Transcript The Prokaryotic Cell Wall

Lecture 3
Prokaryotes & Eukaryotes
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Components of ALL cells
Plasma membrane = lipid bilayer that forms
a physical barrier to all cells
Cytoplasm = the semisolid components within the
cell (Cytosol = Fluid portion)
Chromosomes = DNA structure containing genes
Ribosomes = tiny structures of RNA/protein
that synthesize new proteins using instructions from
the genes
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Prokaryotes v. Eukaryotes
nucleoid versus a nucleus
Cell size
- Prokaryotic cells are smaller (Most 0.2 - 5 µm)
1000 X magnification
- Eukaryotic cells are larger (Most 10 - 100 µm)
200 to 500 X magnification
Membrane-bound organelles
- Almost none in prokaryotes
- Eukaryotic cells have many organelles of specialized
form and function
- Complex cytoskeleton composed of various types of
filaments
- Large ribosomes
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Distinguishing Features of Prokaryotes
• Nucleoid
• No histones
• No numerous organelles
• Cell walls
• Peptidoglycan
• Binary fission
• Pili or fimbriae
• Single Circular Chromosome
• Some exceptions
• Plasmids
• Smaller usually circular pieces of DNA
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The Prokaryotic Cell Wall
Many Types of Bacterial Cell Walls
but Two Main Types…
1. Gram Positive
2. Gram Negative
Both contain peptidoglycan but differ
on amount
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Hans Christian Gram (1853-1938)
Hans Christian Gram was a Danish
doctor studying in Berlin who
studied lung tissues of pneumonia
victims. He noticed that different
bacteria behaved differently when
stained with a cationic dye and
classified them as Gram positive
(stained) or Gram negative (didn’t
stain).
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Fig.
4.p097
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Gram Stain Slide
Gram + have a thick layer of peptidoglycan
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N-acetylmuramic acid
(NAM)
Peptidoglycan
• Macromolecule composed of a
repeating framework of long chains
cross-linked by short peptide fragments
– Unique to bacteria
– Composed of 2 sugars: NAG &
NAM
– Sugars alternate in the backbone
N-acetylglucosamine
– Rows linked by polypeptides
(NAG)
• Provides strong, flexible support to keep
bacteria from bursting or collapsing
because of changes in osmotic pressure
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Be able to identify all the parts of
a Gram + & - cell wall for the next exam.
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Gram-positive versus Gram-negative Cell Walls
Fig. 4.16
Thick – 20-80 nm
Thin – 8-11 nm
Teichoic acids are found only in Gram-positive cell walls. They are
negatively charged and their function is unknown.
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Lipopolysaccharide and outer membrane are only found in Gram-negative cell walls.
Eukaryotic Cell Wall
• Many eukaryotes have a cell • Animal cells have no cell wall
wall composed of a
• Elaborate extracellular matrices
carbohydrate
• Collagen & glycoproteins
• Cell wall of algae & plants is • No eukaryotic cell has
made of cellulose
peptidoglycan in their cell
• A carbohydrate chain
wall
• Cell wall of fungi is made of
• Peptidoglycan is unique to bacteria
chitin
• A carbohydrate chain
• Cell wall of yeasts is made of
glucan and mannan
• A carbohydrate chain
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Plant Cell Wall
Cellulose
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Fungal cell
Illustration shows
relationship between the
cell membrane and cell
wall.
Glycocalyx is the outermost
section.
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All Cells have a Membrane
Plasma membrane functions as a selective barrier
O2 & nutrients must enter the cell
Waste products must exit the cell
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Lipid Bilayer
• Two layers of phospholipids
• Main component of cell
membranes
• Membrane has fluid properties
• Most phospholipids and some
proteins can drift through
membrane
– It’s FLUID & not static
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Fig. 2.18
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Fluid Mosaic Model
• Membrane is a mosaic of
– Phospholipids
– Glycolipids
– Sterols
Carbohydrates
• Eukaryotes
– Proteins
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Cell Membrane Pro v. Euk
• Prokaryotes
– Lipid bilayer
– Selectively
permeable
– Allows secretion
– Site for metabolic
rxns
• Respiration
• Photosynthesis
– Nutrient processing
– Synthesis of
proteins & other
molecules
• Eukaryotes
– Lipid bilayer
– Selectively
permeable
– Endocytosis
– Exocytosis
– Sterols
• Cholesterol
• Reinforces cell wall
– All organelles have
a membrane very
similar to the cell
membrane
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• Cell membranes of both Prokaryotes and Eukaryotes perform
• Diffusion, osmosis & active transport
• Endocytosis is unique to Eukaryotes
• Phagocytosis
• Uses pseudopods - surround and engulf
• Pinocytosis
• Cell drinking
• Plasma membrane folds in on itself
• Often times receptor mediated
• Exocytosis
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Cell Membranes Show
Selective Permeability
Glucose and other large,
O2, CO2, and other
polar, water-soluble
small, nonpolar
molecules, H+, Na+, K+, Ca++,
molecules; some
Cl–, H2O
H2O molecules
Diffusion
Other
Mechanisms
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Plasma Membrane
• Passive Transport
– Diffusion
• Active Transport
– Requires energy as ATP (adenosine triphosphate)
• Cell membrane proteins carry out many tasks
– Highly specialized proteins
• Enzymes
• Recognition and signaling
• Energy Reactions (Prokaryotes)
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Osmosis
• Diffusion of water molecules across a selectively
permeable membrane
• Direction of net flow is
determined by water
concentration gradient
• Side with the most
solute molecules has the
lowest water
concentration
water molecules
protein molecules
semipermeable membrane
between two compartments
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Biological Relevance of Osmosis
Cells can be in one of 3 conditions
Cell lysis = death
Isotonic - solutes
balanced
Good Situation!
