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Black Chapter 3 – Characteristics of prokaryotic and Eukaryotic cells

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					Chapter 4 Characteristics of prokaryotic and Eukaryotic cells
Basic cells Type
Both prokaryotic and eukaryotic cells have membranes that define the bounds of the
living cell, and both contain genetic information stored in DNA.
Prokaryotic cells differ from eukaryotic cells in that they
        1. lack a defined nucleus
        2. lack membrane-bound organells (except for a few membrane-covered
             bodies in certain type of prokaryotes).
        3. Peptidoglycan is found in prokaryotic cells only.

Three Domains
   - Bacteria, Archaea and Eukarya (Protista, Fungi, Plantae and Animalia)
   - Bacteria and Archaea are prokaryotic , Eukarya is eukaryotic
   - “bacteria” applies to Bacteria and Archaea

Six Kindoms: Bacteria, Archaea, Protista, Fungi, Plantae and Animalia)

Size, Shape, and Arrangement
Prokaryotes are the smallest living organisms, 0.5 to 2 microns (however some spiral
ones are much bigger; some cyanobacteria can be as long as 60 microns).

Shape:
Coccus (cocci - spherical),
Bacillus (bacilli - rod-shaped),
Spirillum (spirilli - rigid wavy-shaped),
Vibrio (vibrios - comma-shaped), and
Spirochete (spirochetes - cockscrew-shaped),
Square bacteria – discovered on the shores of the Red sea.

Note pleomorphism in some bacteria – a variety of form even within a single species; in
aging cultures this may be also be observed.

Arrangement:
Diplo – 2 in pair
Staphylo - grapelike clusters
Strepto - long chains
Tetrad – four cells in a cube
Sarcinae – 8 in cluster

An Overview of Structures
     - cell membrane, usually surround by a cell wall and sometimes by an
         additional outer layer
     - cytoplasm with ribosomes, nuclear region, granules and/or vesicles
     - external structures, such as capsules, flagella and pili.
Write the name of bacteria in Italic.ex. E. coli.

The Cell Wall
      - Complex, semirigid, maintain shape
      - maintains osmotic pressure by inhibiting lysis
      - Transport (pores)
      - protect

COMPONENTES OF CELL WALLS
Peptidoglycan
      - murein
      - N-actetylglucosamine alternates with N-acetylmuramic acid ( 2
          polysaccharides) as backbone then joined by peptide chains with
          tetrapeptides.

Outer Membrane
      - found primarily in Gram-negative bacteria
      - bilayer membrane, forms the outmost layer of cell wall, attached to the
        peptidoglycan
      – protects against certain antibodies (penicillin), lysozyme.

Lipopolysaccharide (LPS)
      – diagnostic importance (salmonella sero variance)
      – also called endotoxin
      – important part of outer membrane
      – not released until the cell walls of dead bacteria are broken down
      – consists of polysaccharide and lipid A
      – polysaccharides are used for the identification of Gram-negative
      – Lipid A is responsible for the toxic properties, cause septic shock

Periplasmic space
       – Between the cell wall and cell membrane
       – contains a high concentration of degrading enzymes and transport proteins.

Distinguishing Bacteria by Cell Walls
       - certain properties of cell walls produce different staining reactions
       - Gram-positive, Gram-negative and acid fast bacteria

After enzyme digestion
       - Gram-positive bacteria become protoplast – cell with cell membrane , no cell
          wall.
       - Gram-negative bacteria become spheroplast – cell with cell membrane and
          most of outer membrane
Gram Positive                                 Gram negetive
Thick layer of peptidoglycan                  Thin layer of peptidoglycan
Teichoic acid                                 No teichoic acid
No Lipopolysaccharide                         Lipopolysaccharide
No Periplasmic membrane                       Periplasmic membrane
No Outer membrane                             Outer membrane
High sensitivity to penicillin                Low sensitivity to penicillin
Low sensitivity to streptomycin               High sensitivity to streptomycin


Gram-negative bacteria fail to retain the crystal violet-iodine dye during the
decolorizing procedure due to the thin layer of peptidoglycan and many
liposaccharides.

Penicillin blocks the final stages of peptidoglycan synthesis.
Lysozyme, found in tears and other human body fluids can digests peptidoglycan.

Acid –Fasts bacteria
      -      Mycobacterium tuberculosis causes tuberculosis
      -       can be diagnosed by acid-fast stain,
      -      cell walls – unique waxy layer made of mycolic acid
      -      60% lipids
      -      Grow slow, lipid impede entry of nutrients
      -      Gram positive
      -      Skin test of an induration of 15 mm in diameter is positive.
      -       Isoniazid (INH) daily for 9 months to treat. which inhibits synthesis of
             components of the waxy layer.
      .
Wall-Deficient Organisms
Mycoplasma
      - filterable
      - no cell wall, no outer membrane
      - plasma membrane strengthened with sterols to maintain shape.
      - Extreme pleomorphism
      - Form colonies look like egg fried sunny-side up.

