids.

    Salix spp.: All species present in New Zealand are susceptible. Stem and twig dieback is more common than leaf spotting on these species. Alnus cordata—Leaf spotting and twig dieback.

    Geographical Distribution

    Throughout New Zealand, particularly in localities with high summer rainfall.

    Disease Development

    Leaf symptoms first appear in spring when temperatures are rising and moisture levels are high. Throughout the growing season, during periods of continuous rainfall, spots are produced on new leaves. For example, a severe attack of Pseudomonas syringae occurred on foliage and stems of poplars growing in a nursery at Aokautere during a 4-month period when rainfall was 64% (194  mm) more than average, and it rained on 52 of that 120  days. Depending on the cultivar, spots may either remain discrete or merge, forming extensive blotches. In poplars, leaf spot is generally more common than stem cankering and is often seen on plants that do not exhibit any other symptoms.

    Bacterial leaf spot on a poplar leaf

    Fig. Bacterial leaf spot on a poplar leaf.

    Bacterial canker on poplar shoot

    Fig. Bacterial canker on poplar shoot.

    Formation of stem and twig cankers also depends on high moisture levels; however, symptoms vary, and sometimes stems may be roughly fissured or have sunken black lesions oozing bacteria. Sometimes the whole stem is affected, killing the plant; more often only the top one-third to one-half of the plant, or only lateral branches, is involved. When there is extensive shoot and twig dieback with blackened dead foliage the condition is referred to as “blast.” New shoots grow from below the infected areas on stems and branches. Although stem fissures and cankers may heal and the plant continues to grow, this often leaves a weak point that makes the plant susceptible to breakage in high winds.

    Some severe outbreaks of the disease occur when sudden frosts follow a warmer wet period. Approximately 50% of P. syringae isolates, tested from poplars and willows in New Zealand were capable of causing ice-nucleation. Ice-nucleating bacteria initiate the formation of ice crystals within host cells during frosts, and the combination of bacteria and frost causes more extensive tissue disruption than if either factor were present independently.

    Economic Importance

    Losses due to this disease are generally not great. Outbreaks of disease due to P. syringae on 1- and 2-year-old nursery-grown poplars are sporadic and very dependent on prevailing weather conditions. In rare instances, damage can be severe when P. syringae is combined with late frosts.


    Control of the disease is generally not warranted. Traditionally, copper-based inorganic compounds have been used to reduce bacterial populations but with only limited success. There is potential for biological control with competitive, nonpathogenic strains of other Pseudomonas species.

    Crown Gall in poplar

    Pathogen: Agrobacterium tumefaciens


    Crown gall caused by Agrobacterium tumefaciens can be a major nursery problem for the production of 1-year-old rooted plants of white poplars. Large galls may form at a ground level causing girdling of the main stem, poor growth, restricted shoot growth, and toppling. Large galls may occasionally form on the trunk of the older trees at the crown level or at first 1-2 m height from the crown level.

    Disease Cycle

    Crown gall bacterium exists in the soil and infects trees through wounds. The bacterium can be spread by ground-inhabiting insects, rain splash, irrigation, cultivation, pruning, and movement of infested soil particles. The bacterium is also spread from infected to healthy trees when infected trees are pruned or otherwise cut and the contaminated tools are used to prune healthy trees.

    Crown Gall in poplar

    Fig. Formation of gall at the crown region of a poplar tree. 

    Economic Importance

    The galls themselves may be considered unsightly. More important is that galls disrupt nutrient and water transport in the vascular tissues, which results in poor growth of young trees. Affected stems are weakened at the points of infection and can be invaded by organisms that cause discoloration and decay resulting in stem breakage.

    Wednesday, 3 June 2020

    Important plants used in Dentistry

    Medicinal plants are mostly used by domestic herbs. This herb cures many types of diseases, due to which people use it, it is used when any medicine advised by the doctor does not work. Medicinal plants are often used where there is less hospitalization and are mostly used by the villagers. The people of the village believe more in herbs. Many times, the big disease is also cured with herbs. Sometimes herbal medicine is also used.

    The medicinal plant cures many diseases. But in this article, the teeth are treated by a medicinal plant and the name of the medicinal plant will also be mentioned. The drugs described here are used to treat teeth.

