Cell Theory: History and Tenets

• Cell theory states that living organisms are composed of cells, which are the basic units of structure/organization and reproduction.

Tenets of Cell Theory:

• All living organisms comprise one or more cells.

• Cells define the basic unit of structure and organization in organisms.

• Cells come from pre-existing cells.

• No universally accepted definition of life exists, non-cellular entities like viruses are considered by some as living organisms.

• Continuous microscope improvements allowed for cell discovery in the 17th century.

• Robert Hooke is credited with initiating cell biology.

• Debates around cell regeneration and cells as a fundamental unit of life occurred for over a century.

• Cell theory was formulated in 1839, owing credit to Matthias Schleiden and Theodor Schwann, Rudolf Virchow also contributed.

History of Cell Discovery:

• Romans made glass in the first century BC, noticing objects appearing larger under glass.
• Salvino D'Armate created a glass piece to fit over one eye in 12th century Italy, creating a magnification impact.
• The use of lenses in eyeglasses during the 13th century made simple microscopes more widely used (magnifying glasses) with limited magnification.
• Compound microscopes, combining an objective lens with an eyepiece for higher magnification, appeared around 1620 in Europe.
• Robert Hooke used a six-inch microscope with two convex lenses in 1665, examining specimens under reflected light for Micrographia.
• Hooke also used a simpler single-lens microscope to inspect specimens with directly transmitted light.
• Anton van Leeuwenhoek, a draper, advanced microscopic study after seeing a microscope in Amsterdam in 1648.
• Before 1668, Leeuwenhoek learned to grind lenses, leading to a unique single-lens microscope allowing 270x magnification, far more than the previous 50x.
• Carl Zeiss, a German engineer, improved microscope lenses starting in the 1850s.
• Optical quality improvements occurred in the 1880s when Otto Schott and Ernst Abbe were hired.
• Optical microscopes can only focus on objects of a wavelength or larger.
• Electron microscopes in the 1920s allowed viewing of smaller objects, opening new scientific avenues.

Discovery of Cells:

• Robert Hooke discovered cells in 1665, documented in Micrographia.
• Micrographia has 60 ‘observations' detailing various objects under a compound microscope.
• Hooke observed thin bottle cork slices, discovering tiny pores named "cells," from the Latin "Cella" for ‘a small room.'
• "Cellulae" referred to honeycomb's six-sided cell.
• Hooke did not understand the cells' real structure/function; he saw only empty cell walls of plant tissues because of low magnification.
• Hooke's cell observations gave no indication of a cell nucleus and other organelles.
• Hooke observed bluish mould on leather in Micrographia and proposed spontaneous generation caused by natural/artificial heat because he was unable to observe “seeds”.
• Anton van Leeuwenhoek later saw cells with improved lenses magnifying objects 300x, or 270x.
• Leeuwenhoek observed motile objects and wrote a letter to The Royal Society on October 9, 1676, stating motility as a quality of life, therefore, he was observing living organisms.
• Leeuwenhoek described microorganisms in many papers, naming them “animalcules” like bacteria and protozoa.
• Leeuwenhoek, despite less formal education, provided the first accurate red blood cell depiction, and discovered bacteria upon tasting the tongue of an ox, later studying "pepper water" in 1676.
• He discovered sperm cells in animals and humans.
• Leeuwenhoek realized fertilization occurs when the sperm enters the egg cell - ending the previous theory of spontaneous generation.
• Hooke confirmed Leeuwenhoek's observations.
• Animal tissues were observed after plants due to fragility, making thin slice preparation difficult.
• Biologists suspected the existence of a fundamental life unit.
• Henri Dutrochet stated “the cell is the fundamental element of organization", connecting it to animal or plant cellular structure over a hundred years later
• Karl Rudolphi and J.H.F. Link were awarded in 1804 for proving independent cell walls through the Königliche Societät der Wissenschaft, Göttingen, as previously, cells were believed to share walls and fluid flow.
• Credit for developing cell theory is given to Theodor Schwann and Matthias Jakob Schleiden.
• Though Rudolf Virchow contributed, his contributions were less recognized.
• Schleiden suggested in 1839 that every plant structural part was cells or cell results.
• He hypothesized that cells form through crystallization, independently or within other cells - not an original idea of Schleiden, as Barthelemy Dumortier stated this years earlier.
• The crystallization process is no longer accepted within cell theory.
• Theodor Schwann declared in 1839 that animals, like plants, are composed of cells or cellular byproducts.
• Two of the cell theory tenets were postulated from conclusions about animals and plants.
• Schleiden's free cell formation through crystallization was refuted in the 1850s by Robert Remak, Rudolf Virchow, and Albert Kolliker.
• Rudolf Virchow added the third tenet to cell theory in 1855: Omnis cellula e cellula, meaning all cells arise only from pre-existing cells
• Robert Remak originally proposed that all cells arise only from pre-existing cells.
• Robert Remak suggested Rudolf Virchow may have plagiarized his work, as he published observations in 1852 about cell division claiming Schleiden and Schwann incorrect about previous generation schemes.
• He instead noted that binary fission, introduced first by Dumortier, generated new animal cells.
• Once the tenet to all cells arising from pre-existing cells was added, the classical cell theory was said to be complete.

