Structure and functional anatomy of bacteria Flashcards
What does a prokaryotic cell look like?
- circular DNA free in the cytosol
- ribosomes in the cytosol
- capsule around the outside provides a stickly adhesive surface
- multiple pilli in different directions
- Cell wall (different peptidoglycan compositions)
- cell membrane
Prokaryotes: What is the capsule?
- The slime layer
- Polysaccharide & Polypeptide rich
- sticky adhesive layer that allows attchment to surfaces
- May provide protection
- Protect against desiccation (for hydration)
- (Environmental persistence)
- protects against phagocytosis by masking biomarkers detected by immune cells
- Not all bacteria have this layer (not always present)
- The slime layer can extend beyond the microorganisms themselves
describe the ability of bacteria to supress phagocytosis
They mask biomarkers – reduces immune response
Streptococcus mutans:
Describe the role of biofilms as a physiological advantage to bacteria
What can be done to reduce the formation of biofilms when putting in a central venous line?
Biofilms form on clean shiny surfaces, perfect for bacteria to bind e.g.
- Teeth (plaque)
- Catheters: Central venous line- at the site at which the catheter penetrates the skin, there is a interaction between the plastic penetrating the skin and the microbes on the surface
- Use sterile wound dresings, disinfect the area to reduce the formation of biofilms
- plastic
Sterilisation necessesary
Interior bacteria persist, titration (reducted availability of the drug)- antibiotic can only kill external bacteria
A big problem; complex communities can form
Describe the bacterial cell wall
- Complex, semi-rigid structure→peptidoglycan provides movement and flexibility as well as strength
- Characteristic shape of the cell, bacteria are under considerable osmotic pressure
- Surrounds the fragile cell membrane (phospholipid bilayer)
- Prevents osmotic rupture
- Contributes to disease mechanisms→Helps bacteria to evade host immune responses
- can contribute toward toxic shock syndrome
- Almost all bacteria have a cell wall
Describe the structure of peptidoglycan (PG)
Composed of N-acetylglucosamine (NAG) and N-acetylemueramic acid (NAM) repeating units linked by glycosidic bonds
These are alternating molecues that form chains with cross links that have peptide crossbridges
Overall:
Carbohydrate backbone (N-acetylglucosamine (NAG) and N-acetylemueramic acid (NAM) + and amino acid side chain
Describe gram negative cell walls
- lipopolysaccharides (LPS)
- periplasm which has peptidoglycan layer
- outer membrane which is anchored to the thin peptidoglycan layer
- transmembrane proteins
- plasma membrane
- lipoproteins
Describe gram positive cell wall
- smooth exterior
- peptidoglycan layer leafleted with lipoteichoic acid (anchors peptidoglycan to plasma membrane)
- membrane proteins distributed
Describe the Cell (Cytoplasmic) Membrane
- Encloses cytoplasm of the cell
- Mainly phospholipids (amphipathic- hydrophobic + hydrophilic)
- Lipid bi-layer (fluid mosaic model)
- Polar head►hydrophilic
- Non-polar tail ►hydrophobiic
- Protein channels and porins through membrane
- (fluid mosaic model- dynamic system)
Cytoplasmic Membrane: Main functions
- (i) Permeability barrier:
prevents leakage and functions as a gateway for transport of nutrients into and wastes out of the cell
- (ii) Protein anchor:
site of many proteins that participate in transport, bioenergetics and chemotaxis
- (iii) Energy conservation:
Site of generation and dissipation of the proton motive force
Describe the composition of Cytoplasm
What is contained within the cytoplasm?
What physiological characteristic contribute to survival?
Internal matrix of the cell:
- 80% H2O
- Proteins, carbohydrates, lipids
Contained within the cytoplasm:
- DNA
- Ribosomes
- Inclusion bodies (storerooms within bacterial cells that contain proteins, fats and carbohydrates
- -function as energy reserves which contribute to survival)
What is the structure and function on flagella?
Provides motility
4 arrangements relating to poles:
- Monotrichous (Mono = one)
Single polar flagellum
- Lophotrichous (Lopho = tufted)
Two or more at one/both ends
- Amphitrichous (Amphi = both)
Single polar flagellum at each end
- Peritrichous (Peri = all around)
Distributed over entire cell
Describe the differences in flagellum structure in gram positive and gram negative bacteria
State the location of each ring
How do they work to cause whipping of the flagellum?
- Gram positive, no L ring, larger P ring that goes right out through the peptidoglycan layer
- C ring and MS rings present within cytoplasmic membrane
- P ring which is very small and anchored into the peptidoglycan
- L ring present within outer membrane
- Hook protein that creates a kink in the tail made of flagellin which rotates (whips)
- The rings turn, driven by the proton motive force (proton translocation across the electrochemical gradient) that causes turning and whipping of the flagellum
Describe monotricious and peritricous bacterial motility
A series of runs and tumbles
- CW = clockwise
- CCW = counter clockwise
- If monotricious= roation of polar flagellum in CCW direction that will cause the organism to run in whatever direction its facing. The organism will then tumble (due to brownian motion) within the liquid/matrix (whatever the bacterium is present in) and when it stabilises there is another run in whatever direction it is facing
- If peritrichious= as its runing the flagella bundle together as they all whip in a CCW direction then when the run has finished (as the electrochemical gradients resets) they tumble due to (Brownian motion) then the flagella just float in solution. Whatever direction the bacterium is facing, rotation in a CCW causes another run and the organism moves in a different direction
What is Chemotaxis?
What happens when bacteria are heading towards an attractant?
- A Chemotaxis is response to chemical stimulus (also phototaxis (moevement towards light), aerotaxis (movements towards oxygenation), osmotaxis (moving towards a particular solute) and hydrotaxis (moving out of salty conditions)
- Runs are extended if they are moving towards the attractant and shortened if they are moving away
- Positive/negative chemotaxis (runs towards or away)
- Series of runs and tumbles where runs are extended if in direction of a chemical attractant (chemoreceptors) if not there is just random walking