Bacteria structure and growth 1

all bacteria are prokaryotic organisms

• have been on earth long before multicellular life

• all bacteria are prokaryotes

• habitats range from moderate to extreme

• also live in human digestive system and skin - rough 10 to 1 ratio of bacteria to human cells

prokaryotes vs eukaryotes cell structure

• pro lack a nucleus surrounded by a complex nuclear membrane

• pro contain a single, circular chromosome located in a nucleoid

• pro lack membrane bound organelles

• euk have a nucleus that contain multiple, linear chromosomes

• euk are more complex - processes that compartmentalised in its organelles

• pro are unicellular which means they consist of a single cell

• euk are unicellular and multicellular - yeast and plants

shapes of bacteria

cocci - spherical shaped

bacilli - rod shaped

spirilli - spiral shaped

diplococcus

pair of two cocci

tetrad

group of four

streptococcus

chain of cocci

staphylococcus

cluster of cocci

streptobacillus

chain of rods

components of bacterial cells

• plasma membrane, single chromosome

• ribosomes for protein synthesis

• cell wall outside the plasma membrane

• capsule outside the cell wall

• some species contain flagella, pili and fimbriae

• plasmids which consist of extra chromosomal DNA

Cell wall of bacterial cells

• the protective layer that surrounds the cell

• it provides protection from lysis, maintains shape and integrity

• cytoplasm has a high conc of dissolved solutes therefore osmotic pressure within the cell is relatively high

• presence of cell wall protects from lysing - bursting due to increased volume

• main component of bacterial cell wall is peptidoglycan

• it resembles a layer of meshwork/fabric

gram positive bacteria cell wall

• first layer is the lipid bilayer/plasma membrane

• exterior layer is a thick layer of peptidoglycan which prevents cell lysis

• space between two layers is the periplasmic space

gram negative bacteria cell wall

• first layer is the lipid bilayer/plasma membrane

• exterior layer is a thin layer of peptidoglycan

• second membrane/bilayer is the outer plasma membrane

• outer membrane contains special lipids - lipopolysaccharides LPS

mordant of gram staining

• Grams Iodine which intensifies complexes and colour

decolouriser of gram staining

ethanol alcohol which removes primary stains

what colour is gram positive cells

purple

what colour is gram negative cells

red/pink

peptidoglycan in bacteria cell wall

• peptidoglycan is made up of proteins and sugars

• lysozyme is an enzyme in saliva and tears which breaks down peptidoglycan

• lysozyme protects from bacteria by weakening its cell wall

• it is unique to bacteria

capsule

• it is made up of carbohydrates - polysaccharides

• polysaccharides trap and absorb water to hydrate the cell

• it protects bacteria from attacks by the immune system - white blood cells, phagocytes and macrophages

• helps with adhering to host cells for replication

• only exists in some species of bacteria not all

• if capsule is removed, it is no longer pathogenic as its easier to kill

fimbriae

• exterior projection of bacterial cells

• attach to host cells in the attachment6 phase - pathogenic bacteria

• typically numerous and short in length

flagella/flagellum

• projections of bacterial cells that enable movements

• they act as propellars that propel the bacteria forward

• not all bacteria contain them

• motile - ability to propel themselves forward

• motility medium is the semi solid used to test for motility of bacteria

• growth outwards means its motile

• no growth outwards means it is not motile

nucleoid regiom

• a piece of circular double stranded DNA

• they are not membrane bound

plasmids

• consist of extrachromosomal DNA

• it is always circular and double stranded DNA

• they are small and contain specific DNA which codes to specific protein that is advantageous

endospores

• dormant structures resistant to unfavourable conditions

• can survive long periods without food and oxygen

• only produced by some gram positive bacteria

• can be killed by autoclaving - 121 degree and 15 psi pressure

sporulation

process by which vegetative cells transform into endospore

tough and highly resistant to high temperatures, boiling and no oxygen

vegetative state

growing and dividing cells where they are metabolically active

germination

spores are inactive until favourable conditions arise, they germinate and reform back to the vegetative state

endospore formation

• the process begins with the formation of a septum in the vegetative bacterial cell

• the septum divides the cell asymmetrically, separating a DNA forespore from the mother cell

• the forespore which will form from the core of the endospore is essentially a copy of the cell’s chromosome

• a protective protein coat forms around the spore

• the endospore is released upon disintegration of the mother cell completing sporulation

key features of endospores