Modern Cell Theory includes:

• All known living things are made of one or more cells
• All living cells arise from pre-existing cells by division.
• The cell serves as the fundamental unit of structure and function in all living organisms.
• The activity of an organism depends upon all activities of independent cells.
• Energy flow (metabolism and biochemistry) occurs within cells.
• Cells harbor DNA in the chromosome and RNA in the cell nucleus and cytoplasm.
• All cells are chemically similar in organisms of similar species.

Modern Version of Cell Theory includes:

• Energy flow occurs within cells.

• Heredity information (DNA) is passed from cell to cell.

• Essentially the same basic chemical composition make up all cells

• Due to its lack of a plasma membrane and its own metabolic driving force, a virus does not meet the criteria to be considered a cell.

• Protozoa (like paramecium and amoeba) divide by binary fission and protoplasm lacking cellular organization create Rhizopus' pseudo-roots and stems.

• Felix Dujardin coined the term sarcode in 1835 while working with protozoans that have mass of indivisible cell filled with multi-nucleus and the inner fluid

• H.von Mohl worked with animal embryos, explained cell division and Purkinje named embryonic cell contents the protoplasm.

• Max Schultze propounded the protoplasm theory in 1861.

Protoplasm Theory includes:

• Plants and animals are formed from a living matter known as protoplasm.
• Cells are accumulation of living matter or protoplasm enclosed within limited space.
• Cell protoplasm is composed of two distinct compartments of fluid/slimy parts known as the cytoplasm and membrane enclosed part known as the nucleus.
• The fluid filled part of protoplasm outside the nucleus is the cytoplasm while the part within the nucleus is the nucleoplasm.

Cell structures and components:

• Prokaryotic cells are simplest, smallest and most primitive cells.
• Prokaryotic cells lack components of true cells, whilst maintaining the ability to live freely in the environment.
• Prokaryotic cells are unicellular organisms, like bacteria and blue-green algae, with inner cellular components in an enclosed cell membrane.
• Bacteria, in conjunction with cell membrane, also possess a cell wall called a capsule.
• Prokaryotic cells lack membrane-bound organelles, containing circular DNA naked in the cytoplasm without a specific location.
• Prokaryotic cell structure is simple and does not have membrane bound organelles.
• RNA and ribosomes do not have membrane bounds and are found floating in the fluidy-like cytoplasm, which exert an osmotic pressure to the wall of the cell and bring about turbidity of the bacterial cell as gas and other materials are exchanged across the semi-permeable cell membrane with the outside of the cell.
• Prokaryotic cells are ubiquitous and exist in different forms of interrelationship called colonies, these are generally called bacteria colonies.
• Exist in diploid form, tetra-, staphy- and strepto-forms of living.
• Monoform is a single living cell such as monococcus, diploid is two partially divided attached cell e.g. diplococcus, tetracoccus refers to four partly attached cells living separately.
• Staphy- are clusters that are independent; cluster form of cells attached together e.g. staphylococcus, and strepto- are chain like structure cells living differently but attached in a straight form e.g. streptococcus.

