Describe the cellular structures of bacteria.

1. Flagellum
- A flagellum is an extremely thin hair like appendage used by bacteria for locomotion / motility.
- It’s usually longer than a bacterial cell.
Types of flagellation
1. Monotrichous – single flagellum e.g pseudomonas aeruginosa
2. Lophotrichous – several flagella developing from a single spot e.g pseudomonas flourescens
3. Amphitrichous – flagella arising from two opposite ends e.g spirillum serpens
4. Peritrichous – cell with flagella all around e.g Escherichia coli

2. Fimbriae
These are bacterial surface appendages that are involved in interactions with other cells but do not provide locomotion.
- Fibriae are small, bristle like fibres emerging from the surface of many bacterial cells and made of proteins.
- They stick to each other and to surfaces
- They help in microbial colonization on surfaces like rocks and glass
- Help pathogens to adhere to epithelial cells e.g. colonization of intestines by E. Coli and genitourinary tract by gonococcus.
2b. pili also sex pilus
Is an elongate, rigid, tubular structure made of special protein – pilin.
Pili are used for “mating process” between cells known as conjugation which involves partial transfer of DNA from one cell to another (in gram-negative bacteria).
A pilus from the donor cell unites with a recipient cell thereby providing a cytoplasmic connection for making the transfer.

3. Capsule
A viscous jelly like substance outside bacterial cell.
Functions
1. Protects bacteria by making them resistant to phagocytosis by white blood cells.
2. Acts as a food reserve during depletion of food in the environment
3. Increases virulence of bacteria / makes them more pathogenic
4. Plays a role in synthesis of hydrolytic enzymes for food digestion e.g Ruminococcus

4. Cell wall
(a) The cell wall is rigid and gives the cell its shape. It consists of 2% of the cell volume.
(b) It’s important in bacterial cell division and multiplication
(c) It’s composed of peptidoglycan (murein player) consists of basic acidulated amino sugars N-acetylglucosamine (G) and N-acetylmuramic acid (M) and amino acids – D-alamine, D-Iysine D-glutamic acid.
(d) Provides structural support to prevent a bacterium from bursting or collapsing because of changes in osmotic pressure.

5. Cell membrane
- A very thin (5-10 mm) flexible sheet molded around the cytoplasm.
- Composed of lipid together with proteins embedded to varying degrees.
Functions
1. The membrane provides a site for energy reactions, nutrient processing and synthesis.
2. To regulate transport (passage of nutrients into the cell and the discharge of wastes- its selectively permeable).
3. Secretion – the release of metabolic products into the extracellular environment (enzymes & toxins).
11

6. Cell cytoplasm
A dense, gelatinous solution surrounded by cell membrane. Its major component is water (70-80%) which serves as a solvent for a mixture of nutrients such as sugars, amino acids, other organic molecules and salts.
- The components of cytoplasm serve as building blocks for cell synthesis or as sources of energy.
- It also holds basis such as the chromosome, ribosomes, granules, etc.

7. Bacterial chromosome and plasmids
The hereditary material in most bacteria exists in the form of single circular strands of DNA (bacterial chromosome). A few have linear or multiple chromosomes.
- Bacteria lack true nucleus, their DNA is not enclosed by a nuclear membrane but is aggregated in a central area of the cell called nucleoid.
- Many bacteria contain other extra chromosomal pieces of DNA called plasmids.
- These strands exist as separate double stranded circles of DNA.
- During bacterial reproduction they are duplicated and passed on to offspring
They are not essential to bacterial growth and metabolism but they confer protective traits such drug resistance, metal tolerance, production of toxins (biocins) and enzymes.
NB: Plasmids are an important agent in modern genetic engineering techniques because they can be manipulated and transferred from one bacterial cell to another.

8. Ribosomes
A bacterial cell contains ribosomes made of RNA and proteins. They occur in chains (polysomes) and are dispersed throughout the cytoplasm
- Many are also attached to the cell membrane
- A ribosome is a combination of special type of RNA known as ribosomal RNA or rRNA (60%) and protein (40%).
- They serve as the sites of protein synthesis.

9. Inclusions or Granules - Are storage bodies.
They contain condensed, energy-rich organic substances e.g glycogen within special single-layered membranes.
- Inclusions found in some aquatic bacteria are gas vesicles that provide buoyancy and flotation.

10. Bacterial Endospore
- It’s an extremely resistant structure that withstands hostile conditions and facilitates survival.
- They are dormant bodies produced by the bacterial genus Bacillus & Clostridium
- The bacteria have two-phase life cycle – a vegetative cell and an endospore
- The vegetable cell is the metabolically active and growing phase
- When exposed to adverse environmental conditions it forms an endospore by a process termed sporulation
- A spore may be terminal sub-terminal or central

---

Kavungya answered the question on March 12, 2019 at 13:17