CELL
Introduction
•All living things are made up of
cells – the smallest unit of life
• 1 cell = unicellular
•>1 cell = multicellular
•All cells arise from pre-existing
cells
•Called?
•Scientist?
Types of cells
Contain unicellular
organisms called “prokaryotes” with
prokaryotic cells
Contains unicellular and multicellular
organisms called “eukaryotes” with
eukaryotic cells
Types of cells
Compartments – DNA within nucleus
No compartments – DNA naked
“Pro” = before, “karyon” = nucleus “Eu” = true, “karyon” = nucleus
Origin of cells
•All cells arose from a common prokaryotic ancestor 3.5-4
billion years ago
Prokaryotic vs. eukaryotic cells
PROKARYOTIC CELL
Structure
Morphology – shape and arrangement
•Coccus – spherical
•Diplococci – in pair (Neisseria gonorrhoeae)
•Streptococci – in chain (Streptococcus
pyogenes – strep throat)
•Staphylococci – in grape-like cluster
(Staphylococcus aureus – HAIs like sepsis,
pneumonia...)
•Rod (bacillus)
•Coccobacillus – short rod
•Bacillus anthracis, E. coli, Clostridium tetani
Structure
Morphology – shape and arrangement
•Vibrio – short curved rod
•Vibrio cholerae – cholera
•Spirillum – rigid long curved rod
•Helicobacter pylori – stomach ulcers
•Campylobacter jejuni – diarrhea
•Spirochete – flexible long curved rod
•Treponema pallidum – syphilis
•Borrelia burgdorferi – Lyme disease
Structure
Size: 0.3 – 2 µm
Components
•Plasma membrane
•Cell wall (+/-)
•Capsule (+/-)
•Flagella (+/-)
•Pili (+/-)
•Cytoplasm with cytosol, cytoskeleton and internal
structures including nucleoid
Structure
Plasma membrane
Structure
•Phospholipid bilayer
•Proteins
Functions
•Protects, forms border
•Semipermeable membrane
•Senses environment
•Transport
•Energy production
Plasma membrane
Plasma membrane
Transport
•Passive
•No energy required
•From high to low concentration – down the gradient
•Types
•Simple diffusion
•e.g. O2, CO2
•Facilitated diffusion
•e.g. glucose
Plasma membrane
Transport
•Passive
•Osmosis – movement of water across a selectively
permeable membrane towards more solute
•Osmotic pressure
Solution
outside cell
Solute
Concentration
Net water
movement
Result
Isotonic In = Out No None
Hypotonic In > Out Inside cell Lysis
Hypertonic In < Out Outside cell Plasmolysis
Plasma membrane
Plasma membrane
Transport
•Active
•energy required to move solute from low to high concentration
Comprehension Check
Which of the following is not a function of the prokaryotic
plasma membrane?
1. Protein production
2. Energy production
3. Osmosis
4. Protection
Cell wall
Structure
•Peptidoglycan (PG) in bacteria
•Proteins – peptide bridges
•Carbohydrates – sugar (glycan) chains
Functions
•Rigid border that provides protection
•Prevents cell lysis
Cell wall
•Gram-positive vs. Gram-negative
Cell wall – Gram-positive
•Examples
•Bacillus
•Staphylococcus
•Streptococcus
•Many PG layers (up to 30)
•Teichoic acids – help
stabilize and anchor PG
layers to plasma
membrane
•wall teichoic acids
•lipoteichoic acids
Cell wall
Cell wall – Gram-negative
•Examples
•E. coli
•Pseudomonas
•Salmonella
•One to a few PG layers
•Outer membrane
•Bilayer with porins that acts as
another permeability barrier
•Lipopolysaccharides (LPS) form
outer part of bilayer
•O and core polysaccharides
•Lipid A is endotoxin