Properties of Prokaryotic Cells:

• Do not possess a definite nucleus, hence, lack membrane-bound nuclear materials.
• Their genetic materials (DNA/RNA) are exposed in the cytosol without a definite location.
• Consist of double-stranded circular DNA on a single chromosome.
• Chromosomes lack histones and are loosely situated in the cytosol.
• Lack vital membrane bound organelles like mitochondria, golgi-apparatus, ER, plastid etc.
• Cells are smaller compared to those of eukaryotic organisms.
• True, definite and well-organized cells, eukaryotic cells contain organelles enclosed in an inner membrane.
• Eukaryotic cells contain higher plants and animals, fungi and protozoans.
• Eukaryotic cells can be unicellular (certain fungi, protozoans) or multicellular (higher plants and animals.
• Composition commonly includes a plasma membrane, cytoplasm and embedded membrane-bound organelles.
• Internal semi-permeable membranes surround the organelles (mitochondria, Golgi bodies, endoplasmic reticulum etc.).
• Perforated nuclear membranes separate the nucleus and interior nucleolus, cytoplasm and nucleoplasm respectively.
• Eukaryotic cells have a nucleus, a large structure controls the workings of the cell because it contains the genes.
• Both animals and plants have eukaryotic cells.
• Eukaryotic cells are larger than prokaryotic cells due to the presence of cells with specific organelles not found in prokaryotic cells.
• Cell sizes vary, some can be seen by the naked eye and microscope e.g muscle fibres
• Unicellular eukaryotic cells are larger than multicellular cells - enabling an increase in size.
• Examples of cell size for Amoeba is about 1000μm and for Diatom is 200µm and algae acetabularia is up to 10cm.
• Human cells range from 20 to 30µm; red blood cells are about 8µm; the largest plant cells (fibre cells) are over 100cm in length.
• Cell shape depends on function and environmental adaptations.
• Multicellular cells have a definite shape due to pressure from adjacent cells, eukaryotic cells as plant cells are typically round or rectangular.
• Plant cells are rigid shaped by a cellulose cell wall while animal cells have flexible shapes due to various structures like microtubules and shape according to function.
• Cell in-depth is determined by its volume to surface area ratio.
• Increase in volume reduces area in contact with the environment, also reducing the rate of material exchange.
• Volume to surface area must be within range for efficient function, otherwise cell divides by binary fission.
• This process is reproduction in unicellular organisms.
• Cells exchange materials through diffusion or osmosis, either with the environment or adjacent cells.
• Organisms consist of multiple or single cells which determines height and size.
• The higher the number of cells in an organism, the larger their size/height (e.g. elephants vs. goats).

Eukaryotic Structures:

• Cell Wall: Found in plants only, made of cellulose and fibres for support and protection.
• Plasma Membrane: Defines boundary, regulates passage.
• Nucleus: Nuclear membrane, contains nucleoplasm, chromatin, and nucleoli which contains storage of genetic material and synthesis of RNA and DNA.
• Nucleolus: Concentrated area for ribosomal subunit formation.
• Ribosome: Protein and RNA in a two subunit composition which is where protein synthesis happens.
• Endoplasmic Reticulum (ER): Includes synthesis and/or modification of proteins and other substances, and distribution by vesicle formation performed by membranous flattened channels and tubular canals.
• Rough ER: Protein synthesis.
• Smooth ER: Synthesis of lipids in certain cells.
• Golgi apparatus contains Stack of membranous sacs which has Processing, packaging and distribution of proteins and lipids
• Lysosome: Intracellular digestion, membranous vesicle that contains digestive enzymes.
• Vacuole and vesicle: Storage of substances with membranous sacs.
• Peroxisome: Metabolically diverse, membranous vesicle.
• Mitochondrion: Inner with outer membranes, which contains Cellular respiration
• Chloroplast: Photosynthesis, two membranes bound grana.
• Cytoskeleton: Microtubules and filaments that aid in shape and movement.
• Cilia and flagella: Movement using microtubules.
• Centriole: Formation of basal bodies also by microtubules.
• Only plants have a Cell Wall. Animal cell do not
• Only Animal Cells have a Centriole. Plant cell do not

Outer Boundaries of Animal and Plant Cells:

• Both are made up of a lipid bilayer that contains protein molecules.
• The plasma membrane is a living boundary regulating entrance and exit of molecules for cells from the non-living environment.
• Cytoplasm surrounds the nucleus and contain organelles.
• Plant cells have a permeable, protective cell wall (not animal cells), primary and seconadary.
• Cellulose molecules form fibrils to make a primary cell wall.
• The secondary cell wall, if present, forms inside the primary cell wall, and contains lignin, a substance that makes them even stronger than primary cell walls.

