1. Prokaryote Cell Structure & Function
Lecture 5
Prokaryote Cell
Structure & Function
Cell Diagram: Mariana Ruiz, pub domain

2. Size of Living Things
1 m = 100 cm = 1,000mm = 1,000,000 µm = 1,000,000,000nm
1mm = 1000 µm = nm
1 µm = 1000nm
Diagrams:

3. The Cellular Level of Organization
Living things are constructed of cells.
Living things may be unicellular or multicellular.
Cell structure is diverse but all cells share common characteristics.
Cells are small so they can exchange materials with their surroundings.
Surface area relative to the volume decreases as size of cell increases.
- limits the size of cells
Cell Theory states:
1. All organisms are composed of one or more cells.
2. Cells are the basic unit of structure and function in organisms.
3. All cells come only from other cells.
Cell Theory

4. Two basic types of cells
Prokaryotic Cells (Prokaryotes)
Eukaryotic Cells (Eukaryotes)
Prokaryotic
Eukaryotic
Diagrams:
Prokaryotic & Eukaryotic Cell, Mariana Ruiz

5. Prokaryotes Binary Fission Prokaryotes
Almost always single-celled (except for prokaryote colonies).
Always reproduces by means of binary fission.
Does not have a cell nucleus or any other organelles within membranes.
DNA travels openly around the cell.
- All bacteria are prokaryotes.
Diagrams:
Prokaryotic Mariana Ruiz
Binary Fission, JW Schmidt

6. Prokaryote Genetics - Antibiotic resistance
Nucleoid
Region of cytoplasm where chromosomal DNA is located.
Usually a singular, circular chromosome
Few or no proteins “naked DNA”; no introns
Plasmid
Small extra piece of chromosome/genetic material.
genes
Not critical to everyday functions.
Can provide genetic information to promote:
- Antibiotic resistance
- Virulence factors
(molecules produced by pathogen that specifically influence host's function to allow the pathogen to thrive)
- Promote conjugation
(transfer of genetic material between bacteria through cell-to-cell contact)
Nucleoid
Plasmid
STRUCTURE OF MICOBIAL CELLS

7. Prokaryotes Cytoplasm Also known as proto-plasm.
Gel-like matrix of water, enzymes, nutrients, wastes, and gases and contains cell structures.
Location of growth, metabolism, and replication.
Granules
Bacteria’s way of storing nutrients
Staining of some granules aids in identification
Cytoplasm
Granules
STRUCTURE OF MICOBIAL CELLS

8. Prokaryotes Ribosomes
Found within cytoplasm or attached to plasma membrane.
What are they made of?
What do they do?
Composed of a small (30S) subunit and a large (50S) subunit.
Cell may contain thousands of ribosomes.
Cytoskeleton
Cellular "scaffolding" or "skeleton" within the cytoplasm.
Major advance in prokaryotic cell biology in the last decade has been discovery of the prokaryotic cytoskeleton.
Previously thought to be a feature only of eukaryotic cells.
Eukaryotic Cells
Ribosome
Cytoskeleton
Diagrams/Photos:
Fluorescent Cell: NIH, Pub Domain

9. Prokaryotes - Plasma Membrane
Separates the cell from its environment.
Phospholipid molecules oriented so that hydrophilic phosphate heads directed outward and hydrophobic tails directed inward.
Proteins embedded in two layers of lipids (lipid bilayer).
Proteins allow substances to pass into and out of the cell.
Water loving
Water hating
Semi Permiable
Diagrams:
Prokaryotic Cell, Mariana Ruiz
Membrane: NIST

10. Prokaryotes – Cell Wall
Peptidoglycan is a huge polymer of interlocking chains of identical peptidoglycan monomers.
Backbone of peptidoglycan molecule composed of two derivatives of glucose:
N-acetylglucosamine (NAG)
N-acetlymuramic acid (NAM)
NAG / NAM strands are connected by interpeptide bridges.
Peptidoglycan
- Rigid mechanical support
- Freely permeable to solutes
Image:
Peptindoglycan Structure: NicolasGrandjean

11. Prokaryotes - Cell Wall
From the peptidoglycan inwards all bacteria are very similar. Going further out, the bacterial world divides into two major classes (plus a couple of odd types). These are:
Gram-positive Gram-negative
Images: PHIL Public Health Image Library

12. Prokaryotes - Cell Wall: Gram-Negative & Gram-Positive
Peptidoglycan makes up as much as 90% of the thick, compact cell wall.
Gram-negative
More chemically complex and thinner.
Peptidoglycan only 5 – 20% of the cell wall.
Peptidoglycan not outermost layer, between the plasma membrane and the outer membrane.
Outer membrane is similar to the plasma membrane, but is less permeable and composed of lipopolysaccharides (LPS).
LPS is a harmful substance classified as an endotoxin,
The space between the cell wall and the plasma membrane is called the periplasm.
Image:
Prokaryotic Cell, Mariana Ruiz
Gram +-, Julian Onions

