1. Chapter 3 and 4
An Introduction to Prokaryotic and Eukaryotic Cell Structure and Function

2. Characteristics of Cells and Life
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: eukaryotic and prokaryotic

3. Characteristics of Cells
Eukaryotic 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
Prokaryotic cells: bacteria and archaea
no nucleus or other membrane-bound organelles

4. Prokaryotic cell

6. External Structures Appendages Glycocalyx – surface coating
two major groups of appendages:
motility – flagella and axial filaments (periplasmic flagella)
attachment or channels – fimbriae and pili
Glycocalyx – surface coating

7. Flagellar Arrangements
Monotrichous – single flagellum at one end
Lophotrichous – small bunches arising from one end of cell
Amphitrichous – flagella at both ends of cell
Peritrichous – flagella dispersed over surface of cell; slowest

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

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

11. Glycocalyx
Coating of molecules external to the cell wall, made of sugars and/or proteins
Two types:
slime layer - loosely organized and attached
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

12. The Cell Envelope 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 membrane, thin peptidoglycan layer, and cell membrane

15. Structure of Cell Walls
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

16. Gram-positive Cell Wall
Thick, homogeneous sheath of peptidoglycan
20-80 nm thick
includes teichoic acid and lipoteichoic acid: function in cell wall maintenance and enlargement during cell division; move cations across the cell envelope; stimulate a specific immune response

17. Gram-negative Cell Wall
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

18. Gram-negative Cell Wall
Single, thin sheet of peptidoglycan
Protective structure while providing some flexibility and sensitivity to lysis
Periplasmic space surrounds peptidoglycan

19. The Gram Stain
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

20. Atypical Cell Walls
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

21. Bacterial Internal Structures
Cell cytoplasm:
dense gelatinous solution of sugars, amino acids, and salts
70-80% water
serves as solvent for materials used in all cell functions

22. Bacterial Internal Structures
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

23. Bacterial Internal Structures
Ribosomes
made of 60% ribosomal RNA and 40% protein
consist of two subunits: large and small
Prokaryotic differ from Eukaryotic ribosomes in size and number of proteins
site of protein synthesis
present in all cells

24. Bacterial Internal Structures
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)

25. Endospores
Resistance linked to high levels of calcium and dipicolinic acid
Dehydrated, metabolically inactive
thick coat
Longevity verges on immortality – 25 to 250 million years
Resistant to ordinary cleaning methods and boiling
Pressurized steam at 120oC for minutes will destroy

26. Bacterial Shapes, Arrangements, and Sizes
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

28. Bacterial Shapes, Arrangements, and Sizes
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:
palisades

30. Species and Subspecies
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)

31. The History of Eukaryotes
They first appeared approximately 2 billion years ago
Evidence suggests evolution from prokaryotic organisms by symbiosis
Organelles originated from prokaryotic cells trapped inside them

32. Eukaryotic

33. External Structures Glycocalyx
an outermost boundary that comes into direct contact with environment
usually composed of polysaccharides
appears as a network of fibers, a slime layer or a capsule
functions in adherence, protection, and signal reception
beneath the glycocalyx
fungi and most algae have a thick, rigid cell wall
protozoa, a few algae, and all animal cells lack a cell wall and have only a membrane

34. External Boundary Structures
Cell wall
rigid, provides structural support and shape
Fungi have thick inner layer of polysaccharide fibers composed of chitin or cellulose and a thin layer of mixed glycans
algae – varies in chemical composition; substances commonly found include cellulose, pectin, mannans, silicon dioxide, and calcium carbonate

35. External Boundary Structures
Cytoplasmic (cell) membrane
typical bilayer of phospholipids and proteins
sterols confer stability
serves as selectively permeable barrier in transport
Eukaryotic cells also contain membrane-bound organelles that account for 60-80% of their volume

36. Internal Structures Nucleus
compact sphere, most prominent organelle of eukaryotic cell
nuclear envelope composed of two parallel membranes separated by a narrow space and is perforated with pores
contains chromosomes
nucleolus – dark area for rRNA synthesis and ribosome assembly

37. Internal Structures Endoplasmic reticulum – two types:
Rough endoplasmic reticulum (RER)– originates from the outer membrane of the nuclear envelop and extends in a continuous network through cytoplasm; rough due to ribosomes; proteins synthesized and shunted into the ER for packaging and transport; first step in secretory pathway
Smooth endoplasmic reticulum (SER)– closed tubular network without ribosomes; functions in nutrient processing, synthesis and storage of lipids, etc.

38. Internal Structures Golgi apparatus
consists of a stack of flattened sacs called cisternae
closely associated with ER
Transitional vesicles from the ER containing proteins go to the Golgi apparatus for modification and maturation
Condensing vesicles transport proteins to organelles or secretory proteins to the outside

39. Internal Structures Lysosomes
vesicles containing enzymes that originate from Golgi apparatus
involved in intracellular digestion of food particles and in protection against invading microbes

40. Internal Structures Mitochondria
consists of an outer membrane and an inner membrane with folds called cristae
Cristae hold the enzymes and electron carriers of aerobic respiration
divide independently of cell
contain DNA and prokaryotic ribosomes
function in energy production

41. Internal Structures Ribosomes composed of rRNA and proteins
40S and 60S subunits form 80S ribosomes
larger than prokaryotic ribosomes
function in protein synthesis

42. Kingdom Fungi 100,000 species divided into 2 groups:
macroscopic fungi (mushrooms, puffballs, gill fungi)
microscopic fungi (molds, yeasts)
Majority are unicellular or colonial; a few have cellular specialization

43. Microscopic Fungi Exist in two morphologies:
yeast – round ovoid shape, asexual reproduction
hyphae – long filamentous fungi or molds
Some exist in either form – dimorphic – characteristic of some pathogenic molds

44. Fungal Nutrition All are heterotrophic
Majority are harmless saprobes living off dead plants and animals
Some are parasites, living on the tissues of other organisms, but none are obligate; mycoses – fungal infections
Growth temperature 20o-40oC
Extremely widespread distribution in many habitats

45. Fungal Reproduction
Primarily through spores formed on reproductive hyphae
Asexual reproduction – spores are formed through budding or mitosis; conidia or sporangiospores
Sexual reproduction – spores are formed following fusion of male and female strains and formation of sexual structure
Sexual spores and spore-forming structures are one basis for classification

46. Fungal Classification
The Fungi kingdom is subdivided into two subkingdoms
Amastigomycota - common inhabitants of terrestrial habitats. Several of them are human pathogens
Mastigomycota - primitive filamentous fungi that live primarily in water and may cause disease in potatoes and grapes

47. Amastigomycota Fungi that produce sexual and asexual spores (perfect)
Zygomycota – zygospores; sporangiospores and some conidia
Ascomycota – ascospores; conidia
Basidiomycota – basidiospores; conidia
Fungi that produce only asexual spores
Deuteromycota – majority are yeasts and molds; no sexual spores known; conidia

49. Roles of Fungi Adverse impact Beneficial impact
mycoses, allergies, toxin production
destruction of crops and food storages
Beneficial impact
decomposers of dead plants and animals
sources of antibiotics, alcohol, organic acids, vitamins
used in making foods and in genetic studies

50. Distribution and Importance of Parasitic Worms
Approximately 50 species parasitize humans
Afflict billions of humans
Distributed worldwide; some restricted to certain geographic regions with higher incidence in tropics