overview of cells ,structure and functions.

1. Chapter 4
An Introduction to Cells and
Procaryotic Cell
Structure and Function

2. All living things (single and multicellular) are made of
cells that share some common characteristics:
◦ basic shape – spherical, cubical, cylindrical
◦ internal content – cytoplasm, surrounded by a membrane
◦ DNA chromosome(s), ribosomes, metabolic capabilities
Two basic cell types: eucaryotic and procaryotic
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3. Eucaryotic cells: animals, plants, fungi, and protists
◦ contain double-membrane bound nucleus with DNA
chromosomes
◦ contain membrane-bound organelles that
compartmentalize the cytoplasm and perform specific
functions
Procaryotic cells: bacteria and archaea
◦ no nucleus or other membrane-bound organelles
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4.  Growth and development
 Reproduction and heredity – genome composed
of DNA packed in chromosomes; produce
offspring sexually or asexually
 Metabolism – chemical and physical life
processes
 Movement and/or irritability – respond to
internal/external stimuli; self-propulsion of many
organisms
 Cell support, protection, and storage mechanisms
– cell walls, vacuoles, granules and inclusions
 Transport of nutrients and waste
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5. 5

6. 6

7.  Appendages
◦ two major groups of appendages:
 Motility – flagella and axial filaments (periplasmic
flagella)
 Attachment or channels – fimbriae and pili
 Glycocalyx – surface coating
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8.  3 parts:
◦ filament – long, thin, helical structure composed of
protein flagellin
◦ hook- curved sheath
◦ basal body – stack of rings firmly anchored in cell wall
 Number and arrangement of flagella varies:
◦ monotrichous, lophotrichous, amphitrichous, peritrichous
 Functions in motility of cell through environment
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9. 9

10. 1. Monotrichous – single flagellum at one end e.g.
Pseudomonas
2. Lophotrichous – small bunches arising from one
end of cell
3. Amphitrichous – flagella at both ends of cell
4. Peritrichous – flagella dispersed over surface of
cell; slowest e.g. E. coli
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11. 11

12. Guide bacteria in a direction in response to external
stimulus:
chemical stimuli – chemotaxis; positive and negative
light stimuli – phototaxis
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13.  Fine, proteinaceous, hairlike bristles from the
cell surface
 Function in adhesion to other cells and
surfaces
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14.  Rigid tubular structure made of pilin protein
 Found only in Gram negative cells
 Function to join bacterial cells for partial DNA transfer
called conjugation
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15.  Coating of molecules external to the cell wall,
made of sugars and/or proteins
 Two types:
1. slime layer - loosely organized and attached
2. capsule - highly organized, tightly attached
 Functions:
◦ protect cells from dehydration and nutrient loss
◦ inhibit killing by white blood cells by phagocytosis
contributing to pathogenicity – S. pneumoniae, H.
influenzae 1 cause of meningitis, B. anthracis
◦ attachment - formation of biofilms
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16. 16

17. 17

18.  External covering outside the cytoplasm
 Composed of two basic layers:
◦ cell wall and cell membrane
 Maintains cell integrity
 Two generally different groups of bacteria
demonstrated by Gram stain:
◦ Gram-positive bacteria: thick cell wall composed
primarily of peptidoglycan and cell membrane
◦ Gram-negative bacteria: outer cell membrane, thin
peptidoglycan layer, and cell membrane
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19. 19
Insert figure 4.12
Comparative cell envelopes

20.  Determines cell shape, prevents lysis
(bursting) or collapsing due to changing
osmotic pressures
 Peptidoglycan is primary component:
◦ unique macromolecule composed of a repeating
framework of long glycan chains cross-linked by short
peptide fragments
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21. 21

22.  Thick, homogeneous sheath of peptidoglycan
◦ 20-80 nm thick
◦ function in cell wall maintenance and enlargement during
cell division; move cations across the cell envelope;
stimulate a specific immune response
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23. 23