     Six types of medical plants name and their use

    1. Aloe vera

    Aloe vera

    Aloe vera is mainly a medicinal plant that helps in fighting many types of diseases. These include chemical components such as anthraquinones, saccharides, and prostaglandins. Vitamins, minerals, enzymes, amino acids, gibberellins, cholesterol, uric acid, lignin, triglycerides, step-rides, salicylic acid, and beta-sitosterol. These are analgesic, antifungal, antioxidant immune-modulating, antibacterial, antiseptic, and anti-inflammatory. Aloe vera use has been associated with aphasia ulcers, chemical burns, toothpick injuries, lichen planus, dry sockets, periodontal surgery, gum boils, leukemia, and AIDS. It is used for gum problems, tongue and burning mouth, beneficial pemphigus, glossitis, migraine geographic syndrome. Used for candidiasis, acute monocytic leukemia denture mouth, vesiculobullous diseases, and xerostomia.

    2. Blood Root (Sanguinaria canadensis)

    Blood Root

    The major component of the bloodroot (Sanguinaria canadensis) is Sanguinarine, which has medicinal properties such as antibacterial and antifungal properties. This plant is mainly used for the treatment of enamel wounds, acute sore throat, gingivitis, and periodontal disease. However, it is considered unsafe in the case of children and pregnant or lactating women. When used for a long period of time such as glaucoma, abdominal pain, diarrhea, edema, heart disease, nausea and vomiting, miscarriage, visual changes, it has side effects.

    3. Cranberry (Vaccinium macrocarpon) 


    Cranberries have many medicinal properties and key components include flavonoids and polyphenols, which have antibacterial, antifungal, antiviral, anticarcinogenic, and antioxidant properties.

    4. Chamomile (Matricaria recutita) 


    The chemical composition of chamomile includes essential oils, volatile oils. Other components include flavonoids, α-bisabolol, luteolin, and related quercetin, sesquiterpenes, and apigenin. It has antibacterial and antiviral activity in the presence of its ingredients, major uses include gingivitis, periodontal disease. Usually, chamomile is considered safe during pregnancy or breastfeeding.

    5. Black Cohosh (Rhizoma Cimicifugae racemosae)

     Black Cohosh

    The components of black cohosh are acetylacetone, cycloartenol-based triterpenes action, 26 deoxy acetol, and imidazole. It is used for the treatment of periodontitis, although there is not much evidence and studies about it. It is contraindicated during pregnancy and breastfeeding and in children under 12 years of age. Minor adverse effects of black cohosh include headaches and gastrointestinal upset.

    6. Caraway (Carum carvi) 

     Caraway (Carum carvi)

    The pharmacological properties of caraway are antihistaminic, antimicrobial, antiseptic, spasmolytic, and flavoring agents. The major components of caraway are limonene (40%) and carvone (50–60%). It also contains 3–7% volatile oil.

    Saturday, 9 May 2020

    Plant structure ( Morphology and Anatomy)

    In this article, we are providing information about plant structure include anatomy and morphology, you can also know cell wall structure and more. The state of the plant is very diverse, not only among its many phyla but also within species. Many of these have become extinct, with distinct distinctions in the body parts of the oldest vascular plants such as roots and leaves.

    Figure. Morphological plant structure.

    The presence of these organs reflects increased specialization, especially among modern vascular plants in relation to the demands of terrestrial existence. Obtaining water, for example, is a major challenge, and roots are adapted for water absorption from the soil. Leaves, roots, branches, and flowers all vary in size from plant to plant.
    The development of the plant structure can be precisely controlled as these parts, but some aspects of leaf, stem, and root development are quite flexible. This article emphasizes the integrated aspects of plant form, using a flowering plant as a model.

    Vascular plants have roots and shoots

    The avascular plant has a root system and a pellet system. Among their tips are roots and shoots, called apes.
    The root system anchors the plant and enters the soil, allowing it to absorb water and ions to nourish the plant. Root systems are often widespread, which can produce great strength to advance growing roots. Roots evolved later than the shoot system as an adaptation to living on land.

