membrane structure and function Flashcards
how are all eukaryotic cells bounded by
plasma membrane
what is the plasma membrane made of and what does this result in
it is a lipid bilayer therefore acts as a barrier allowing selective molecules into and out of the cell
how many layers is the membrane and how is it arranged
two layers of phospholipids, hydrophilic phosphate groups facing outwards and hydrophobic tails inwards
what is hydrophobic
molecule that is water hating
what is hydrophilic
molecule water loving
what is found between the lipids
proteins, glycoproteins, cholesterol
what is a glycoprotein
protein joined to a carbohydrate
what is the purpose of the membrane
membrane forms the external barrier and encapsulates sub cellular organelles
create a barrier for movement of molecules creating osmotic gradients and electrostatic gradients
what is the composition of a phospholipid
- phosphate group
- 2 fatty acids
- glycerol
why is there more than one type of phospholipid in the membrane
- have different structural and cellular roles eg signalling roles
what is the role of cholesterol
- structural role and helps cluster membrane proteins together in cholesterol rich regions of the membrane called lipid rafts which help regulate function of membrane protein
- increases fluidity of membrane
what do liquid rafts help with
help regulate function of membrane protein
how can lipid rafts be disrupted and what can this result in
- rafts can be disrupted through diet high in cholesterol and alcohol
- this can alter protein function - implicated in Alzheimer disease
what role do membrane proteins play and how are they classed
- play a role in structure and function of the membrane
- can be classed as extrinsic (just on surface)
- or intrinsic (spanning the membrane)
- or receptors - signalling molecule
- or membrane bound enzymes
name the three phospholipids
- phosphatidylcholine (most common)
- phosphatidylethanolamine
- phosphatidylserine
five functions and properties of phosphatidylcholine
- makes up most of the membrane
- mainly a structural component
- naturally form a bilayer
- kinked fatty acid tail therefore resulting in fluidity of membrane
- may have a role in signalling
five functions and properties of phosphatidylethanolamine
- second most common membrane lipid
- mainly in inner leaflet
- does not form bilayer alone
- stabilises membrane structure
- hydrogen bonds form with proteins due to amine group
what four mechanisms are used to regulate transport of molecules
- facilitated diffusion
- gated channels
- active transport
- diffusion
how do diffusion and facilitated diffusion differ
- facilitated diffusion requires the presence of a protein
what is diffusion and what two factors affect the rate of diffusion
- diffusion is the movement from a high to low concentration
- size and charge affect diffusion rate
small uncharged polar molecules
examples of molecules that can pass through the membrane
oxygen, water, lipids
describe facilitative diffusion
- solute binds to protein
- protein changes shape allowing solute to move into the cell
- moving solute into cell
- no energy required
how do gated channels work
- open and close by ligand binding
- proteins in membrane form a pore
- open and close in response to a stimuli
- move down a conc gradient
what does active transport require and what are the two types of active transport
- requires atp
- primary and secondary active transport
what is primary active transport
involves the pumping of a single solute against its concentration gradient
what is secondary active transport
uses the electrochemical gradient by actively transporting one substrate to provide and electrochemical gradient to transport a different solute
what is membrane anchors and what are they called
- many membrane proteins anchor a cell to its surrounding
- cells are surrounded by a mixture of proteins - ECM
- most anchors are called integrins
what are membrane receptors and what do they do
- receptors are another class of membrane proteins
- membrane receptors binds specific molecules outside of the cell termed LIGANDS and translate this event via interactions with other proteins into signals within the cell, allowing cells to adapt and respond to changes in the environment
name the most common receptors
- ion channel receptors
- heptahelical receptors
- kinase associated receptors
where do the external signals come from
- autocrine (same cell)
- juxtacrine (neighbouring cell)
- paracrine (cell nearby)
- endocrine (distant cell elsewhere in body)
ion channel receptors
- often bind neuropeptides
- binding causes conformational changes in associated ion channel
hepthahelical receptors
- binding of signal to receptor causes intracellular changes
- often involves non protein ‘second messenger’
- this triggers signals to nucleus
kinase associated receptors
- binding of single molecule causes phosphorylation of intracellular region
- triggers changes in other proteins - signal cascade
what is major function of membrane bound enzymes
- catalyse reactions
- modifying function of other proteins
