This document provides an overview of prokaryotic cell structure and function. It describes the key characteristics of prokaryotic cells, including their lack of a nucleus and membrane-bound organelles. The document outlines the structures and functions of bacterial cell walls, flagella, pili, and other appendages. It also summarizes bacterial classification systems and important groups such as photosynthetic bacteria, intracellular parasites, and extremophiles in the Archaea domain.

1. 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
2

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
3

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
7

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
8

9. 1. Monotrichous – single flagellum at one end
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
9

10. 10

11. Guide bacteria in a direction in response to
external stimulus:
chemical stimuli – chemotaxis; positive and negative
light stimuli – phototaxis
11

12.  Fine, proteinaceous, hairlike bristles from
the cell surface
 Function in adhesion to other cells and
surfaces
12

13.  Rigid tubular structure made of pilin protein
 Found only in Gram negative cells
 Function to join bacterial cells for partial DNA
transfer called conjugation
13

14.  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
◦ attachment - formation of biofilms
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15. 15

16. 16

17.  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
17

18. 18
Insert figure 4.12
Comparative cell envelopes

19.  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
19

20.  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
20

21. 21

22.  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
22

23.  Single, thin sheet of peptidoglycan
 Protective structure while providing some
flexibility and sensitivity to lysis
 Periplasmic space surrounds peptidoglycan
23

24. 24

25.  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
25

26. 26

27.  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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28.  Phospholipid bilayer with embedded proteins
 Functions in:
◦ providing site for energy reactions, nutrient
processing, and synthesis
◦ transport into and out of the cell
28

29. 29

30.  Cell cytoplasm:
◦ dense gelatinous solution of sugars, amino acids,
and salts
◦ 70-80% water
 serves as solvent for materials used in all cell functions
30

31.  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.
31

32.  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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33.  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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34.  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-b-hydroxybutyrate, gas
vesicles for floating, sulfur and phosphate granules
(metachromatic granules)
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35. 35

36.  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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37. 37

38.  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 120oC for 20-30
minutes will destroy
38

39.  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 - helical, comma, twisted rod,
 spirochete – spring-like
39

40. 40

41.  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
41

42. 42

43. 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
43

44.  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
44

45.  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
45

46.  Uses phenotypic qualities in identification
◦ restricted to bacterial disease agents
◦ divides based on cell wall structure, shape,
arrangement, and physiological traits
46

47.  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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48.  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
48

49.  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
49

50. ◦ 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
50

51.  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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