Chapter 3: Cellular Structure

Transcription

1 Chapter 3: Cellular Structure 1. Prokaryotic Cell Structure 2. Eukaryotic Cell Structure

2 1. Prokaryotic Cell Structure A. Cell Shape B. External Structures C. Internal (Cytoplasmic) Structures

3 A. Cell Shape Chapter Reading pp

4 Prokaryotic Cell Shape One convenient characteristic with which to identify and classify prokaryotes is their size and shape as seen in the microscope. the diameter of prokaryotic cells ranges from ~0.2 to 2.0 mm prokaryotes are essentially unicellular and more or less maintain a constant shape (monomorphic) most prokaryotes have a spherical, rod-shaped or spiral appearance though other shapes exist as well

5 Spherical Cells spherical prokaryotes are referred to as cocci (singular = coccus) different kinds of cocci exhibit characteristic arrangements: diplo- = found in pairs strepto- = found in chains staphylo- = irregular clusters tetrad = group of 4 sarcina = cube structure of 8

6 Rod-Shaped Cells rod-shaped prokaryotes are referred to as bacilli (singular = bacillus) also found in various arrangements: diplo- = length-wise pairs strepto- = length-wise chains cocco- = rounded bacilli palisade = bacilli side by side

7 Curved or Spiral Cells vibrio = curved rod spirillum = twisted rod spirochete = corkscrew rod

8 B. External Structures Chapter Reading pp

9 Prokaryotic Cell Structures Ribosome Inclusions Cytoplasm Nucleoid Glycocalyx Cell wall Flagellum Cell membrane

10 Plasma Membrane true barrier between internal & external Head, which contains phosphate (hydrophilic) Tail (hydrophobic) Phospholipid Integral proteins Phospholipid bilayer Integral protein Peripheral protein Cytoplasm Integral glycoprotein phospholipid content is a bit different compared to eukaryotes

11 Diffusion & Osmosis Extracellular fluid Cytoplasm Diffusion through the phospholipid bilayer Facilitated diffusion through a nonspecific channel protein Facilitated diffusion through a permease specific for one chemical; binding of substrate causes shape change in channel protein Osmosis, the diffusion of water through a specific channel protein or through a phospholipid bilayer

12 Concentration Gradients Na + Cl Cell exterior (extracellular fluid) Different concentrations of ions inside vs outside the cell are set up & maintained by : Integral protein Protein Cell interior (cytoplasm) Cytoplasmic membrane DNA Protein protein pumps active transport from low to high conc. protein channels & transport proteins facilitated diffusion Creates a net negative charge inside vs outside.

13 Bacterial Cell Wall The bacterial cell wall provides structure & support: main component is a structure called peptidoglycan repeating disaccharide backbone polypeptide-linked chains of a repeating disaccharide Glucose N-acetylglucosamine NAG N-acetylmuramic acid NAM tetrapeptide (amino acid) crossbridge connecting chains of amino acids (protects cell from osmotic lysis!)

14 Osmosis & Cell Lysis Cells without a wall (e.g., mycoplasmas, animal cells) H 2 O H 2 O H 2 O Cells with a wall (e.g., plants, fungal and bacterial cells) Cell wall H 2 O Cell wall H 2 O H 2 O Cell membrane Isotonic solution Cell membrane Hypertonic solution Hypotonic solution

15 Porin Outer membrane of cell wall Peptidoglycan layer of cell wall Porin (sectioned) Periplasmic space Cell membrane O side chain (varies in length and composition) Core polysaccharide n Lipopolysaccharide (LPS) Integral proteins Phospholipid layers Gram-negative Cell Wall thin layer of peptidoglycan Lipid A (embedded in outer membrane) Gram-negative cell wall Fatty acid outer membrane containing lipopolysaccharide (LPS) Lipid A (endotoxin) + polysaccharide

16 Gram-positive Cell Wall Peptidoglycan layer (cell wall) Cell membrane Lipoteichoic acid Teichoic acid Integral protein Gram-positive cell wall thick-layered peptidoglycan cell wall w/teichoic acids NO outer membrane

17 Bacterial Glycocalyx ( sugar cup ) Outermost layer that surrounds the bacterium called a capsule if compact, tightly attached to cell wall called a slime layer if loosely attached, water soluble mediates adhesion, biofilm formation protects from dessication, phagocytosis

18 Bacterial Flagellum basal body, hook & filament basal body anchors flagellum in PM, cell wall, rotates hook & filament to propel bacterium

19 Flagella & Bacterial Motility Bacteria undergo taxis, i.e. movement in response to something. e.g., chemotaxis (movement in response to a chemical substance) Tumble Run attractant (RUN = flagella rotate counterclockwise) Run Tumble (TUMBLE = clockwise) Involves random runs & tumbles : longer runs, less tumbles in direction of good stuff

20 Axial Filament Bundle of endoflagella found in spirochetes anchored at one end of cell and rotate in unison rotates cell like a corkscrew to propel it forward

21 Fimbriae & Pili Non-motile appendages that are chemically and functionally different than flagella. Fimbriae involved in adhesion Pili (singular = pilus) used in conjugation Fimbria Flagellum Conjugation pilus