L-forms
      --      suddenly lose their ability to form cell walls
      -       Gram positive or gram-negative bacteria that do not make a cell wall.
      -       occur naturally or be caused by chemical treatment
      -       when treatment is discontinued, the L-forms can convert to walled forms
              and regrow
       -      Mycobacterium paratuberculosis with Crohn’s disease, a chronic disorder
              of the intestine
CELL MEMBRANE
     - Unit membrane, have the same general structure as other cell membrane,
     - Phospholipids bilayer, hydrophilic head (phosphate), hydrophobic tail (fatty
       acid
     - fluid-mosaic structure with mobile proteins moved like fluid, and proteins
       embedded in a mosaic pattern.
     - No sterol.

Internal Structures
Cytoplasm
       - semifluid substance inside the cell membrane,
       - 80% water, contains organic materials, ribosomes , cytoplasmic inclusions.
       -
 Ribosomes
       - consist of RNA and protein
       - sites for protein synthesis
       - grouped in long chains, polyribosomes
       - size measured by sedimentation rate, Svedberg (S) unit
       - bacteria: 70S, streptomucin and erythromycin bind to 70S ribosomes, disrupt
           protein synthesis
       - antibiotics do not affect 80S in Eukaryotic cells, they kill bacteria without
           harming host cells, subunits : 30S & 50S
       -

Nuclear Region (Nucleoid)
      - one circular double strands DNA (20% of cell volume)
      - small circular DNA called plasmids, encode specialized, nonessential
         functions.
      - One chromosome

Internal membrane Systems
       - in photosynthetic bacteria and cyanobacteria
       - chromatophores, derived from cell membrane
       - capture sunlight energy for synthesis of sugars

Inclusions
       - granules, not bounded by membrane, store glycogen
       - vesicles (have membrane), filled with iron compounds (magnetosomes)
       - volutin, or metachromatic granules, polyphosphate granules, display
           metachromasia – exhibit different intensities of color

Endopores
     - Dormant structures (resting cells)
     - found in three Gram positive genera: Clostridium, Bacillus and Sporosarcina
       -   formed in response to adverse condition. They are durable, have thick walls,
           survive extreme heat, toxic chemicals, radiation.
       -   Sporulation, or endospore formation - germination, when environment
           conditions are favorable
       -   help bacteria survive is not a means of reproduction
       -   Fungus produces many spores, which help the organism survive and provide a
           means of reproduction
       -   The core of an endopore contain living material and is surrounded by a cortex,
           spore coat, and exosporium( a delicate thin layer), DNA, ribosomes, large
           amounts of dipicolinic acid, calcium ions.

External Structure to the Cell Wall
Falgella
       – monotrichous (one), lophotrichous (with tuft at one end or both ends),
          amphitrichous ( two, one at each ends), peritrichous (all over), atrichous
          (no flahella)
       – Parts of flagellum – filament, hook, and basal body (anchors flagellum to cell
          wall/plasma membrane)
       – Flagellin protein organized into hollow cylinders (9 + 2 pattern)  motility

Chemotaxis
     movement toward attractions and away from repellents

Phototaxis
      movement toward or away from light

Axial filament
       - In spirochetes
       - bundles of fibrils that arise at the ends of the cell beneath the outer sheath and
           spiral around the cell
       - rotation propels spirochetes in a spiral motion

Pili
       –  hairlike appendages (for attachment rather than motility)
       –  long conjugation pili ,sex pili, furnish a pathway for DNA transfer -
          conjugation
      – short attachment fimbriae, allow cell to attach to surfaces
              -       hemagglutination – cause red blood cells to clump
              -       in Neisseria gonorrhoeae, strains with pili are highly infectious,
                      attach to epithelial cells of urogential system, also attach to sperm,
                      can spread to next individual
              -       some bacteria form a thin layer at the air-water interface of a broth
                      culture called pellicle – many bacteria adhere to the surface by
                      attachment pili, near air, where the oxygen concentration is
                      greatest.
Glycocalyx
       –   viscous gelatinous polymer (polysaccharides and small proteins)
       –   makes a thick capsule or thin slime layer.
       –   Function (capsules) – bacterial virulence, protect against phagocytes, slows
           dehydration
       –   (slime layer) – loosely arranged polysaccharide, protect the cell against
           drying, help trap nutrients, and bind cells together, as in dental plaque, trap
           nutrients.

ARCHAEON CELL
    - Archaeon cell walls are composed of either protein or a peptidoglycan called
      pseudomurein, not found in any other living things. Some archaea do not
      have cell walls.
    - The bonds in the cytoplasmic membrane of archaea cells enter linkages, which
      are stronger than the ester bonds fond in bacteria.,hydrocarbon molecules are
      joined to glycerol by ether linkage instead ester linkage.

EUKARYOTIC CELLS
An Overview of Structure
Eukaryotic cells, which are generally larger and more complex than prokaryotic cells are
the basic structural unit of microscopic and macroscopic organisms of the kingdoms
Protista, Plantae, Fungi, and Animalia.

