3. cell structure and function.pdf

Cell Structure and Function Lecture Outline • Prokaryotic cells structures and functions • Eukaryotic cells overview Prokaryotic Eukaryotic Two Cell Types  Cell wall  Cell membrane Cell Types  Membrane bound organelles  Ribosomes  Nucleoid  Cytoplasm  Vacuoles  Granules  Nuclear...

Cell Structure and Function Lecture Outline • Prokaryotic cells structures and functions • Eukaryotic cells overview Prokaryotic Eukaryotic Two Cell Types  Cell wall  Cell membrane Cell Types  Membrane bound organelles  Ribosomes  Nucleoid  Cytoplasm  Vacuoles  Granules  Nuclear envelope  Unicellular  Multicellular  DNA as genetic code  Nucleus Structure of a Bacterial Cell Main Structures of Bacterial Cells Appendages Glycocalyx Cell envelop Bacterial chromosome Plasmid Ribosomes Appendages Two major groups: • Flagella - Motility • Fimbriae and pili- Attachment or channels Flagella Long protein structure Propeller like movements push bacteria For motility-enable organism to move toward stimuli • Chemotaxis, phototaxis Ex. Helicobacter pylori Flagellar Arrangements Monotrichous Lophotrichous Amphitrichous Peritrichous Campylobacter jejuni – flagella allows it to move through mucus layer https://www.mdpi.com/microorganisms/microorganisms-08-00482/article_deploy/html/images/microorganisms-08-00482-g001-550.jpg Fimbriae and Pili • Eye of Science/Science Source Fimbriae and Pili Fine, proteinaceous, hairlike bristles emerging from the cell surface Fimbriae • Main function - surface attachment Pili • Main function – gene transfer • Some function in motility • In Gram - bacteria Fimbriae and Pili Glycocalyx Coating of sugars and/or proteins external to the cell wall Two types: • Capsule - highly organized coating, tightly attached • Acts as virulence factor- promote infection, reduces phagocytosis • Streptococcus pneumonia, E.coli • Slime layer - loosely organized and attached • Allow adherence to cell surface and foreign substances • Pseudomonas The Cell Envelope Composed of two basic layers: • Cell wall • Cell membrane Maintains cell integrity Cell Walls Bacterial cell wall Rigid structure Surrounds cytoplasmic membrane Determines shape of bacteria Holds cell together Prevents cell from bursting Contribute to ability to cause disease Targeted by antibiotics Cell Walls Two groups of bacteria based on Gram stain: • Gram-positive bacteria • Gram-negative bacteria Structure of Cell Wall Peptidoglycan Alternating series of two monosaccharides • N-acetylglucosamin (NAG) • N-acetylmuramic acid (NAM) • Joined NAG and NAM subunits form glycan chain • Four amino acids form tetrapeptide chain • Glycan chains held together by tetrapeptide chain Gram-Positive Cell Wall Gram-Negative Cell Wall More complex than G+ Outer membrane Outer membrane contains lipopolysaccharides (LPS) Region between outer membrane and cytoplasmic membrane is called periplasm Thin layer of PTG between outer membrane and cytoplasmic membrane Gram-Negative Cell Wall Structures of Gram-Positive and Gram-Negative Bacterial Cell Walls Antibiotics Target Cell Wall Peptidoglycan as a target for antimicrobials • Penicillin • Prevents cross-linking of glycan chains by tetrapeptides • Lysozyme • Breaks bond linking NAG and NAM 24 The Gram Stain Differential stain that distinguishes cells based on cell wall Important basis of bacterial classification and identification diagnosing infection and guiding drug treatment • Gram-positive - stain purple • Gram-negative - stain red https://ib.bioninja.com.au/_Media/gram-bacteria_med.jpeg https://i1.wp.com/images.slideplayer.com/20/5940714/slides/slide_93.jpg Non typical Cell Walls Some bacteria lack a cell wall • Mycoplasma species have extremely variable shape • Penicillin, lysozyme do not affect • Cytoplasmic membrane contains sterols that increase strength Cell Walls of the Domain Archaea • Members of Archaea have variety of cell walls • Probably due to wide range of environments • Archaea less well studied than Bacteria • No peptidoglycan Cell Membrane Structure Phospholipid bilayer with embedded proteins Functions in: • Site for reactions, nutrient