1. Cell Structure and Function By Dr. Zarina Zakaria
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Week 7
Cell Structure and Function By
Dr. Zarina Zakaria

2. A Preview of Procaryotic Cell Structure and Function
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A Preview of Procaryotic Cell Structure and Function
procaryotes differ from eucaryotes in many traits including size and lack of internal membrane systems
procaryotes are divided into Bacteria and Archaea
Bacteria are divided into 2 groups based on their Gram stain reaction

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Figure 3.1: Common procaryotic cell shapes under scanning electron microscope

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Figure 3.2

5. Size, Shape, and Arrangement
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Size, Shape, and Arrangement
cocci (s., coccus) – spheres
diplococci (s., diplococcus) – pairs
streptococci – chains
staphylococci – grape-like clusters
tetrads – 4 cocci in a square
sarcinae – cubic configuration of 8 cocci

6. Size, Shape, and Arrangement
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Size, Shape, and Arrangement
bacilli (s., bacillus) – rods
coccobacilli – very short rods
vibrios – resemble rods, comma shaped
spirilla (s., spirillum) – rigid helices
spirochetes – flexible helices
mycelium – network of long, multinucleate filaments

7. Size, Shape, and Arrangement
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Size, Shape, and Arrangement
mycelium – network of long, multinucleate filaments
pleomorphic – organisms that are variable in shape

8. largest – 50 μm in diameter 0.3 μm in smallest – Figure 3.3
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largest –
50 μm in
diameter
smallest –
0.3 μm in
Figure 3.3

9. An Overview of Eucaryotic Cell Structure
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An Overview of Eucaryotic Cell Structure
membrane-delimited nuclei
membrane-bound organelles that perform specific functions
more structurally complex than procaryotic cell
generally larger than procaryotic cell

10. Figure 3.4: Morphology of a procaryotic cell
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Figure 3.4: Morphology of a procaryotic cell

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Table 3.1

12. Figure 4.2: Yeast ultrastructure
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AV= autophagic vacuole; C=centriole; Ch=chloroplast; CI=cilium; CR=chromatin; DV=digestion vacuole; F=microfilaments; G=glycogen; GA=Golgi apparatus; GE=GERL; LD=lipid droplet; M=mitochondrion; MT=microtubules; N=nucleus; NU=nucleolus; P=peroxisome; PL=primary lysosome; PM=plasma membrane; PV=pinocytotic vesicle; R=ribosomes and polysomes; RB=residual body; RER=rough endoplasmic reticulum; SER=smooth endoplasmic reticulum; SV=secretion vacuole
Figure 4.2: Yeast ultrastructure

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AV= autophagic vacuole; C=centriole; Ch=chloroplast; CI=cilium; CR=chromatin; DV=digestion vacuole; F=microfilaments; G=glycogen; GA=Golgi apparatus; GE=GERL; LD=lipid droplet; M=mitochondrion; MT=microtubules; N=nucleus; NU=nucleolus; P=peroxisome; PL=primary lysosome; PM=plasma membrane; PV=pinocytotic vesicle; R=ribosomes and polysomes; RB=residual body; RER=rough endoplasmic reticulum; SER=smooth endoplasmic reticulum; SV=secretion vacuole
Figure 4.3:

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Table 4.1

15. Procaryotic Cell Membranes
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Procaryotic Cell Membranes
membranes are an absolute requirement for all living organisms
plasma membrane encompasses the cytoplasm
some procaryotes also have internal membrane systems

16. Functions of the plasma membrane
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Functions of the plasma membrane
separation of cell from its environment
selectively permeable barrier
some molecules are allowed to pass into or out of the cell
transport systems aid in movement of molecules

17. More functions… location of crucial metabolic processes
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More functions…
location of crucial metabolic processes
detection of and response to chemicals in surroundings with the aid of special receptor molecules in the membrane

18. Fluid Mosaic Model of Membrane Structure
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Fluid Mosaic Model of Membrane Structure
Lipid bilayer in which proteins float
Figure 3.5

19. The asymmetry of most membrane lipids
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The asymmetry of most membrane lipids
polar ends
interact with water
hydrophilic
nonpolar ends
insoluble in water
hydrophobic
Figure 3.6

20. Membrane proteins peripheral proteins integral proteins
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Membrane proteins
peripheral proteins
loosely associated with the membrane and easily removed
integral proteins
embedded within the membrane and not easily removed

