2.5 cell membranes Flashcards
no. membranes around nucleus
2
no. membranes around ER
1
no. membranes around GOLGI
1
no. membranes around LYSOSOME
1
no. membranes around CHLOROPLAST
2
no. membranes around MITOCHONDRIA
2
partially permeable defintion
allows some substances to pass through but not all
purpose of plasma membrane
- BARRIER : controls movement of substances in and out of the cell (cell membrane)
- Compartmentalisation (golgi apparatus)
- cell signalling (receptors on csm)
- electrical communication (nerve csm)
- attachment site for enzymes (inner membrane of mitochondria)
phopholipid properties
- hydrophilic head (charged)
- hydrophobi tails (uncharged)
phospholipid bilayer orientation
orientate so that hypdrophilic heads are faced towards water and hydrophobic tails away from water
- can form a micelle (sphere) HPI heads outside and in the middle
7 components of CSM
- glycoprotein
- glycoplipid
- phospholipid bilayer
- cholestrol
- channel / carrier protein
- extrinsic protein
- actin microfilament
fluid mosaic model
- phospholipid bilayer
- hydophilic heads facing external environment
- hydophobic tails away from external environment
- proteins free to move inside membrane
- proteins randomly arranged throughouy
cholestrol
- 4 carbon rings
- regulates fluidiity of membrane
- ONLY IN EUKARYOTIC
channel proteins
- ALLOW facilitated diffusion to happen
- only specific substances can diffuse through
carrier proteins
- change shape to allow specific substances through
- facilitated diffusion AND active transport
glycoproteins and glycolipids
- polysaccharaide chain attached to lipid or protein
- act as antigens for cell recognition (tissue formation)
- receptors for cell signalling
temperature effect on membranes
- as temp increaes, KE increases
- membrane bceoms more fluid
- gaps created
- more permeable
organisms in COLD environments membranes
- MORE cholestrol to prevent membrane freezing
- more UNSATURATED and SHORTER fatty acid tails to make it more fluid
organisms in HOT environments membrane adaptation
- more SATURATED and longer fatty acid tails to make membrane less fluid
role of membrane bound receptors for hormones and drugs to bind
- a receptor (glycoprotein or glycolipid) on the outer surface of the membrane has a BINDING SITE complementary in shape to the hormone or drug
- hormone or drug is the ‘first messenger’. it binds to the receptor which then activates enzymes in the membrane
- the enzymes activate a scong messenger which then has an effect on cellular function
what can diffuse across with simple diffusion?
- small
- non polar
- FAT SOLUBLE (eg lipid) molecules
channel proteins are involved in
facilitated diffusion
carrier proteins are involved in
(facilitated diffusion) AND active transport
endocytosis transports …
large quantities of material into the cell (bulk transport)
describe endocytosis
- membrane folds in around the solid OR liquid
- fuses with itself and pinches off, forming a vesicle
- triggers by binding of molecule to receptor site
- vesicle moves through cytoplasm
USES ATP
how does the active transport using proteins work
- carrier protein changes shape using ATP
- AT pump (protein) is shaped so that the molecule being carried fits to one side only
how to describe permeability when using the proteins
selectively permeable
extrinsic proteins
proteins held on the outer surface of the membrane
2 examples of what cannot go across by simple diffusion
- water
- ions
how does cholestrol work
- fits between the tails of phospholipids
- inhibits their movement, reducing fluidity
waht happens if the temp is too high
- loses mechanical stability
- fully permeable
- proteins denature
effect of solvents like alcohol
- dissolve fatty substances by inserting into bilayer and breaking IMFs
OTHER use of cholestrol
steroid hormones
- make vitamin D
- make bile salts
3 example of active transport
- mineral ions into root hair cells
- h+ out of companion cells
- sucrose out of sieve tube at sink
freezing effect on permeability
increases
how does x pass through membrane
- non-polar lipid
- soluble in the phospholipid bilayer so can pass through
why is rate of transport not constant in active transport
- uses carrier proteins
- proteins become saturated