The Plasma Membarne
Plasma membranes of eukaryotic cells are almost identical to those of prokaryotic cells,
except that they contains sterol. The function of eukarotic plasma membranes, however,
is limited primarily to regulating movement of substances into and out of cells.

Internal Structure
Eukaryotic cells are characterized by the presence of a membrane-enclosed cell nucleus,
with a nuclear envelope, nucleoplasm, nucleoli (stor RNA), and chromosomes
(typically paired) that contain DNA and proteins called histones. chromatin (uncoiled
chromosomes, fine threads)

In body cell division by mitosis, each cell receives one of each chromosomes found in
parent cells.
 In sex cell division by meiosis, each cell receives one chromosomes from each pair -
haploid, and can become gametes ( in sexual reproduction, two gametes form a diploid
zygote)or spores ( dormant or by mitosis as haploid vegetative cells)

Mitochondria, the powerhouse of eukaryotic cells, carry out the oxidative reactions that
capture energy in ATP.Has outer and inner membrane and matrix. Inner membrane
folded to form cristae, embedded in matrix.

Photosynthetic cells contain chloroplasts, which capture energy from light.
Thylakoids: inner membrane of a choloplast is arranged in stacks.
Cholorophyll is embedded in thylakoids.
Eukaryotic ribosomes (80S)are larger than those of prokaryotes (70S) and can be free or
attached to endoplasmic reticulum. Free ribosomes make protein to be used in the cell;
those that are attached to endoplasmic reticulum make proteins to be secreted.

The endoplasmic reticulum is an extensive membrane network. Without ribosomes
(smooth ER), the endoplasmic reticulum synthesize lipids; when combined with
ribosomes (rough ER), it produces protein.

The Golgi apparatus is a set of stacked membranes that are receive, modify, and
package proteins into secretory vesicles.

Lysosomes, in animal cells, are organelles that contain digestive enzymes, which destroy
dead cells and digest contents of vacuoles.

Peroxisomes are membrane-enclosed organelles that convert peroxides to water and
oxygen and sometimes oxidize amino acids and fats.

Vacuoles contain various stored substances and materials engulfed by phagocytosis.

The cytoskeleton is a network of microfilaments and microtubles that support and give
rigidity to cells and provide for cell movements.

External Structure
Eukaryotic cells do not have pili or axial filaments, but some have flagella and smaller
versions called cilia that also function for locomotion.

Most external components of eukaryotic cells are concerned with movement. Eukaryotic
flagella are composed of microtubules; sliding of proteins at their bases causes them to
move.

Cilia are shorter and more than flagella and beat in coordinated waves, same structure of
microtubule.

Pseudopodia are projections into which cytoplasm flows, causing a creeping movement.
Eukaryotic cells of the plant and fungi kingdoms have cell walls, as do the algal protests.

Cell Walls
      - do not contain peptidoglycan like bacteria
      - algal cell walls consist cellulose
      - fungi consist of cellulose, chitin or both
      - some protozoa have a pellicle, which functions much as a cell wall, though it
           is more flexible and skin-like


EVOLUTION BY ENDOSYMBIOSIS
The endosymbiont theory holds that organelles of eukaryotic cells arose from
prokaryotes that had been engulfed and survived to develop a symbiotic
relationship by living inside the larger cell.
Mitochondria, chloroplasts, flagella, and microtubules are believed to have originated
from endosymbiont prokaryotes.
Many examples exist of modern prokaryotes living endosymbiotically inside eukaryotes.

THE MOVEMENT OF SUBSTANCES ACROSS MEMBRANES
Simple diffusion
Simple diffusion results from the molecular kinetic energy and random movement of
particles. The role of diffusion in living cells depends on the size of particles, nature of
membranes, and distances substances must move inside cells.

Facilitated Diffusion
Facilitated diffusion uses protein carrier molecules or protein-lined pores in membranes
in moving ions or molecules from high to low concentrations.

Osmosis
Osmosis is the net movement of water molecules through a selective permeable
membrane from a region of higher concentration of water to a region of lower
concentration.The osmotic pressure of a solution is the pressurerequired to prevent such
a flow.

Active transport
Active processes that move substances across membranes generally result in movement
from regions of lower concentration of the substances to regions of higher concentration
and require the cell to expand energy.
Active transport requires a protein carrier molecule in a membrane, a siurce of ATP, and
an enzyme that releases energy from ATP.
Active transport is important in cell functions because it allows cells to take up
substances that are in low concentration in the environment and to concentrate those
substances within the cell.

Endocytosis and Exocytosis
Endocytosis and exocytosis , which occur only in eukaryotic cells, involve formation of
vesicles from fragments of plasma membrane and fusion of vesicles with the plasma
membranes, respectively.
In endocytosis the vesicles enters the cell, as in phagocytosis.
In exocytosis the vesicle leaves the cell, as in secretion.
Endocytosis and exocytosis are important because they allow the movement of relatively
large quantities of materials across plasma membranes.

				
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