Introduction to the Medical Biology. General characteristic of the life. Structural and functional organization of cells and viruses.Lector: professor Fedonyuk L.Ya.

Questions for discussion:General and medical Biology as the sciences. Levels of living organization.Characteristics of living things.The cell theory in its modern form.Cellular level of life organization: -prokaryotic and eukaryotic cells -the differences between plant and animal cells.The main components of eukaryotic cell.Cell membrane (plasmalemma)Cytoplasm (organelles and inclusions)Nucleus

Biology literally means "the study of life".

Biology is such a broad field, covering the minute workings of chemical machines inside our cells, to broad scale concepts of ecosystems and global climate change.

Biologists study intimate details of the human brain, the composition of our genes, and even the functioning of our reproductive system.

Biologists recently all but completed the deciphering of the human genome, the sequence of deoxyribonucleic acid (DNA) bases that may determine much of our innate capabilities and predispositions to certain forms of behavior and illnesses. DNA sequences have played major roles in criminal cases (OJ. Simpson, as well as the reversal of death penalties for many wrongfully convicted individuals), as well as the impeachment of President Clinton (the stain at least did not lie). We are bombarded with headlines about possible health risks from favorite foods (Chinese, Mexican, hamburgers, etc.) as well as the potential benefits of eating other foods such as cooked tomatoes. Infomercials tout the benefits of metabolism-adjusting drugs for weight loss.

Modern biology is based on several great ideas, or theories:The Cell Theory The Theory of Evolution Gene Theory Homeostasis

Levels of living organizationBiosphere Ecosystem Community Populations IndividualsOrgan SystemOrganTissueCellOrganelleMolecule

LEVELS OF LIVING ORGANIZATION

MICROSYSTEMS

molecular(size - 1 nm)

subcellular(size - 1 nm 100 nm)

cellular(size 0,2 20 mkm)

MESOSYSTEMS

Tissue(size 10-100 mkm)

Organ(size - 0,1 mm and more)

Organism(size 1 sm and more)

MACROSYSTEM

Community

Ecosystem

Biosphere

Levels of living organizationBiosphere Ecosystem Community Populations IndividualsOrgan SystemOrganTissueCellOrganelleMolecule

Levels of living organizationBiosphere Ecosystem Community Populations IndividualsOrgan SystemOrganTissueCellOrganelleMolecule

Population level

Community level (I)A community is the set of all populations that inhabit a certain area. Communities can have different sizes and boundaries. These are often identified with some difficulty.An ecosystem is a higher level of organization the community plus its physical environment. Ecosystems include both the biological and physical components affecting the community/ecosystem. We can study ecosystems from a structural view of population distribution or from a functional view of energy flow and other processes.

Community level (II)There are two basic categories of communities: terrestrial (land) and aquatic (water). These two basic types of community contain eight smaller units known as biomes. A biome is a large-scale category containing many communities of a similar nature, whose distribution is largely controlled by climateTerrestrial Biomes: tundra, grassland, desert, taiga, temperate forest, tropical forest. Aquatic Biomes: marine, freshwater

BiosphereThe sum of all living things taken in conjunction with their environment. In essence, where life occurs, from the upper reaches of the atmosphere to the top few meters of soil, to the bottoms of the oceans. We divide the earth into atmosphere (air), lithosphere (earth), hydrosphere (water), and biosphere (life)

Levels of the living organization

MAIN METHODS OF SCIENTIFIC INVESTIGATIONlight microscopy;lectron microscopy;

Steps in the scientific method commonly include: Observation: defining the problem you wish to explain. Hypothesis: one or more falsifiable explanations for the observation. Experimentation: Controlled attempts to test one or more hypotheses. Conclusion: was the hypothesis supported or not? After this step the hypothesis is either modified or rejected, which causes a repeat of the steps above.

ROBERT HOOKE microscope

ANTON VAN LEEUWENHOEK microscope

Characteristics of living thingsuse energy have a metabolism - the building up and breaking down of chemicals grow and develop become larger and more complex respond to their surrounding reproduce- produce offspring that are similar to the parents have the chemicals of life, carbohydrates, proteins, lipids and nucleic acids (genetic material) have cells The fundamental characteristics of living things:reproduction (self-reproduction), which is the process that gives rise to offspring; genes (self-renewal) are the units of inheritance, passed prom parent to offspring, that control many daily functions. Finally, populations of living organisms adjust to environment variations through evolution, a change in the traits of a species over time (self-regulation).

