Download Chap 3 Cell Structure and Function Spring 2015

Chapter 3 – Cell Structure and Function
9/10/14
MDufilho
1
Processes of Life
What is the difference between a living thing and a
non-living thing?
9/10/14
MDufilho
2
Figure 3.1 Examples of types of cells.
9/10/14
MDufilho
3
Processes of Life
• Tell Me Why
• The smallest free-living microbe—the bacterium
Mycoplasma—is nonmotile. Why is it alive, even though
it cannot move?
9/10/14
MDufilho
4
How are these cells similar?
Prokaryote
9/10/14
Eukaryote
MDufilho
5
Prokaryotic and Eukaryotic Cells: An Overview
• Tell Me Why
• In 1985, an Israeli scientist discovered a single-celled
microbe, Epulopiscium fishelsoni. This organism is
visible with the naked eye. Why did the scientist think
Epulopiscium was eukaryotic?
• What discovery revealed that the microbe is really a
giant bacterium?
9/10/14
MDufilho
6
External Structures of Bacterial Cells
• Two Types of Glycocalyces
• Capsule
• Composed of organized repeating units of organic chemicals
• Firmly attached to cell surface
• May prevent bacteria from being recognized by host
• Slime layer
• Loosely attached to cell surface
• Water soluble
• Sticky layer allows prokaryotes to attach to surfaces as biofilms
9/10/14
MDufilho
7
Figure 3.5 Glycocalyces.
Glycocalyx
(slime layer)
Glycocalyx
(capsule)
9/10/14
MDufilho
8
External Structures of Bacterial Cells
• Flagella
• Are responsible for movement
• Have long structures that extend
beyond cell surface
• Are not present on all bacteria
• Structure
• Composed of filament, hook, and
basal body
• Basal body anchors the filament
9/10/14
MDufilho
9
Figure 3.6 Proximal structure of bacterial flagella.
Filament
Direction
of rotation
during run
Rod
Peptidoglycan
layer (cell wall)
Protein rings
Cytoplasmic
membrane
Cytoplasm
Filament
Outer
protein
rings
Outer
membrane
Rod
Gram +
Gram –
Basal
body
Peptidoglycan
layer
Integral
protein
Inner
protein
rings
Cell
wall
Cytoplasmic
membrane
Cytoplasm
Integral
protein
9/10/14
MDufilho
10
Figure 3.8 Axial filament.
Endoflagella
rotate
Axial filament
Axial filament
rotates around
cell
Outer
membrane
Cytoplasmic
membrane
© 2015 Pearson Education,
Inc.
Spirochete
corkscrews
and moves
forward
Axial filament
Figure 3.10 Fimbriae.
9/10/14
Flagellum Fimbria
MDufilho
12
Figure 3.11 Pili.
Pilus
9/10/14
MDufilho
13
Bacterial Cell Walls
• Provide structure and shape and protect cell from osmotic
forces
• Assist some cells in attaching to other cells or in resisting
antimicrobial drugs
• Can target cell wall of bacteria with antibiotics
• Give bacterial cells characteristic shapes
• Composed of peptidoglycan
• Scientists describe two basic types of bacterial cell walls
• Gram-positive and Gram-negative
9/10/14
MDufilho
14
Bacterial Cell Walls
• Gram-Positive Bacterial Cell Walls
• Relatively thick layer of peptidoglycan
• Contain unique polyalcohols called teichoic acids
• Appear purple following Gram staining procedure
• Presence of up to 60% mycolic acid in acid-fast bacteria
helps cells survive desiccation
9/10/14
MDufilho
15
Prokaryotic Cell Walls
• Gram-Negative Bacterial Cell Walls
• Have only a thin layer of peptidoglycan
• Bilayer membrane outside the peptidoglycan contains
phospholipids, proteins, and lipopolysaccharide (LPS)
• Lipid A portion of LPS can cause fever, vasodilation,
inflammation, shock, and blood clotting
• May impede the treatment of disease
• Appear pink following Gram staining procedure
9/10/14
MDufilho
16
Prokaryotic Cell Walls
• Bacteria Without Cell Walls
• A few bacteria lack cell walls
• Often mistaken for viruses because of small size and
lack of cell wall
• Have other features of prokaryotic cells, such as
ribosomes
9/10/14
MDufilho
17
Bacterial Cytoplasmic Membranes
• Structure
• Referred to as phospholipid bilayer
• Composed of lipids and associated proteins
• Integral proteins
• Peripheral proteins
• Fluid mosaic model describes current understanding of membrane
structure
9/10/14
MDufilho
18
Bacterial Cytoplasmic Membranes
• Functions???
9/10/14
MDufilho
19
Cytoplasm of Bacteria
• Cytosol
• Liquid portion of cytoplasm
• Mostly water
• Contains cell's DNA in region called the nucleoid
• Inclusions
• May include reserve deposits of chemicals
• Endospores
• Unique structures produced by some bacteria
• Defensive strategy against unfavorable conditions
9/10/14
MDufilho
20
Figure 3.23 Granules of PHB in the bacterium Azotobacter chroococcum.
Polyhydroxybutyrate
9/10/14
MDufilho
21
Figure 3.24 The formation of an endospore.
Steps in Endospore Formation
Cell wall
Cytoplasmic
membrane
1 DNA is replicated.
DNA
5 Spore coat forms
around endospore.
Spore coat
6 Endospore matures:
Completion of spore coat.
Increase in resistance
to heat and chemicals by
unknown process.
Outer
spore coat
Vegetative cell
2 Cytoplasmic membrane
invaginates to form
forespore.
3 Cytoplasmic membrane
grows and engulfs
forespore within a
second membrane.
Vegetative cell's DNA
disintegrates.
Forespore
First
membrane
Endospore
7 Endospore is released from
original cell.
Second
membrane
8
4 A cortex of peptidoglycan is deposited
between the membranes;
meanwhile, dipicolinic
acid and calcium ions
accumulate within the
center of the endospore.
9/10/14
Cortex
MDufilho
22
Cytoplasm of Prokaryotes
• Nonmembranous Organelles
• Ribosomes
• Sites of protein synthesis
• Cytoskeleton
• Can play different roles in the cell
• Cell division
• Cell shape
• Segregation of DNA molecules
• Movement through the environment
9/10/14
MDufilho
23
Endosymbiotic Theory
Mitochondria and chloroplasts have 70S ribosomes,
circular DNA, and two membranes. Why????
9/10/14
MDufilho
24