Presentation on theme: "Comparative study of typical prokaryotic cell and eukaryotes By DR SAMUEL AGUAZIM."— Presentation transcript:
Comparative study of typical prokaryotic cell and eukaryotes By DR SAMUEL AGUAZIM
STRUCTURE, FUNCTION & GROWTH OF PROKARYOTIC & EUKARYOTIC CELLS
Prokaryotic and Eukaryotic Cells. All living creatures are made up of CELLS, small membrane bound units filled with aqueous solutions of chemicals, which have the ability to create copies of themselves by growing and dividing.
Living organisms can be classified into 3 major domains: Prokaryotes *Bacteria *Archaea Eukaryotes *Plant cells *Animal cells Prokaryotes and Eukaryotes are 2 distinct cell types with STRUCTURAL differences
The Prokaryotic Cell The Prokaryotic Cell Simply stated, prokaryotes are molecules surrounded by a membrane and cell wall.
Prokaryotes Lack a membrane bound nucleus enclosing the DNA DNA is present as a single circular molecule called a BACTERIAL CHROMOSOME DNA is naked having no associated histone proteins No membrane bound organelles Apart from the DNA nucleoid, there is little internal structure apart from dissolved substances and a large number of RIBOSOMES essential for PROTEIN SYNTHESIS The cytosol is an effective site for bacterial cell metabolism. This allows bacteria to adapt quickly to changing nutritional conditions, but means the regulation of genetic and metabolic activity has to be tightly regulated. Divide by BINARY FISSION Some prokaryotic cells have external whip-like FLAGELLA for locomotion or hair like PILI for adhesion. Prokaryotic cells come in multiple shapes: cocci (round), baccilli (rods), and spirilla or spirochetes (helical cells).
External Prokaryotic Structures Cell wall Contains PEPTIDOGLYCAN (only found in bacteria). Large complex molecule consisting of polysaccharide polymers cross-linked by short chains of amino acids Capsules Sometimes the cell wall is further surrounded by a gelatinous polysaccharide sheath called an attach CAPSULE, GLYCOCALYX or SLIME LAYER Plasma Membrane Basic structure of the phospholipid bilayer is the same for all bacteria Flagella Motile bacteria usually have long, thin appendages called FLAGELLA. These protein sub-units are used to propel bacteria through liquids
Pili or Fimbrae A pilus ( Latin ; plural : pili ) is a hairlike protein structure on the surface of a bacterial cell, required for bacterial conjugation (transfer of genetic material) A fimbrium (Latin; plural: fimbria ) is a short pilus that is used to attach the cell to a surface. Mutant bacteria that lack fimbria cannot adhere to their usual target surfaces and, thus, cannot cause diseases
Spores & Cysts These are produced by some bacteria to survive unfavourable environmental conditions. Dormant forms are metabolically inactive and only germinate under suitable conditions ENDOSPORES : a dormant, tough, non-reproductive structure produced by a small number of bacteria. The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress. They are therefore resistant to ultraviolet and gamma radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants. Endospores are commonly found in soil and water, where they may survive for long periods of time e.g. Clostridium (tetanus, gas gangrene), Bacillus (anthrax) CYSTS : also dormant, but unlike endospores are not resistant to heating at high temperatures
StructureChemical Composition Function Cell wall Peptidoglycan Sugar backbone with peptide side chains that are cross-linked Gives rigid support, protects against osmotic pressure; is the site of action of penicillins and cephalosporins and is degraded by lysozyme. Outer membrane of gram- negative bacteria Lipid AToxic component of endotoxin. PolysaccharideSurface fibers of gram- Teichoic acid positive bacteria Gives rigid support, protects against osmotic pressure; is the site of action of penicillins and cephalosporins and is degraded by lysozyme. Toxic component of endotoxin.Major surface antigen used frequently in laboratorydiagnosis. Cytoplasmic membraneLipoprotein bilayer without sterols Site of oxidative and transport enzymes.
RibosomeRNA and protein in 50S and 30S Protein subunits Protein synthesis; site of action of aminoglycosides, subunits erythromycin, tetracyclines, and chloramphenicol. NucleoidDNAGenetic material. Mesosomelnvagination of plasma membrane Participates in cell division and secretion. PeriplasmSpace between plasma membrane and outer membrane Contains many hydrolytic enzymes, including P-lactamases.
Non-essential components Capsule PolysaccharideProtects against phagocytosis Pilus or fimbriaGlycoproteinTwo types: (1) mediates attachment to cell surfaces; (2) sex pilus mediates attachment of two bacteria during conjugation FlagellumProteinMotility. SporeKeratinlike coat, dipicolinic acid Provides resistance to dehydration, heat, and chemicals. PlasmidDNAContains a variety of genes for antibiotic resistance and toxins.
GranuleGlycogen, lipids, polyphosphates. Site of nutrients in cytoplasm. GlycocalyxPolysaccharideMediates adherence to surfaces.
