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8/6/2019 Lecture 3; Prokaryotic and Eukaryotic Cells
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A. Eukaryotes - includeplants, animals, fungi,protozoa, and algae.
B. Prokaryotes includebacteria and Archaea.
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POINT OF COMP ARISONEUK ARYOTES P ROK ARYOTES
Nuclearenvelope
(Present ) T heir genetic materialis enclosed within a membrane[nucleus ]
(Absent ) T heir geneticmaterial is enclosed withina membrane [ nucleoid region ]
DNAassociatedstructure
Their D
NA is associated withhistones (simple proteins bound
to DNA, involved in the coiling ofchromosomes)
Their D
NA is notassociated with histones
O rganelles T hey possess membrane bound organelles
T hey lack membrane-bound organelles
Cell wall T heir cell walls are complex (having many parts)
T heir cell walls aresimpler
Means ofreproduction
T hey usually divide by mitosis &meiosis
T hey usually divide bybinary fission .
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1 . Viruses- are acellular organisms- structures/parts:
a. Viral capsid outer surface which iscomposed of repeating sub-units calledCAPSOMERES .
b. Viruses possess only one type of nucleic acid,either R N A or DN A, but never both.
- other characteristics:
a. Viruses do not possess the necessary cellularparts that can allow them to replicateindependent of the host cell.
b. T hey also lack the genes and enzymes thatare necessary for energy production.
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- classification : (they are classified based on
the ff:)a. type of nucleic acid they possess ( DNAviruses/R NA viruses)b. Shape of the capsid ( Icosahedral/Helical/ Polyhedral/ Complex)c. Number of capsomeresd. Size of capside. P resence or absence of an envelopef. type of host they infect (human/
plant/animal viruses)g. type of disease they produceh. target cell (e.g. T helper cells for H IV)i. Immunologic or antigenic properties
*BACTERIOPHAGES arespecial type of virus thatinfects primarilybacteria. T hey play a rolein the acquisition ofvirulence factors of
certain bacteria ( e.gdiphtheria toxin ofCorynebacteriumdiphtheria ), as well as inthe transfer of geneticmaterial from onebacterium to another(transduction )
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2 . Bacteria- are prokaryotic cells .- parts/characteristics:a. T heir outer surface
(called cell wall ) iscomposed mainly ofpeptidoglycan .
b. Bacteria possess bothDNA & RNA.
c. T hey do not have atrue nucleus, lackmitochondria & havesmaller ribosomes.
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- classification: (Bacteria areclassified broadly based ontheir physicalcharacteristics)
a. Gram negative bacteriawith cell walls ( e.gEs chirichia coli )
b. Gram positive w/ cell
walls ( e.g. Staphylococcu saureu s )
c. T hose that do not have acell wall (e.g. Mycoplasma)
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3 . Fungi
- are eukaryotic cells with an outersurface that is composed mainly ofchitin .-other features/characteristics:
a. Similar to bacteria, fungi possess
both DNA and R NA.b. U nlike bacteria, they possess a true
nucleus that is enclosed by a nuclearmembrane, mitochondria that
function for A TP /energy production.c. Fungal ribosomes are also larger
than bacterial ribosomes ( 80Svedberg units )
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4 . Protozoa
- are the representatives forparasites.- are also eukaryotic cells.- T hey are unicellular organisms that
divide by binary fission.- T heir outer surface is a flexible
membrane called a pellicle , whichis different from the typical cellseen in bacteria & fungi.
- P rotozoa also possess both DNA &RNA, as well as other features seenin typical; eukaryotic cells.
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5 . Algae- are eukaryotic organisms.
- T heir outer surface consistsprimarily of cellulose .
- Algae are described as plant-like organisms.
- Algae seldom produce disease inhumans.
- e.g. DI ATOMS are unicellular algaethat inhabit both fresh- and sea-water
-e.g. DIN OFLAGELLATES , like diatomsare also unicellular algae which are
important members of thephytoplankton group. T hey are alsoresponsible for what is known as redtide.
