Prokaryotic CellsBACTERIA

The Prokaryotic Cell Members of the prokaryotic world make up a vast

heterogeneous group of very small single-celled organisms.

Include bacteria and archae, although the majority are bacteria

The thousands species of bacteria are differentiated by many factors such as: Morphology (shape), chemical composition (often detected by

staining reactions), nutritional requirements, biochemical activities, and sources of energy (sunlight or chemicals)

These differences can only be seen with the use of a microscope

Size, Shape, and Arrangement

Bacteria come in many sizes, and several shapes. Most range from 0.2 to 2.0 µm in diameter and 2-8 µm in length

Basic shapes include: Cocci- round shaped Bacillus- rod shaped Spirillum- spiral shaped, helical shape like corkscrew, have rigid

bodies, and use flagella to move Vibrio- curved Spirochetes- helical and flexible, move by axial filaments found

within flexible external sheath Square Star

Cell Cluster Formation

Bacteria are also classified according to cell cluster formation:

Streptobacillus

Cluster formation DescriptionDiplococci Two cocci cells pairedStaphylococci Number of cells

clustered together (grape-like)

Streptococci & Streptobacillus

Number of cells arranged in a chain

vibrio bacillus spirochete

coccusspirillum

bacillus

Learning Check: What Shape are these bacteria?

1. 2. 3.

5. 6.

Shape and Arrangement The shape of bacteria is determined by heredity.

Most bacteria are monomorphic: maintain a single shape

Environmental factors can alter that shape

Some bacteria like Rhizobium and Corynebacterium are pleomorphic: can have many shapes, not just one.

Source for figure: http://textbookofbacteriology.net/Impact_2.html

*Cell wall- Most bacteria have a cell wall but there are some that do not like Mycoplasma species

Basic Components of Bacteria

Structures External to the Cell Wall

Possible structures external to the prokaryotic cell wall are: Glycolax Flagella Axial filaments Fimbrae and Pili

What is the Glycocalyx? Means sugar coat & is the general term used for

substances that surround cells

Bacterial glycocalyx is a viscous (sticky), gelatinous polymer that is external to the cell wall

Composed of a polysaccharide, polypeptide, or both

Two types:

Capsule: substance is organized and is firmly attached to the cell wall

Slime layer: substance is unorganized and only loosely attached to the cell wall glycocalyx

Fig. 1

Source for Fig. 1: http://emp.byui.edu/wellerg/The%20Cell%20Lab/Prokaryotic%20Cells/The%20Prokaryotic%20Cell.html

(a) Micrograph of Streptococcus pneumoniae, the common cause of pneumonia, showing a prominent capsule. (b) Bacteroides, a common fecal bacterium, has a slime layer surrounding the cell

Learning Check

What advantage does a glycocalyx provide a cell? (think about its composition)

Glycocalyx Very important component of biofilms

Biofilms are densely packed communities of microbial cells that grow on living or inert surfaces

A glycocalyx that helps cells in a biofilm attach to their target environment and to each other is called an extracellular polymeric substance (EPS)

EPS protects the cells within itFacilitates communication among themand enables the cells to survive by attaching

to various surfaces in their natural environment

Source for Fig. 2 http://www.microbiologybytes.com/blog/2010/09/08/the-biofilm-matrix/

Fig. 2

Flagella Some prokaryotes have flagella which are long

filamentous appendages that propel bacteria

Peritrichous: flagella distributed over the entire cell

Polar: at one or both poles or ends of the cell Monotrichous: A single flagellum at one pole Lopothrichous: a tuft of flagella coming from

one pole Amphitrichous: flagella at both poles of the

cell

Bacteria that lack flagella re referred to as atrichous (without projections)

Flagellar Movement

Figure 3.9 Motion of a peritrichous bacterium. In peritrichous bacteria, runs occur when all of the flagella rotate counterclockwise and become bundled. Tumbles occur when the flagella rotate clockwise, become unbundled, and the cell spins randomly. In positive chemotaxis (shown), runs last longer than tumbles, resulting in motion toward the chemical attractant.

Axial Filaments Spirochetes have unique structure and motility

Move my means of axial filaments Bundles of fibrils that arise at the ends of the cell

beneath an outer sheath and spiral around the cell

The rotation of the filaments produces a movement of the outer sheath that propels the spirochetes in a spiral motion

Fimbriae and Pili Many gram-negative bacteria contain hair-like

appendages that are shorter, straighter, and thinner than flagella are used for attachment and transfer of DNA rather than for

motility Fimbrae can occur at the poles of the bacterial cell or entire

surface of cell Have a tendency to adhere to each other and to surfaces

Pili are usually longer than fimbrae but shorter than flagella and are found as one or two per cell

Involved in motility and DNA transfer

Conjugation Pili

Learning Check

Several Escherichia coli cells are connected byconjugation pili. How are pili different from bacterial flagella?