Anatomy of Prokaryotic Cells

Dyzza Lei L. AlbaricoJulian Philip A. SorianoShaina Mavreen D. Villaroza

What are Prokaryotic Cells?

Prokaryotes are single-celled organisms that are the earliest and most primitive forms of life on earth.

 They have no true nucleus as the DNA is not contained within a membrane or separated from the rest of the cell

Prokaryotes do not have a nucleus, mitochondria, or any other membrane-bound organelles. In other words, neither their DNA nor any of their other sites of metabolic activity are collected together in a discrete membrane-enclosed area.

They have a single, circular chromosome.

They have cell walls containing peptidoglycan

Their DNA is not associated with Histones.

Cell StructureCapsule - Found in some bacterial cells, this

additional outer covering protects the cell when it is engulfed by other organisms, assists in retaining moisture, and helps the cell adhere to surfaces and nutrients.

Cell Wall - Outer covering of most cells that protects the bacterial cell and gives it shape.

Cytoplasm - A gel-like substance composed mainly of water that also contains enzymes, salts, cell components, and various organic molecules.

Cell Structure

Cell Membrane or Plasma Membrane - Surrounds the cell's cytoplasm and regulates the flow of substances in and out of the cell.

Pili - Hair-like structures on the surface of the cell that attach to other bacterial cells. Shorter pili called fimbriae help bacteria attach to surfaces.

Cell StructureFlagella - Long, whip-like protrusion

that aids in cellular locomotion.Ribosomes - Cell structures

responsible for protein production.

Plasmids - Gene carrying, circular DNA structures that are not involved in reproduction.

Nucleiod Region - Area of the cytoplasm.

Cell Structure

Cell ShapeProkaryotes appear in 3 basic

shapes:1. Coccus – Spherical shaped

(plural,Cocci)

2. Bacillus – Rod shaped (plural, Bacilli)

3. Spirillium – Spiral known

CoccusThe cocci are spherical or oval bacteria having

one of several distinct arrangements based on their planes of division.

a.Division in one plane produces either a diplococcus or streptococcus arrangement.1. diplococcus: cocci arranged in pairs2.streptococcus: cocci arranged in chains

b. Division in two planes produces a tetrad arrangement.1.a tetrad: cocci arranged in squares of 4

Coccusc. Division in three planes produces

a sarcina arrangement.1.sarcina: cocci in arranged cubes of 8

d. Division in random planes produces a staphylococcus arrangement.1.staphylococcus: cocci arranged in irregular, often grape-like clusters

An average coccus is about 0.5-1.0 micrometer (µm) in diameter.

(A micrometer equals 1/1,000,000 of a meter.)

Coccus Shape

SpirillumSpirals come in one of three forms,

a vibrio, a spirillum, or a spirochete.

a) vibrio: a curved or comma-shaped rod

b) spirillum: a thick, rigid spiral

c) spirochete: a thin, flexible spiral

Spirals range in size from 1 µm to over 100 µm in length.

BacillusBacilli are rod-shaped bacteria. Bacilli all divide in

one plane producing a bacillus, streptobacillus, or coccobacillus arrangement.

a) bacillus: single bacilli

b) streptobacillus: bacilli arranged in chains

c) coccobacillus: oval and similar to a coccus

An average bacillus is 0.5-1.0 µm wide by 1.0-4.0 µm long.

Bacillus Shape

Example:

Staining TechniquesSimple Stains

◦Differential Stains1. Gram Staining2. Acid-fast Stain

◦Special Stains1. Endospore Staining2.Flagella Staining3.Capsule Staining

Simple StainingStaining can be performed with

basic dyes such as crystal violet or methylene blue, positively charged dyes that are attracted to the negatively charged materials of the microbial cytoplasm.

Differential Staining Gram Staining

This differential technique separates bacteria into two groups, Gram-positive bacteria and Gram-negative bacteria.

Crystal violet is first applied, followed by the mordant iodine, which fixes the stain .Then the slide is washed with alcohol, and the Gram-positive bacteria retain the crystal-violet iodine stain; however, the Gram-negative bacteria lose the stain.

The Gram-negative bacteria subsequently stain with the safranin dye, the counterstain, used next. These bacteria appear red under the oil-immersion lens, while Gram-positive bacteria appear blue or purple, reflecting the crystal violet retained during the washing step. 

Figure 1. The Gram stain procedure used for differentiating bacteria into two groups.

• Acid Fast Stain

This technique differentiates species of Mycobacterium from other bacteria.

Heat or a lipid solvent is used to carry the first stain, carbolfuchsin, into the cells. Then the cells are washed with a dilute acid-alcohol solution. Mycobacterium species resist the effect of the acid-alcohol and retain the carbolfuchsin stain (bright red).

Other bacteria lose the stain and take on the subsequent methylene blue stain (blue). Thus, the acid-fast bacteria appear bright red, while the nonacid-fast bacteria appear blue when observed under oil-immersion microscopy.

Special StainingNegative Staining for Capsule

Capsule staining uses a mixture of the bacteria in a solution containing a fine colloidal suspension of colored particles to provide a dark background and then stain the bacteria with a simple stain such as safranin.

Example of Negative Staining

Endospore Staining

◦An endospore is a special resistant dormant structure formed within a cell that protects a bacterium from adverse environmental conditions. Endospores cannot be stained by ordinary methods such as simple stains and gram staining. Malachite green the primary stain is applied to a heat fixed smear and heated to steaming for about 5 min. Then the perparation is washed for about 3o sec. with water to remove the malachite green from all the cells parts except for the endospores.

Example of Endospore Staining

Flagella Staining

A tedious and delicate staining procedure uses a mordant and the stain carbolfuchsin to build up the diameters of the flagella until they become visible under the light microscope

Example of Flagella Staining

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