CELLULAR LEVEL OF LIVING ORGANIZATION

no cellular living forms - viruses

CLASSIFICATION OF CELLSAccording to the cells nucleus presence:Prokariotic Eukaroitic2. According to the nature:Plant cellsAnimal cells3. According to the type:Somatic cellsSex cells

cellular living forms - cells

Kingdoms of living organisms

Monera Monera, the most primitive kingdom, contain living organisms remarkably similar to ancient fossils. Organisms in this group lack membrane-bound organelles associated with higher forms of life. Such organisms are known as prokaryotes. Bacteria (technically the Eubacteria) and blue-green bacteria (sometimes called blue-green algae, or cyanobacteria) are the major forms of life in this kingdom. The most primitive group, the archaebacteria, are today restricted to marginal habitats such as hot springs or areas of low oxygen concentration.

ProtistaProtista were the first of the eukaryotic kingdoms, these organisms and all others have membrane-bound organelles, which allow for compartmentalization and dedication of specific areas for specific functions. The chief importance of Protista is their role as a stem group for the remaining Kingdoms: Plants, Animals, and Fungi. Major groups within the Protista include the algae, euglenoids, ciliates, protozoa, and flagellates.

FungiFungi are almost entirely multicellular (with yeast, Saccharomyces cerviseae, being a prominent unicellular fungus), heterotrophic (deriving their energy from another organism, whether alive or dead), and usually having some cells with two nuclei (multinucleate, as opposed to the more common one, or uninucleate) per cell. Ecologically this kingdom is important (along with certain bacteria) as decomposers and recyclers of nutrients. Economically, the Fungi provide us with food (mushrooms; Bleu cheese/Roquefort cheese; baking and brewing), antibiotics (the first of the wonder drugs, Penicillin, was isolated from a fungus Penicillium), and crop parasites (doing several billion dollars per year of damage).

Plantae Plantae include multicelled organisms that are all autotrophic (capable of making their own food by the process of photosynthesis, the conversion of sunlight energy into chemical energy). Ecologically, this kingdom is generally (along with photosynthetic organisms in Monera and Protista) termed the producers, and rest at the base of all food webs. A food web is an ecological concept to trace energy flow through an ecosystem. Economically, this kingdom is unparalleled, with agriculture providing billions of dollars to the economy (as well as the foundation of "civilization"). Food, building materials, paper, drugs (both legal and illegal), and roses, are plants or plant-derived products.

AnimaliaAnimalia consists entirely of multicelluar heterotrophs that are all capable (at some point during their life history) of mobility. Ecologically, this kingdom occupies the level of consumers, which can be subdivided into herbivore (eaters of plants) and carnivores (eaters of other animals). Humans, along with some other organisms, are omnivores (capable of functioning as herbivores or carnivores). Economically, animals provide meat, hides, beasts of burden, pleasure (pets), transportation, and scents (as used in some perfumes).

Cell theory

ROBERT HOOKE- first (1665) looked at a slice of dried cork. He noticed that plant tissues are made up of small, regulatory cavities surrounded by walls. Hooke called this cell. ANTON VAN LEEUWENHOEK made his own lenses made first compound microscope drew pictures that we can still identify today SCHLEIDEN concluded all plants are made of cellsTEODOR SCHWANN concluded all living things are made up of cells. The first strong statement that all living organisms consist of cell was made by him in 1839. In 1858 Rudolf Virchov suggested that all cells come from pre-existing cells. ROBERT HOOKE- first to look at cells looked at a thin section of corkANTON VAN LEEUWENHOEK made his own lenses made first compound microscope drew pictures that we can still identify today Schleiden concluded all plants are made of cells Schwann concluded all living things are made up of cells

MAIN PRINCIPLES OF THE CELL THEORY: 1. All organisms are composed of one or more cells, within which the life processes of metabolism and hereditary occur.2. Cells are the smallest living things, the basic unit of organization of all organisms.3. Cells arise only by division of a previously existing cell.

The cell is the basic unit of life. Microorganisms such as bacteria, yeast, and amoebae exist as single cells. By contrast, the adult human is made up of about 30 trillion cells (1 trillion = 1012) which are mostly organized into collectives called tissues.

