CBS Cells And Organelles BACKGROUND PDF

CBS Cells & Organelles BACKGROUND Learning Outcomes State the nature of cells and limitations on their size Understand methods to visualize cells and organelles and their limitations State definitions and function of organelles in animal cells Kn...

CBS Cells & Organelles BACKGROUND Learning Outcomes State the nature of cells and limitations on their size Understand methods to visualize cells and organelles and their limitations State definitions and function of organelles in animal cells Know definitions of eukaryote, prokaryote and virus Details for each learning outcomes State nature of cells and limitations on their size Cell biology definitions Cell Semi-independent, living unit within the body, (in unicellular organisms, completely independent) in which are sited the mechanisms for metabolism, growth and replication (by division). It consists of an aqueous solution of organic molecules surrounded by a membrane Organelle Subunit within a cell, with a defined structure and performing specific, integrated activities. Some are bounded by membranes, others are non- membranous e.g. ribosomes Tissue Organised assembly of cells and their extracellular products which carry out similar and coordinated activities within the body (connective, lymphoid) Organ Assembly of tissues coordinated to perform specific functions within the body (eye, ear, heart, lungs, liver) System Assembly of organs with specific, related activities, sharing regulatory influences (e.g. respiratory). OR it may be a diffuse functional network of cells situated in many parts of the body, sharing specific activities (e.g. immune) Cells have a maximum size. Normal range of volume 1,000-5,000 µm3. Some exceptions: erythrocyte 100 µm3 and oocyte 4,000,000 µm3. Size is limited by the rate of diffusion: movement of metabolites within the cell, uptake of oxygen from outside the cell, movement of mRNA from the nucleus, movement of vesicles inside the cell. Diffusion at distances >50µm are less efficient. Solution to these problems include use of cytoskeleton to actively move things around cells [CBS cytoskeleton]; creation of “giant” cells with multiple nuclei so that gene expression can occur in more than one place (e.g. skeletal muscle cells); gap junctions between cells so there is efficient movement of metabolites between cells. Understand methods to visualize cells and organelles and their limitations Light microscope has limited ability to visualise components of cells (only nucleus and plasma membrane can be resolved) [FAH microanatomy]. Electron microscope (EM) is needed to visualise full range of organelles. EM sample preparation is highly artificial: cells are dead, fixed and dehydrated.  Figure 1 Electron microscope image of a liver cell Minimum resolvable unaided by eye 0.2mm Range resolvable by light microscope: 10mm – 200nm Range resolvable by electron microscope: 10mm – 0.1nm Cells : 200µm - 1µm Organelles: 10µm – 0.5µm State definitions and function of organelles in animal cells Figure 2 stylised image of eukaryotic cell  definition function plasma phospholipid bilayer defines the boundary of cell, regulates entry membrane and exit of chemicals [CBS Lipids and membrane structure] cytosol aqueous environment within the plasma membrane cytoplasm cytosol plus organelles cytoskeleton consists of three types of Mechanical strength of cell, control of shape, protein polymers: actin facilitation of movement, guide movement filaments, microtubules within cells, interaction with other cells [CBS (tubulin) and intermediate Cytoskeleton] fibres nucleus surrounded by nuclear storage of chromosomes; site of DNA membrane; largest organelle: replication [MCG Replication and visible by light microscopy size: Mutagenesis]; site of gene expression 3-10μm [MCG Molecular Basis of Gene Transcription] nucleolus region of nucleus site of rRNA synthesis and ribosome biogenesis nuclear Double phospholipid bilayer Regulates the entrance and exit of mRNA membrane / (inner and outer nuclear and proteins; maintains the integrity of the nuclear envelope membrane; perinuclear space nucleus between bilayers; nuclear lamina is protein layer underneath the inner nuclear membrane mitochondria Surrounded by membrane; Aerobic oxidation of glucose to generate ATP also second inner membrane (Krebs cycle); components of Electron that is folded into cristae that Transport Chain are located in the inner increases its surface area; only