Lecture 5- cell structure Flashcards
what is the role of the cell wall and cell membrane?
cell wall
Protection from osmotic stress
Maintenance of shape
Structural support
cell membrane
Subdivision of compartments
Prevents cytoplasmic leakage
Selective transport of molecules
Together, cell walls and cell membranes separate self from non-self
where are cell walls and membranes present?
cell walls are present in most organisms whereas cell membranes are present in all cells
what is the role of the cell membrane?
Cell membranes distinguish ‘self’ from the environment, mediating the selective transfer of molecules
Fragile, self-assembling barrier easy transfer of lipid soluble molecules
Able to sense the environment through receptors/proteins
what does the strength of the membrane allow?
Membrane strengthening agents enable organisms to survive environmental stresses by reinforcing the membrane
what are hopenes?
Most abundant natural product on Earth
Important in oil prospecting
what are membrane proteins?
-Membrane proteins involved in transport, communication and structural support
-Able to sense the environment through receptors/proteins
integral = embedded within the lipid bilayer
peripheral = located on either surface on the bilayer
what are membrane contents?
Most membranes contain more protein than lipid – 3:1
Few molecules can pass across the membrane unaided – lipid soluble
The selective permeability of membranes is conferred by proteins that are inserted into the lipid bilayer membrane
how are membranes used as filters?
-It is essential for the cell to control what enters/leaves
-energy transduction, metabolism and waste removal require selective permeable membrane
-Cells derive ATP by pumping ions across the membrane.
Uses a protein that sits on the bilayer.
-Molecules involved in moving ions across the membrane need to be present in the membrane.
-Efflux pumps help remove toxic agents including antimicrobials.
-Membrane proteins act as transporters or channels in the membrane, passing molecules based on biophysical characteristics
-Small, uncharged molecules (O2, CO2, H2O) easily pass through the membrane.
-Large polar (sugars) and charged (amino acids) molecules require proteins for transport.
Move across the membrane based on a gradient
-Move across the membrane based from low to high.
Expends energy by doing this.
how are membranes used as interface?
The cell membrane is the interface with the environment and is critical for pathogenesis
Molecules presented at the surface and effectors molecules released by the microbes must pass through the cell membrane.
Secretion systems can move across multiple membranes
what are the
what is peptidoglycan?
Present only in bacteria
Consists of a polymer of two sugars
-N-acetyl glucosamine (NAG)
-N-acetylmuramic acid (NAMA)
Can be destroyed by certain agents e.g. lysozyme
Amino acids can vary
100’s of different types of peptidoglycans
Peptidoglycan runs in cables along the bacterial cell wall, glycosidic bonds convey strength in one direction and peptide bonds in the other direction
what are Teichoic acids/lipoteichoic acids?
- responsible for overall negative charge of cell surface
- bind calcium/magnesium for transport into cells
- contributes to biofilm formation, environmental tolerance
how much of the cell wall is peptidoglycan?
90%
what are lipopolysaccharides?
Polysaccharide portion consists of 3 components
- lipid A, core polysaccharide and O-specific polysaccharide/antigen
Lipid A can be toxic to animals and comprises the endotoxin complex
Core polysaccharide contains a range of sugars, connect other components together
O antigen varies depending on the organism
what is a capsule?
Polysaccharide gel coating the surface of some organisms (S. pyogenes, S. aureus, E. coli)
Usually synthesised from sugars
- single sugar polymerised e.g. glucose polymerised to glucan
- repeating units of two or more derivatives e.g. glucosamine (amine of glucose) or glucuronic acid (carboxylic acid of glucose)
Confers protection against adverse conditions including desiccation and the immune system
what are surface appendages?
Surface structures with roles in bacterial life cycle and pathogenicity
what are flagella?
Assists in the movement of bacteria, eukaryotes and archaea
- structure and movement differs
Very thin (20 nm), need to stain to visualise
Locomotion and sensory organelle
what are fimbriae?
Involved in adherence of bacteria to surfaces
- assist in colonisation, biofilm formation
- primary mechanisms of virulence
Consist of protein, much smaller than flagella
- 3 to 10 nm
Genetic manipulation can be used to demonstrate importance
- no fimbriae = no disease
what are features of the fungal cell membrane?
Cytoplasmic membrane-
typical lipid bilayer interspersed with protein
phospholipids and variety of sterols - ergosterol
functionally similar to prokaryotes
permeability barrier
serves in transport of materials
what are features of a fungal cell wall?
Cell wall functions
shape/support
thick layer of nitrogenous polysaccharide fibres - chitin
chitosan, glucans, mannoproteins, glycoproteins, melanins
how does fungi differ from other cells?
they are eukaryotic as
they Differ from prokaryotic cells
Nucleus
Nuclear envelope
Mitochondria
Golgi apparatus
Endoplasmic reticulum
Differ from plants, no chlorophyll no photosynthesis
Eukaryotic cells other than fungi lack a cell wall
what is differentiation?
Change in phenotype in response to environment or developmental programming
May or may not be evident in altered morphology
changes in appearance resulting from changes in cell wall/surface
gene expression, production of toxins
For pathogens, differentiation may be critical for survival or virulence
what are endospores?
An endospore is an inert, environmentally resistant structure
Unlike spores, endospores are formed within bacteria
what is a resistant coat?
Dipicolinic acid stabilises and protects the DNA.
10-30% water content
Small acid soluble proteins (SASP’s)
how are endospores used as bioweapons?
Bacillus anthracis, aetiological agent of anthrax
- resist extreme temperatures, dessication, osmotic stress
Weaponised by multiple states, including UK
Gruinard island intentionally infected with B. anthracis
- feasibility of anthrax as a bioweapon
- could pollute cities for decades
- decontamination began in the 1980’s
- returned to owner in 1990
what are biofilms?
Many organisms can adhere to each other, and/or a surface to form a biofilm
Organisms in biofilms are distinct from their planktonic counterparts
what are porins, periplasm and LPS on gram negative?
Porins
– non-selective transmembrane proteins in OM, transport of nutrients/drugs
Periplasm - site of enzymatic activity, more protected than Gram +ve
Lipopolysaccharide (LPS) – of medical importance as it acts as an endotoxin
what happens when the cell wall is negative?
Most prokaryotes cannot survive without cell walls
- Mycoplasma e.g. M. pneumoniae, M. genitalium
- smallest known prokaryote (0.1 µM diameter)
Susceptible to osmotic stress as they lack a cell wall
Unusually tough cell membranes
- most have sterols in their membranes
- live in osmotically protected environments