Properties - biomembrane enclosed - four biomolecules: proteins, polysacharides, nucleic acids, lipids - metabolism and energy transformation

Lots of shapes and sizes

What are the differences between prokaryotic and eukaryotic cells?Kindoms Kindoms1. Monera (Fubacteria) 1. Protista2. Archaea (Archaebacteria) 2. Fungi 3. Plantae 4. AnimaliaCharacteristics Characteristics1. Lack a nuclear membrane 1. Have a nuclear membrane2. Have no membrane bound organels 2. Have membrane bound organels

Current evidence indicates that eukaryotic evolved from prokaryotic between 1 and 1,5 billion years ago

Eukaryotic cell hasthree main components: 1) nucleus; 2) cytoplasm; 3) cell membrane.

Separates the living cell from its nonliving surroundings. It is 7,5-11nm (that is, 7,5-11 billionths of a meter) thick. This membrane envelops the cell, and nothing can enter or leave the cell without crossing it.

CELL MEMBRANE (plasma membrane)

Plasma membrane Composed of:outer leaflet GLYCOCALIX facing the extracellular environment

lipid bilayer with associated proteins BIOLOGICAL MEMBRANE)

inner leaflet CORTICAL LAYER facing the cytoplasm

Biological membrane Organization: The widely accepted fluid mosaic model describes biologic membranes as protein icebergs in a lipid sea. It is omposed of lipid bilayer and associated proteins.

Lipids are present in cell membranes as phospholipids, sphingolipids, and cholesterol. Each phospholipid molecule has a polar (hydrophilic) phosphate-containing head group and a nonpolar (hydrophobic) pair of fatty-acid tails. Membrane phospholipids are arranged in a bilayer with their tails directed toward one another at the center of the membrane. In electron micrographs of osmium-stained tissue, a single membrane, or unit membrane, has 2 dark outer lines with a lighter layer between them.1 heads; 2 tails; 3 integral proteins.

Fluid-mosaic structure of the cell membrane

Protein may comprise over 50 % of membrane weight. Most membrane proteins are globular and belong to one of the following 2 groups:

Integral membrane proteins are tightly lodged in the lipid bilayer; detergents are required to extract them. They are folded, with their hydrophilic amino acids in contact with the phosphate groups of the membrane phospholipids and their hydrophobic amino acids in contact with the fatty-acid tails. Some protrude from only one membrane surface, while others, called transmembrane proteins, penetrate the entire membrane and protrude from both sides.

b. Peripheral membrane proteins are more loosely associated with the inner or outer membrane surface; some are globular, some filamentous.

Cell membrane proteins

GLYCOCALYXCarbohydrates occur on plasma membranes mainly as oligosaccharide moieties of membrane glycoproteins and glycolipids. Membrane oligosaccharides have a characteristic branching structure and project from the cells outer surface, forming a superficial coat called the glycocalyx that participates in cell adhesion and recognition.

Glycocalyxis a sugar coat commonly associated with the extracytoplasmic aspects of the outer leaflet of plasma membrane (in animal cells). Functions aiding in cellular attachment to extracellular matrix components binding of cellular and enzymes to the cell

CORTICAL LAYERIs located inside the cytoplasm of the cell. It is composed by microtubules and microfilaments, which formed the cytoskeleton of the cell. Aids in cellular support and movement.Cytoskeleton is composed of three components:1.Microfilaments - globular protein (actin)- support and cellular contraction2.Intermediate filaments - fibrous protein- support3.Microtubles - globular protein (tubulin)- support and cell motility

In these cells, actin filaments appear light purple, microtubules yellow, and nuclei greenish blue. This image, which has been digitally colored, won first place in the 2003 Nikon Small World Competition.

FUNCTIONS OF THE CELL MEMBRANE:

Acts as selective barrier

Regulate movement of material into and out of the cell

Cellular recognition

Plasma Membrane Transport Processes.These processes include transport of a single molecule (uniport) or cotransport of two different molecules in the same (symport) or opposite (antiport) direction.