Cell Components, Composition and Functions:

• Organelles of Animal and Plant Cells includes both membraneous and organized subcellular structures and each assembly line in a factory acts simultaneously to produce various products.
• Chemical are also process by organelles.
• Mitochondria is in both cells whilst Plant cells only have Chloroplasts. Centrioles are in Animal cells only.

Plasma Membrane:

• It is attached to the cell wall and separates the cell wall from cell cytoplasm, is a semi-permeable membrane.
• Separates plasma and cytoplasm, also called plasmalemma, is a three-dimensional, translucent layer.
• Transverse protein molecules exist across the lipid bi-layer and control the transport of both small and large molecules across the membrane either through diffusion, osmosis or active passive transport mechanisms.
• The phospholipids in membrane have hydrophilic positive head end and hydrophobic negative tail end, with Materials transporting through either an ion-gated channel or protein channel.
• Functions by increasing the plasma membrane surface area to maximize the absorption of nutrients or inorganic molecules with hair-like microvilli.
• In fluid-mosaic assembly, forms a living, dynamic and selective permeability transport barrier controlling nutrient entry and waste removal.
• A difference is created between the internal and external environment concentration via the membrane.

Chemical Composition of a Plasma Membrane:

• Composed of three different molecules (lipids, proteins, and carbohydrates).
• Lipids: Lipid bilayer of phospholipids with sphingolipids, glycolipids and sterols (cholesterol) that is amphipathic which contains both hydrophilic and hydrophobic tails.
• Proteins: Presence varies which determines cell and functions or organelles while transporting specific substances like food molecules or minerals into the cell
• Carbohydrates: Present in oligosaccharide attached to protein or polar ends of phospholipids as glycoprotein and glycolipid with D-mannose and D- galactose, N-acetylgalactosamine.

Membrane structures:

• fluid-mosaic has consistency assembly that is fluid with considerable sideways movement of the lipid and protein molecules.
• Fluid-mosaic also suggests the plasma membrane contains bimolecular fat, which is the infolding or layer of lipid and protected by polar film, forming a bilayer.
• Unsaturated are used for assembly because it makes it hard to pack the molecules together.

Functions of Plasma Membranes:

• Thin layers work a a barrier which separates the intra-cellular cytoplasm from the cell environment.
• As it is a semi-permeable, membranes regulate influx/outflux of materials within the cell.
• Enables cells to maintain a constant internal state known as homeostasis, which provides sensory functions and protects from harm.
• Cell Coat: outer part of plasma membrane, covalently attached to protein moieties (sugar units) and glycoproteins/glycolipids.
• Sometimes is called the glycocalyx.
• Rich in glycoproteins and polysaccharides that contains sialic acid with a negative charge to enhance Ca2+ and Nat binding.
• In eggs and cartilage, collagen is joined and used as the shell.

Cell Coat features:

• Protects from external injuries and dehydration.
• Filtration in blood capillaries and glomerulus.
• Contains enzymes that are terminal digestion of carbohydrates and proteins.
• Contains an antibody, the receptor sites for viruses in blood plasma, for immunity.
• Cell Wall: The outmost parts of both eukaryotic and prokaryotic cells, is a long chain glucose monomers arranged in fibers of microfibrils.
• Plant cell walls protect and prevent collapse, excessive water loss as well maintain rigidity and shape depending on cellulose, microfibrils, pectin and lignin.
• Plasmodesmata, provides plants with channels for cell material exchange for interactions with the environment, protecting prevent organisms and maintain shapes of the cell.
• Bacterial use murein, polysaccharide-amine, for protection prevent lyses and serve a pathogenic effect.
• Chemical Composition of Cell Walls: various polysaccharides, lipids, proteins and minerals.

Cellulose:

• Linear and unbranched polymer of polysaccharide made of glucose units by cellulose, producing the building block.
• Each Microfibrils have almost 2000 glucose that act as a resistant.
• Also synthesized using bacteria, fungi, cellulose rhizobium, fungi.
• Hemicelluloses: A branched chain that consist is a heteropolymer that contain xylose and arabinose.
• Pectins: Heterogenous insoluble that bind to Na catinos or Ca2+ cations that also produces semirigid gel to hold cell wall components together.
• Mannan: It is a yeast homopolysaccharide and for bacteria.
• Agar: Galactose is weed and used.
• Lignin: A non plastic/fibrosis alcohol. Known as plastic biology.
• Cutin is a wax for plants or biological plastic with sublerin for assistance.Also it is the surface resistence.
• Minerals provides Calcium and magnesium (silicate) for wall cell with elastin a shape (like pectin).