    Structure of plant cell wall

    Figure. Anatomy structure of plant cell wall.

    The shoot system consists of leaves and stems. The major sites of photosynthesis serve as a scaffold for the position of the stem leaves, the arrangement, shape, and other characteristics of the leaves are important in the production of plant food. Flowers, other reproductive organs, and ultimately, fruits and seeds are also formed on the shoot.

    The repeating unit of the vegetative shoot consists of the internode, node, leaf, and axillary bud, but not reproductive structures. An axillary bud is the latest shoot apex that allows the plant to replace a branch or main shoot if it is eaten by a shepherd. A vegetative axillary bud has the capacity to replace the primary shoot. When the plant is transferred to the reproductive stage of development, these axillary buds can produce flower shoots.

    The root and the shoots are made up of three types of tissue

    Plant cell types can be distinguished by the size of their vacuoles, whether they are living or not at maturity, and by the thickness of their cellulose cell walls, a distinguishing feature of plant cells. Some cells have only a primary cell wall of cellulose, synthesized by the protoplast near the cell membrane. Microtubules align within the cell and determine the orientation of the cellulose fibers. Cells that support the plant body have more heavily reinforced cell walls with multiple layers of cellulose and other strengthening molecules, including lignin and pectin. Cellulose layers are laid down at angles to adjacent layers like plywood; this enhances the strength of the cell wall.

    The sprouts, roots, and leaves all have three types of basic tissue: ground, dermal, and vascular tissue. Because each of these tissues extends through the root and shoot systems, they are called tissue systems. In most plants, the cell layer of the epidermis, and cutaneous tissue is thick, and it forms an outer protective covering for the plant. Ground tissue cells perform storage, photosynthesis functions in addition to supporting plants and making protective fibers. Vascular tissue carries fluids and dissolved substances throughout the body. Each of these issues and their many functions are described in more detail in later sections.

    New growth occurs at meristems

    When a seed sprout, only a tiny portion of the adult plant exists. Although embryonic cells can undergo division to form many types of cells, most adult cells are more restricted. The development of the plant body is based on the activity of shoots and root apices as well as properties found in other parts of the plant. depends on. Meristem cells are indifferent which can divide indefinitely and give rise to many differentiated cells.

    Overview of meristems

    Meristems are clusters of small cells with dense cytoplasm and proportionately large nuclei that act as stem cells do in animals. One cell divides to give rise to two cells, one of which remains meristematic, while the other contributes to the body of the plant. In this way, cells of the meristem continuously renew. 

     Meristem cell division

    Figure.  Meristem cell division.

    Molecular genetic evidence supports the hypothesis that animal stem cells and plant meristem cells may share some of the commonest of gene expression. For example, both plant meristem and animal stem cells share the Retinoblastoma gene, which determines whether a cell continues dividing or differentiates. The expanding cell of both the root and shoot results in repeated divisions and subsequent elongation of the cells produced by the epistemic merge. In woody plants, lateral meristems produce an increase in root and shoot diameter.

    Apical meristems

    The apical meristem and roots are located at the tips showing in this anatomy structure diagram. The cells of the epistemic meristem divide, during the period of development, and continuously add more cells to the tips. The tissues derived from the apical meristems are called primary tissues, the expansion of the root and stem is known as the primary plant body structure. Some plants have young, soft sprouts and a tree body in the primary plant body. Both the root and shoot apical meristems are made up of fragile cells that need protection. The root apical meristem is protected by the root cap, the anatomy of which is described in section 36.3. Root meristem cells are formed by the root cap, closed and transferred to the root through the soil. In contrast, the leaf primordia give rise to the shoot apical meristem, which is particularly susceptible to desiccation due to exposure to air and sun.

     Apical meristems

    Figure. Anatomy structure of Apical meristems.

    The apical meristem gives rise to the three tissue systems by first initiating primary meristems. The three primary meristems are the protoderm, which forms the epidermis; the procambium, which produces primary vascular tissues (primary xylem for water transport and primary phloem for nutrient transport); and the ground meristem, which differentiates further into ground tissue. In some plants, such as horsetails and corn, intercalary meristems arise in stem internodes (spaces between leaf attachments), adding to the internode lengths. If you walk through a cornfield on a quiet summer night when the corn is about knee-high, you may hear a soft popping sound. This sound is caused by the rapid growth of the intercalary meristems. The amount of stem elongation that occurs in a very short time is quite surprising.