Passive transport includes simple and facilitated diffusion. Neither of these processes requires energy because molecules move across the plasma membrane down a concentration or electrochemical gradient.1. Simple diffusion transports small nonpolar molecules (02 and N2) and small, uncharged, polar molecules (H20, C02, and glycerol). 2. Facilitated diffusion occurs via ion channel and/or carrier proteins, structures that exhibit specificity for the transported molecules. It is faster than simple diffusion.3. Osmosis is the diffusion of water across a selectively permeable membrane in response to its concentration gradient.

Active transportis an energy-requiring process which transports a molecule against an electrochemical gradient via carrier proteins.Na+-K+pump. The Na+-K+ pump involves the antiport transport of Na+ and K+ ions mediated by the carrier protein, Na+-K+ ATPase.Na+ ions are pumped out of the cell and two K+ ions are pumped into the cell.

Comparison active and passive transport

Exocytosisis way that substances can exit cells. Part of the plasma membrane pinches off and forms a small membrane-bound sac, or vesicle, around some substance. Vesicles even form around tiny cells (such as a bacterium) and fluids. In exocytosis vesicles form inside the cytoplasm and then move to the plasma membrane and fuse with it, so that their contents are moved to the outside.

Endocytosis is way that substances can exit cells. a patch of plasma membrane encloses material at the cell surface. it sinks in and pinches off, forming a vesicle that either transports the material into the cytoplasm or stores it there.

PhagocytosisPhagocytosis (cell eating) is transport process by which amoeboid-type cells engulf large material, forming an intracellular vacuole.

PinocytosisWhen macromolecules are taken in by endocytosis, the process is called Pinocytosis (cell drinking), and the result is formation of vesicle.

Both phagocytic vacuoles and pinocytic vesicles can fuse with lysosomes, whose enzymes digest their contents.

CYTOPLASM- inner environment of the cell, working apparatus, were take place main metabolic processes

ORGANELLES are membrane-bound, enzyme-containing, permanent subcellular compatrmentsOrganelles are divided to: general (are present in all cells) special (are present only in some)

General organelles:Mitochondria and plastidsRibosomesEndoplasmic reticulumGolgi apparatus (complex)LysosomesPeroxisomesVacuolesCell centerMicrotubulesMicrofilamentsSpecial organelles:tonofibrils,neurofibrils,myofibrils,villi,flagella.

Mitochondria and plastidsEndoplasmic reticulumGolgi apparatus (complex)LysosomesPeroxisomesVacuoles

RibosomesCell centerMicrotubulesMicrofilamentsMembranedorganellesNonmembaned organellesMICROSCOPIC

SUBMICROSCOPIC

MITOCHONDRION general microscopic membraned organelle

The largest of the cytoplasmic organelles, mitochondria are the energy providers (powerhouses) of the cell.Structure. Mitochondria are comparable in size to bacteria (usually 2-6 mm in lenght and 0.2 mm in diameter but quite variable) and have various shapes: spheric, ovoid, filamentous. Each mitochondrion is bounded by 2 unit membranes.The outer mitochondrial membrane has a smooth contour and forms a continuous but relatively porous covering. It is freely permeable to various small molecules.The inner mitochondrial membrane is less porous and is therefore semipermeable. It has numerous infoldings, or cristae, that project into the mitochondrions interior. The mitochondrial cristae of most cells are shelflike, but those in steroid-secreting cells are typically more tubular.

MitochondrionThe mitochondrial membranes create 2 membrane-limited spaces. The intermembrane space is located between the inner and outer membranes and is continuous with the interacristal space that extends into the cristae. The intercristal space, or matrix space, is enclosed by the inner membrane and contains the mitochondrial matrix.The mitochondrial matrix contains water, solutes, and large matrix granules, believed to be concerned with mitochondrial calcium-ion concentrations. It also contains circular DNA and mitochondrial ribosomes similar to those of bacteria.

Mitochondrion Function. Mitochondria provide the cell with the energy for chemical and mechanical work by storing energy generated from cellular metabolites in the high-energy bonds of ATP. Location. Mitochondria are found in nearly all eukaryotic cells, and in most they are dispersed throughout the cytoplasm. However, they accumulate in the highest concentrations in cell types and intracellular regions with the highest energy requirements. Cardiac muscle cells are notable for the abundance of their mitochondria. Epithelial cells lining the kidney tubules have abundant mitochodria interdigitated between basal plasma membrane infoldings where active transport of ions and water occurs.