Types of Cell Walls in plants:

• Primary cell (outer): Made with merisemastic, virtually thin.
• Secondary cell: Made with cellulose +lignin, for mature plants contained in layers.
• Tertiary Cell - Impenetrable, made from cellulose-xylan that protct loss of water.

Functions of the cell wall:

• Provides mechanical strength frame and rigidity to enable the cell to diffuse.
• The Protoplasm (cytoplasmic matrix and nucleus): Non-living.
• Cytoplasm: cytosol that is jelly +cell organelles for synsthesis.
• Endoplasmic Reticulum: Membrane to tube for cisternae

Key Characteristics:

• Functions by providing a network with a cross linking for cell framework allowing the molecules can pass inside the vesicles and controls cells the fibers in muscle.
• Chemical Composition rich in phospholipids such as phosphotidyl-choline.
• Network of cell that is with suspension that that enables molecule to take place which is synthesis and regulates flux

Vesicles

• Act as a bond membrane cisternae that perform organazing proteins which act on packing, by preparing transport that also divide.
• They are known as cistaene which a plate or saucer, and it is divided into Cis, and Trans region.
• It is for secretary transfer .
• Structure is a Sac, tube and vessels.

Golgi Apparatus

• Consist in protein sorting, procession (the enzmyes), labels(synthetizaion of the protein) and secretary cell components( glycoprotein.
• Lymosomes membrane with dense material to the function and digestion for proteases
• Primary(form brand new) vs heterosphones ( contain substances that digest)vs Authophosomes (help cell death for regeneration).

Functions of Lysosomes

• Digest external particles the lysosomes of which digest that cell and use them for processes.
• Functions by digestion via autophage and ease penetration for a cell.
• Help with hydrogen

Microbodies:

• Are a single membrane found organelle of peroxidase but has peroxisome (plant(catalyse oxidate), fungi-help germinate.
• Function to process by and oxydidation.
• Mitochondria and its membrane are a transport
• The inner membrane is a crest and filled with composition.

Chemical compositions:

• Has sections that performs. Porin has the materials and proteins with DNA.
• Function the ATP, regulates the temp to generate, DNA and the enzyme in the processes.
• Plastid: Are only important for the algae the are like shapes and have storages which have self replication function depending is color which makes the cell a leucoplast, chromo, chlopro.
• They have different functions in different colors and lights, plus compostions.

Cytoskeltons:

• The interconnected fibers/organes, arranged like tubulin with cell of the brain in vertebrates, filament and the meristeam.
• And can give motion.
• Functions by preventing the protuberance, and distribution.
• Has cell and aids differentiation.

Cilla

• Projections of contractile. the beating for organisms with a system such as follows. The are shorter of the cytoplasm.
• They occur on cell on the cell surface.
• Flegella exhibits waving, while cilia stroke.
• Can bet independtly.
• fractionation for function and chemicality for cell with solution. In order to is the process Has steps 3
• First extract: with mild solution, salt, and cell free.
• Suspended cell homogenation ,which break small the openings or blend.
• Lastly, with centrifuge: we can do both equilibrium/ density by mass and to create a cell which is separated base density.
• The pellet becomes supernatant.
• Solution : osmosis a semi-membrane and to have the substance (solute with) . H2O is solvent.
• Osmotic pressure which is used to push and the formula for it is n=nV/RT.
• Solutions for for different is isotonic or hypo- and which help the function.

Acid pH

• Is based of the ph of the acidity of a alkility

• It tells the hydrogen concentration

• Which can be either hydrogen or hydroxyl.

• pH has its state with it can be that hydrogen which makes it acid or alkine depending on what side it tows which measure .

• p = 1014 the solution is nuetral or equal with a value reach the 0 the acid will equal to .Log107 =7 the pure water and equals neutral=acid.

• It water has properties helps body.

Key point

• Water (the formula )and heat with causes the function, hydrogen level. The are molecular with range and the body will regulate.
• Buffer: mix of high acidic salts or acid with lower.
• Considers HCl with H= .2= cl with the solution will H be in that OH?
• Also phosphate help with this and the ration function is the buffer that helps prevent the range and prevent it by help balancing.