13. Why are these differences in cell wall structure so important?
Gram-negative bacteria: fewer interpeptide bridges but have an outer membrane made of lipopolysaccharides LPS.
Penicillins and cephalosporins interfere with linking of interpeptides, but can’t easily get to in gram- bacteria.
Cell walls without enough of these intact cross-links are structurally weak, and disintegrate when cells divide. This is how penicillins and cephalosporins work.
Since the eukaryotic cells of humans do not have cell walls, our cells are not damaged by these drugs.
Microorganisms that do not contain peptidoglycan are not susceptible to these drugs.
Images: Sources unknown

14. Prokaryotes - Glycocalyx
Some bacteria have an additional layer outside of the cell wall called the glycocalyx.
This additional layer can come in one of two forms:
Slime Layer
Capsule
Slime layer
Capsule
STRUCTURE OF MICOBIAL CELLS

15. Prokaryotes - Glycocalyx
Some bacteria have an additional layer outside of the cell wall called the glycocalyx.
This additional layer can come in one of two forms:
1. Slime Layer
glycoproteins loosely associated with the cell wall.
Slime layers cause bacteria to adhere to solid surfaces and help prevent the cell from drying out.
Streptococcus
The slime layer of Gram+ Streptococcus mutans allows it to accumulate on tooth enamel (yuck mouth and one of the causes of cavities).
Other bacteria in the mouth become trapped in the slime and form a biofilm & eventually a buildup of plaque.
Staphylococcus
The slime layer of Gram+ Staphylococcus allows it to thrive in the salty, hypertonic environment of the skin.
Glycocalyces are not specific to Gram+ or Gram- bacteria, sometimes only some members of a certain species (strains) have a glycocalyx, whereas others don’t.
Slime layer
Capsule
STRUCTURE OF MICOBIAL CELLS

16. Prokaryotes - Glycocalyx
2. Capsules
polysaccharides firmly attached to the cell wall.
Capsules adhere to solid surfaces and to nutrients in the environment.
Adhesive power of capsules is a major factor in the initiation of some bacterial diseases. Capsule also protect bacteria from being phagocitized by cells of the hosts immune system.
Slime layer
Capsule
STRUCTURE OF PROKAROTIC CELLS

17. Prokaryotes - Endospores
Dormant, tough, non-reproductive structure produced by small number of bacteria.
Primary function of endospores:
Allow bacteria to survive adverse conditions
Resistant to radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants.
Endospores commonly found in soil and water, where they may survive for long periods of time.
A stained preparation of Bacillus subtilis showing endospores as green and the vegetative cell as red
Allow bacteria to survive in “suspended animation” when environmental conditions are not suitable. Kind of like a plant seed..When conditions are right the endospore will ‘sprout’ a living bacterium.
Image:
Stain: Jerry Keplinger, James H. Quillen College of Medicine
Procedure: Source link no longer works
STRUCTURE OF PROKAROTIC CELLS

18. Prokaryotes – Surface Appendages
Some prokaryotes have distinct appendages that allow them to move about or adhere to solid surfaces.
Consist of delicate stands of proteins.
Flagella
Long, thin extensions that allow some bacteria to move about freely in aqueous environments.
Axial filaments (endoflagella)
Wind around bacteria, causing movement in waves.
Fimbriae
Most Gram- bacteria have these short, fine appendages surrounding the cell. Gram+ bacteria don’t have.
No role in motility. Help bacteria adhere to solid
surfaces. Major factor in virulence.
Pili
Tubes that are longer than fimbriae, usually shorter than flagella. Use for movement, like grappling hooks, and also use conjugation pili (singular = pilus) to transfer plasmids.
Flagella
Axial filaments
Fimbria
Pili
Images:
Flagella: Mike Jones Wiki
Axial Filament: Indiana USchool of Med
EColi: Pub Library of Science

19. Endosymbiotic Theory Proposed by Lynn Margulis (1970)
Explains the origin of eukaryotic cells
Major evolutionary event occurred by merging two or more lineages through symbiosis (2 organisms living together)

20. Endosymbiosis

21. Endosymbiosis
Mitochondria came from bacteria (probably the group that includes typhus)
Chloroplast came from cyanobacteria (blue-green algae)
Flagella came from
spiral shaped bacteria

22. Evidence for Endosymbiosis
Similar structure – double membrane, free ribosomes, similar DNA
Mode of asexual reproduction – binary fission
DNA processing is similar (RNA is translated immediately in both mitochondria and bacteria
DNA sequence evidence ( Carl Woese)