Plastids are membrane-bound organelles that only occur in plants and photosynthetic eukaryotes.

Plastids

roughsmoothENDOPLASMIC RETICULUM -general submicroscopic membraned organelle The endoplasmic reticulum is a complex organelle involved in the synthesis, packaging, and processing of various cell substances. It is a freely anastomosing network (reticulum) of membranes that form cisternae; these may be elongated, flattened, rounded, or tubular. ER occurs in 2 forms, called rough and smooth. ROUGH ENDOPLASMIC RETICULUMStructure. RER, also called granular endoplasmic reticulum, is studded with ribosomes, many of them in polysomal clusters. RER cisternae are typically parallel, flattened, and elongated, especially in cells specialized for protein secretion (eg, pancreatic acinar cells, plasma cells), in which RER is particularly abundant. The ribosomes give RER basophilic staining properties. The fine structure of RER (membranes and individual ribosomes) is visible only with the electron microscope.Function. RER is mainly concerned with the synthesis of proteins for sequestration from the rest of the cytoplasm, ie, secretory proteins such as collagen, proteins for incorporation into cell membranes, and lysosomal enzymes (separated from the rest of the cytoplasm to prevent autolysis). RER in protein-secreting epithelial cells often lies in the basal cytoplasm, between the plasma membrane and the nucleus.

Endoplasmic reticulumStructure. SER lacks ribosomes and thus appears smooth in electron micrographs. SER cisternae are more tubular or vesicular than those of RER. SER stains poorly, if at all, so with the light microscope it is indistinguishable from the rest of the cytoplasm.Function. Because it lacks ribosomes, the SER cannot synthesize proteins. It has many enzymes, important in lipid metabolism, steroid hormone synthesis, glycogen synthesis (glucose-6-phosphatase), and detoxification.Location. The SER is suspended in the cytoplasm of many cells and is especially abundant in cells that synthesize steroid hormones (eg, cells of the adrenal cortex and the gonads). It is also abundant in liver cells (hepatocytes), where it is involved in glycogen synthesis and drug detoxification. Specialized SER termed sarcoplasmic reticulum is found in striated muscle cells, where it helps to regulate muscle contraction by sequestering and releasing calcium ions.SMOOTH ENDOPLASMIC RETICULUM

RIBOSOMES general submicroscopic nonmembraned organelles The ribosomes are protein-synthesizing organelles. There are 2 basic types. Mitochondrial (like prokaryotic) ribosomes are smaller (20 nm) than the cytoplasmic ribosomes of eukaryotes (25 nm).Structure. Each type of ribosome has 2 unequal ribosomal subunits. Cytoplasmic ribosomes are composed of ribosomal RNA (rRNA) synthesized in the nucleos and associated proteins synthesized in the cytoplasm. They are intensely basophilic. Light microscopy reveals cytoplasmic accumulations of ribosomes as basophilic patches, formerly termed ergastoplasm in grandular cells and Nissl bodies in neurons. In electron micrographs, ribosomes appear as small, electron-dense cytoplasmic granules.

Location and function. Cytoplasmic ribosomes occur in 2 forms. Free ribosomes are individual ribosomes dispersed in cytoplasm. Polyribosomes, or polysomes, are groups of ribosomes evenly distributed along a single strand of messenger RNA (mRNA), an arrangement that permits synthesis of multiple copies of a protein from the same message. Polysomal ribosomes read (translate) the mRNA code and thus play a critical role in assembling amino acids into specific proteins. Polysomes are found free in the cytoplasm (free polysomes) and attached to membranes of the rough endoplasmic reticulum (polysomes of the endoplasmic reticulum). Free polysomes are involved in the synthesis of structural proteins and enzymes for intracellular use. Polysomes of the rough endoplasmic reticulum are involved in synthesizing proteins that are secreted or isolated.

GOLGI COMPLEX general microscopic membraned organelle

This membranous organelle is composed of 3 major compartments:(1) a conspicious stack of 3-10 discrete, slightly curved, flattened cisternae; (2) numerous small vesicles peripheral to the stack; and (3) a few large vacuoles, sometimes called condensing vacuoles, at the concave surface of the stack. The cis face (convex face, forming face) of the stack is usually closest to adjacent dilated ER cisternae and is surrounded by transfer vesicles. Its cisternae stain more darkly with osmium. The trans face (concave face, maturing face) often harbors several condensing vacuoles and generally faces away from the nucleus.