21. The Plasma Membrane and Membrane Structure of Eucaryotic
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The Plasma Membrane and Membrane Structure of Eucaryotic
the fluid mosaic model is based on eucaryotic membranes
major membrane lipids include phosphoglycerides, sphingolipids and cholesterol

22. The Plasma Membrane and Membrane Structure
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The Plasma Membrane and Membrane Structure
eucaryotic membranes contain microdomains called lipid rafts
They are enriched for certain lipids and proteins
They participate in a variety of cell processes such as cell movement and transduction

23. Bacterial Membranes 1.differ from eucaryotes in lacking sterols
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Bacterial Membranes
1.differ from eucaryotes in lacking sterols
do contain hopanoids, sterol-like molecules
2.a highly organized, asymmetric system which is also flexible and dynamic-enable bacteria to adapt at various temperature range

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Cytoplasmic Matrix
substance in which nucleoid, ribosomes and inclusion bodies are suspended
lacks organelles bound by unit membranes
composed largely of water
is a major part of the protoplasm (the plasma membrane and everything within)

25. Ribosomes complex structures consisting of protein and RNA
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Ribosomes
complex structures consisting of protein and RNA
sites of protein synthesis
smaller than eucaryotic ribosomes
procaryotic ribosomes  70S
eucaryotic ribosomes  80S
S = Svedburg unit

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Figure 3.15

27. The Nucleoid irregularly shaped region location of chromosome
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The Nucleoid
irregularly shaped region
location of chromosome
usually 1/cell
not membrane-bound
Figure 3.4

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Procaryotic chromosomes are located in the nucleoid, an area in the cytoplasm
Figure 3.14a: growing Bacillus cells stained with HCl-Giemsa and viewed with light microscope
Figure 3.14b: section of growing E. coli immunostained specifically for DNA; viewed with TEM
Figure 3.15c: model of 2 nucleoids in an actively growing E. coli cell
Figure 3.16

29. The procaryotic chromosome
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The procaryotic chromosome
a closed circular, double-stranded DNA molecule
looped and coiled extensively
nucleoid proteins probably aid in folding
nucleoid proteins differ from histones

30. Plasmids usually small, closed circular DNA molecules
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Plasmids
usually small, closed circular DNA molecules
exist and replicate independently of chromosome
have relatively few genes present
genes on plasmids are not essential to host but may confer selective advantage (e.g., drug resistance)

31. Plasmids curing is the loss of a plasmid
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Plasmids
curing is the loss of a plasmid
classification of plasmids based on mode of existence, spread, and function

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Table 3.3

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The Bacteria Cell Wall
rigid structure that lies just outside the plasma membrane
Figure 3.4

34. Functions of cell wall provides characteristic shape to cell
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Functions of cell wall
provides characteristic shape to cell
protects the cell from osmotic lysis
may also contribute to pathogenicity
very few procaryotes lack cell walls

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Cell walls of Bacteria
bacteria are divided into two major groups based on the response to gram-stain procedure.
gram-positive bacteria stain purple
gram-negative bacteria stain pink
staining reaction due to cell wall structure

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Figure 3.17

37. Exoenzymes secreted by gram-positive bacteria
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Exoenzymes
secreted by gram-positive bacteria
perform many of the same functions that periplasmic enzymes do for gram-negative bacteria

38. Peptidoglycan (Murein) Structure
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Peptidoglycan (Murein) Structure
meshlike polymer composed of identical subunits
contains N-acetyl glucosamine and N-acetylmuramic acid and several different amino acids
chains of linked peptidoglycan subunits are cross linked by peptides

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Figure 3.18

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Top: E. coli peptidoglycan; direct cross-linking, typical of many gram-negative bacteria
Bottom: Staphylococcus aureus peptidoglycan
NAM= N-acetylglucosoamine; NAG= N-acetylmuramic acid
Figure 3.19

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Top: E. coli peptidoglycan; direct cross-linking, typical of many gram-negative bacteria
Bottom: Staphylococcus aureus peptidoglycan
NAM= N-acetylglucosoamine; NAG= N-acetylmuramic acid
Figure 3.20

