L27 - Prokaryotes Flashcards
Estmate of bacteria on earth
5 x 10ˆ30
Why are microbes everywhere
Because they have been around for 3.8 billion years
Two kingdoms of bacteria
Archaea (ancient bacteria) and Eubacteria
DNA present in Bacteria
Single circular chromosome in the nucleoid
Parameters of the bacteria
rod shaped, 1-2µm long and 1/2 µm in diameter
What helps with bacteria motility
Flagella
Glycocalyx
Extracellular cell protection
Do prokaryotes have nuclear envelope or organelles
no
What component present in the cell wall allows antibiotics to be effective against bacteria
Peptidoglycan
What are Plasmids?
Small circular, self-replicating DNA molecules found in the cytosol, can be v small/big
Prokaryotes that lack cell walls
Mycoplasms
What does peptidoglycan do?
*Its a rigid macromolecular shape that gives strength to the cell
*Protects the cells from osmotic lysis and confers cell shape
What does penicillin do to the peptidoglycan
*Targets the enzymes that makes this
*Makes the cell shape from rod to round
What is peptidoglycan made of?
A mesh like structure:
*Make of short stretches of amino acids that stack to make a macromolecule
*Repeating units of NAM-NAG Glycan
Where is NAM-NAG synthesised
Made in the cell and transported through constitutive exocytosis
What is on the NAM side
The tetrapeptide bond
How is the structure of the cell wall formed
The NAM-NAG are strong and resists tension one way
*The tetrapeptide on the NAM is linked to another tetrapeptide to another NAM through crossbridge of amino acids
What enzyme catalyses the cross-linking of the NAM units
Transpeptidase - flemings penicillin targets
Colour for gram positive w example
Purple - staph. Aureus
Colour for gram negative w example
Red - E. coli
How to carry out a gram stain
*Crystal violet to stain culture purple
*Add iodine (mordant) - fixes the stain to the cell wall
*Alcohol - washed crystal violet, not from all cells only gram neg ones
*Stain with red safranin
Why do different cells stain differently
Due to differences in the chemical and structural composition of the peptidoglycan wall
Why do some cells stain purple
Due to a thick peptidoglycan cell wall (20-80nm):
*Traps crystal violet
*OH cannot wash away the crystal violet cause wall so thick
*Safarin stains but cant see because of violet stain
Why do gram negative stain red
Have two layers and pepti inbetween the layers i.e the plasma and outer membrane
*Thinner (5-10nm) hence the OH washes away the crystal violet
How fast do bacteria move in liquid media
100m in 5s
How do the bacteria move in liquid media?
Flagella that acts as a propellor
What are the flagella made of?
They are made of proteins, 10-20nm in diameter and 5/10 per cell
They all move to the back and propel the bacteria in one direction
Tactic response of the bacteria
Chemotaxis - has +ve and -ve chemotaxis
*Bacteria moves along conc. gradient towards a chem attractant or away from it
How do bacteria detect sugar if they are too small?
Move around to sense the temporal gradient, sense and remembers the higher conc through chemoreceptors and send info to the flagellar motor
What are Fimbriae?
Protein structures with adhesions aka adhesion pili/adhesins
*Causes bacteria to stick to surfaces
*Have receptors to recognise the structures that they are colonising
Are fimbriae involved in motility
No
Do all bacteria have Fimbriae
No, it is an inherited trait
Exp in lab showed that overtime, trait is lost if no surface to attatch to
Parameters of Fimbraie
Much shorter and more numerous than flagalla
*Hair like
*100-1000/cell
*2-8nm in diameter
1µm in length
What is Pili (sing.pillus) aka?
Sex pilli/ F pilli
What do Pili do?
Attaches to another cell and transfers DNA through Conjugation, a form of horizontal gene transfer
What is a Glycocalyx?
*Gelatinous polysaccharide (like snot hehe) and/or polypeptide outer covering
*Forms a sticky meshwork
Where is Glycocalyx made?
Synthesised in the outside of the cell
2 forms of Glycocalyx
*Capsule
*Slime layer
Capsule
*Organised into a define structure that is stuck to the cell wall
*Made from sugar + peptide so prevents from dessication
*Strep dangerous as our immune cells cant do phagocytosis
Slime layer
*Disorganised and surrounds the cell, loosely attached without shape
What are bacterial endospores?
Form during unfavourable conditions and germinate under favourable ones
Where are bacterial endospores present?
In gram pos bacteria i.e Bascillus anthracis and Clostridium difficile
Usual state of the bacteria
Vegetative state - binary fission
State of bacteria under nutrient starvation and high cell density
Asymm division, endospore with nutrients and chromosomes at one end, mother dies
*Process takes 8 hours
What are dangerous part of endospores
*Resistant to heat, harsh chemicals, antibiotics, disinfectants and radiation
*Has all the machinery for life
*Can stay dormant for millions of years