24.  Composed of an outer membrane and a thin
peptidoglycan layer
 Outer membrane is similar to cell membrane
bilayer structure
◦ outermost layer contains lipopolysaccharides and
lipoproteins (LPS)
 endotoxin that may become toxic when released during
infections
 may function as receptors and blocking immune response
 contains porin proteins in upper layer – regulate molecules
entering and leaving cell
◦ Bottom layer composed of phospholipids and lipoproteins
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25.  Single, thin sheet of peptidoglycan
 Protective structure while providing some
flexibility and sensitivity to lysis
 Periplasmic space surrounds peptidoglycan
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26. 26

27.  Differential stain that distinguishes cells with a
Gram-positive cell wall from those with a Gram-
negative cell wall
◦ Gram-positive - retain crystal violet and stain purple
◦ Gram-negative - lose crystal violet and stain red from
safranin counterstain
 Important basis of bacterial classification and
identification
 Practical aid in diagnosing infection and guiding drug
treatment
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28. 28

29.  Some bacterial groups lack typical cell wall
structure i.e. Mycobacterium and Nocardia
◦ Gram-positive cell wall structure with lipid mycolic acid
(cord factor)
 pathogenicity and high degree of resistance to certain
chemicals and dyes
 basis for acid-fast stain used for diagnosis of infections
caused by these microorganisms
 Some have no cell wall i.e. Mycoplasma
◦ cell wall is stabilized by sterols
◦ pleomorphic
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30.  Phospholipid bilayer with embedded proteins
 Functions in:
◦ providing site for energy reactions, nutrient processing,
and synthesis
◦ transport into and out of the cell
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31. 31

32.  Cell cytoplasm:
◦ dense gelatinous solution of sugars, amino acids, and
salts
◦ 70-80% water
 serves as solvent for materials used in all cell functions
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33.  Chromosome
◦ single, circular, double-stranded DNA molecule that
contains all the genetic information required by a cell
◦ DNA is tightly coiled around a protein, aggregated in
a dense area called the nucleoid.
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34.  Plasmids
◦ small circular, double-stranded DNA
◦ free or integrated into the chromosome
◦ duplicated and passed on to offspring
◦ not essential to bacterial growth and metabolism
◦ may encode antibiotic resistance, tolerance to toxic
metals, enzymes and toxins
◦ used in genetic engineering- readily manipulated and
transferred from cell to cell
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35.  Ribosomes
◦ made of 60% ribosomal RNA and 40% protein
◦ consist of two subunits: large and small
◦ procaryotic differ from eucaryotic ribosomes in size
and number of proteins
◦ site of protein synthesis
◦ present in all cells
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36.  Inclusions and granules
◦ intracellular storage bodies
◦ vary in size, number and content
◦ Bacterial cell can use them when environmental sources
are depleted.
◦ examples: glycogen, poly-β-hydroxybutyrate, gas
vesicles for floating, sulfur and phosphate granules
(metachromatic granules)
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37. 37

38.  Endospores
◦ inert, resting, cells produced by some G+ genera: Clostridium,
Bacillus and Sporosarcina
 have a 2-phase life cycle:
 vegetative cell – metabolically active and growing
 endospore – when exposed to adverse environmental conditions;
capable of high resistance and very long-term survival
◦ sporulation -formation of endospores
 hardiest of all life forms
 withstands extremes in heat, drying, freezing, radiation and
chemicals
 not a means of reproduction
◦ germination- return to vegetative growth
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39. 39

40.  Resistance linked to high levels of calcium
and dipicolinic acid
 Dehydrated, metabolically inactive
 thick coat
 Longevity verges on immortality - 25,250
million years.
 Resistant to ordinary cleaning methods and
boiling
 Pressurized steam at 120o
C for 20-30
minutes will destroy
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41.  Variety in shape, size, and arrangement but
typically described by one of three basic
shapes:
◦ coccus - spherical
◦ bacillus – rod
 coccobacillus – very short and plump
 vibrio – gently curved
◦ spirillum – rigid helix, twisted twice or more along its
axis like a corkscrew, helical, comma, twisted rod,
 spirochete – a more flexible form, spring-like
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42. 42

