1. Comparative study of typical prokaryotic cell and eukaryotesBy
DR SAMUEL AGUAZIM

2. STRUCTURE, FUNCTION & GROWTH OF PROKARYOTIC & EUKARYOTIC CELLS

3. Prokaryotic and Eukaryotic Cells .
All living creatures are made up of CELLS , small membrane bound units filled with aqueous solutions of chemicals, which have the ability to create copies of themselves by growing and dividing.

4. Living organisms can be classified into 3 major domains:
Prokaryotes
*Bacteria
*Archaea
Eukaryotes
*Plant cells
*Animal cells
Prokaryotes and Eukaryotes are 2 distinct cell types with STRUCTURAL differences

5. The Prokaryotic Cell
The Prokaryotic Cell Simply stated, prokaryotes are molecules surrounded by a membrane and cell wall.

6. Prokaryotes Lack a membrane bound nucleus enclosing the DNA
DNA is present as a single circular molecule called a BACTERIAL CHROMOSOME
DNA is naked having no associated histone proteins
No membrane bound organelles
Apart from the DNA nucleoid, there is little internal structure apart from dissolved substances and a large number of RIBOSOMES essential for PROTEIN SYNTHESIS
The cytosol is an effective site for bacterial cell metabolism. This allows bacteria to adapt quickly to changing nutritional conditions, but means the regulation of genetic and metabolic activity has to be tightly regulated.
Divide by BINARY FISSION
Some prokaryotic cells have external whip-like FLAGELLA for locomotion or hair like PILI for adhesion.
Prokaryotic cells come in multiple shapes: cocci (round), baccilli (rods), and spirilla or spirochetes (helical cells).

7. External Prokaryotic Structures
Cell wall Contains PEPTIDOGLYCAN (only found in bacteria). Large complex molecule consisting of polysaccharide polymers cross-linked by short chains of amino acids
Capsules
Sometimes the cell wall is further surrounded by a gelatinous polysaccharide sheath called an attach CAPSULE , GLYCOCALYX or SLIME LAYER
Plasma Membrane
Basic structure of the phospholipid bilayer is the same for all bacteria
Flagella Motile bacteria usually have long, thin appendages called FLAGELLA . These protein sub-units are used to propel bacteria through liquids

8. Pili or Fimbrae
A pilus ( Latin ; plural : pili ) is a hairlike protein structure on the surface of a bacterial cell, required for bacterial conjugation (transfer of genetic material)
A fimbrium (Latin; plural: fimbria ) is a short pilus that is used to attach the cell to a surface. Mutant bacteria that lack fimbria cannot adhere to their usual target surfaces and, thus, cannot cause diseases

9. Spores & Cysts
These are produced by some bacteria to survive unfavourable environmental conditions. Dormant forms are metabolically inactive and only germinate under suitable conditions
ENDOSPORES : a dormant , tough, non-reproductive structure produced by a small number of bacteria . The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress. They are therefore resistant to ultraviolet and gamma radiation , desiccation , lysozyme , temperature , starvation , and chemical disinfectants . Endospores are commonly found in soil and water, where they may survive for long periods of time e.g. Clostridium (tetanus, gas gangrene), Bacillus (anthrax)
CYSTS : also dormant, but unlike endospores are not resistant to heating at high temperatures

10. Lipoprotein bilayer without sterols
Structure
Chemical Composition
Function
Cell wall
Peptidoglycan
Sugar backbone with peptide side chains that are cross-linked
Gives rigid support, protects against osmotic pressure;
is the site of action of penicillins and
cephalosporins and is degraded by lysozyme.
Outer membrane of gram-
negative bacteria
Lipid A
Toxic component of endotoxin.
Polysaccharide
Surface fibers of gram- Teichoic acid positive bacteria Gives rigid support, protects against osmotic pressure; is the site of action of penicillins and cephalosporins and is degraded by lysozyme. Toxic component of endotoxin.Major surface antigen used frequently in laboratorydiagnosis.
Cytoplasmic membrane
Lipoprotein bilayer without sterols
Site of oxidative and transport enzymes.

11. Ribosome
RNA and protein in 50S and 30S Protein subunits
Protein synthesis; site of action of aminoglycosides,
subunits erythromycin, tetracyclines, and chloramphenicol.
Nucleoid
DNA
Genetic material.
Mesosome
lnvagination of plasma membrane
Participates in cell division and secretion.
Periplasm
Space between plasma
membrane and outer membrane
Contains many hydrolytic enzymes, including
P-lactamases.

12. Non-essential components
Capsule
Polysaccharide
Protects against phagocytosis
Pilus or fimbria
Glycoprotein
Two types: (1) mediates attachment to cell surfaces;
(2) sex pilus mediates attachment of two bacteria
during conjugation
Flagellum
Protein
Motility.
Spore
Keratinlike coat, dipicolinic acid
Provides resistance to dehydration, heat, and
chemicals.
Plasmid
DNA
Contains a variety of genes for antibiotic resistance
and toxins.

13. Granule
Glycogen, lipids, polyphosphates.
Site of nutrients in cytoplasm.
Glycocalyx
Polysaccharide
Mediates adherence to surfaces.