Classifying Prokarotes Main method is using the GRAM’S STAIN This separates bacteria into GRAM-POSITIVE (purple) and GRAM-NEGATIVE (red) depending on the percentage of PEPTIDOGLYCAN in the cell walls - GRAM-POSITIVE bacteria have a cell wall only 1 layer thick - GRAM-NEGATIVE bacteria have a cell wall several layers thick
Differences between cell wall of Gram positive and Gram negative bacteria CharacterGram positiveGram negative ThicknessThicker Thinner Periplasmic spaceAbsentPresent LipidsAbsent or smallPresent Teichoic acidPresentAbsent Peptidoglycan16- 80nm2nm
Eukaryotes More complex multicellular organisms e.g. plants, animals, fungi and also many single-celled organisms e.g. amoeba, yeast Possess an NUCLEUS and other organelles all of which are surrounded by a MEMBRANE, which divided the cell up into compartments COMPARTMENTALISATION: very important ! ADVANTAGES: Molecules are ‘concentrated’ together, increases rate of reactions Keeps reactive molecules away from other parts of the cell that may be affected by them Large work surface area … many enzymes are bound in membranes
Eukaryotes The basic eukaryotic cell contains the following: - membrane-bound nucleus - plasma membrane - glycocalyx (components external to the plasma membrane) - cytoplasm (semifluid) - cytoskeleton – microfilaments, intermediate filaments and microtubules that suspend organelles, give shape, and allow motion. - presence of characteristic membrane enclosed subcellular organelles e.g. mitochondria, golgi, rER, sER etc
Plant & Animal Cells For ANIMAL CELLS only: – Peroxisomes & Lysosomes often present – Some have microvilli on their surface – Centrioles organise spindle fibres during cell division For PLANT CELLS only: – Cell walls made from cellulose – Communication with neighbouring cells occurs through plasmodesmata – Usually a large central vacuole – Photosynthesis occurs in cells containing chloroplasts
Plasma Membrane A lipid/protein/carbohydrate complex, providing a barrier and containing transport and signalling systems.
Nucleus Double membrane surrounding the chromosomes and the nucleolus. Pores allow specific communication with the cytoplasm. The nucleolus is a site for synthesis of RNA making up the ribosome
Mitochondria Surrounded by a double membrane with a series of folds called cristae. Functions in energy production through metabolism. Contains its own DNA, and is believed to have originated as a captured bacterium.
Rough endoplasmic reticulum (RER) A network of interconnected membranes forming channels within the cell. Covered with ribosomes (causing the rough appearance) which are in the process of synthesizing proteins for secretion or localization in membranes. Ribosomes Protein and RNA complex responsible for protein synthesis
Golgi Apparatus Golgi apparatus *A series of stacked membranes. Vesicles (small membrane surrounded bags) carry materials from the RER to the Golgi apparatus. *Vesicles move between the stacks while the proteins are processedto a mature form. *Vesicles then carry newly formed membrane and secreted proteins to their final destinations including secretion or membrane localisation.
Centrioles Centrioles are found only in animal cells. They function in cell division.
Lysosymes A membrane bound organelle that is responsible for degrading proteins and membranes in the cell, and also helps degrade materials ingested by the cell.
Peroxisomes Peroxisomes or Microbodies Produce and degrade hydrogen peroxide, a toxic compound that can be produced during metabolism
Chloroplasts Surrounded by a double membrane, containing stacked thylakoid membranes. Responsible for photosynthesis, the trapping of light energy for the synthesis of sugars. Contains DNA, and like mitochondria is believed to have originated as a captured bacterium.
Vacuoles Membrane surrounded “bags” that contain water and storage materials in plants.
Cell wall Plants have a rigid cell wall in addition to their cell membranes. They provide support for the plant.
Similarities between P & E cells Prokaryotes & Eukaryotes are CHEMICALLY & METABOLICALLY similar: – Both have genetic material – Both have a cell membrane – Both have a cytosol – Both have ribosomes – Both contain nucleic acids, proteins, carbohydrates & lipids – Both use similar reactions for storing energy and metabolic activities e.g. building proteins
Differences between P & E cells main differences are structural Main differences are STRUCTURAL : Prokaryoteseukaryotes No membrane bound organelles nucluesMembrane bound nucleus Cell walls made of peptidoglycan (Thickness of wall depends on whether the cell is Gram +ve or –ve) Cell walls, if present, made of cellulose (chitin in fungi) No membrane bound organellesMembrane bound organelles (compartmentalisation) Have pili & fimbriae (for adhesion) and flagella (for propulsion) Have cilia or flagella (for movement) Mucilaginous capsuleNo mucilaginous capsule present (numerous internal structures present including microtubules, ER, Golgi, secretory vesicles etc) ranges from 0.5um to 100um bound nucleusCell size ranges from 10 – 150um Cell size
Comparison of prokaryotic and eukaryotic cells ProkaryotesEukaryotes OrganismsMonera: Eubacteria & archebacteria Protists, fungi, plants and animals Level of organizationSingle celledSingle celled (protists mostly) or multicellular usually with tissues and organs Typical cell sizeSmall(1-10microns)Large( microns) Celll wallAlmost all have cell walls(murein) Fungi and plants(cellulose and chitin): none in animlas OrganellesUsually none many different ones with specialized functions MetabolismAnaerobic and aerobic: diverse Mostly aerobic
Comparison of prokaryotic and eukaryotic cells Genetic materialSingle circular double stranded DNA Complex chromosomes usually in pairs: each with a single double stranded DNA molecule and associatied proteins contained in a nucleus Mode of divisionBinary fission mostly: budding Mitosis and meiosis using a spindle: followed by cytokinesis