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POINT OF COMPARISON ALGAE P LANTSEukaryotic Yes YesPhotosynthetic Yes YesCells contain chlorophyll Yes YesU
se CO2
as energy source Yes YesStore energy in the formof starch
Yes Yes
Composed of roots, stems& leaves
No Most
Cell walls containcelluloseM
ost (except diatoms& dinoflagellates) YesMethod of reproduction Both asexual and
sexualSexual
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Bacteria have 3 basicshapes:
1 . coccus (pl. cocci) are spherical, oval, or
round-shaped bacteria(eg. Staphylococcus,Neisseria).- they may be seensingly , in pairs(diplococci ), in chains(streptococci ), in clusters(staphylococci ), in groupsof four ( tetrad ), or ingroups of eight ( octad ).
S treptococcusBacteria
Coccus Diplococci Streptococci
Staphylococci
Tetrad O ctad
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2 . bacillus (pl. bacilli) are rod-shaped organisms(e.g., E. coli , Salmonella )- some maybe very short,resembling elongated cocci
called coccobacilli (eg.H aemophilus influenzae )Salmonella
E. coli
H . influenzae
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3 . spirilla curved & spiral
shaped organisms may havedifferent variations:
Comma-shaped V ibriocholerae , the cholera-producing bacterium
Spiral in shape T reponema pallidum , the causative agentof syphilis
Club-shaped C orynebacterium diphtheriae ,the agent causing diphtheria
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C. diphtheriae
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1 . ENVELOPE STRUCTURESa. Glycocalyx
the outermost covering (some bacteria).- a gelatinous substance located external to the
cell wall.- composed of polysaccharide.- referred to as the capsule (strongly attachedto
the cell wall), & slime layer (loosely attached).
- functions:(1) indicative of the virulence of an organism(2 ) it is antigenic(3) it protects the organism from dehydration
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b. Outer membrane- the outer membrane of Gram negativebacteria is composed of L PS(lipopolysaccharide).
- functions:(1) T here is lipid portion in the L PS - Lipid A
responsible for endotoxin production.(2 ) T he polysaccharide component of the
outer membrane called O polysaccharideis antigenic .
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c. Cell Wall referred to as murein sacculus- principal component is peptidoglycan- Gram positive bacteria (multilayered) & Gram-negative
bacteria (monolayered).- functions :
(1) P rovides support & gives shape(2 ) It provides protection from osmotic
damage.(3) It is the site of action of beta-lactam antibiotics.(4) T he teichoic acid (Gram-positive bacteria like
S taphylococcus ) functions for attachment & is alsoantigenic.
(5) T he mycolic acid in the cell wall of M ycobacterium isresponsible for its acid fastness.
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d. Periplasmic space
a fluid filled space between the outermembrane & the plasma membrane
- functions:(1) Contains enzymes for breakdown of large
molecules.(2 ) Transports proteins for the regulation of the
osmolality (water movement) of the cell.
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2 . P ROJE CTIN G ST RU CTU RES
a. P ilus (pl., pili) or fimbria(pl., fimbriae)
- is a thread like structurethat projects from thecapsule.
- are commonly seen inGram negative organisms.
- functions:(1) F or adherence to cell
surface ( common pilus ).(2 ) F or attachment duringconjugation ( sex pilus ).
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b. Axial filaments & Flagella
- are whip-like structures projectingfrom the capsule and are organsfor motility.
- are classified into 5 types, namely:(1) Monotrichous single polar
flagellum ( V ibrio cholerae )(2 ) Lophotrichous a tuft of flagella
at one end of the bacterium(Bartonella baciliformi s )
(3) Amphitrichous flagella at bothends of the bacterium ( Spirillums erpen s )
(4) Peritrichous flagella all aroundthe bacillus ( Es cherichia coli )
(5) Atrichous without flagellum
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3 . INTERNAL STRUCTURES
a. Nucleoid no nucleoplasm & nuclear membrane- contains the genetic material ( DNA),w/c is a single, circular, doublestranded DNA.
b. Mesosome functions for cell division & is involved
in the secretion of substances by thebacteria
c. Ribosomesthe sites for protein synthesis- the target or site of action of some
antibiotics
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d. Granules or Inclusion bodies- found in certain bac teria &
serve for storage of food & energy(eg., metachromatic granule s ofCorynebacterium diphtheriae ).
e. Endospores- is composed of dipicolinic acid
- resistant to heat, drying,chemical agents & radiation -produced when theenvironmental conditions aredetrimental to the bacteria(sporulation ).
