Prokaryotic vs Eukaryotic Cells: Structural Organization and Key Differences, Lecture notes of Cell Biology

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Prokaryotic and Eukaryotic cells

• OBJECTIVE(S)
• After going through this topic, you should be able to:

1. Explain the structural organization of Prokaryotic and Eukaryotic cells.

Prokaryotic and Eukaryotic cells ● Cells can be categorized depending on how their genetic material is packaged. ● All cells fall into one of two categories.

• Prokaryotic cells
• Eukaryotic cells

The description of different structural features of prokaryotic cells

• Pili (singular pilus) are hair-like appendages found on the surface of bacteria and made of a protein called pilin. These structures are for attachment and allow bacteria to colonize environmental surfaces or cells and resist flushing.
• Flagellum
• A flagellum is attached to the bacterial capsule is a central feature of most of the prokaryotic cells.
• Flagellum is a part of cell wall. It is made of a protein called flagellin

• It provides motion or locomotion to the bacteria. Prokaryotic flagellum move in a rotary corkscrew like fashion.

Bacterial Surface Layers

• Bacteria possess 3 anatomical barriers (i.e., capsule, cell wall and plasma membrane) to protect the cells from external damage 1. Bacterial capsule
• The outer most layer and made of polysaccharides.
• It is impermeable to the water or other aqueous solvent and is also responsible for antigenicity of bacterial cells.

2. Bacterial cell wall - composition and structure

• Bacterial cell wall is made of peptidoglycan - a carbohydrate cross-linked with polypeptides.
• Cell wall in bacteria is used to classify bacterial species depending on their response to gram staining technique developed by Hans Christian Gram.
• During the staining procedure bacterial sample is stained with two dyes, Crystal Violet ( purple to blue-violet color) and Safranin ( pink to red color ).

• Peptidoglycan is a polymer (polymers are large molecules made of repeated units) of NAG (N-Acetyl-Glucosamine) and NAM (N-Acetyl-Muramic Acid) linked together.
• Peptidoglycan present in one layer is cross linked to the next layer to form a mesh work and to give the cell physical strength.
• Some antibiotics such as penicillin target the Peptidoglycan synthesis by degrading the bond connecting NAG and NAM

Cytoplasm of prokaryotic cells

• Prokaryotic cells lack membrane bound organelle except ribosomes
• Prokaryote cell contains genetic material in the form of circular DNA, known as bacterial chromosome
• Besides the main circular DNA, bacteria also contains extra chromosomal circular DNA known as ‘plasmid’.

Cytoplasm of prokaryotic cells

• Plasmid contain resistance genes that confers resistance towards known antibiotics.
• Exchange of extra-chromosomal DNA between different bacterial strains is one of the mechanisms responsible for spread of antibiotic resistance across the bacterial population.

Structure of Eukaryotic Cell

• Organelles allow eukaryotic cells to carry out more functions than prokaryotic cells can.
• Eukaryotic cells are usually larger than prokaryotic cells, and they are mainly found in multicellular organisms (e.g., plants, animals and fungi) although there are also unicellular eukaryotic cells e.g., protozoans.
• Organisms with eukaryotic cells are called eukaryotes.
• Some eukaryotes like protozoans (amoeba and paramecium) are free-living single-celled (unicellular) organisms.

Comparison btw

Prokaryotic cells

• Average size of cell 1 – 10 μm
• Genetic material not separated from cytoplasm (i.e., lacks membrane-bound nucleus)
• DNA is circular and free in the cytosol, not bound by histone proteins
• Nucleolus absent
• Cell division is amitotic i.e., binary fission or budding
• Sexuality absent i.e., no male and female gametes Eukaryotic cells
• Average size of a cell 10 – 100 μm
• Genetic material enclosed in a nucleus by a double layered membrane called nuclear envelope.
• DNA is linear as it is bound to histone proteins
• Nucleolus present, dense granular structures within the nucleus that has nucleolar DNA and ribosomal RNA
• Mitosis and meiosis occur
• Sexuality present in many, male and female partners, gametes that fuse