membrane [NAM Aerobic Metabolism]; visible by EM; size 0.5-2μm involved in oxidation of fatty acids; involved long; number per cell reflects in gluconeogenesis [NAM The Liver and metabolic activity; contains Gluconeogenesis]; involved in regulated DNA that encodes ~1% of the intrinsic apoptotic pathway [CBS Cell death] mitochondrial specific proteins. rough Membrane bilayer surrounded Coated with ribosomes; mRNA translation endoplasmic endosomes; membrane and and synthesis of proteins for secretion or reticulum (RER) inner space (lumen) insertion into cell membrane; proteins are continuous from the outer folded; Cys-Cys bridges form [CBS Protein nuclear membrane Structure]; vesicles are budded from RER and transported to the Golgi body [CBS Protein targeting] smooth Membrane bilayer surrounded Biosynthesis of membrane lipids and endoplasmic endosomes; continuation of steroids; start of N-linked glycosylation [CBS reticulum (SER) RER Protein structure], detoxification of xenobiotics (e.g. P450 system) ribosome Protein – rRNA complex Assembly responsible for the translation of mRNA and the synthesis of proteins Golgi (body, Consists of 4-8 closely stacked, Directs new proteins within vesicles to their complex, membrane-bound channels correct location in cell [CBS Protein apparatus) (cisterna). Protein containing targeting]. Transport of membrane lipids vesicles delivered from the around cell. Creates lysosomes. Site of RER glycosylation modifications (modifying N- linked carbohydrates, glycosylation of O- linked carbohydrates and lipids). Synthesis/packaging materials to be secreted secretory vesicles Membrane bound spheres Bud off from the Golgi, vesicles fuse with inner surface of the plasma membrane and release their contents (exocytosis) lysosome Membrane bilayer surrounded Involved in organelle turnover/replacement vesicle; size 0.2-0.5µm. – autophagy. Lysosome fuses with other Contains >50 hydrolytic organelles. Low pH is maintained by ATPase enzymes for all major cellular proton pump. macromolecules inside is ~ pH5.0. peroxisome Surrounded by membranes, Detoxification; phospholipid synthesis e.g. only visible by EM: not very plasmalogens; oxidation of Very Long Chain electron dense; 0.5-1.5μm Fatty Acids (VLCFA); contains enzymes which generate (and degrade) H2O2 cilia Hair-like extension of the Different types of cilia – (i) sensing plasma membrane, contains a movement of fluid, (ii) moving liquid (iii) central core of modified detection of sound tubulin [CBS cytoskeleton] extracellular Protein and carbohydrate Mechanical support for cells/tissues matrix (ECM) supporting network outside of cells – this is not an organelle  Know definitions of eukaryote, prokaryote and virus Prokaryote Single-celled organism in which the chromosome is a circular strand lying free in the cell (i.e. no nucleus) and has no membranous organelles e.g. Bacteria Eukaryote One or more cells in which chromosomes are enclosed in a nucleus; typically have cytoplasmic, membrane-bound organelles, DNA divided into a series of linear chromosomes, and considerable differences occur between cells within the same organism. All complex organisms (plants, fungi, animals, protozoa, algae) are eukaryotes Virus Assemblage of nucleic acid (DNA or RNA) and proteins (and often other molecules) which is parasitic on prokaryotes/eukaryotes. Viruses invade cells, subvert their protein synthesis machinery to make more viruses instead of normal cell proteins, then escape to infect other cells. Viruses are not cells or organisms in the strict sense (lack a plasma membrane and only operate chemically within host cells). Comparison of Prokaryote & Eukaryote cells – Intracellular Structure Prokaryotic Eukaryotic Mitotic Spindle Absent Present Sterols in Plasma Membrane Absent Present Only for Photosynthetic Numerous Membrane-Bound Internal Membranes Organisms Organelles Endoplasmic Reticulum Absent Present Mitochondria Absent Present Lysosomes Absent Present Golgi Absent Present Peroxisomes Absent Present Cytoskeleton Absent Present Cell Wall Present Absent (apart from some Fungi) Comparison of Prokaryote & Eukaryote cells – Genetic Material Prokaryotic Eukaryotic Chromosomes Single circular Paired linear Location Nuclear region Membrane-bound Nucleus Nucleolus Absent Present Histones Absent Present In Mitochondria (and Extrachromosomal DNA In Plasmids Plasmids) 80S Cytoplasmic / 70S Ribosomes 70S Mitochondrial Cell Division Binary Fission Mitosis or Meiosis