- [when the endospores aredamaged by chemical or physicalattacks it returns to its vegetativestate thru a process known asgermination ].
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I. NUTRITIONAL REQUIREMENTS1 . CARBON- backbone/skeleton of all organic molecules
* groups of microorganisms based on their carbonsources:
(a) Autotrophs/lithotrophs utilize inorganic compounds (C O 2 ), inorganic
salts & water- source of energy is derived from light
photolithotrophs; the source is from oxidationof inorganic substances chemolithotrophs
b) Heterotrophs /organotrophs utilize organic substances like sugars or glucose- source of energy is derived from light
photoorganotrophs ; from oxidation they arecalled chemoorganotrophs .
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2 . NITROGEN, SULFUR &
PHOSPHORUS are necessary for the
synthesis of cellular materialslike proteins & nucleic acids
* N & S synthesis of proteins.* N & P synthesis of nucleicacids and A TP
*NOTE : Approximately 14% ofthe dry weight of a bacterialcell is Nitrogen & about 4% issulfur & phosphorus
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3 . INORGANIC IONS includes magnesium, potassium, calcium, iron &
trace elements such as manganese, zinc, copper& cobalt. ( MgKCaFe; MnZnCuCo)
* Mg stabilizes ribosomes, cell membranes& nucleic acids ; cofactor for many enzymes
* K normal functioning & integrity of ribosomes ;also for certain enzymatic activities* Ca constituent of the cell walls of Gram-positive
bacteria; contributes to the resistance ofbacterial endospores
* Fe a part of cytochrome & as a co-factor inenzymatic activities.
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4 . GROWTH FACTORS include vitamin B
co mplex, aminoacids, purines &pyrimidines.
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II. PHYSICALREQUIREMENTS
1. MOISTU RE O R WATE R where bacteriaacquire nutrients from(bacterial cell iscomposed mainly ofwater)
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2 . OXYGEN* Classification of Microorganisms based on
their oxygen requirement:(a) Aerobes utilize molecular oxygen for energy those microbes that strictly require
oxygen for growth ( strict aerobes) .(b) Anaerobes do not utilize oxygen for energy
those that cannot survive in thepresence of oxygen ( obligate or strict
anaerobes lack enzymes l ike superoxidedismutase & catalase.y Aerotolerant anaerobes can resist
exposure to oxygen & therefore arenot killed by its presence.
y Microaerophilic anaerobes are ableto grow at l ow oxygen tension but its
rate of growth is diminished.***FACULTAT I V E ORGA NI SMS are those that cangrow under both aerobic & anaerobicconditions. Most medically important bacteriabelong to this group.
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3. TEMPE RATU RE
based on temperaturerequirements, microbes aregrouped into:
(a) T hermophiles (heat-loving)
grow best at an optimumtemperature range of 50 60 0C.(b) M esophiles require an optimum
temperature of 2 0 40 0C(c) P sychrophiles require an
optimum temperature of 10 2 00C** Most medically important
bacteria are mesophiles .
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4 . pH
degree of acidity or alkalinityof a solution
microorganisms are classifiedas:
(a) alkalophiles pH is 8.4 9.0(b) neutrophiles pH is 7.5 8.0(c) acidophiles pH is 6.5 7.0 T he most medically important
bacteria grow best at a pH of6.7 to 7.5, hence, they areconsidered neutrophiles
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5. OSMOTIC CONDITIONS
(concentration gradientof salt/solute againstsolvent/water)
- some microorganisms
require high saltconcentrations forgrowth, hence, they arereferred to ashalophiles .
- some require highosmotic pressure & arereferred as osmophiles .
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Population (n)
T ime
A
B
C
D
LEGEND:A Lag PhaseB Log PhaseC Stationary PhaseD Death Phase
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