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Figure 3.21

43. Gram-Positive Cell Walls
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Gram-Positive Cell Walls
composed primarily of peptidoglycan
may also contain large amounts of teichoic acids
some gram-positive bacteria have layer of proteins on surface of peptidoglycan
Isolated cell wall from Bacillus megaterium; latex spheres are 0.25 micrometer in diameter
Figure 3.22

44. Periplasmic Space of Gram + bacteria
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Periplasmic Space of Gram + bacteria
lies between plasma membrane and cell wall and is smaller than that of Gram - bacteria
periplasm has relatively few proteins
enzymes secreted by Gram + bacteria are called exoenzymes

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Figure 3.23

46. teichoic acids polymers of glycerol or ribitol joined by
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teichoic acids
polymers of glycerol
or ribitol joined by
phosphate groups
Figure 3.24

47. Gram-Negative Cell Walls
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Gram-Negative Cell Walls
consist of a thin layer of peptidoglycan surrounded by an outer membrane
outer membrane composed of lipids, lipoproteins, and lipopolysaccharide (LPS)
no teichoic acids

48. Gram-Negative Cell Walls
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Gram-Negative Cell Walls
more complex than gram + walls
peptidoglycan is ~2-5% of wall weight
periplasmic space differs from that in gram + cells
may constitute 20-40% of cell volume
many enzymes present in periplasm

49. Gram-Negative Cell Walls
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Gram-Negative Cell Walls
outer membrane lies outside the thin peptidoglycan layer
Braun’s lipoproteins connect outer membrane to peptidoglycan

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Figure 3.25

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Figure 3.26: A chemical model of the E. coli outer membrane and associated structures

52. Important connections
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Important connections
adhesion sites
sites of direct contact (possibly true membrane fusions) between plasma membrane and outer membrane
substances may move directly into cell through adhesion sites

53. The Mechanism of Gram Staining
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The Mechanism of Gram Staining
thought to involve shrinkage of the pores of the peptidoglycan layer of gram-positive cells
constriction prevents loss of crystal violet during decolorization step
thinner peptidoglycan layer and larger pores of gram-negative bacteria does not prevent loss of crystal violet

54. The Cell Wall and Osmotic Protection
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The Cell Wall and Osmotic Protection
osmotic lysis
can occur when cells are in hypotonic solutions
movement of water into cell causes swelling and lysis due to osmotic pressure
cell wall protects against osmotic lysis

55. Evidence of protective nature of the cell wall
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Evidence of protective nature of the cell wall
lysozyme breaks the bond between N-acetyl glucosamine and N-acetylmuramic acid
penicillin inhibits peptidoglycan synthesis
If cells are treated with either of the above they will lyse if they are in a hypotonic solution

56. protoplast – cell completely lacking cell wall
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Figure 3.29
protoplast – cell completely lacking cell wall
spheroplast – cell with some cell wall remaining

57. Archaeal cell walls lack peptidoglycan
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Archaeal cell walls
lack peptidoglycan
cell wall varies from species to species but usually consists of complex heteropolysaccharides
Methanogens have walls containing pseudomurein

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Figure 3.30

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Figure 3.31

60. Components External to Cell Wall
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Components External to Cell Wall
Figure 3.4

61. Bacterial Glycocalyx Figure 3.35
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Bacterial Glycocalyx
Figure 3.35

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More functions…
protection from viral infection or predation by bacteria
protection from chemicals in environment (e.g., detergents)
facilitate motility of gliding bacteria
protection against osmotic stress

63. Pili and Fimbriae fimbriae (s., fimbria) sex pili (s., pilus)
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Pili and Fimbriae
fimbriae (s., fimbria)
short, thin, hairlike, proteinaceous appendages
up to 1,000/cell
mediate attachment to surfaces
some (type IV fimbriae) required for twitching motility or gliding motility that occurs in some bacteria
sex pili (s., pilus)
similar to fimbriae except longer, thicker, and less numerous (1-10/cell)
required for mating

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Figure 3.37

65. Flagella and Motility Figure 3.4
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Flagella and Motility
Figure 3.4

66. The filament extends from cell surface to the tip
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The filament
extends from cell surface to the tip
hollow, rigid cylinder
composed of the protein flagellin
some procaryotes have a sheath around filament

67. Other Types of Motility
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Other Types of Motility
spirochetes
exhibit flexing and spinning movements of axial filaments which are composed of periplasmic flagella
gliding motility
cells coast along solid surfaces
no visible motility structure has been identified

