membrane structure and transport Flashcards
Why proteins are required for transport of glucose across cell surface membrane? (3m)
-Non-polar fatty acid tails of phospholipids make up the hydrophobic core of the cell membrane (cm)
cm is impermeable to glucose.
- glucose is a polar molecule. glucose repelled by hydrophobic core of cm
- for it to move across CSM via facilitated diffusion
arrangement of phospholipids in cell membrane (2m)
-polar hydrophilic phosphate head of phospholipids face outwards and interact with the aqueous medium
-the non-polar hydrophobic fatty acid tails face inwards and are shielded from aqueous medium
why ions can only cross cell surface membrane via transport proteins? (3m)
-non-polar hydrophobic fatty acid tails make up the hydrophobic core
-membrane is impermeable to charged ions and polar molecules, as they are repelled by the hydrophobic core of the cell membrane.
-channel/ proteins which allow facilitated diffusion
how membrane holds onto intrinsic proteins (3m)
-embedded in the phospholipid bilayer in a random manner
-non-polar R-groups of amino acids of the proteins form hydrophobic interactions with the non-polar fatty acid tails of the ℗ lipid molecules
-polar R groups of amino acids of the proteins form hydrogen bonds with the polar phosphate heads of the phospholipids molecules
roles of cholesterol (2m)
-acts as a plug, reducing the escape or entry of charged ions and small polar molecules
-increases stability and flexibility of membranes ( membrane fluidity changes with temperature)
roles of membrane proteins (4m)
-act as enzymes to catalyse reactions
- act as receptors
- for cell-cell adhesion
-act as transport proteins
roles of glycolipids and glycoproteins (3m)
- involved in cell-cell recognition
-involved in cell-cell adhesion
-act as receptor sites
fluid mosaic definition (3m)
fluid- phospholipids and proteins are free to move around in the membrane. phospholipids held by weak hydrophobic interactions and hence move rapidly by diffusion in their own layers
mosaic- proteins are embedded within the phospholipid bilayer in a random manner
facilitated diffusion definition
-passive (does not require energy) movement of polar molecules or charged ions from a region of higher concentration of that molecule to a region of lower concentration of the same molecule
-down a concentration gradient across a selectively permeable membrane via the aid of transport proteins.
carrier protein
-binding sites specific to polar molecule or charged ion
-shape of molecule transported complementary to shape of binding site
-can undergo a change in conformation
channel protein
- amino acid residues with polar or charged R groups make up the inner lining of the hydrophilic channel
-transport hydrophilic polar molecules or charged ions
active transport
-active movement of polar molecules or charged ions
-from a region of lower concentration of that molecule to a region of high concentration of the same molecule against a concentration gradient
-across a selectively permeable membrane via the aid of a specific carrier protein
exocytosis
-bulk transport whereby cell secretes macromolecules by the fusion of vesicles with plasma membrane, require energy, ATP process
1. secretory vesicle containing the material to be secreted moves towards the csm
2. membrane of the secretory vesicle fuses with the csm
3. vesicle opens to the exterior and release its content to the outside of cell via exocytosis
endocytosis
-bulk transport whereby cell takes in macromolecules by forming new vesicles from the csm
- active process which requires energy in form of ATP
-macromolecule in the extracellular fluid brought into cells
1. csm invaginates to form a flask-shaped depression which engulf/envelops the material from the exterior of the cell
2. invagination becomes sealed off, enclosing the extracellular material to form a endocytic vesicle