Golgi Apparatusflattened membranes, secretory vesicles, transport vacuolesLocation. The Golgi complex is typically near the nucleus (juxtanuclear) and is often found near centrioles (which may also have an important role in directing vesicle traffic). Golgi complexes are best developed in neurons and glandular cells, which are specialized for secretion.

Golgi Apparatus: FunctionsAfter leaving the ER, many transport vacuoles travel to the GA. GA involved in packaging and secretion of proteins

GA is a center of :1) modification of proteins and lipids;2) storing of macromolecules;3) storing of biological compounds;4) shipping of macromolecules;5) formation of lysosomes.

LYSOSOMES general submicroscopic membraned organelles Lysosomes are spherical, membrane-limited vesicles that may contain more than 50 enzymes each and function as the cellular digestive system. Their characteristic enzyme activities distinguish them from other cellular granules. The enzyme most widely exploited for their identification is acid phosphate, because it occurs almost exclusively in lysosomes. Other enzymes common in lysosomes are ribonucleases, deoxyribonucleases, cathepsins, ,sulfatases, b-glucoronidase, and phospholipases and other proteases, glucosidases, and lipases. Lysosomal enzymes usually occur as glycoproteins and are most active at an acidic pH.

Lysosomes occur in various sizes and electron densities, depending on their level of activity.Primary lysosomes are small (5-8 nm in diameter), with electron-dense contents; they appear as black circles in electron micrographs. They are the storage form of lysosomes, and their enzymes are mostly inactive. Lysosomes enzymes synthesized and coreglycosylated in the RER are transferred to the Golgi complex for further glycosylation; it is uncertain whether their final packaging as primary lysosomes occurs in the Golgi complex or in GERL. The primary lysosomes disperse through the cytoplasm. They are found in most cells but are most abundant in phagocytic cells (eg, macrophages, neutrophils).

Secondary lysosomes are larger and less electron-dense and have a mottled appearance in electron micrographs. They are formed by the fusion of one or more primary lysosomes with a phagosome. Their primary function is the digestion of products of heterophagy and autophagy; when the lysosomal enzymes mix with the phagosome contents, they become active. Lysosomal enzymes also catabolize certain products of cell synthesis, thus regulating the quality and quantity of secretory material. Secondary lysosomes occur throughout the cytoplasm in many cells, in numbers that reflect the cells lysosomal and phagocytic activity.

Residual bodies are membrane-limited inclusion of varying size and electron density associated with the terminal phases of lysosome function. They contain undigestible materials such as pigments, crystals, and certain lipids.FUNCTION:1. participation indigestion of all classes of macromolecules2. phagocytosis3. recycling the cells own organic material (autophagy)

VacuolesLarge membrane-closed sac for cellular storageThree typesFood vacuole (lysosomes attach)Contractile vacuole (Protozoons)Central vacuole (mature plant cell)

CELL CENTER general microscopic nonmembraned organelle - found in animal cells only

- paired cylindrical organelles near nucleus - composed of nine tubes, each with three tubules - involved in cellular division lie at right angles to each other

CYTOSKELETON IS A NETWORK OF FIBERS THROUGHOUT THE CYTOPLASM

Cytoskeleton is constructed from three types of fibers. microtubules are the thickest microfilaments (actin filament) are the thinnest intermediate filaments are a collection of fibers.

Actin miofilaments - red,microtubuls - green.

ELEMENTS OF THE CYTOSKELETON - give mechanical support to the cell and help maintain its shape.- enables a cell to change its shape. - is associated with motility: movement of the entire cell or movement of organelles and vesicles within the cell. The fibers of the cytoskeleton are not only the cells bones but also its muscles.- contractile component of cytoskeleton manipulate the plasma membrane to form vacuoles during phagocytosis.

INCLUSSIONS

, , . : , , , .

NUCLEUS is a conspicuous membrane-bound cellular component.Nucleus of an eukaryotic cell contains the cell's hereditary apparatus and isolates it from the rest of the cell.

