Chapter 4

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Prokaryote

comes from the Greek words for prenucleus.
 One circular chromosome, not in a membrane
 No histones
 No organelles
 Peptidoglycan cell walls
 Binary fission
EX:
Staphylococcus
.. E. coli

Eukaryote

comes from the Greek words for true nucleus.
 Paired chromosomes, in nuclear membrane
 Histones
 Organelles
 Polysaccharide cell walls
 Mitotic spindle
EX:
1)Amoeba
2)Paramecium

Size of Bacteria

0.2 -2.0 μm  2 - 8 μm

Bacillus

(rod-shaped)

Coccus

(spherical)

Spiral

 Spirillum
 Vibrio
 Spirochete

Arrangement of cocci:

based on plane of division.
a) One plane,
b) two planes,
c) three planes, and
d) multiple planes

Arrangement of Bacilli

Single bacilli are most common, however, some bacilli remain attached to each other forming chains.

Arrangement of Spiral bacteria

-Curved rods
- Helical and rigid body
- Helical and flexible body

Unusual shapes of Bacteria

 Star-shaped Stella (a)
 Square Haloarcula (b)

Most bacteria are

monomorphic. A few are pleomorphic (e,g. Rhizobium and Corynebacterium)

Pairs:

Diplococci, diplobacilli

Clusters:

Staphylococci

Chains:

Streptococci, streptobacilli

Glycocalyx:

a network of polysaccharides on the surface of a bacterium
 Is formed outside cell wall
 Usually sticky
 Such extracellular polysaccharide allows cell to attach

A capsule

-is neatly organized
-prevent phagocytosis of
>Bacillus anthracis
>Streptococcus pneumoniae
>Klebsiella pneumoniae
-supports attachment of: Streptococcus mutans

A slime layer

is unorganized and loose

Flagella

 Long filamentous appendages that propel bacteria
 Outside cell wall
 Made of chains of flagellin
 Attached to a protein hook
 Anchored to the cell wall and membrane by the basal body

Motile Cells

 rotate flagella to move ("run" or tumble)
 The direction of flagella rotation determines which of
these movements will occur

Importance of Motile Cells

 Movement toward or away from stimuli (taxis)
 Flagella proteins are H antigens

Axial Filaments

 an endoflagella consisting of a bundle of fibrils
 Found in spirochetes
 Anchored at one end of a cell
 Rotation causes cell to move in a spiral motion

Many Gram negative bacteria contain

hairlike appendages that are shorter, thinner and
straighter than flagella - fimbriae

Fimbriae

allow attachment

Pili

are used to transfer DNA from one cell to another
- Unlike fimbriae that can be numerous at the poles or evenly distributed all over the cell surface, pili number one or two per cell

Cell Wall

 A complex semirigid structure
>responsible for cell shape.
> Prevents osmotic lysis
 Made of peptidoglycan (in bacteria)

Peptidoglycan

 Polymer of disaccharide
>N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM)
 Linked by polypeptides

Gram-Positive Cell Walls

 Thick peptidoglycan
 Teichoic acids
 No outer membrane
 In acid-fast cells, contains mycolic acid
 Teichoic acids: consist primarily of an alcohol (glycerol
or ribitol) and phosphate
>Lipoteichoic acid links to plasma membrane
>Wall teichoic acid links to peptidoglycan
 Importance
> May regulate movement of cations.
> Polysaccharides provide antigenic variation.

Gram-Negative Cell Walls

 Thin peptidoglycan
 No teichoic acids
 Outer membrane

Gram-Negative Outer Membrane

 Consists of lipopolysaccharides, lipoproteins, phospholipids
 Forms the periplasm between the outer membrane and the plasma membrane.
 Protects cells from phagocytes, complement, and antibiotics
 Contain O polysaccharide, an antigen, e.g., E. coli O157:H7
 Contain Lipid A, an endotoxin
 Contain Porins, proteins that form channels through
membrane.

