Lecture 3; Prokaryotic and Eukaryotic Cells

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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Documents

Lecture 3; Prokaryotic and Eukaryotic Cells