    Lateral meristems

    Many herbaceous plants (that is, plants with fleshy, not woody, stems) exhibit only primary growth, but others also exhibit secondary growth, which may result in a substantial increase of diameter. In anatomy structure of Secondary growth is accomplished by the lateral meristems—peripheral cylinders of meristematic tissue within the stems and roots that increase the girth (diameter) of gymnosperms and most angiosperms. Lateral meristems form from ground tissue that is derived from apical meristems. Monocots are the major exception.

    Although secondary growth increases girth in many nonwoody plants, its effects are most dramatic in woody plants, which have two lateral meristems. Within the bark of a woody stem is the cork cambium—a lateral meristem that contributes to the outer bark of the tree. Just beneath the bark is the vascular cambium—a lateral meristem that produces secondary vascular tissue. The vascular cambium forms between the xylem and phloem in vascular bundles, adding secondary vascular tissue to both of its sides. Xylem is added to the inside of the vascular cambium, and the phloem is added to the outside.

    Apical and lateral meristems.

    Figure. Anatomy structure of Apical and lateral meristems.

    In this anatomy structure, Secondary xylem is the main component of wood. Secondary phloem is very close to the outer surface of a woody stem. Removing the bark of a tree damages the phloem and may eventually kill the tree. Tissues formed from lateral meristems, which comprise most of the trunk, branches, and older roots of trees and shrubs, are known as secondary tissues and are collectively called the secondary plant body.

    Friday, 24 April 2020

    Basic Structure and Function of DNA

    DNA, Chromosomes, and genomes

    The ability of organisms necessary to sustain life depends on the ability of cells to store and translate by translating and retrieving genetic instructions. This hereditary information is passed on from a cell to its daughter cells at cell division, and from one generation of an organism to the next through the organism’s reproductive cells. The instructions are stored within every living cell as its genes, the information-containing elements that determine the characteristics of a species as a whole and of the individuals within it.

    As soon as genetics emerged as a science at the beginning of the twentieth century, scientists became intrigued by the chemical structure of genes. The information in genes is copied and transmitted from cell to daughter cell millions of times during the life of a multicellular organism, and it survives the process essentially unchanged. What form of a molecule could be capable of such accurate and almost unlimited replication and also be able to exert precise control, directing multicellular development as well as the daily life of every cell? And how can the enormous amount of information required for the development and maintenance of an organism fit within the tiny space of a cell?.

    The answers to several of these questions began to emerge in the 1940s. At this time researchers discovered, from studies in simple fungi, that genetic information consists largely of instructions for making proteins. Proteins are phenomenally versatile macromolecules that perform most cell functions. They serve as building blocks for cell structures and form the enzymes that catalyze most of the cell’s chemical reactions. They also regulate gene expression and they enable cells to communicate with each other and to move The properties and functions of cells and organisms are determined to a great extent by the proteins that they are able to make.

    Painstaking observations of cells and embryos in the late nineteenth century had led to the recognition that the hereditary information is carried on chromosomes—threadlike structures in the nucleus of Light microscopy that makes a cell visible by eukaryotic as soon as the cell begins to divide. Later, when the biochemical analysis was possible, the chromosomes were found to contain deoxyribonucleic acid DNA and protein, both of which were present in approximately equal amounts. For many decades, DNA was considered only a structural one. However, the other crucial advance made in the 1940s was the identification of DNA as the likely carrier of genetic information. This breakthrough in our understanding of cells came from studies of inheritance in bacteria.

    But still, as the 1950s began, both how proteins could be specified by instructions in the DNA and how this information might be copied for transmission from cell to cell seemed completely mysterious. The puzzle was suddenly solved in 1953 when James Watson and Francis Crick derived the mechanism from their model of DNA structure. The determination of the double-helical structure of DNA immediately solved the problem of how the information in this molecule might be copied, or replicated. It also gave the first clue as to how DNA uses a sequence of its subunits to form a molecule protein and encode a directive. Today, the fact that DNA is the genetic material is so fundamental to biological thought that it is difficult to appreciate the enormous intellectual gap that was filled by this breakthrough discovery.