14. Classifying Prokarotes
Main method is using the GRAM’S STAIN
This separates bacteria into GRAM-POSITIVE (purple) and GRAM-NEGATIVE (red) depending on the percentage of PEPTIDOGLYCAN in the cell walls
- GRAM-POSITIVE bacteria have a cell wall only 1 layer thick
- GRAM-NEGATIVE bacteria have a cell wall several layers thick

15. Differences between cell wall of Gram positive and Gram negative bacteria
Character
Gram positive
Gram negative
Thickness
Thicker
Thinner
Periplasmic space
Absent
Present
Lipids
Absent or small
Teichoic acid
Peptidoglycan
16- 80nm
2nm

16. Eukaryotes
More complex multicellular organisms e.g. plants, animals, fungi and also many single-celled organisms e.g. amoeba, yeast
Possess an NUCLEUS and other organelles all of which are surrounded by a MEMBRANE , which divided the cell up into compartments
COMPARTMENTALISATION: very important !
ADVANTAGES:
Molecules are ‘concentrated’ together, increases rate of reactions
Keeps reactive molecules away from other parts of the cell that may be affected by them
Large work surface area … many enzymes are bound in membranes

17. Eukaryotes The basic eukaryotic cell contains the following:
- membrane-bound nucleus
- plasma membrane
- glycocalyx (components external to the plasma
membrane)
- cytoplasm (semifluid)
- cytoskeleton – microfilaments, intermediate filaments and microtubules that suspend organelles, give shape, and allow motion .
- presence of characteristic membrane
enclosed subcellular organelles e.g. mitochondria, golgi, rER, sER etc

18. Plant & Animal Cells For ANIMAL CELLS only: For PLANT CELLS only:
Peroxisomes & Lysosomes often present
Some have microvilli on their surface
Centrioles organise spindle fibres during cell division
For PLANT CELLS only:
Cell walls made from cellulose
Communication with neighbouring cells occurs through plasmodesmata
Usually a large central vacuole
Photosynthesis occurs in cells containing chloroplasts

19. Plasma Membrane Plasma Membrane
A lipid/protein/carbohydrate complex, providing a barrier and containing transport and signalling systems.

20. Nucleus
Nucleus
Double membrane surrounding the chromosomes and the nucleolus. Pores allow specific communication with the cytoplasm. The nucleolus is a site for synthesis of RNA making up the ribosome

21. Mitochondria Mitochondria
Surrounded by a double membrane with a series of folds called cristae.
Functions in energy production through metabolism.
Contains its own DNA, and is believed to have originated as a captured bacterium.

22. Rough endoplasmic reticulum (RER)
A network of interconnected membranes forming channels within the cell.
Covered with ribosomes (causing the rough appearance) which are in the process of synthesizing proteins for secretion or localization in membranes.
Ribosomes
Protein and RNA complex responsible for protein synthesis

23. Golgi Apparatus Golgi apparatus
*A series of stacked membranes. Vesicles (small membrane surrounded bags) carry materials from the RER to the Golgi apparatus.
*Vesicles move between the stacks while the proteins are processedto a mature form.
*Vesicles then carry newly formed membrane and secreted proteins to their final destinations including secretion or membrane localisation.

24. Centrioles Centrioles
Centrioles are found only in animal cells. They function in cell division.

25. Lysosymes
Lysosymes
A membrane bound organelle that is responsible for degrading proteins and membranes in the cell, and also helps degrade materials ingested by the cell.

26. Peroxisomes Peroxisomes or Microbodies
Produce and degrade hydrogen peroxide, a toxic compound that can be produced during metabolism

27. Chloroplasts Chloroplasts
Surrounded by a double membrane, containing stacked thylakoid membranes.
Responsible for photosynthesis, the trapping of light energy for the synthesis of sugars.
Contains DNA, and like mitochondria is believed to have originated as a captured bacterium.

28. Vacuoles
Vacuoles
Membrane surrounded “bags” that contain water and storage materials in plants.

29. Cell wall
Plants have a rigid cell wall in addition to their cell membranes. They provide support for the plant.

30. Similarities between P & E cells
Prokaryotes & Eukaryotes are CHEMICALLY & METABOLICALLY similar:
Both have genetic material
Both have a cell membrane
Both have a cytosol
Both have ribosomes
Both contain nucleic acids, proteins, carbohydrates & lipids
Both use similar reactions for storing energy and metabolic activities e.g. building proteins

31. Differences between P & E cells main differences are structural
Prokaryotes
eukaryotes
No membrane bound organelles nuclues
Membrane bound nucleus
Cell walls made of peptidoglycan (Thickness of wall depends on whether the cell is Gram +ve or –ve)
Cell walls, if present, made of cellulose (chitin in fungi)
No membrane bound organelles
Membrane bound organelles (compartmentalisation)
Have pili & fimbriae (for adhesion) and flagella (for propulsion)
Have cilia or flagella (for movement)
Mucilaginous capsule
No mucilaginous capsule present (numerous internal structures present including microtubules, ER, Golgi, secretory vesicles etc)
ranges from 0.5um to 100um bound nucleus
Cell size ranges from 10 – 150um Cell size
Main differences are STRUCTURAL :

32. Comparison of prokaryotic and eukaryotic cells
Prokaryotes
Eukaryotes
Organisms
Monera: Eubacteria & archebacteria
Protists, fungi, plants and animals
Level of organization
Single celled
Single celled (protists mostly) or multicellular usually with tissues and organs
Typical cell size
Small(1-10microns)
Large( microns)
Celll wall
Almost all have cell walls(murein)
Fungi and plants(cellulose and chitin): none in animlas
Organelles
Usually none
many different ones with specialized functions
Metabolism
Anaerobic and aerobic: diverse
Mostly aerobic

33. Comparison of prokaryotic and eukaryotic cells
Genetic material
Single circular double stranded DNA
Complex chromosomes usually in pairs: each with a single double stranded DNA molecule and associatied proteins contained in a nucleus
Mode of division
Binary fission mostly: budding
Mitosis and meiosis using a spindle: followed by cytokinesis