cell biology Flashcards
importance/function of plasma membrane (3)
- separate contents of cell from environment and control exchange of substances between the 2
- receptor sites for recognising external stimuli eg. hormones
- reactions can occur there, eg. light dependant reaction
facilitated diffusion
polar and large molecules move across membrane with aid of channel and carrier proteins
how does active transport work
- molecules bind to carrier protein and ATP attached to membrane protein on inside of cell/organelle
- binding of phosphate ion causes protein to change shape so that access for the molecule is open to the inside of the membrane but closed to the outside
isotonic
2 solutions have sae water potential
hypertonic
when a cell has a HIGHER water potential then its surroundings (net loss of water)
hypotonic
when a cell has a LOWER water potential then its surroundings (net gain of water)
2 main methods of cell fractionation
- homogenisation
- centrifugation
μm in 1m
1000, 000
μm in 1cm
10, 000
μm in 1mm
1,000
max resolution of scanning electron microscope
20nm
max resolution of transmission electron microscope
0.1nm
advantages of electron microscope
high resolving power = produces a very detailed imagine
disadvantages of electron microscope
- specimen must be dead as vacuum needed
- artefacts may be produced
- expensive
size of chloroplast
3-10 μm
size of mitochondria
2.5 μm
prokaryotes
smaller then eukaryotes, and have no nucleus or nuclear envelope
how to prokaryotes differ from eukaryotes (6)
- smaller
- no nucleus/nuclear envelope
- smaller ribosomes
- no membrane-bound organelles
- single circular loop of DNA which is not associated with any histone proteins
- has a cell wall containing murein
prokaryotes may also have… (3)
- 1+ plasmid
- a capsule surrounding the cell
- 1+ flagella
how do channel proteins work
- water filled channels across the membrane
- allow specific water-soluble ions to pass through
- selective - each open in presence of specific ion
- ion binds to protein, causing it to change shape in a way that opens to one side of the membrane and closes to the other
how to carrier proteins work
molecule binds with protein, changing its shape so that it is open to one side of the membrane and closed to the other
how do prokaryotic cells replicate?
binary fission
stages of binary fission
- circular DNA molecule replicates and both copied attach to cell membrane
- plasmids replicate
- cell membrane begins to grow between 2 DNA molecules and pinches inwards - dividing cytoplasm in 2
- new cell wall forms between 2 molecules of DNA
how to viruses replicate?
- attach to host cell using attachment proteins
- inject nucleic acid into host cell
- nucleic acid contains ‘instructions’ for host cell’s metabolic processes to produce viral components (eg. enzymes and structural proteins)
- these are then assembled into new proteins
why aren’t viruses ‘cells’ (3)
- no metabolism
- cannot-self reproduce
- no cytoplasm
role of capsid in viral cells
- protect nucleic acid from degradation
- surface sites enable viral particle to bind to/enter host cell