    The DNA structure of the chemical properties of DNA makes it ideally suited as the raw material of genes. This DNA arranges how many proteins and packages in chromosomes. The packing has to be done in an orderly fashion so that the chromosomes can be replicated and apportioned correctly between the two daughter cells at each cell division. And it must also allow access to chromosomal DNA, both for the enzymes that repair DNA damage and for the specialized proteins that direct the expression of its many genes.

    In the past two decades, there has been a revolution in our ability to determine the exact order of subunits in DNA molecules. As a result, we now know the sequence of the 3.2 billion nucleotide pairs that provide the information for producing a human adult from a fertilized egg, as well as having the DNA sequences for thousands of other organisms. Detailed analyses of these sequences are providing exciting insights into the process of evolution.

    This is the first of four chapters that deal with basic genetic mechanisms—the ways in which the cell maintains, replicates, and expresses the genetic information carried in its DNA. We shall discuss the mechanisms by which the cell accurately replicates and repairs DNA; we also describe how DNA sequences can be rearranged through the process of genetic recombination. Gene expression—the process through which the information encoded in DNA is interpreted by the cell to guide the synthesis of proteins—is we describe how this gene expression is controlled by the cell to ensure that each of the many thousands of proteins and RNA molecules encrypted in its DNA is manufactured only at the proper time and place in the life of a cell.

    The Structure and Function of DNA

    The molecule seemed too simple: a long polymer composed of only four types of nucleotide subunits, which resemble one another chemically. In the early 1950s, by X-ray analysis of DNA, a technique for determining the three-dimensional atomic structure of a molecule. Initially X-ray diffraction results in two strands of DNA polymer lesion formed in the helix. The observation that DNA was double-stranded provided one of the major clues that led to the Watson–Crick model for DNA structure that, as soon as it was proposed in 1953, made DNA’s potential for replication and information storage apparent.

    The nucleotide DNA molecule has two complementary chains

    Deoxyribonucleic acid (DNA) the molecule consists of two long polynucleotide chains composed of four types of nucleotide subunits. The chains run antiparallel to each other, and hydrogen bonds between the base portions of the nucleotides hold the two chains together nucleotides are composed of a five-carbon sugar to which are attached one or more a nitrogen-containing based and phosphate groups. Among nucleotides, a single phosphate group is deoxyribose attached to sugar, and its base may be either adenine (A), cytosine (C), guanine (G), or thymine (T). Nucleotides are covalently linked together in a series of phosphates and sugars, which thus "sugar" the sugar-phosphate-sugar-phosphate alternatively. Because only the base differs in each of the four types of nucleotide subunit, each polynucleotide chain in DNA is analogous to a sugar-phosphate necklace (the backbone), from which hang the four types of beads the bases A, C, G, and T. These same symbols A, C, G, and T) are commonly used to denote either the four bases or the four entire nucleotides—that is, the bases with their attached sugar and phosphate groups.
    Building blocks of DNA diagram
    Fig. DNA and its building blocks

    The way in which the nucleotides are linked together gives a DNA strand a chemical polarity. If we think of each sugar as a block with a protruding knob (the 5 ʹ phosphates) on one side and a hole (the 3 ʹ hydroxyls) each completed Interlocking series with holes made by knobs, all of its subunits will be lined up in the same orientation.  Moreover, the two ends of the chain will be easily distinguishable, as one has a hole (the 3 ʹ hydroxyls) and the other a knob (the 5 ʹ phosphates) at its terminus. This polarity in a DNA chain is indicated by referring to one end as the 3 ʹ ends and the other as the 5 ʹ ends, names derived from the orientation of the deoxyribose sugar. With respect to DNA’s information-carrying capacity, the chain of nucleotides in a DNA strand, being both directional and linear, can be read in much the same way as the letters on this page.
    DNA Complementary base pairs diagram

    Fig.  Complementary base pairs in the DNA double helix.