Hypotonic - more
solute
inside
cell
Plasmolysis = death
Hypertonic - more
solute
outside
cell
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Animal Cell
[H2O] is greater
in the cell than
outside
[H2O] is greater
outside the cell
than inside
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Plant Cell
Hypertonic
[H2O] is greater
in the cell than
outside
Isotonic
Hypotonic
[H2O] is greater
outside the cell
than inside
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Flagella & Cillia
Prokaryotic & Eukaryotic flagella are
not similar in size or structure
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Prokaryotic Flagella
• Long filamentous projections used to propel bacteria – 18-20 nm
• Several types of flagella arrangements
Monotrichous – One flagellum usually
at one pole (Polar)
Amphitrichous - tufts of flagella at both poles
Lophotrichous - two or more flagella at one pole
Petritrichous - flagella distributed over entire
surface
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• Filament - main body of
flagella, made of flagellin
Parts of the Flagellum
• Hook - attaches flagella to basal
body
• Basal body - attaches flagella to
cell
• Movement is accomplished by
rotating basal body
• ATP
• Results in rotation of filament
• Smooth running or tumbling
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Direction of Flagellar Rotation
Important for Motility
• Counterclockwise rotation
results in movement
• Clockwise results in tumbling
• Responds to chemo and
phototaxis possible
• Attractants induce “running”
• Repellants induce “tumbling”
•This model is for Escherichia coli
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Axial Filaments
• Spirochetes
• Endoflagella
• Bundle of fibrils
• Run length of organism
• Drives spirochete forward
in a spiral motion
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Eukaryotic Flagella and Cilia
• Flagella - long (~40 um), few
• 10X larger (diameter) than Pro
flagella (~180-200 nm in width)
• Cilia – short (10 um long),
many
• Oars
• Ciliated protozoa & animal cells
• Both used for motility
• Both have 9+2 microtubule
structure
• Hollow tubes that slide past one
another (made up of tubulin)
• Waves and whips
• Doesn't rotate - different from
bacterial flagella
• Pull & push
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Motor Protein
Dynein
ATP
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Prokaryotic Genome Size
Bacteria
Escherichia coli
Bacillus subtilis
Streptococcus pyrogenes
Mycobacterium genitalium
Archaea
Methanococcus jannaschii
Sulfolobus solfactaricus
Pyrococcus furiosus
Size (Mbp)
4.64
4.20
1.85
0.58
Size (Mbp)
1.66
2.25
1.75
Genome consists of usually one circular chromosome
and plasmids (if present)
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Eukaryotic Genome Size
Organism
Mbp
Homo sapiens
Drosophilia melanogaster
Plasmodium falciparum
Saccharomyces cerevisiae
3000
165
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12.07
Eukaryotes also have
Mitochondrial DNA
Chloroplast DNA
Genome usually consists of a number of linear chromosomes
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Glycocalyx, Capsule & Slime
Glycocalyx
Outermost layer of cell that come into contact with environment
This term is used for both Eukaryotes and Prokaryotes
Sticky carbohydrates attached to proteins
Important in protection & adhesion
Capsule
Repeating units of polysaccharide, protein or both (a polymer)
Adheres tightly, thick & gummy
Mostly a Prokaryotic term – interchangeable with glycocalyx
Slime Layer
Polysaccharide, protein or both that is easily washed off
Mostly a Prokaryotic term
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Pili & Fibriae
• Prok surface appendages
– Pilus is longer
• Gram negative bacteria
• Conjugation
– Fibria is shorter
• Bristlelike
• Stick to surfaces
• Colonize host tissue
• Euk do not produce these
structures
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Ribosomes – RNA and Protein
Prok
Euk
All ribosomes are made up of two subunits
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• Prok Ribosomes
• Smaller
– 70S
• 50S & 30S
• Free ribosomes
– Located in the cytosol
• Euk Ribosomes
• Larger
– 80S
• 60S & 40S
• Free ribosomes
– Located suspended in the cytosol
– Synthesize proteins that function
within the cytosol
• Bound ribosomes
– Are attached to the outside of the
endoplasmic reticulum
– Synthesize proteins that are
included into membranes or43
exported from the cell
Organelles
•
•
•
•
•
Membrane-bounded functional units
Compartmentalized tasks instead of a mixture
