microbio functional anatomy of prokaryotic cells

Prokaryotic cell

simple cell type lacking a true nucleus and membrane bound organelles

Eukaryotic cell

complex cell type containing a nucleus and membrane bound organelles

Common features of all cells

DNA and chromosomes and cell membrane and cytosol and ribosomes

Prokaryotic chromosome

single circular DNA molecule not enclosed by a membrane

Histones in prokaryotes

absent

Prokaryotic organelles

lacking true membrane bound organelles

Prokaryotic cell wall

composed mainly of peptidoglycan

Binary fission

process by which prokaryotic cells divide

Average bacterial size

0.2–1.0 µm wide and 2–8 µm long

Basic bacterial shapes

bacillus and coccus and spiral

Spiral forms

include vibrio and spirillum and spirochete

Monomorphic

organisms that maintain a single shape

Pleomorphic

organisms that can assume multiple shapes

Coccus arrangement variations

pairs or chains or clusters

External bacterial structures

include glycocalyx and flagella and axial filaments and fimbriae and pili

Glycocalyx

sticky external coating composed of polysaccharide or polypeptide or both

Capsule

organized firmly attached glycocalyx contributing to virulence

Slime layer

unorganized loosely attached glycocalyx

Glycocalyx function

prevents dehydration aids attachment and resists phagocytosis

Biofilm formation

aided by glycocalyx allowing microbial attachment to surfaces

Examples of encapsulated bacteria

Bacillus anthracis and Streptococcus pneumoniae and Streptococcus mutans

Flagellum

long filamentous appendage for motility anchored in the cell wall and membrane

Atrichous

no flagella

Monotrichous

one flagella

Lophotrichous

flagella with tuft

Amphitrichous

flagella on both ends

Petritrichous

flagela all over

Flagellar motion

run and tumble pattern

Taxis

movement toward or away from a stimulus

Chemotaxis

movement in response to chemical gradients

Phototaxis

movement in response to light

Magnetotaxis

movement guided by magnetic fields

Flagellar antigen

H antigen important in bacterial identification such as E. coli O157:H7

Axial filament

internal flagella in spirochetes that allow corkscrew motion

Fimbriae

hairlike appendages used for attachment to surfaces

Pili

longer appendages used for DNA transfer between cells during conjugation

Cell wall

rigid structure that maintains shape and prevents osmotic lysis

Peptidoglycan

polymer composed of N acetylglucosamine and N acetylmuramic acid linked by peptides

Tetrapeptide side chain

attached to NAM providing cross linking sites in peptidoglycan

Function of cell wall

provides shape and structural support and protection against osmotic pressure

Gram positive cell wall

thick peptidoglycan layer containing teichoic acids

Teichoic acids

negatively charged molecules that regulate cation movement and provide antigenic specificity

Lipoteichoic acid

links to plasma membrane

Wall teichoic acid

links to peptidoglycan

Gram negative cell wall

thin peptidoglycan layer with outer membrane containing lipopolysaccharides

Lipid A

endotoxin component of lipopolysaccharide that causes fever and shock

O polysaccharide

antigenic portion of LPS used in serotyping

Periplasmic space

region between plasma membrane and outer membrane in gram negative bacteria

Gram negative resistance

due to outer membrane acting as barrier to certain drugs and detergents

Gram stain mechanism

crystal violet iodine complex trapped in thick peptidoglycan of gram positives but washed out from thin layer of gram negatives

Mycoplasma

bacteria lacking cell wall but containing sterols in plasma membrane for rigidity

Acid fast bacteria

genera Mycobacterium and Nocardia with waxy mycolic acid covering thin peptidoglycan

Lysozyme

enzyme that digests disaccharide in peptidoglycan

Penicillin

antibiotic that inhibits peptide bridge formation in peptidoglycan

Protoplast

gram positive cell with wall removed by lysozyme

Spheroplast

gram negative cell with wall partially removed

L form

wall less bacterial variant that can reproduce

Plasma membrane

selectively permeable phospholipid bilayer with proteins following fluid mosaic model

Plasma membrane function

controls transport and site of energy generation via electron transport chain

Damage to plasma membrane

caused by alcohols and detergents and polymyxin antibiotics leading to leakage of contents

Cytoplasm

aqueous interior of the cell where most biochemical reactions occur

Nucleoid

irregularly shaped region containing bacterial chromosome

Plasmid

small circular DNA molecule carrying nonessential genes such as antibiotic resistance

Ribosome

site of protein synthesis with 70S size in prokaryotes and 80S in eukaryotes

Inclusion body

storage granule for nutrients or materials such as phosphate sulfur or glycogen

Magnetosome

iron containing inclusion that orients bacteria along magnetic fields

Endospore

dormant resistant structure produced by certain genera under adverse conditions

Spore forming genera

include Bacillus and Clostridium

Sporulation

process of endospore formation within a vegetative cell

Germination

return of an endospore to metabolically active vegetative state

Endospore resistance

high resistance to heat radiation desiccation and chemicals

Function of endospore

ensures bacterial survival under harsh environmental conditions

Relationship of spores to disease

many spore formers are pathogenic due to persistence and toxin production

Energy metabolism location

cell membrane in prokaryotes due to lack of mitochondria

Selective permeability

property of plasma membrane allowing controlled entry and exit of substances

Transport mechanisms in bacteria

include diffusion and osmosis and facilitated diffusion and active transport

Run and tumble motion

alternating swimming and reorientation caused by flagellar rotation

Peptidoglycan function

maintains cell integrity against osmotic pressure while allowing permeability to small molecules

gram positive bacteria

have thick peptidoglycan and no outer membrane.

gram negative bacteria

have thin peptidoglycan and outer LPS layer