    The three-dimensional structure — the double helix of DNA — arises from the structural and chemical characteristics of its two polynucleotide chains. Because the two chains are held together by hydrogen bonding based on different strands, all the bases are inside the double helix, and the sugar-phosphate backbones are paired with a single-ring base (a pyrimidine): A always pairs with T, and G with C.This complementary base-pairing enables the base pairs to be packed in the interior of the double helix has the most energetically friendly arrangement. In this arrangement, each base pair is of similar width, thus holding the sugar-phosphate backbones a constant distance apart along the DNA molecule. To maximize the efficiency of base-pair packing, the two sugar-phosphate backbones wind around each other to form a right-handed double helix, with one complete turn every ten base pairs.

    The members of each base pair can fit together within the double helix only if the two strands of the helix are antiparallel—that is, only if the polarity of one Is oriented opposite to the other strand. A consequence of DNA’s structure and base-pairing requirements is that each strand of a DNA molecule contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand.

    DNA structure for the mechanism of heredity

    The discovery of the structure of DNA immediately suggested answers to the two most fundamental questions about heredity. First, how could the information specify an organism be carried in a chemical form? And second, how could this information be duplicated and copied from generation to generation?
    The answer to the first question came from the realization that DNA is a linear polymer of four different kinds of monomer, strung out in a defined sequence like the letters of a document written in an alphabetic script.

    The answer to the second question came from the double-stranded nature of the structure: because each strand of DNA contains a sequence of nucleotides that is exactly complementary to each strand can serve as a template for the synthesis of a strand complementary to the nucleotide sequence of its new partner strand. In other words, if we designate the two DNA strands as S and S ʹ, strand  S can serve as a template for making a new strand S ʹ, while strand S ʹ can serve as a template for making a new strand S.Thus, the genetic information in DNA can be accurately copied by the beautifully simple process in which strand S separates from strand S ʹ, and each separated strand then serves as a template for the production of a new complementary partner strand that is identical to its former partner.
    DNA double helix diagram

    Fig. The DNA double helix

    The ability of each strand of a DNA molecule to act as a template for producing a complementary strand enables a cell to copy or replicate, its genome before passing it on to its descendants. We shall describe the elegant machinery that the cell uses to perform this DNA. Before determining the structure of DNA, genes contain instructions for the production of proteins. If genes are made of DNA, the DNA must therefore somehow encode proteins. A protein that is responsible for a biological function is characterized by its three-dimensional structure. This structure is determined in turn by the linear sequence of the amino acids of which it is composed. The exact correspondence between the four-letter nucleotide alphabet of DNA and the twenty-letter amino acid alphabet of proteins—the genetic code—is not at all obvious from the DNA structure. We will describe this code in detail in the course of elaborating the process of gene expression, through which a cell converts the nucleotide sequence of an RNA molecule first consists of genes, then an amino acid sequence of the protein.
     Duplication of DNA diagram

    Fig. DNA as a template for its own duplication

    The complete store of information in an organism’s DNA is called its genome, and it specifies all the RNA molecules and proteins that the organism will ever synthesize. The amount of information contained in genomes is staggering. The nucleotide sequence of a very small human gene, written out in the four-letter nucleotide alphabet, while the complete sequence of nucleotides in the human genome would fill more In addition to other critical information, it includes roughly 21,000 protein-coding genes, which give rise to a much greater number of distinct proteins.

    In Eukaryotes, DNA Is Enclosed in a Cell Nucleus

    Nearly all the DNA in a eukaryotic cell is sequestered in a nucleus, which in many cells occupies about 10% of the total cell volume. This compartment is delimited by a nuclear envelope formed by two concentric lipid bilayer membranes. These membranes are punctured at intervals by large nuclear pores, through which molecules move between the nucleus and the cytosol. The nuclear envelope is directly connected to the extensive system of intracellular membranes called the endoplasmic reticulum, which extends out from it into the cytoplasm. And it is mechanically supported by a network of intermediate filaments called the nuclear lamina—a thin feltlike mesh just beneath the inner nuclear membrane.
    The nuclear envelope allows the many proteins that act on DNA to be concentrated where they are needed in the cell, and it also keeps nuclear and cytosolic enzymes separate, a feature that is crucial for the proper functioning of eukaryotic cells.