Red blood cells dont have a nucleus.Skeletal muscle cells have multiple nucleiFunctions of the nucleus are:Store genes into chromosomes to allow cell divisionTransport regulatory factors and gene products vie nuclear poresProduce messages (messenger ribonucleic acid or mRNA) that code for proteinsOrganise the incoiling of DNA to replicate key genes

MAIN COMPONENTS OF THE NUCLEUS:nuclear envelope;nucleoplasm;nucleolus;chromatin..

Nuclear envelopeThe nuclear contents are set apart from the cytoplasm by a double membrane called the nuclear envelope and a narrow (40-70 nm) intermembrane space called the perinuclear space. The nuclear envelope is often considered an exctension of the RER, because its outer surface is often peppered with ribosomes and shows occasional continuities with the RER. The inside of the inner membrane is lined with the fibrous lamina, a layer consisting of proteins called lamins. The envelope is perforated by many nuclear pores, each of which has a diameter of about 70 nm and is bounded by 8 globular subunits called annular proteins, which present an octagonal appearance in some preparations. Each pore is covered by a proteinaceous diaphragm that is thinner than the envelope. The pores provide a channel for the movement of important molecules between the nucleus and cytoplasm; these molecules include nucleic acids synthesized in the nucleus and used in the cytoplasm (mRNA, rRNA, tRNA) and proteins synthesized in the cytoplasm and used in the nucleus (histones, polymerases).

Structure of the nuclear pores

Nuclear pores are embedded -with many proteins that act as molecular channels, permitting certain molecules to pass into and out of the nucleus. Passage is restricted primarily to two kinds of molecules: (1) proteins moving into the nucleus, where they will be incorporated into nuclear structures or serve to catalyze nuclear activities; and (2) RNA and protein-RNA complexes formed in the nucleus and subsequently exported to the cytoplasm.NUCLEOPLASM. The nucleoplasm is the matrix in which the other intranuclear components are embedded. It is composed of enzymatic and nonenzymatic proteins, metabolites, ions, and water. It includes the nuclear matrix a fibrillar nucleoskeletal structure that appears to bind certain hormone receptors-and newly synthesized DNA.

NUCLEOLUSDuring interphase (between mitoses), each nucleus usually has at least one (or2) intensely basophilic body called a nucleolus. Nucleoli are the synthesis sites for most ribosomal RNA (rRNA). The nucleolus disappears in preparation for mitosis and reappears after mitosis is completed.

The pars fibrosa consists of densely packed ribonucleoprotein fibers, 5-10 nm in diameter. These fibers consist of the newly synthesized primary transcripts of the rRNA genes and associated proteins.The pars granulosa contains dense granules, 15-20 nm in diameter, that represent maturing ribosomal subunits during assembly for export to the cytoplasm.

The term nucleolonema is used by light microscopists to refer to a threadlike basophilic substructure of the nucleolus. The nucleolonema contains 2 rRNA-rich components distinguishable by electron microscopy.

ChromatinNuclear chromatin is an intensely basophilic substance consisting of DNA and associated histone and nonhistone proteins visible at interphase nuclei. Types of the chromatin:euchromatin,heterochromatin.

EUCHROMATIN. Uncoiled chromatin, termed euchromatin, stains poorly and is difficult to distinguish even with electron microscopy. Large, pale-staining (euchromatic) nuclei usually indicate greater transcriptional activity and faster cell division.

HETEROCHROMATIN. Nuclei containing highly coiled chromatin, termed heterochromatin, stain darkly with basic dyes. Because the DNA of chromatin must uncoil to be transcribed, cells with dark-staining (heterochromatic) nuclei are less active in DNA transcription than other cells, using a smaller portion of their total genome.

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CHROMOSOMES. The chromosomes, the most highly condensed form of chromatin, are visible during mitosis.

In females, only one X chromosome (either of the 2) is used by each cell; the inactive X chromosome is often visible as a clump of heterochromatin termed sex chromatin, or the Barr body. In most cells, the Barr body is attached to the inner surface of the nuclear envelope. In a neutrophilic leukocyte, it may appear as a drumstick-shaped appendage of the lobulated nucleus.

Types of chromosomes

KARYOTYPE is a diploid number of chromosomes and it is a characteristics of the number and morphology of chromosomes, that is peculiarities of each species. Human karyotype includes46 chromosomes:44 autosomes2 sex chromosomesFemale karyotype46=22A+XXMale karyotype46=22A+XY

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