43.  Arrangement of cells is dependent on pattern of division
and how cells remain attached after division:
◦ cocci:
 singles
 diplococci – in pairs
 tetrads – groups of four
 irregular clusters
 chains
 cubical packets
◦ bacilli:
 chains
 Palisades – is formed when the cells of a chain remain partially
attached by a small hinge region at the ends.
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44. 44

45. 1. Microscopic morphology
2. Macroscopic morphology – colony
appearance
3. Physiological / biochemical characteristics
4. Chemical analysis
5. Serological analysis
6. Genetic and molecular analysis
• G + C base composition
• DNA analysis using genetic probes
• Nucleic acid sequencing and rRNA analysis
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46.  Bergey’s Manual of Determinative Bacteriology – five
volume resource covering all known procaryotes
◦ classification based on genetic information –phylogenetic
◦ two domains: Archaea and Bacteria
◦ five major subgroups with 25 different phyla
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47.  Domain Archaea – primitive, adapted to
extreme habitats and modes of nutrition
 Domain Bacteria -
◦ Phylum Proteobacteria – Gram-negative cell
walls
◦ Phylum Firmicutes – mainly Gram-positive with
low G + C content
◦ Phylum Actinobacteria – Gram-positive with high
G + C content
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48.  Uses phenotypic qualities in identification
◦ restricted to bacterial disease agents
◦ divides based on cell wall structure, shape,
arrangement, and physiological traits
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49.  Species –a collection of bacterial cells which share
an overall similar pattern of traits in contrast to other
bacteria whose pattern differs significantly
 Strain or variety – a culture derived from a single
parent that differs in structure or metabolism from
other cultures of that species (biovars, morphovars)
 Type – a subspecies that can show differences in
antigenic makeup (serotype or serovar),
susceptibility to bacterial viruses (phage type) and in
pathogenicity (pathotype)
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50.  Free-living nonpathogenic bacteria
 Photosynthetic bacteria - use photosynthesis,
can synthesize required nutrients from
inorganic compounds
◦ Cyanobacteria (blue-green algae)
 Gram-negative cell walls
 extensive thylakoids with photosynthetic chlorophyll
pigments and gas inclusions
◦ Green and purple sulfur bacteria
 contain photosynthetic pigment bacteriochlorophyll
 do not give off oxygen as a product of photosynthesis
◦ Gliding, fruiting bacteria
 Gram-negative
 Glide over moist surfaces
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51.  Unusual forms of medically significant obligate
intracellular parasites
◦ Rickettsias
 Very tiny, Gram-negative bacteria
 Most are pathogens that alternate between mammals and
fleas, lice or ticks.
 Obligate intracellular pathogens
 Cannot survive or multiply outside of a host cell
 Cannot carry out metabolism on their own
 Rickettsia rickettisii – Rocky Mountain spotted fever
 Rickettsia prowazekii – epidemic typhus
 Coxiella burnetti – Q fever
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52. ◦ Chlamydias
 Tiny
 Obligate intracellular parasites
 Not transmitted by arthropods
 Chlamydia trachomatis – severe eye infection and one of
the most common sexually transmitted diseases
 Chlamydia psittaci – ornithosis, parrot fever
 Chlamydia pneumoniae – lung infections
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53.  Constitute third Domain Archaea
 Seem more closely related to Domain Eukarya than
to bacteria
 Live in the most extreme habitats in nature,
extremophiles
 Adapted to heat, salt, acid pH, pressure and
atmosphere
 Includes: methane producers, hyperthermophiles,
extreme halophiles, and sulfur reducers
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