Module 2: Prokaryote Cell Structure

Bacteria

a cell that is capable of carrying out all necessary life activities, such as reproduction, metabolism, and nutrient processing

they can act as a single cell or as a group in either colonies or biofilms

Bacterial arrangements

coccus: spheres, oval, bean-shaped, pointed

bacillus: cylindrical rods

spiral: rigid helix

Pleomorphism

variations in size and shape in cells of one species, usually due to environment

Diplococci

coccus bacteria in pairs

Tetrads

coccus bacteria in groups of 4

Staphylococci

coccus bacteria in irregular shapes

Streptococci

coccus bacteria in chains of a few to a hundred

Sarcina

coccus bacteria in cubical packets of 8, 16, 32…

Diplobacillus

bacillus bacteria in pairs attached by ends

Streptobacilli

bacillus bacteria in chains

Palisades

bacillus bacteria in side-by-side chains

Spiral Bacteria

spirilla, vibrious, and spirochetes

sometimes in short chains, rarely stay attached after cell division

Flagella

external structure of bacteria that provides mobility

Polar flagellar arrangement

attached at one or two poles of the cell

can be monotrichous(single pole), liphotrichous(small bunches/tufts), or amphitrichous(at both poles)

Peritrichous flagellar arrangement

flagella are dispersed randomly over the cell surface

Chemotaxis

movement in response to a chemical, a flagellar function

can be positive(towards a favorable chemical) or negative(away from a harmful chemical

Phototaxis

movement in response to light, a flagellar function

can be positive(towards light) or negative(away from light)

Run

counterclockwise turning of the flagella, allows the cell to swim in a smooth and linear direction

Tumble

flagella reverses direction and turns clockwise which changes the direction of the cell

Periplasmic flagella

internal flagella that creates a twisting/flexing motion of the cell which creates movement, spirochetes have these

Fimbriae

appendage for attachment, small bristle-like fibers on cell surface, allows them to stick to each other and surfaces, main way bacteria stick to humans to make people sick

Pilus

long and rigid tubular structure made of pilin protein, only found in gram-negative bacteria, used in conjugation

Conjugation

the transfer of DNA between different cells

S-layer

surface coating, provides protection from environmental conditions but is only produced in hostile environments

Glycocalyx

surface coating, has 2 different types

Slime layer: loose around the cell, protects from water and nutrient loss

Capsule: tightly bound to cell and is denser and thicker, protects against the immune system, water loss, and aids in adherence

Gram-positive cell

2 layers; cell membrane and thick cell wall, contains teichoic acid and lipoteichoic acid

Gram-negative cell

3 layers; cell membrane, thin cell wall, and outer membrane

Mycobacterium

has very long chain of fatty acids, mycolic acid in the cell wall, uses acid fast stain

Mycoplasma

lacks a cell wall, no outer membrane, membrane is stabilized by sterols and is resistant to lysis

Gram-negative outer membrane components

Lipopolysaccharides(LPS): helps with structure and acts as receptors, also stimulates fever and shock reactions in humans

Lipoproteins: anchor over outer membrane to peptidoglycan

Porin proteins: completely span outer membrane of G- bacteria, allows passage of small molecules

Cytoplasm

site for biochemical and enzymatic activities

Bacterial chromosomes

one circular strand of DNA, aggregated in the nucleoid

Plasmids

non-essential DNA, separate small DNA circles, duplicated and passed to offspring during replication

Ribosomes

dispersed through cytoplasm to make proteins

Inclusion bodies

storage sites for nutrients and excess proteins

Cytoskeleton

contributes to cell shape, under cell membrane

Endospores

only in some bacteria, allows bacteria to survive in hostile conditions, inert and resting condition of bacteria

Vegetative cell

metabolically active, normal bacterial cell