processing, and synthesis • Selectively permeable • Passage of nutrients and wastes Cell Cytoplasm Dense gelatinous solution of sugars, amino acids, and salts 70 to 80% water Internal Structures Internal structures essential for life • Chromosome • Ribosome Optional and confer selective advantage • Plasmid • Storage granules • Endospores 31 Genetic material Chromosome • Single, circular, double-stranded DNA molecule that contains all the required genetic information Plasmids • Small circular, double-stranded DNA • Not essential to bacterial growth and metabolism • May be transferred from cell to cell Ribosome Involved in protein synthesis Composed of large and small subunits Made of protein and ribosomal RNA 33 Ribosome Prokaryotic ribosomal subunits • Large = 30S • Small = 50S • Total = 70S Eukaryotic ribosomes subunits • Large = 40S • Small = 60S • Total = 80S Difference used as target for antimicrobials 34 Granules Storage granules • Intracellular storage bodies • Used when when environmental sources are depleted • Gas vesicles • Provides buoyancy to cell Endospores Dormant form of cell Extremely resistant to heat, desiccation, chemicals, ultraviolet light, boiling water Endospores that survive can germinate to become vegetative cell Found virtually everywhere Common in members of Bacillus, Clostridium Endospore formation • (photo): SJ Jones, CJ Paredes, B Tracy, N Cheng, R Sillers, RS Senger, ET Papoutsakis, “The transcriptional program underlying the physiology of clostridial sporulation”, Genome Biol, 2008. 9:R114. Morphology of Prokaryotic Cells: Shapes Bacterial shapes • Coccus: spherical • Rod: cylindrical • Vibrio, spirillum, spirochete • Pleomorphic (many shapes) Morphology of Prokaryotic Cells: Groupings • Arrangement of cells is dependent on pattern of division and how cells remain attached after division: • Most prokaryotes divide by binary fission • Cells often stick together following division • Form characteristic groupings • Neisseria gonorrhoeae (diplococcus) • Streptococcus (long chains) • Sarcina (cubical packets) • Staphylococcus (grapelike clusters) Multicellular Associations • Some prokaryotes live as multicellular associations • Some bacteria form swarms of cells that glide over moist surfaces as a pack • Collectively release enzymes and degrade organic material, including other bacterial cells • When water or nutrients become limiting, cells form fruiting body visible to naked eye The Eukaryotic Cell Eukaryotic cells larger than prokaryotic cells Internal structures far more complex Have membrane-bound organelles 2 kinds • Animal • Plant The Eukaryotic Cell Eukaryotic and Prokaryotic Cells The Eukaryotic Cell • Organelles compartmentalize functions • Vesicles can transport compounds • Buds off from organelle, fuses with membrane of another Transfer of Molecules • Transport proteins similar to prokaryotes • Carriers: facilitated diffusion, active transport • Channels: form small gated pores, allow ions to diffuse • Aquaporins • Endocytosis and exocytosis additional processes Protein Structures Within the Cell • Ribosomes: protein synthesis • Eukaryotic cytoplasmic ribosome is 80S • Prokaryotic are 70S • Cytoskeleton: cell framework Membrane-Bound Organelles • Nucleus contains DNA • Mitochondria – generate ATP • Chloroplast - photosynthesis Membrane-Bound Organelles • Endoplasmic reticulum • Golgi apparatus • Lysosomes- vesicles with enzymes Photo credit • Cells- https://www.thoughtco.com/what-are-prokaryotes-and-eukaryotes-129478 • Bacetrial cell - https://www.pharmapproach.com/bacterial-cell-structure-and-function/ • Flagella - https://www.alpfmedical.info/causative-agent/images/4582_101_122-polar-flagella.jpg • Fimbriae pili - https://www.easybiologyclass.com/bacterial-cell-surface-structures-and-appendages-flagella-fimbriae-and-pili/amp/ • Conjugation - https://en.citizendium.org/wiki/Pilus • Slime layer/capsule - https://quizlet.com/318386820/micro-chapter-4-flash-cards/ • Cell wall - https://microbiologyinfo.com/differences-between-gram-positive-and-gram-negative-bacteria/ • Microbiology book: Nester's Microbiology: A Human Perspective