1. Eukaryotic Cell Structure 2. Prokaryotic Cell Chapter 4 (notes).pdf · PDF file1...

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Transcript of 1. Eukaryotic Cell Structure 2. Prokaryotic Cell Chapter 4 (notes).pdf · PDF file1...

  • 1

    Chapter 4:Cellular Structure

    2. Prokaryotic Cell Structure

    1. Eukaryotic Cell Structure

    1. Eukaryotic Cell Structure

    Eukaryotic Organelles

  • 2

    Nucleus Holds Genetic Material DNA associated with

    histone proteinsChromosomes whencondensed in M phase

    Chromatin in G1, S & G2when uncondensed

    Ribosome Assembly assembled in nucleolus rRNA + ribosomal prot. carry out protein

    synthesis in cytoplasm

    *all gene expression begins in nucleus (transcription)*

    Endoplasmic Reticulum (ER) Rough ER (RER)

    ribosomes on cytoplasmicface of ER membrane

    synthesize proteins acrossER membrane into lumen

    beginning of thesecretory pathway

    Smooth ER (SER) no ribosomes has membrane-associated

    enzymes that catalyzenew lipid synthesis(also found in RER)

    The Golgi Complex

    Proteins destined to leave ER next go to the Golgi transported in vesicles, next stop in secretory pathway undergo any necessary modifications or processing then sent via vesicles to various destinations

    e.g., plasma membrane, exterior of cell, lysosomes

  • 3

    Mitochondria ATP productionvia respiration

    Krebs cycle

    e- transport

    chemiosmosis

    Mitochondrialstructure is keyfor H+ gradient

    high [H+] in the intermembranespace producedby e- transportin inner membr.*H+ gradient fuels ATP synthesis *

    Chloroplasts Organelle of photosynthesis:

    light reactionsoccur in thethylakoids

    convert sunlightto energy in ATPand NADPH

    dark reactionsoccur in stroma

    energy from ATP& NADPH used tomake sugars fromCO2 and H2O

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

    Cilia short & many

  • 4

    Other OrganellesLysosomes

    acidic compartments for the breakdown ordigestion of foreign or waste material

    Vacuoles large storage compartments

    Peroxisomes metabolize fats for heat production, degrade toxins H2O2 byproduct is neutralized by catalase

    Centrosomes region containing centrioles and other proteins organizing center for mitotic spindle fibers

    2. Prokaryotic Cell Structure

    A. Cell Shape

    B. External Structures

    C. Internal Structures

    A. Cell Shape

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    Prokaryotic Cell Shape One convenient characteristic with which toidentify and classify prokaryotes is theirsize and shape as seen in the microscope.

    the diameter of prokaryotic cells ranges from~0.2 to 2.0 m

    prokaryotes are essentially unicellular and moreor less maintain a constant shape (monomorphic)

    most prokaryotes have a spherical, rod-shapedor spiral appearance though other shapes existas well

    Spherical or Round Cells spherical prokaryotes arereferred to as cocci(singular = coccus)

    diplo- = found in pairs

    different kinds of cocciexhibit characteristicarrangements:

    strepto- = found in chains

    staphylo- = irregular clusters

    tetrad = group of 4

    sarcina = cube structure

    Rod-Shaped Cells rod-shaped prokaryotesare referred to as bacilli(singular = bacillus)

    also found in variousarrangements:

    diplo- = length-wise pairs

    strepto- = length-wise chains

    cocco- = rounded bacilli

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    Curved or Spiral Cells

    vibrio = curved rod

    spirillum = twisted rod

    spirochete = corkscrew rod

    B. External Structures

    Prokaryotic Cell Structures

  • 7

    Plasma Membrane true barrier between

    internal & external

    a phospholipid bilayer like any other membrane thoughphospholipid content a bit different from eukaryotes

    Diffusion & Osmosis Plasma membraneis a semi-permeablebarrier across which some substances can diffuse:

    diffusion = movement from high to low conc.

    osmosis = diffusion of water

    lysis preventedby cell wall

    Concentration Gradients Different concentrations of various substances (i.e., ions) inside vs outside the cell are set up & maintained by various membrane proteins:

    protein pumps move substances from lower to higher conc.

    active transport requires energy (ATP)

    protein channels, transport proteins facilitated diffusion of specific molecules

    The overall result of all these gradients is a net negativecharge inside the plasma membrane relative to outside.

