Lecture 27 Flashcards
Prokaryotic cell structure
Chromosomes
Single circular chromosome
1 - 2 micrometer long
Three types of prokaryotic cells
Cocci
Rods
Spirals
Circular Chromosome nuclear membrane?
No nuclear membrane
Region of the chromosome within the cell
Defined region known as nucleoid
What can be found in the cytosol of the bacteria?
Other small self-replicating DNA moleculecules (seperate to the main chromosome)
- these are known as plasmids
Average bacteria genome compared to human
Bacteria: 5000 genes / 5 million base pairs
Human: 20-25000 genes / 3 billion base pairs
Greater then 90% of the genome is giving rise to functional proteins
Major structural component of the cell wall of bacteria
Peptidoglycan
Cell wall, peptidoglycan function:
- rigid macromolecular layer that provided strength to cell
- protect cells from osmotic lysis and confers cell shape
Structure that betalactin targets and how they target them
Peptidoglycan
They target the enzymes that are involved in assembling peptidoglycan
Prokaryotes that lack cell walls
Mycoplasmas - group of pathogenic bacteria
Physical structure of the cell wall - mesh like structure
Structure of petioglycan
Petdiglycan stucture and how its made kinda
- consists of a network of fibres
- chain of sugars called NAM and NAG all linked together and repeating
- on NAM molecules there is a sort stretch of amino acids - a tetrapeptide - 4 amino acids are assembled onto NAM
- all chains stack together to create macromolecular molecule
- glycan chains are being wrapped around the cell
- cell is synthesising them inside cytoplasm and exports them to outside of cell and get assembled into larger network
- nag nams held together by strong bonds
- glycan chains are linked by tetrapeptides (a cross bridge)
Therefore strong
What enzyme catalyses the cross linking of the peptidoglycan chains to form rigid cell walls ?
Trandpeptidate (penacilin targets this enzyme)
Gram stain
A gram stain of mixed:
- staphylococcus aureus, gram-positive cocci (purple)
- Escherichia, gram negative bacilli (red)
Most common bacteria in reference bacteria
Gram stain proceedure
- Application of crystal violet (purple die)
- Application of iodine (mordant - fixes cell into cell wall)
- Alcohols wash (decolourization)
- Application of safranin (counterstain
Structure of gram- positive bacterial cell wall
- peptidoglycan traps crystal violet, which masks the red safranin dye - when washed away - too thick to leave.
- they will stain a darker colour and have a thicker cell wall of peptidoglycan (20-80nm)
What is the reason for the difference in the Gram stain reaction?
Structural differences between cell walls of gram-positive and gram-negative bacteria
Structure of gram negative bacterial cell wall
- crystal violets is easily rinsed away, revealing the red safranin dye
- there is a thinner layer (5-10mm) of peptidoglycan between plasma and outer membranes
Function of bacterial flagella
Some bacteria are capable of movement in liquid medium
How are bacterial flagella capable of movement in a liquid medium
- motile bacteria produce flagella
- long flexible appendage resembling “tails”
- proteinaceous 10-20nm in diameter, 5-10 per cell
- number of flagella and location on cell surface varies
- act like a propellant; cell rotates them to move through a liquid medium
Tactic responses: chemotaxis
Bacteria move along a concentration gradient towards a chemical attractant (positive) or away form a chemical repellent
From lecture voice
- too small to sense glucose difference at each end of cell
- thus it senses the tempal gradient (swims along, senses conc outside the cell, swims off again, senses concentration again, senses whether that concentration was either higher or lower)
Fimbiae - bacterial adherence factors
Function: structures with adhesive properties that cause bacteria to stick/adhere to surfaces
- not all bacteria possess fimbriae: it is an inherited trait
- can be mistaken for flagella but are not involved in motitily
- much shorter and more numerous then flagella “hair-like”
- 100-1000 per cell and 2-8 nm in diameter
- 1 micrometer in length
- receptors that recognise the cells they’re colonises - they are specific
Pili (sex conjugation pili or F pili)
- attachment to other bacteria
- transfer genetic material from one cell to another
- the genetic transfer is called conjugation
- conjugation is a form of horizontal gene transfer
Glycocalyx
A gelatinous polysaccharide and / or polypeptide outer covering
Forms a sticky mesh work of fibres
Another structure bacteria can use to attach to surfaces
Glycocalyx - capsules and slime layers
Two arrangements of Glycocalyx - capsules and slime layers
Organised into a friended structure attached firmly to a cell wall: CAPSULE
Disorganised without cell shape, attached loosely to cell wall = slime layer
Functions of capsules
- Virulence factors - protecting bacteria from phagocytosis and engulfment by immune cellls
- bacterial that make capsules are difficult to eradicate
- prevent cell from drying out (desiccation)
When are Bacterial Endo spores formed
- during unfavourable growth conditions and germinate under favourable conditions
What do bacterial Endo spores do
- protect cells from stress
Only two gram-positive bacteria that contain bacterial Endo spores
- genus bacillus (anthrax caused by the bacterium bacillus anthracis)
- clostridium (e.g clostridium difficle)
Stresses that trigger endospore formation
- nutrient starvation
- high cell density
- mother cell produces endospore via asymmetric cell division and dies
Endospore definition
- highly defines differentiated cells resistant to heat, harsh chemicals, antibiotics, disinfectants and radiation.
- dormant stage of bacterial life cycle
- can stay dormant for a very long time - all machinery for life is preserved on the inside of the endospore so when conditions become right they can germinate and goes back to normal life cycle
- survival strategy