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Chemotaxis
movement towards a chemical attractant or away from a chemical repellent
concentrations of chemical attractants and chemical repellents detected by chemoreceptors on surfaces of cells

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Figure 3.38: On left is positive chemotaxis by E. coli; outer ring is composed of bacteria consuming serine and the second ring was formed by cells consuming aspaartate, a less powerful attractant; top right colony is composed of motile but nonchemotactic mutant; bottom right colony is composed of nonmotile bacteria.
Figure 3.39: negative chemotaxis by E. coli in response to acetate; bright disks are plugs of agar containing acetate; acetate concentration increases from 0 at the top right to 3 M at top left; as acetate concentration increases, size of bacteria-free zone increases
Figure 3.43
Figure 3.44

70. Chemotaxis Towards Attractant
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Chemotaxis Towards Attractant
in presence of attractant (b) tumbling frequency is reduced and runs in direction of attractant are longer
Figure 3.45

71. Chemotaxis away from repellent
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Chemotaxis away from repellent
involves similar but opposite responses

72. The Bacterial Endospore
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The Bacterial Endospore
formed by some bacteria
dormant
resistant to numerous environmental conditions
heat
radiation
chemicals
desiccation

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Figure 3.46

74. Mitochondria site of tricarboxylic acid cycle activity
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Mitochondria
site of tricarboxylic acid cycle activity
site where ATP is generated by electron transport and oxidative phosphorylation
Figure 4.3

75. Mitochondrial structure
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Mitochondrial structure
outer membrane
contains porins similar to the outer membrane of gram negative bacteria
inner membrane
highly folded to form cristae (s., crista)
location of enzymes and electron carriers for electron transport and oxidative phosphorylation

76. Mitochondrial structure…
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Mitochondrial structure…
matrix
contains ribosomes, mitochondrial DNA, and large calcium phosphate granules
contains enzymes of the tricarboxylic acid cycle and enzymes involved in catabolism of fatty acids

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Figure 4.11

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Figure 4.12

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Figure 4.13

80. Chloroplasts type of plastid site of photosynthetic reactions
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Chloroplasts
type of plastid
pigment-containing organelles observed in plants and algae
site of photosynthetic reactions
surrounded by double membrane
Figure 4.3

81. Chloroplast structure
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Chloroplast structure
the stroma (a matrix) is within inner membrane
contains DNA, ribosomes, lipid droplets, starch granules, and thylakoids
thylakoids
flattened, membrane-delimited sacs
grana (s., granum) – stacks of thylakoids
site of light reactions (trapping of light energy to generate ATP, NADPH, and oxygen)

82. Chloroplast structure
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Chloroplast structure
stroma is site of dark reactions of photosynthesis (formation of carbohydrates from water and carbon dioxide)
algal chloroplasts many contain a pyrenoid
participates in polysaccharide synthesis

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Figure 4.14

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Figure 4.15

85. The Nucleus and Cell Division
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The Nucleus and Cell Division
nucleus
membrane-bound structure that houses genetic material of eucaryotic cell
Figure 4.3

86. Nuclear structure chromatin dense fibrous material within nucleus
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Nuclear structure
chromatin
dense fibrous material within nucleus
contains DNA
condenses to form chromosomes during cell division

87. Nuclear structure… nuclear envelope
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Nuclear structure…
nuclear envelope
double membrane structure that delimits nucleus
penetrated by nuclear pores
pores allow materials to be transported into or out of nucleus

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freeze-etch preparation of the conidium of the fungus Geotrichous candidum; note large convex nuclear surface with nuclear pores scattered over it
Figure 4.15

89. The Nucleolus  1 nucleolus/nucleus not membrane enclosed
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The Nucleolus
 1 nucleolus/nucleus
not membrane enclosed
important in ribosome synthesis
directs synthesis and processing of rRNA
directs assembly of rRNA and ribosomal proteins to form ribosomes

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Figure 4.16

91. Comparison of Procaryotic and Eucaryotic Cells
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Comparison of Procaryotic and Eucaryotic Cells
Figure 4.24

92. Comparison of Procaryotic and Eucaryotic Cells
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Comparison of Procaryotic and Eucaryotic Cells
Table 4.2

93. The molecular unity of procaryotes and eucaryotes
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The molecular unity of procaryotes and eucaryotes
same basic chemical composition
same genetic code
same basic metabolic processes