22 C. Internal (Cytoplasmic) Structures Chapter Reading pp

23 Prokaryotic Ribosomes Carry out protein synthesis (i.e., translation of mrna). Ribosomes consist of 1 large and 1 small subunit. both subunits are made of rrna & ribosomal proteins smaller, somewhat different from eukaryotic ribosomes specifically targeted by some antibiotics

24 1 DNA is replicated. Cell wall Vegetative cell DNA aligns along the cell s long axis. Cytoplasmic membrane invaginates to form forespore. Cytoplasmic membrane grows and engulfs forespore within a second membrane. Vegetative cell s DNA disintegrates. Endospores Cytoplasmic membrane DNA When conditions are bad, some Gram + bacteria can form endospores: Forespore First membrane Second membrane inactive, dormant cells enclosed in a highly resistant spore coat remain dormant until conditions are good (even 1000 s of yrs!) very resistant to heating, freezing, dessication

25 Completion of Endospore Formation 5 A cortex of calcium and dipicolinic acid is deposited between the membranes. Cortex 6 Spore coat forms around endospore. Spore coat 7 Maturation of endospore; completion of spore coat and increase in resistance to heat and chemicals by unknown process. Outer spore cost Endospore 8 Endospore released from original cell. Outer spore cost

26 The Genetic Material A region called the nucleoid contains the circular bacterial chromosome (DNA + non-histone proteins): usually several million base pairs (bp) in size e.g. the E. coli genome is ~4 mega-bp s (4 Mbp) contains all bacterial genes plus an origin of replication (Ori) Ori is where DNA replication starts, essential to copy the chromosome

27 Plasmids Some bacteria have >1 extrachromosomal, non-essential circular DNA molecules called plasmids: plasmid map much smaller than bacterial chromosome several kilo-base pairs (usu. 3-6 Kb) have own Ori so it is copied when cell divides

28 What s the Role of Plasmids? Plasmids generally contain genes that confer some sort of advantage for survival and reproduction: 1) genes providing protection from toxic substances including antibiotic resistance 2) genes enabling the metabolism of additional sources of energy 3) genes for toxins to kill microbial competitors, enhance pathogenicity 4) genes involved in gene transfer by conjugation

29 Inclusions & Chromatophores Inclusions are deposits of various materials found in certain types of bacteria (e.g., magnetosomes). Chromatophores are pigment-containing infoldings of the plasma membrane in some photosynthetic bacteria.

30 2. Eukaryotic Cell Structure Chapter Reading pp

31 Eukaryotic Organelles Nucleolus Perinuclear space Cilia Ribosomes Nuclear envelope Nuclear pore Lysosome Mitochondrion Centriole Secretory vesicle Golgi body Transport vesicles Cytoskeleton Rough endoplasmic reticulum Cell membrane Smooth endoplasmic reticulum

32 Nucleus Storage of Genetic Material: Nucleolus Nucleoplasm Chromatin Nuclear envelope Two phospholipid bilayers Nuclear pores DNA + histones = Chromosomes when condensed in M phase Chromatin when uncondensed Rough ER Nucleolus assembly of ribosomes from rrna & proteins Rough ER

33 Endoplasmic Reticulum (ER) Rough ER (RER) ribosomes on cytoplasmic face of ER membrane synthesize proteins across ER membrane into lumen beginning of the secretory pathway Membrane-bound ribosomes Mitochondrion Smooth ER (SER) Free ribosomes no ribosomes has membraneassociated enzymes that catalyze new lipid synthesis (also found in RER) Smooth endoplasmic reticulum (SER) Rough endoplasmic reticulum (RER)

34 The Golgi Complex Proteins destined to leave ER next go to the Golgi transported in vesicles, next stop in secretory pathway Secretory vesicles undergo any necessary modifications or processing then sent via vesicles to various destinations Vesicles arriving from ER e.g., plasma membrane, exterior of cell, other organelles

35 Mitochondrion ATP production via cellular respiration Krebs cycle e - transport chemiosmosis Outer membrane Inner membrane Crista high [H + ] in the intermembrane space due to e - transport in inner membr. Matrix *H + gradient fuels ATP synthesis* Ribosomes

36 Chloroplast Organelle of photosynthesis: light reactions occur in the thylakoids Granum convert sunlight to energy in ATP and NADPH dark reactions occur in stroma energy from ATP & NADPH used to make sugars from CO 2 and H 2 O Stroma Thylakoid Inner bilayer membrane Outer bilayer membrane

37 Flagella & Cilia Microbial structures used for locomotion: Flagella long & few wave-like motion Cilia short & many

38 Other Organelles Lysosomes acidic compartments for the breakdown or digestion of foreign or waste material Vacuoles large storage compartments Peroxisomes metabolize fats for heat production, degrade toxins H 2 O 2 byproduct is neutralized by catalase Centrosomes region containing centrioles and other proteins organizing center for mitotic spindle fibers

39 Key Terms for Chapter 3 coccus, bacillus, vibrio, spirillum, spirochete diplo-, strepto-, staphylo-, tetrad, sarcina peptidoglycan, teichoic acid, LPS, endotoxin glycocalyx, capsule, fimbriae, pili chemotaxis, endospores, plasmids, nucleoid inclusions, chromatophores, vegetative periplasmic space (periplasm) Relevant Chapter Questions MC: 1, 5, 7-10, Matching: 1, 2 Labeling (both) SA: 1-4, 7-10, 12-16