Gram Positive Stain Mechanism

 Crystal violet-iodine crystals form in cell.
 Alcohol dehydrates peptidoglycan
- but no holes in peptidoglycan
 CV-I crystals do not wash out

Gram Negative Stain Mechanism

 Alcohol dissolves outer membrane
>leaves holes in peptidoglycan.
 CV-I washes out

Mycoplasmas

(smallest bacteria and pass through filters)
 Lack cell walls
 Contain sterols in plasma membrane

Sterol

thought to help protect cell lysis (rupture)

Archaea

 Lack peptidoglycan cell wall (wall-less)
- or
 have walls of pseudomurein
-Similar to peptidoglycan but differs as follows:
> Contains N-acetyltalosaminuronic acid instead of NAM
> D amino acids found in bacterial cell walls

Atypical Cell Walls (Acid-fast cell walls)

 Like gram-positive, however
- Waxy lipid (mycolic acid) bound to peptidoglycan
 Mycobacterium
 Nocardia

Lysozyme

digests the disaccharide in peptidoglycan.

Penicillin

inhibits formation of peptide bridges in peptidoglycan.

Protoplast

is a wall-less Gram positive bacterium or plant cell

L forms are wall-less cells

that swell into irregular shapes.(Named for the Lister institute where they were discovered)

Spheroplast

is a wall-less Gram-negative cell.

Protoplasts and Spheroplasts

are susceptible to osmotic lysis.

Plasma Membrane

 Consists of:
-Phospholipid bilayer
-Peripheral proteins
-Integral proteins (inside)
-Transmembrane proteins (integral proteins that
penetrate membrane completely)

Fluid Mosaic Model of Membrane Structure

 Is the dynamic arrangement of proteins and phospholipids
- Membrane is as viscous as olive oil.
>Proteins move to function.
> Phospholipids rotate
and move laterally.
- Viscous nature ensures
> movement does not
destroy membrane.

Plasma Membrane

 Selectively permeable
- allows passage of some molecules
 Contain enzymes for ATP production
 Contain photosynthetic pigments on foldings (plasma
membrane folds) called chromatophores or thylakoids

Damage to Plasma Membrane

 Can be damaged by:
- alcohols,
- quaternary ammonium (detergents),
- polymyxin antibiotics
>Consequence
---- leakage of cell contents.

Simple diffusion:

Movement of a solute from an area
of high concentration to an area of low concentration.

Facilitative diffusion:

Solute combines with a
transporter protein in the membrane.

Osmosis:

The movement of water across a selectively
permeable membrane from an area of high water
concentration to an area of lower water.

Osmotic pressure:

The pressure needed to stop the movement of water across the membrane.

Active transport

of substances requires a transporter protein and ATP.

Group translocation

of substances requires a transporter protein and high energy supplied by high energy compound, phosphoenolpyruvic acid (PEP).
 The substance is modified in the process
>Example by phosphorylation
---make it not possible to be transported out
---Example is transport of glucose

Cytoplasm

is the substance inside the plasma membrane.

Nuclear area (nucleoid) - consists of:

 Long, continuous, circular thread of double-stranded
DNA (bacterial chromosome)
 Carries genetic information
 lacks cell membrane (unlike eukaryotic chromosome).

Ribosomes

-- Function as the site for protein synthesis. The cytoplasm of prokaryotic cell contains tens of thousands of these small structures which gives the cytoplasm a granular appearance
--Contrarily, eukaryotic ribosomes are 80s, which is divided into 60s for the large, and 40s for the small subunit.

S in 30s, 50s, 70s is

Svedberg units and refers to the relative rate of sedimentation during ultra-high speed centrifugation. Sedimentation rate is a function of the size, weight and shape of a particle.

Streptomycin and gentamycin
attach to the 30s

while chloroamphenicol and erythromycin attach to the 50s subunit inhibiting protein synthesis. Some antibiotics work by inhibiting protein synthesis on prokaryotic ribosomes.

Eukaryotic Ribosomes

 Protein synthesis
 80S
>Membrane-bound: Attached to ER
> Free: In cytoplasm
 70S
> In chloroplasts and mitochondria

Endospores

are specialized "resting cells" or structures formed inside certain gram-positive bacterial cells
 When essential nutrients are depleted
 Endospores are resistant to desication, heat, chemicals
 Bacillus, Clostridium form endospores -can be located terminally (at one end), subterminally (near one end) and centrally in the vegetative cell

Sporulation

is endospore formation

Germination

is return to vegetative state

Metachromatic granules (volutin)

Phosphate reserves

Polysaccharide granules

Energy reserves

Lipid inclusions

Energy reserves

Sulfur granules

Energy reserves

Carboxysomes

Contain ribulose 1,5-diphosphate carboxylase for CO2 fixation

Gas vacuoles

Protein covered cylinders (buoyancy)

Magnetosomes

Iron oxide (acts as magnet) (destroys H2O2)

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