  • 8

    Bacterial Cell Wall The bacterial cell wall provides structure & support: general component of cell wall isa structure called peptidoglycan chains of a repeating disaccharideconnected by polypeptides

    *protects cell from osmotic lysis*

    structurevariesamongdifferentbacteria

    Gram-positive Cell Wall

    multi-layered peptidoglycan cell wall w/teichoic acids NO outer membrane Gram-positive since 1o stain/mordant trapped by the

    thick peptidoglycan layer (i.e., not removed by wash step)

    Gram-negative Cell Wall

    single layer of peptidoglycan

    outer membrane containing lipopolysaccharide (LPS)

    Gram-negative since 1o stain/mordant lost with wash

    LPS contains Lipid A, also referred to as endotoxin

    *

  • 9

    Some Features of Gram-negativevs Gram-positive Bacteria

    *

    Bacterial Glycocalyx (sugar coat)Outermost layer that surroundsthe bacterium

    Made of protein,polysaccharide,or both

    varies greatly among bacteria

    called a slime layer if loosely attached, water soluble mediates adhesion, biofilm formation

    protects from dessication, phagocytosis

    called a capsule if compact, tightly attached to cell wall

    Bacterial Flagella

    Some bacteria get around via 1 or more flagella:0 = atrichous 1 = monotrichous 1 @ ea end = amphitrichous

    >1 @ ea end = lophotrichous all over = peritrichous

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    Flagellum Structure

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

    consists of basal body, hook & filament

    different from wave-like motion of eukaryotic flagellum

    Flagella & Bacterial Motility Bacteria can undergomovement toward or away from something (taxis):

    e.g., chemotaxis toward or away froma chemical substance

    Involves random runs& tumbles:

    longer runs, less tumblesto move toward good stuff

    shorter runs, more tumblesto avoid bad stuff

    (RUN = flagella rotate counterclockwise)

    (TUMBLE = clockwise)

    Axial Filaments Endoflagella found in spirochaetes.

    anchored atone end androtate

    propel cell likeacorkscrew

  • 11

    Fimbriae and Pili Non-motile appendages that are chemically and functionally different than flagella.Fimbriae

    many in number (usu.) involved in adhesionto specific targets

    Pili (or singular pilus) >1 used in conjugation

    C. Internal Structures

    Prokaryotic Ribosomes

    Ribosomes consist of 1 large and 1 small subunit.

    Carry out protein synthesis (i.e., translation of mRNA).

    both subunits are made of rRNA & ribosomal proteins smaller, somewhat different from eukaryotic ribosomes specifically targeted by some antibiotics

  • 12

    Endospores When conditions are bad, some Gram+bacteria can formendospores:

    inactive or restingcells enclosed in ahighly resistantspore coat

    remain dormant untilconditions are good(can be 1000s of yrs)

    very resistant toheating, freezing, dessication(active cells are called vegetative)

    The Genetic MaterialA region called the nucleoid contains the circular bacterial chromosome (DNA + non-histone proteins):

    usually several millionbase pairs (bp) in sizee.g.

    the E. coli genome is ~4 mega-bps (4 Mbp)

    contains all bacterialgenes plus an originof replication (Ori)

    Ori is where DNAreplication starts,essential to copy the chromosome

    PlasmidsSome bacteria have >1extrachromosomal,non-essential circular DNA molecules calledplasmids:

    much smaller thanbacterial chromosome

    have own Ori so it is copied when cell divides

    several kilo-base pairs(usu. 3-6 Kb)

    plasmidmap

  • 13

    Whats the Role of Plasmids?Plasmids generally contain genes that confersome sort of advantage for survival andreproduction:

    1) genes providing protection from toxic substances

    2) genes enabling the metabolism of additionalsources of energy

    3) genes for toxins to kill microbial competitors,enhance pathogenicity

    4) genes involved in gene transfer by conjugation

    including antibiotic resistance

    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.

    Key Terms for Chapter 4

    diplo-, strepto-, staphylo-, tetrad, sarcinae

    glycocalyx, capsule, fimbriae, pili

    peptidoglycan, teichoic acid, LPS, endotoxin

    a-, mono-, amphi-, lopho-, peritrichous flagella

    coccus, bacillus, vibrio, spirillum, spirochete

    chemotaxis, endospores, plasmids, nucleoid

    Relevant Chapter Questions rvw: 1, 3-7, 9, 11 MC: 1-7, 9

    inclusions, chromatophores, vegetative periplasmic space (periplasm)