L5 - Compartmentalisation Flashcards
What is a compartment?
part of a cell that is closed from rest of cell and has its own function e.g. mitochondria
Roles of compartmentalisation and differentiation
- A new compartment can add a new process in a cell to help its survival.
- Some functions need to be done in specific isolated environments.
- Differentiation can be essential for cell survival to new conditions or as a part of a cell cycle.
What is magnetotaxis
- cell direction determined by magnetic field (not the movement thats flagella, just the direction of swimming)
- Cell motility directed by the Earth magnetic field.
- The field influences the swimming direction of the bacterium.
- The field has no effect on the speed of movement.
Describe magnetosomes in magnetotactic bacteria
- Generally Gram-negative = 2 membrane with perismatic space
- Contains magnetosomes (may not always be there)
- Geomagnetically sensitive, able to move with earth’s field
- Motile (flagella).
- Widespread worldwide distribution.
- Aquatic or in sediment (mostly free living organisms).
- Microaerophilic or/and anaerobe (require low or no O2).
Shape diversity of magnetotactic bacteria
spirillum, coccus, rod, multicellular, watermelon shaped
What is magnetosome
magnetic nanoparticules
- intracellular enveloped magnetic grains visible by EM
shapes of magnetosome
chains or aggregates
magnetosome formation
- ctoplasmic membrane becomes a vesicle and attracts specific proteins needed to make magnetosome
- proteins import irons and attach to smt like actin that goes along the cell
- all the vesicles gets attached togetgher
what is the native role of magnetosomes
- Magnetotactic bacteria live in places where there are O2 and chemical vertical gradients (water and sediments). They need little or no O2 and specific nutrients.
- they dont need oxygen so they need to be somewhere withh optimal amount of oxygena and nutrients → magnetosomes and chemotaxis help do this
- Main role: To ensure that cells find and maintain their optimal location for survival and growth.
- Magnetotaxis and chemotaxis work together to reduce a 3D problem into a 1D problem.
What are carboxysomes?
- Found in all cyanobacteria and some proteobacteria.
- Microcompartments.
- Have defined subcellular localisations in a cell.
Site of CO2 fixation, hence its name
2 main reactions inside a carboxysome
- carbonic anhydrase transforms HCO3- into CO2
- rubisco uses D RuBP and Co2 to make 3-PGA which fixes CO2 into a sugar
Oxygen is also a substrate of RUbisCO so how does carboxysome inhibit this?
- CO2 and HCO3- are actively transported into the cell
- the carboxysome is very selectively permeable so HCO3- can enter directly but CO2 has to be turned into HCO3- first
- in cell: HCO3- → CO2 using CA, CO2 cant get out so it builds up and accumulate
- RuBP can enter carboxysome and rubisco uses RuBP
- lots of sugar bc lots of CO2 build up in carboxysome
- oxygen can’t enter
What is cyanobacteria?
- basis of food chains
- almost ubiquitous symbiotic interaction with plants and animals
- cycling of carbo and nitrogen
oxygenic photosynthesis
advantages of being multicellular
- defines against predation
- sharing info
- reduce competition
- more complicated activities than individual cell
- division of labour
describe the structure of filamentous cyanobacteria
chains of cells in a gram negative type of envelope where they are encased in a double membrane but share periplsmic space where exchange of goods take place
What are heterocyst
differentiated form of cyanobacteria. made under nitrogen deprivation, specialised in the fixation of nitrogen.
- Necks form at poles in contact with vegetative cells (narrow cytoplasm and septum) and the additional cell envelope is thicker = reservoir of organic nitrogen.
- Honeycomb form near poles in contact with vegetative cells (contorted intracellular membranes used in respiration). it doesnt like oxygen so it respires a lot to remove the excess oxygen
2 main reactions inside a heterocyst
nitrogenase : N2 into NH4+
glutamine synthesise: NH4+ + glutamate = glutamine (glutamate comes from vegetative cells and glutamine is exported to vegetative cells
what are the specific functions of each compartments : magnetosome, carboxysomes, heterocyst
- find perfect environment
- fix CO2
- fix N2