Allows for much more variety of functionality
Present in Euk
Absent in Prok
• Prok conduct the similar activities at the cell membrane
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A View of the Eukaryotic Cell
Much more complex - many levels of compartmentalization
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The Nucleus
• Largest organelle - contains DNA
• Enclosed by double layered lipid envelope
• Pores allow transport of various cytoplasmic substances
• Contain nucleoli - sites of rRNA synthesis
• DNA organized by histones
• Further organized into chromatin - thread like
• Further condenses to chromosomes for replication
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The Endoplasmic Reticulum
• Extensive network of flattened
cisterns continuous with the
nuclear envelope
• Rough ER - studded with
ribosomes
• Protein entry point
• Modifications made, lipids
and carbohydrates attached
• Smooth ER - no ribosomes
• More enzymatic diversity
• Synthesize lipids,
oils, phospholipids, steroids
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Be able to
identify all
structures listed
in this
illustration
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The Golgi Complex
• Receives all proteins transported from RER
• Mail station of the cell - all proteins sorted for transport
• Composed of cisterns - flattened membranous stacks
• Many post-translational modifications made
• Determines fate of protein
• Packaged into secretory
vesicle
• Can be packaged into
transport vesicle (transfer
between stacks, transfer to
storage vesicles)
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Lysosomes
• Single membrane enclosed vesicles
• Contain many digestive enzymes
• Play important role in immune
response
• White blood cells engulf bacteria
• Phagosome fuses with lysosome
• Digestive enzymes kill bacteria
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Central Vacuoles
• Found in many mature plant cells
• Can occupy up to 90% of plant cell cytoplasm
• Surrounded by a tonoplast that can
• Selectably transport solutes
• Functions
• Stockpiling proteins or inorganic ions
• Storing pigments
• Storing defensive compounds against herbivores
• Increase the surface to volume ratio for the whole
cell
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Mitochondria
• Generates ATP
• Double membrane - structure similar to plasma membrane
• Inner membrane - complex folds (cristae), large surface area
• Center is matrix
• Reactions occur on
cristae - ATP generation
• Have own ribosomes
• Have some DNA
•Divide by binary fission
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Chloroplasts
• Found in algae and green plants
• Membrane enclosed structure
• Contains chlorophyll
• Contains other enzymes required for photosynthesis
• Chlorophyll contained in flattened sacs - thylakoids
• Stacks of thylakoids make grana
• Have DNA
• Have ribosomes
• Divide by binary fission
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Peroxisomes
- Degrade hydrogen peroxide (H2O2)
- Unavoidable by-product of oxygen respiration
- Peroxisomes convert H2O2 to water
- Some break down fatty acids to smaller
molecules that are transported to mitochondria
for fuel
- Others detoxify alcohol and harmful
compounds
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Cytoskeleton
• Complex in Eukaryotes
• Various-sized thin protein
“microfilaments” and
microtubules
• Maintain cell shape
• Used for cellular movement
– Cytoplasmic streaming
– Pseuodpodia
• Support motor proteins
– Move molecules in & out of the cell
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Cytoplasm
• Everything inside plasma membrane and
outside nucleus
• Fluid portion termed cytosol
• Packed with enzymes, structural
proteins, ribosomes,
tRNA, mRNA, DNA, pigments
• Eukaryotes show cytoplasmic streaming
• Prokaryotes do not show streaming
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Cell Divsion
• Eukaryotes undergo mitosis – consists of
several steps involving a number of specific
structures… is complex because a number
of chromosomes must divide and thus be
separated
• Prokaryotes do not… one circular
chromosome… binary fission or “budding”
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Centrioles
• Near nucleus
• Organizing center for mitotic organizing
apparatus
• 9 + 0 array organization
• Produces microtubules that separate
chromosomes & chromatids
• Starting material for flagella & cilia
• Found in almost all Eukaryotes, never
in prokaryotes
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